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Join Date: Apr 2008
Posts: 53

Brake Overheating

06/12/2008 4:53 AM

Hello

The brakes on my 20 year old mercedes overheat and fail when I drive around steep mountain roads.

I have changed the brake fluid but the problem persists

I removed the hub caps for better ventilation. Under the hub caps the wheel is very dirty with a black powder deposit

The brake disk pads were changed a few months ago.

Could it be that the replacement pads are no good

I will very much appreciate any suggestions

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#1

Re: Brake Overheating

06/12/2008 5:02 AM

Is this a vehicle with automatic transmission? If not, then how much 'engine braking' is used on descents?

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#2

Re: Brake Overheating

06/12/2008 7:40 AM

You should have replaced or machined the rotors.

Some pads are soft and some contain metal. You may have chosen the wrong type.

The pads are sticking to the rotors.

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#3

Re: Brake Overheating

06/12/2008 7:45 AM

Hello Planet of the Apes

You haven't advised the actual model # of the Mercedes car.

In addition to answering PWSlack above, please advise Model, also whether the "failed brakes" are Front Wheels only, Rear Wheels only, or both the Front and Rear Wheels.

Recent (made in the last 20 years or so) Genuine Mercedes Front brake pads have a sensor built in, so that when they wear and need replacing, (but are still safe to use for a few thousand more kM), a dashboard (instrument panel) warning light comes on when the brakes are applied, reminding the driver.

If your front disk brake pads are worn after 3 months, and no warning light has come on, it is probable you have had some cheap clone pads fitted.

At the front of the car, there should be a wire connected to each disk mechanism, and this can be easily checked - some unscrupulous mechanics cut the wire, so no warning light can come on, ever.

I do understand that cheap clone brake pads and drum linings are being made in an east Asia country, are of very poor quality and sold as the genuine article, to unsuspecting motorists.

Regarding the rear brakes, you would need to advise car model.

Reply here, with

Kind Regards....

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#4

Re: Brake Overheating

06/12/2008 8:54 AM

because we can not use certain materials anymore,we have had to reformulate the brake pad material, and the new materials are not as good at holding up under the conditions.

We have learned and progressed and there are now more costly after market pads that will hold up.

Also as mentioned, use the engine, shift to lower gears to slow you down. When coming off a mountain pass I try to see if I can only brake 4 times or less.

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#5

Re: Brake Overheating

06/12/2008 10:42 PM

Go to a DOT 4 grade brake fluid.

After one heat-induced brake failure, I flush and refill the system with DOT 4 fluid, Castrol SRF brake fluid is the best, NOT cheap, but what's your life worth?

Allen

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#6

Re: Brake Overheating

06/13/2008 12:01 AM

Ask yourself is there a defining moment when this problem first developed? After a heavy towing experience, after a fender bender or more serious accident?

If the amount of brake dust you're finding is approximately similar in consistancy and volume on each wheel, I would rule out any kind of brake rotor distortion, although this will ultimately be the result if you are frequently suffering from an brake overheating problem.

In a disc brake system in normal service the brake pad is in contact with the rotor, albeit "just" in contact. In a 20 year old vehicle - regardless of pedigree, I would suspect the brake calipers are sticking. If the calipers have been sticking, the rubber gaiters protecting the caliper piston is often damaged and upon close inspection show obvious signs of overheating. Exchange after market calipers are fairly inexpensive, and rather than screw around with a complicated diagnostic exercise I would replace the calipers, pads and have the rotors checked for distortion, machining / turning them down if this was found to be the case, and they (rotors) will remain within thickness tolerance. This minimum thickness dimension is normally cast into the metal of the rotor. It's also a good idea to replace the hindge pins that hold the caliper to the mounting bracket. (apply "never seez" or similar to the pins only upon re-assembly.)

Braking effort is divided approximately 60% front and 40% rear. You don't indicate model or if you have a 4 wheel disc or rear drum brakes on this vehicle. Another more exotic possible cause of your problem could be the brake proportioning valve sticking or even a tandem master cylinder problem. Checking for signs of crushed brake lines, restricting the discharge speed and pressure is another thing to check for.

If you find a large flat area and try a cold brake test and then after some heavy braking applications repeatedly, knock the transmission into neutral and see how differently the vehicle slows, if you have everything up to temperature this may give you some indication and feel for how the brakes are performing / sticking on or not?

This is my advice based on experience which is 30 years old, a different time and much simpler vehicle technologies. My apologies if I've unwittingly shown my age or offended anyone with current more up to date procedures for diagnosing similar brake problem.

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#7

Re: Brake Overheating

06/13/2008 12:35 AM

You brakes overheat because you are using them improperly, instead of using engine braking to help control vehicle speed. You could be at risk not only of frequent replacement of new pads, but also fire or extensive damage until you learn proper mountain driving technique.

Driving Primer

  • As you approach the crest of an upgrade, ease off the gas pedal, allowing the car to slow; supplement this with brake tapping as needed depending upon prior cruise speed and on road slope...and upon any warning signs about impending steep or long down grades.
  • Near the crest, on the crest, or within very short distance beyond the crest (do the first until you get the feel of it), shift the transmission to the next lower gear or gear range. (Depending on terrain slope and slope lengths, you might find it necessary to down shift more than one step, in sequence (meaning you will de-clutch before second or third downshifts in the case of a stick shift). (Note: braking on upslope is never a problem since gravity assists.)
  • As you descend, you will notice that the lower gear/range (higher gear ratio) is forcing the engine to run faster at a lower speed, serving to brake the vehicle's forward speed as the engine tends to resist turning at higher RPM at a lower speed.
  • Your aim is to maintain (not vehicle speed but) engine speed within a specific (safe) range within which, because the vehicle is going slower and is constrained from acceleration by the engine, allows braking, both, to be more effective and less stressful on pads and rotors (or shoes and drums). Any adjustments to speed of the vehicle will be able to be done with lighter brake (caliper) application for a shorter durations. (It is the hard braking and long duration required to slow a heavy mass going down hill that is the source of brake component overheating...and potential fade or failure...if not worse. You are also trying to extend the time between brake applications within which the brakes can be cooled by air passing over them.)
  • As you go down the hill making slight (and not radical or sustained) speed adjustments with brakes, you will combine this with one-step shifts, up or down, (depending on unfolding terrain conditions) to attain an ideal overall speed of the vehicle. If you have tachometer and know its "safe-cruise" range, use it to help maintain engine speed you are comfortable with...remember, it's engine speed that matters, not vehicle speed...except that vehicle speed must never be allowed to increase to possible "runaway" (loss of all hope of maintaining control other than by steering). If you have no tachometer, turn down the radio and monitor the engine by sound.)
  • As you essay to master the technique, err on the side of slower vehicle speed...until you have it down pat. Never depend on the vehicle, especially older vehicles. Stay in the slow lane where possible. Turn out if turn outs are provided to allow others to pass...you'd rather have other potential hazards (bad drivers) in front of you than behind you.
  • Learn and practice all this (it's pretty easy) and, provided you don't have other mechanical problems, your brake damage problems should go away.

PS:

Your problem reminds me of my own "smoking brakes" problem I once had. In that case, my situation was that engine braking was not available to me because of faulty lifter seals. When engine braking was (would have been) used, the high vacuum would cause rapid depletion of oil, threatening engine damage. So I had no choice but to "let it ride" going downward, alternatively tapping brakes to slow and gas peddle to (accelerate and) relieve vacuum. To make matters worse, I would have to constantly be looking far ahead for places to pull over, maybe every mile or two, in order to stop and let brakes stop smoking and cool, before continuing. Imagine doing this for the entire distance over a Cascade range mountain pass. It was a harrowing experience to say the least. But, thankfully, I made it home with brakes and engine still intact.

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#12
In reply to #7

Re: Brake Overheating

06/13/2008 4:30 PM

Nice answer. One question though, Can you safely tap the brakes while still in gear? I assume that the problem is, if the engine is working to increase the speed of the car, the braking would be counter-productive and damaging to you engine. But if your RPM is high then the engine is not propelling the vechicle but slowing it, so is it ok than. I only ask because I was told when learning to drive standard to never hit the brakes while in gear. Luckly, there are no mountains where I live. :)

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#13
In reply to #12

Re: Brake Overheating

06/14/2008 8:07 AM

It is definitely OK to brake while in gear. Just don't use the brakes while your foot is still on the gas. Using the right foot for both is the best way to prevent this.

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#15
In reply to #12

Re: Brake Overheating

06/15/2008 4:18 AM

Hi, Kanloop.

Last (and most important) things first, you were told wrong...very wrong. The general principle is that a car (automatic- or standard-shifting) should never be permitted to "free roll," out of gear, at speeds above engine fast idle (around 15+/-MPG). It is unnecessary, detrimental, and dangerous to do so. Consider just one of multiple reasons (no, make that two): When the engine is disengaged from the drive wheels, both power brakes and power steering are effected, because the pumps/augmenters driving those systems are, also, now running "at idle." Now let us go to general principles as we look for the answer to your mountain-driving questions. You will see that these have relevancy also to correct general operation of a stick-shift vehicle.

First Principal: Understand that any engine (all engines...IC, electrical...etc.), are constantly "trying" to slow the car (or the driven machine), not to speed it up! The "favored" state of an engine (under influence of friction and gravity) is "stopped"; and your car's engine would always stop, too, but for the fact that you "give it gas" and force it to keep going or go faster. Even on a down slope, it's the weight —the force of gravity—that works against the engine's "wanting" to slow the car down. So we could say that with a coasting vehicle, engine braking is always in play, even in normal driving on level surfaces—barring gas pedal input to de-throttle, the engine "labors" least to stop itself and the vehicle on upgrades (because gravity helps, and helps in two vectors); more on level grade (because gravity helps less, and in only one vector towards the road); least on upgrades (because gravity helps in one vector but works against in the other vector). So now (addressing your main questions): if we want to slow the vehicle, would it be better to rely on brakes only (with throttled engine disengaged from drive wheels) or on, both, brakes and the engine trying to slow it's self and the vehicle engaged with it? In all three road % grade situations just described, slowing of the car (and minimizing heating of, and wear & tear on, brake friction components) is best accomplished by not relying on brakes alone. This advantage gain—coincidentally, it comes automatically with automatic transmissions—is most critical on mountainous down slopes because gravity, for the greater part, is working against slowing the accumulating forward & downward momentum of the vehicle—I introduce momentum here to show how increasing downhill speed (gravitationally induced acceleration) disproportionately increases braking (both engine and wheel braking) required to slow the vehicle; hence the tendency for the engine towards over speed; and hence the need to hold speed under control (as per the previous post) going down steep and/or long downgrades. (Actually, length of downgrade [in part because this is unregulated] presents the greater hazard, usually, because with steep down grades the next upgrade is usually much closer...less distance in which to gain momentum before gravity again works in your favor, going uphill, to help control speed.) Now let's clarify the emergency driving maneuvers I was trying to describe earlier as these relate to your question.

You asked: Can you [I or anyone] safely tap the brakes while still in gear?

Answer: As said above (and by someone else before I could post this), not only can you safely tap brakes, you can (and should) also (safely) apply brakes with engine and transmission engaged. The only distinction as pertains to grades, is how long you will brake before the car is slowed to the point (fast idle engine speed) at which the clutch must be released (the pedal stepped on) to prevent engine lugging: least time on upgrades, most on downgrades. With stick shifts and automatics alike (and remember, automatics, also, do not declutch during coast; they declutch-re-clutch only as needed to downshift under control of engine torque, or torque requirement), from the moment you take foot off gas pedal (to change the vehicle from powered cruise mode to net-negative-powered coast mode, the now-throttled engine is trying to stop, and is no longer working to propel the vehicle. So it is not the case, as beginner's intuition might superficially suggest, that applying brakes in a coasting (other than free-wheeling) vehicle will cause engine and brakes to work in opposition. In fact, contrary to that, the application of brakes is not, actually, so much to slow a vehicle as it is to assist the engine to slow the vehicle! (...the balance depending on vehicle momentum and applied braking force.) So, if brakes are (incorrectly) forced to work alone to slow and/or stop a vehicle, they (the brake rotors/pans/drums/shoes) undergo very much more stress and heat buildup (with increased likelihood of failure) to do so...that, and much more brake pedal force or force amplification is required than is necessary.

You postulated: .... If, the engine is working to increase the speed of the car, the[n] braking would be counter-productive and damaging to your engine[?]. But, if your RPM is high, then the engine is not propelling the vehicle but slowing it, so is it ok then[?].

I would modify that sentence slightly to make it more consistent with what I think you are saying, and to add one small correction—

If (as when due solely to driver's gas-pedal command), the engine is working to increase the speed of the car, then braking would (normally) be counter-productive, and could be damaging to your brakes, possibly to your engine as well? But, on the other hand, if your engine's RPM is high or increasing for reason other than driver foot command (such as with downhill cruising), in that case the engine is not propelling the vehicle but, rather, is working to slow it; so is it ok then to apply brakes?

Stated the latter way, I would say you have it, in a nutshell. And these are the considerations I had to take into account, and was forced to "violate at the margins" when doing the aforesaid, emergency downhill maneuvers. It had been serendipitous that an Oregon rest stop had appeared near the summit approach (they often do, so drivers can stop while on the upgrade) because stopping (and stopping airflow around the wheels) "afforded" the brakes the chance to start (visibly) smoking; continuing on with smoke dissipating undetected in the wind could well have led to calamity. After two or so hour's delay until the wheels became touchable (without another 3rd degree burn), and after brake testing in the rest stop parking lot, a major problem I had to contend with going downhill was preventing engine over speed as I attempted to continue as far as possible without up shifting. (The transmission was 4-spd with overdrive 5th.) Against my best efforts, the downgrade would get the upper hand and inevitably demand an up shift or two, sometimes three...because I was also trying to "spare the brakes." Endeavoring to minimize up shifting (to maximize distance between up shifts), I employed the "old-times," and now largely forgotten (except in road racing), heel-toe method of gas and brake control: using heel and toe of right foot (simultaneously at times and for brief instances) to control acceleration and braking in rapid succession. This way I could increase engine speed and reduce vacuum (preventing over-speed and mitigating oil loss) in quick, alternating succession with applying brakes momentarily (to forestall the next up shift). At times (both incidentally and by calculated risk) the braking and gas-giving would overlap (not a good thing, as you postulated), but not (it was hoped) to a degree or for a duration that risked serious damage (to my heavy duty metallic pads/shoes) or failure.

I hope all this has provided all the explanation you needed. And please, stop doing what you were told before and start operating your stick shift correctly as indicated here in CR4. You will also save yourself from unnecessarily frequent brake renewals...probably clutch renewals as well. Finally, if you tend to be (what I call) a "digital driver" (a person who "homes" on the car/tail/brake-lights ahead and drives as if "gas-pedal-go, brake-pedal-stop" is the only means to control vehicle speed), then practice being an "analog driver" (who watches far ahead, anticipates, and uses variable gas pedal pressure to control speed so as to minimize brake usage and braking force).

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#16
In reply to #12

Re: Brake Overheating

06/15/2008 4:41 AM

Correction to paragraph 8 in preceding CowAnon post:

  • Now reads: ...reason other than driver foot command (such as with downhill cruising), in that case the engine is not...
  • Should read: ...reason other than driver foot command (such as with downhill coasting), in that case the engine is not...
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#18
In reply to #16

Re: Brake Overheating

06/15/2008 2:57 PM

Other sleepiness induced correction, in Paragraph 3 of original:

engine "labors" least less to stop itself and the vehicle on upgrades (because gravity helps, and helps in two vectors); more on level grade (because gravity helps less, and in only one vector towards the road); least more still on downgrades (because gravity helps in one vector but works against in the other vector).

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#20
In reply to #18

Re: Brake Overheating

06/16/2008 4:21 PM

Thanks CowAnon, what you said makes sense for me. I will have to practise this on the next time out and maybe my downshifting will work better and be a lot smoother. Taking out the clutch on a downslope never made sense to me before, as your car is coasting and that is not good if you are trying to slow down. Thanks for the clarifaction CowAnon.

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#22
In reply to #20

Re: Brake Overheating

06/17/2008 7:36 AM

Kanloop,

I wrote a reply to wish you well with learning...and to add clarification regarding possible misunderstanding I sensed in your final post. However, it was inadvertently deleted before submitting, so I'll need to compose it over...to clarify further what "coasting" is and is not; and to explain that downshifting should not be used for decelerating and stopping; and why. Before my explanation was lost I made a little chart (below) illustrating gear shifting (especially downshifting) technique, when it is truly needed, which (in the case of downshifting) I very much doubt will often, if hardly ever, be the case for you at your location. So, since I deleted my time spent along with my post, I'll fill you in further as soon as I re-do it and get back.

Until then, think of the chart as telling when not to execute a downshift; as illustrating indirectly how many people do it incorrectly...and wear out their drive trains (and tires and gas supply) far too quickly.

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#24
In reply to #20

Re: Brake Overheating... Better Down Shifting Techique

06/21/2008 2:03 AM

Okay, I've now taken another stab at it. Perhaps you didn't mean it like it reads to me; so I'm posting to make sure your recent reply doesn't misconstrue what I said before, both as to what was meant by "coasting," and respecting your seeming belief about the appropriate use downshifting.

Starting with coasting (with emphasis added), you said: "Taking out the clutch on a down slope never made sense..., as your car is coasting and that is not good if you are trying to slow down."

Now let's emend that slightly to remove ambiguity. The statement would more precisely and unambiguously have said: Taking out Pushing pedal to disengage the clutch on a down slope never made sense [anyway]..., as [then] your car is would be coasting free-rolling (or, free-wheeling); and that is not good if you are trying to slow down retard vehicle acceleration [in order to facilitate, and gain engine braking facilitation by, pedal braking].'"

While it might seem a small distinction, and contrary to what many might be heard to say by force of habit, my previous-post (and otherwise) use of the term, coasting, was meant to be reserved only for momentum-induced motion of the car (on any road grade from uphill...to downhill) with drive wheels engaged, both, with the road and with the engine via the clutch and in-gear transmission, but never with clutch (and engine) disengaged (never with clutch pedal pushed). Because free rolling (with clutch pedal pushed or transmission in neutral) is an improper driving technique in all but rare, atypical driving scenarios (e.g., out of gas and rolling to gas pump; stalled engine and rolling to safety), I deem the term coasting to never include vehicle free-rolling.

(Thinking of other "rides"—things like roller coasters—it's easy to see how people might draw (folkway) analogies which equate "free-roll" ride car "coasting" with motor car free rolling; however, closer examination reveals that even roller coaster "coasting" is not without (genuine) analogy to motor car coasting in terms of maintaining vehicle control: whereas the motor car utilizes engine engagement along with foot braking to maintain safe control on all grades, with roller coasters it is the track (design) itself which accomplishes the same end. So we could say that engine and foot braking for a motor car has its analogy in roller-coaster track (&or wheel) design features which, both, regulate speed and maintain engagement between ride car train and track...until track upslope & ride-car train momentum loss, plus manually-applied track brake, can bring the train to a stop.)

Now the other part—

If I understood correctly, then with slight modification, and a change of juxtaposition, your statement might have read: "Taking out Disengaging the clutch ... [so that] your car is coasting free-rolling... is not "good" if you are trying to slow down. ... I will have to practice this [this coasting without declutching]... [then] maybe my downshifting will work better and be...smoother." (In other words, you have drawn a comparison [....albeit a false comparison] between "engine braking" on down slopes and routine slowing/stopping of vehicles on generally level terrain such as in your own locale.)

That statement is close..., and would be correct, except...except that (and keeping in mind your non-mountainous driving locale), the correct application of downshifting (in spite of what many drivers, especially less experienced drivers, might tell you) is not for the purpose of slowing a vehicle (including motorcycle vehicles). In fact, not only does such (improper) use of down shifting...

  • cause fuel to be wasted (and)
    • (if fuel is used to bring car from stopped to cruise speed, what sense... in using added fuel (again) to bring car from cruise to stopped?) [and]
  • impose undue stresses & risk of damage to drive train (and)
    • (for example: tire spin, u-joint or CV joint failure, rod breakage, ...) [and]
  • lead to accelerated wear & tear portending reduced vehicle life and value (and)
  • impose unnecessary burden (and potentially hazardous distraction) on the vehicle operator (including two/three wheeler rider), [but]

...it can also be dangerous, (for example):

  • as a result of driver control loss due to vehicle traction loss and side slippage
    • (made worse still on crowned, sloped, and wet, icy, or otherwise slippery pavements).

So if slowing is not an appropriate use of down shifting, then what is?

Generally speaking, downshifting is used in order to gain (i.e., to re-gain) mechanical advantage, via increase in gear ratio (with concurrent decrease in engine-output torque requirement), for propelling vehicle mass as momentum (of an already slowing vehicle) is "lost" (meaning: momentum has decreased to a point below which torque must be reduced—engine speed must increase—to prevent engine lugging). For practical application (and self-training) purposes, this general principal is exemplified by two down-shifting "rules of thumb":

  1. Down shift only when necessary to accelerate the vehicle after it has (already) slowed, or to halt loss of & thereafter maintain vehicle momentum at a continuing lower driving speed (as with reductions in posted speed limits and/or in reduced-speed zones).
    • Just as with up shifting, the idea is to maintain engine speed (RPM) within (but at the bottom margin of) safe operating range below over-speed and above engine lugging or stall speed; it's not...to force top-of-range engine RPM to counteract vehicle momentum as a substitute for braking or coasting.
    • Engine speed ranges (or equivalent vehicle speeds) are typically shown in owner's manuals; also on analog tachometers in vehicles so equipped.
    • In the absence of tachometers, some stick-shift vehicles indicate approximate gear shift points on their speedometers (shown, for example, as dots or tick marks on the speedometer dial); vehicle speeds between these marks can be taken as approximations of normal engine speed ranges.
    • Experienced stick shifters will have tuned their ears (and innate "vehicle speed sense") to the sounds of upper and lower engine-range speeds...and viscerally sense when to shift...even without reference to instruments.
  2. Shift (as per above valid criteria) to a lower gear only after the vehicle has slowed (has coasted) to a vehicle speed at which engine (flywheel) speed is near the bottom of the "gear" range of the lower gear being selected (which corresponds to the lower portion of the engine "safe speed" range). This technique is depicted in the previously posted diagram.
    • The motivation behind shifting in this manner is twofold:
      1. Shifting down (see diagram) from bottom engine speed in one gear range to bottom engine speed in next lower gear assures reserve gear range (and engine speed range) for vehicle acceleration if needed.
        • Incorrect downshifting from gear range bottom to gear range top (as if downshifting is merely the reverse of up shifting, which it is not), on the other hand, forces the engine to top of its speed range (when clutch pedal is released)...so that, if acceleration is needed, you must up shift again immediately...in effect, wasting the downshift (and the unplanned up shift as well).
      2. Down shifting so as to match pre-shift and post-shift engine speeds facilitates gear meshing (and un-meshing), retarding wear & tear to gear box and clutch components alike, as well as making shift lever engagement a smoother action.
        • Gear box component wear rate shows up first as metal flaking that is captured magnetically by the drain plug and is removed during gear box oil renewal service.
        • It will sometimes be the case that engine speed has dropped too far when shifter re-engagement is attempted during down shifts, for example: (1) when coasting too long such that RPM falls below normal (PT cruise) range, or (2) when vehicle and engaged engine slows more quickly that anticipated due to slight upslope or head wind. A simple trick can overcome such balky stick engagements (and engine lugging and/or other performance problems) when this occurs. At the instant any resistance to gear (stick) engagement (or engine balking) is felt:
          1. Release pressure on shifter (backing it off only very slightly), then
          2. Continuing pressing (or quickly re-press and hold) clutch pedal...then immediately
          3. Press accelerator pedal lightly and momentarily to gently "rev" the engine...and
          4. As engine slows after being revved, again press shifter gently towards selected gear position until...
          5. The shifter slips smoothly into "notch" as "synchronization" speed is reached. Finally,
          6. Release clutch normally and continue driving.

To summarize, the appropriate technique for slowing to a stop on flat terrain is, simply: to take foot off gas; coast with transmission remaining engaged; apply brakes (first gently then progressively more firmly as vehicle stop point is approached, then less firmly as final stop point is reached)—no downshifting.

With practice and experience these principles and techniques will become second nature, and the full vehicle control (and fuel savings) advantages conferred by manual transmissions can be realized.

Finally, it might seem (to some) that the above instructions (the advise against down shifting to slow down) are inconsistent with the prior post regarding engine braking on down grades; but, in fact, they are not; and the techniques described here apply equally (with only modification of driver's timing) whether on up grades, level grade, or down grades. If further clarification of this aspect is desired, please let me know.

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#8

Re: Brake Overheating

06/13/2008 1:50 AM

Many Thanks Gentlemen

It must have been nearly a year since I had the pads changed.

The orange light has been coming on for the last couple of months

I will get a new set of good quality pads and see how it goes

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#9
In reply to #8

Re: Brake Overheating

06/13/2008 2:42 AM

Suggest you find a friend to help you determine whether or not the brakes are being applied on all 4 wheels. Have the helper stand outside the vehicle while you slowly drive on a dirt or gravel road in front of him/her. Jam on the brakes hard enough to lock up all wheels, while the helper watches the wheels to see if, indeed, all wheels skid on the ground. Repeat this test several times with helper watching on both sides while you vary the amount of foot pressure on the brake pedal. It could be that your brakes are heating because only two wheels are being braked, instead of all of them. If this is the case, then more troubleshooting of the braking system is needed to determine the failure. Good luck.

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#10

Re: Brake Overheating

06/13/2008 4:31 AM

...Don't drive around steep mountain roads...

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#11

Re: Brake Overheating

06/13/2008 6:17 AM

Black powdery deposits on outside of wheel, exposed when wheel covers are removed...is how I read your initial description. The fact that the hub caps trap the powdery stuff suggests they are "old style" large caps, not just bearing/grease cup covers. Is this correct. The black (carbon) color is suggestive of burning (an end result of overheating) of pads, but not metallic pads. I have witnessed these to "emit" a rust colored powder, along with rotors, as rust is ground off pads or rotors in a car that has sits for a time (especially in humidity) so that rotors and pads can collect oxidation. There can be significant accumulations if caps are removed infrequently...but yours have been removed with the last year...so that seems to indicate a relationship between the black powder and burning.

If not caused by driver error of brake use, the first thing I would suspect is incomplete caliper retraction...so that brakes are partially applied between actual driver braking. This could be due to weakened retractor spring, inadequate lube of caliper mounting, or sticking or maladjustment of caliper pistons. This could be due to workmanship error at last pad change. Replacement of indicated components would be cheap and relatively easy as a way of eliminating this as the fault to see it that clears the overheat problem. Depending on daily mileage mountain driving, a year could be sufficient for non-metallic pad wearout...but that should not bring about burning (as long as rotor linings remain) so much as scraping noise and weakness or fading of brake power. A quick way to check pad-rotor clearance (if too high) on rear wheels is to apply parking brake, checking for excessive park lever travel or pumping to set the park brakes firmly.

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#14

Re: Brake Overheating

06/14/2008 4:12 PM

1. Have your brakes adjusted by a qualified mechanic. He needs to be looking for the following: minimum 1/8" thickness of the brake pads, and equal application of braking to each wheel as the pedal is depressed.

2. Once that problem is solved, you need to learn to downshift one gear at the top of the hill on any long grade steeper than 4%. If you are driving one of those 80,000 lb semis, you subtract the grade% from 10 to get the gear to shift to going down. My scariest braking problem was on I-15 southbound where it crosses the California State line at the top of Halloran Summit, a 17 mile long downgrade at 4% that looks flat. I smoked them good. There are several good locations to practice on around the country on the Interstate Highway system. One of the best is I-80 going west from Reno Nevada. Another is I-8 eastbound or westbound between San Diego, California and the Arizona State Line. I-24 near Mount Eagle, Tennessee is also fun. But the "Oh My God Hill" between Ranchester and Burgess Junction on hwy 14 in Wyoming should be only run after practice on other hills. From the top, the first 10 miles is at 10%. It is awesome.

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#17

Re: Brake Overheating

06/15/2008 11:20 AM

Buy A new Mercedes....

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#19

Re: Brake Overheating

06/16/2008 11:55 AM

Planet of the Apes:

Slow down, go slowly over the top of hills and lightly apply pressure to the brake pedal until a braking effect is sensed when going down mountain roads and hold that light pressure because frequently applied pressure allows oxygen to get between rotor/drum and pad/shoe an heat builds quickly.

If required you may replace pads with those with metal (copper or aluminium)impregnated or feramic materials but the rotor/drum useable life span will suffer greatly. Though the braking will show a marked improvement.

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#21

Re: Brake Overheating

06/17/2008 1:02 AM

Sell the merc, and start walking - you're going to have to do that, when gas prices get too expensive.

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#23
In reply to #21

Re: Brake Overheating

06/18/2008 8:02 PM

get too expensive.

Like today

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#25

Re: Brake Overheating

06/21/2008 1:12 PM

As a general rule, if you have to go to a lower gear to go up a hill, go to the same lower gear to go down the same hill... ie use engine braking. Whoever informed you to not use this is so busy examining their hemoroids that they are NOT in touch with the real world. Ask any truck driver about this.

Also, last time I did brakes on my wifes car, while buying pads, I was asked which quality of pads did I want? Cheap ($7.00 per set) up through heavy duty ($40.00 per set)... with several grades in between. I suspect that the cheap ones do not meet manufacturers specifications. So use quality parts. Your life depends upon it.

Bill

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#26
In reply to #25

Re: Brake Overheating

06/22/2008 3:28 AM

??

You have posted a reply to PlanetoftheApes (post #0), who said nothing about gears, hills, engine braking, or anal contemplations. Perhaps you might post again and mention the post numbers you meant to disparage? And maybe explain what you take issue with...since I didn't see any post which says what you said it says (so that its author can rejoin the real world).

Asking any truck driver? Assuming you have some knowledge/experience in that regard, you probably realize by now that such advise was a bit overstated, both as to kinds of truck drivers and as to kinds of vehicles or combinations. While there probably is a minority of truck operators who fully understand (fewer still who can explain) the dynamics of gear selection and engine braking, there are no doubt a majority of trucking firm owners who can attest to the very high, undue repair expenses and replacement costs "inflicted" on truck fleets by all too many "typical" truck drivers. So some truck drivers, yes. Any truck driver, definitely not.

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