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How to Tell if Brake Booster or Master Cylinder is Bad

06/08/2008 5:19 PM

the brakes to my honda accord 1992 are randomly dying, where i have to floor the brakes or pump it to stop. the car has new brake pad, brake shoes, and new brake oil. How do i know if the master cylinder or brake boosters are bad.

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#1

Re: how to tell if brake booster or master cylinder is bad

06/08/2008 6:06 PM

The symptoms you are describing definately sound like it could be your master cylinder. I is a failure in the vehicles brake hydraulic system which consists not only of the master cylinder but of the calipers, wheel cylinders, at least one proportioning valve and the steel lines and hoses connecting these. Though the power booster may be damaged as a side effect, it is probably the primary culprit.

Start by looking for fluid leakage. Since the master cyl is first in the chain you may have to remove the nuts that hold it to the power booster, pry it away and check for fluid between the two. Also check the carpet beneith the brake pedal for an oily dampness. Moving down the line check all the steel line fittings at the master cylinder and proportioning valve for wetness.

On to the wheels. Remove wheels with car properly supported and check for leakage at the calipers and hoses. While you are there check the hoses for cracking or swelling.

At the rear wheels, if the car has drum brakes, remove the drums and look at the wheel cylinders. This will be a good time to check the wear on those brake shoes. They should be replaced if they are down to a third or less of thier original thickness or for sure if they are thinner then the metal they are bonded to. Your rear bearings can also be inspected at this time.

If every thing looks good down below it's time to have another look at that master cylinder. With the engine off, hold your foot on the brake pedal, firmly but not alll your weight. If the pedal creeps down after you first get it firmed up (assuming you may have had to pump it a few times) then fluid is bypassing the seals inside the cylinder and it will need to be replaced. There is a more than even chance that some fluid has contaminated the diaphram in the power booster, weakening it or even causing a leak. It will then be time for a new booster.

At 16 years of age, time alone will be an indicator of potential need for a complete brake overhaul.

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#2
In reply to #1

Re: how to tell if brake booster or master cylinder is bad

06/08/2008 9:11 PM

Outstanding answer!!!

milo

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#3

Re: how to tell if brake booster or master cylinder is bad

06/09/2008 2:39 AM

With brakes it is always best to start at the brake pads and work back to the pedal.

Check for a leaking caliper first check all 4!

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#4

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/10/2008 1:21 AM

overhaul the master cylinder

better still rather fit a new one

regards

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#5

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/10/2008 7:31 AM

Post #1 has hit most of the correct buttons already, but a few other points for you and anyone else reading this Blog.

1) If the booster stops functioning, the main effect in an otherwise functioning brake system is that the pedal feels as though it is siezed up and cannot be moved at all with normal foot pressures. If very heavy pressure is exerted, some small braking effect may be noticed.......very, very hard pedal is usually the result.

2) The master cylinder (and I agree this is where to start by replacing it), generally does not leak outside of itself, it leaks internally and the fluid travels back into the reservoir, so usually no fluid will be seen on or under it or lost.

3) If the master cylinder is at fault, then I would replace it (do not attempt a repair, it seldom lasts long as often the culprit is rust internally)......and as it is a major part of the brake system, your life depends on it working 101% of the time correctly.

4) Replace ALL of the fluid in the system, by draining at each wheel till fresh clean fluid arrives, you can usually tell by the color. Buy the best fluid that is fully compatible to your old fluid. Check this carefully in the handbook. Make sure that you keep topping up while replacing and do not draw air into the system. Do this only once the new master cylinder is installed and filled.

5) Brake fluid "wears out", replace it every 2 to 3 years as it takes in water and its boiling point reduces and this can cause the brakes to fail in an emergency stopping situation, though every day braking will seem to be OK.

6) You need to be very hygienic with brakes, no dust or dirt may enter the system, this could cause premature failure of the seals. Clean/power wash everything well around the master cylinder, before unbolting the old one, work under cover so that wind carried dust and dirt are not a problem. Cover everything that has to remain open for a short time with new food grade plastic bags. Wash your hands, keep clean rags handy. Treat it like an operation in a hospital!!!

7) Buy at least a quart of the correct fluid (you may even need more!), do not try to re-use the old (or new) fluid that you drain out at each wheel, it will now have impurities in it!

8) Make sure that you get rid of the old fluid in a correct environmental manner. Usually the shop (if a good one) will take the old fluid back if returned in a proper container......the perfect one being an otherwise empty brake fluid container....

Good luck.

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#20
In reply to #5

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/10/2008 1:50 PM

GA Andy, I would just add to Andy's and the first poster's message that its very easy to check that the brake booster is working properly.

Simply press the brake pedal reasonably hard while you start the engine, the brake pedal should dip down towards the floor slightly, this means the vacuum operated brake booster is working. Its worth a quick check like that before removing wheels etc...

John.

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#6

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/10/2008 8:12 AM

I can't believe no one suggested there might simply be air in the lines.

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#7

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/10/2008 8:29 AM

You crash into the guy in front of you!

Now how many of us idiots are going to give this poor guy the same answer!

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#8

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/10/2008 8:55 AM

Your booster uses vacuum from the intake manifold. There is a check valve that plugs into the booster that could be bad causing intermittent leakage. Check the hose for cracks and make sure the check valve is good. Also there is a diaphragm in the booster so check to be sure it hold a vacuum.

Jay

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#9

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/10/2008 8:57 AM

how about before you do any of that, just simply try bleeding your brake system first then strt with a new master cylinder. If you do buy a new master cylinder you will have to bench bleed the new one before you install it. Just remember, in a brake system you should always check maintenence issues first such as checking for leaks, inspect your brake pads for uneven wear and bleeding the brake fluid to remove air from the system. You should always bleed your brake when installing new brake pads.

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#10
In reply to #9

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/10/2008 9:14 AM

Is correct, specially if the fluid has been changed. there is a great possibility of air in the lines. a propper bleeding procedure should take care of it.

Also if the master cylinder was removed or dryed from fluid, if not properly bleed, it may have been damaged

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#11

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/10/2008 9:16 AM

If you changed the brake fluid try bleeding your brake system again.... a little air in the lines, master cylinder or the calipers/cylinder will give you a sponge feeling

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#33
In reply to #11

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/16/2008 4:59 AM

Just a quicky here... If you are going to bleed the brakes, there is a specific sequence involved. I do not have it of hand. Follow the sequence... but get all the old gold colored brake fluid out of there and replace with new.

With my '83 Accord, it developed a leak in the master cylinder which ran into the brake booster. It pretty much destroyed the booster.

I replaced the master cylinder first, and when that didn't work, I replaced the booster. Regretfully, these days, it is hard to get original parts so if the auto supply place doesn't have them, it is a trip to the junk yard. I replaced the booster with one out of an "84.

Bill

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#12

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/10/2008 9:18 AM

You ought to check the brake lines themselves as well. The rubber lines will deteriorate and then expand as pedal pressure is applied, so the brakes will feel "spongy" even without air in the line. You can also have tiny leaks in the lines that will allow air to be sucked into the system over time. Brake fluid will also absorb water over time. This water will boil in the calipers as they heat up and the steam will act just like air in the line. To add insult to injury the water will rust the brake components from the inside out which tends to make a real mess.

The metal brake lines are probably in bad shape after 16 years as well. Any rust from this source can flake off and jam valves or damage seals.

So a complete overhaul of the system is in order. Going to probably cost more than the car is worth, I would bet. I guess that call is up to you.

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#13

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/10/2008 9:33 AM

First, make sure you bled the brakes completely. Air left in the system will cause this symptom more often than anything else. Second, if they have been bled correctly, it will be the master cylinder. If the booster goes out the brakes get harder not drop to the floor. Lack of boost means you have to put in manual effort to apply the brakes.

Important, rebleed the whole system first and make sure you get all of the air out of the master sylinder, and the calipers or wheel cylinders on each wheel, then look elsewhere.

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#14

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/10/2008 10:15 AM

i had that same problem on my 91 accorn. i replaced the MC (for fear or durt and years of crud in it) which lead me to re bleed everthing and it seemed to fix the issues completely.

(for the record that car is dead and gone now about two years ago, lost the automatic trans. and well $2100 to fix means a dead 15 yearold honda for sure, sad day ;)

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#15

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/10/2008 11:04 AM

Several good comments, but the simple answer to your question is:

Booster: No power assist. Very hard pedal, normal or close to normal travel.

Master cylinder (or caliper) leak: Pedal goes to floor, little or no braking power.

Air in line: Pedal goes to floor, but can be "pumped up" to acheive near-normal braking temporarily.

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#16
In reply to #15

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/10/2008 11:06 AM

Forgot to add: I've had all three problems on different cars. The second is the scariest.

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#18
In reply to #16

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/10/2008 12:53 PM

That and black ice produce similar feelings

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#34
In reply to #15

Re: How to Tell if Brake Booster or Master Cylinder is Bad

04/21/2009 9:12 PM

You nailed it. Erase all the rest, while they are helpful in understanding when and why, your answer gets to the point accuratly.

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#39
In reply to #15

Re: How to Tell if Brake Booster or Master Cylinder is Bad

10/06/2010 8:55 PM

It starts by using brake fluid that you thought was leaking somewhere. After checking the tires for residue and not finding any then the search starts else where. You check all the lines and hoses you can see to no avail. Then one day you start somewhere after adding brake fluid to the master cylinder. The white smoke boils out of both tail pipes. The engine sputters while trying to run on brake fluid and gas. The final results are no brake pedal and no brakes at all. I have a 1984 Ford F-250 that just had these symptoms. I will start with a booster then a master cylinder to repair the problem.

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#17

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/10/2008 12:21 PM

Dear Honda,

You've gotten some very good advise here. Remember that it is only advise. If your engine dies, no else needs to die. If your transmission falls out, no one has to die. If your brakes don't work, regardless of why, and you are traveling, and you can't stop, someone will die.

Unless you are a licenced auto mechanic, take your car to the Honda shop and let them do their job. That way, no one has to die.

Please don't take offense. I am not casting aspersion on you or anyone on the site. My interested in your safety and the safety of others.

Good Luck, buddy,

/Ari (orpheuse)

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#19
In reply to #17

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/10/2008 1:01 PM

Unless you are a licenced auto mechanic,

Qualified is effective enough, hydraulic braking systems are fairly simple with a few fundamental principles anyone capable of passing drivers licence exam should be able to comprehend, otherwise they wouldn't acknowledge a problem existed.

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#25
In reply to #17

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/11/2008 4:54 AM

GA

Only he knows if he has the knowledge, experience and the proper tools to do the job. If he decides wrongly, he could land on the Darwin Awards Page!!! Hopefully alone!!!

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#21

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/10/2008 6:23 PM

Since you have to pump the pedal to get good braking, I would bleed the lines first.This can be accomplished without anyone else to pump the brake thusly:

Get a quart of brake fluid, of the appropriate type, and a small clean container to receive the waste fluid.

Put about 1 inch of clean fluid in the waste container.

Obtain a length of rubber tubing of proper diameter to snugly fit over bleeder valve.

Loosen bleeder valve, and lightly re-tighten it.

Leave the box end wrench on the bleeder valve.

Place one end of the tubing over the bleeder valve, behind the wrench.

Place the other end of the tubing in the waste container, and make certain the end is immersed totally in the fluid.A threaded nut slipped over the tubing works well to keep the tube immersed.

Open the bleeder valve about 1/2 turn.

Pump the brake pedal 3 or 4 times,and check fluid level in the master cylinder.

Top off the fluid level.

Pump 3 more times, and tighten the bleeder valve.

Top off master cylinder fluid level.

Move to the next wheel and repeat proceedure for all wheels, remembering to top off fluid level after each wheel.

The fluid in the waste container acts as a check valve to prevent air from entering the system when you release the brake pedal.

If this does not improve your braking,you may have a master cylinder leaking, either internally, or into the vacuum chamber.

Look under the dash where the pedal goes thru the fire wall ,and check for leaks.Sometimes a leak will show here, other times it will leak into the vaccum booster chamber, and not be seen.The clue here is having to constantly add fluid to the master cylinder,but no evidence of leaks at the wheels or lines.

An intermittent "hard pedal" indicates failure of the vacuum booster or vacuum line, or check valve in the vacuum circuit.

One minor point that needs clearing up:Brake fluid is not an oil.Never put oil in a master cylinder.

It is more closely related to antifreeze than to oil.It will absorb moisture,which reduces it's boiling point, so always use fluid from a freshly opened can.

Hope this helps.

HTRN

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#22

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/10/2008 8:31 PM

Because Honda says: "...randomly dying, where i have to floor the brakes or pump it to stop, " I wonder if 'randomly' means his brakes sometimes actually work, OR... if they require different amounts of pumping at different times.

I wonder if he didn't use 'brake oil' but instead of 'brake fluid'. Don't you put brake fluid one place and brake oil another? What are the results of switching them? Or using even one in just one wrong place?

From reading this blog, it seems his problem is not the brake booster, but could be a lot of air in the lines? But that's being positive. Everyone says, "bleed the air out." After that, it should be obvious that it's the master cylinder. But at 16 years old, Honda should save for a new one anyway.

Could someone let me know if my impressions are correct? Much thanks.

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#23

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/10/2008 9:31 PM

Hi honda,

If you have to pump the brakes, it's the master cylinder, PERIOD. Replace it before you die!

S

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#24

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/10/2008 10:27 PM

Another symptom I forgot to mention in my previous post:

Air in the brake lines will result in a "spongy", soft feeling pedal.Sometimes it is nescessary to pump the pedal to get any back pressure at all, depending on how much air is in the lines.A clarification of your symptoms would help to pinpoint the problem.

A 16 year old Honda is as good as a new domestic car.It is just getting broken in.I gave a 1988 Accord to my brother in law, and it had 250K miles.It now has over 300K and still running fine.Stay ahead of the timing belt (50,000 miles max), and do proper oil/filter change, and it will run practically forever.The brake problem should be relatively cheap to fix.

Good luck.

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#29
In reply to #24

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/12/2008 1:03 AM

Great point... and one I wish I'd made. Accords are fantastic cars.

I've heard it at least six times (and had one). Which points to the value of discussions like this.

If I had followed the advice I'd received to buy a car every three years and work to keep the career that supported that, I'd be a much less happy person. While saying so might seem to some 'off-topic', I've learned I should say so in case that 'attitude' creeps in and shuts communication off.

Could someone here tell me what brake fluid is composed of and why it's different from oil? Thanks.

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#30
In reply to #29

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/12/2008 8:33 AM

For a start its not oil, its hydraulic fluid which is hydroscopic.

I'm sure someone will know exactly what is so different about it..

John.

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#31
In reply to #30

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/12/2008 6:33 PM

Here is a link that provides a lot of info on brake fluids, their designations, and chemical composition.

http://www.danoland.com/nsxgarage/definitions.html

HTRN

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#43
In reply to #29

Re: How to Tell if Brake Booster or Master Cylinder is Bad

12/14/2010 11:25 AM

Brake fluid is a Glycol based liquid,and by it's very nature, it is hygroscopic(absorbs moisture).It has a very high boiling point.If it is allowed to absorb moisture, the boiling point is reduced to the boiling point of water,which will create a bubble(vapor lock) in the system.This will create an unpredictable situation in the braking system.depending on temperature.

The moisture can also freeze in the lines, causing an obvious danger.

'Nuff said

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#40
In reply to #24

Re: How to Tell if Brake Booster or Master Cylinder is Bad

12/13/2010 8:10 PM

i would rather push a ford than drive a honda

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#42
In reply to #40

Re: How to Tell if Brake Booster or Master Cylinder is Bad

12/14/2010 11:16 AM

If you have a Ford,you are used to pushing it,I presume.

I recommend Ford for those that want to stay in shape.

(You started it).

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#26

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/11/2008 5:06 AM

One point just struck me (but I will have to rely on our US Colleagues as to whether it is true or not), in Europe, all cars (as far as I am aware since over 20 years or more) have dual circuit brakes, and as this is a Honda (not a cheaply built car), I would expect Honda (and the other Japanese makes at least) to have dual circuit brakes on all their cars, all over the world, including of course the USA!!

If true, then you should have always something like half the braking effect when only one side of a dual circuit system is down. That is part of both front brakes and one of the rear brakes or something along those lines.....

Maybe that is the effect that is the effects that Honda (?) is seeing here......which again points to most probably the master cylinder (at least to me), but air is still a faint possibility too......

In most European countries, cars have to be checked out every two years after the first 3 years, that is done by the MOT in the UK and either the TÜV or Dekra in Germany. I would not say they catch everything, but in my opinion they are particularly good at checking the brakes, steering, suspension, lights and rust in strategic areas.......does the USA have such a system?

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#27
In reply to #26

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/11/2008 7:03 AM

Good point Andy, you've just reminded me of a problem I had several years ago when I had an odd braking problem...

I took it into the garage without a clue what was causing it and they found the dual circuit relief valve (?) was stuck, so I was only getting braking to two wheels!!

Very simple and cheap to fix but it had me and some others fooled as to why...

John.

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#28
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Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/11/2008 9:27 AM

Interesting.

On Mazdas and other Japanese cars, there is a cockpit indicator to let you know (amongst other things like handbrake still on) if only one circuit of the dual braking is working.

It used to be a piece of metal that got brake fluid pressure equally from both sides (in the master cylinder area) and if one side failed, this piece of metal got deformed by the one sided pressure and operated a micro switch to turn an LED or something on!!

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#41
In reply to #26

Re: How to Tell if Brake Booster or Master Cylinder is Bad

12/13/2010 8:19 PM

no we have no system like that we just drive them until the wheels fall off or the only brakes you have includes running off road and hitting bushes

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Anonymous Poster
#32

Re: How to Tell if Brake Booster or Master Cylinder is Bad

06/13/2008 10:51 PM

check the two slider bolts on your brakes if rusty clean and lube. or replace also check for air in line, water in line, check for leaks, best thing have brake specialist check it out

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Anonymous Poster
#35
In reply to #32

Re: How to Tell if Brake Booster or Master Cylinder is Bad

05/21/2009 10:43 PM

DON"T FORGET TO BENCH BLEED THE MASTER CYLINDER!!!

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Anonymous Poster
#36

Re: How to Tell if Brake Booster or Master Cylinder is Bad

01/17/2010 4:27 PM

Hi- I am in the process of registering but wanted to post my concern-

I have a 2002 Toyota Sequoia with about 118K miles. I recently replaced all pads, rotors, and power flushed the brake fluid.

For the past almost 12 months I have been hearing a "whooshing" or "whistling" noise at about the location of the inside brake pedal. Brake assist boost is normal- pedal is feel is normal.

My guess is that either my brake booster is bas ( contradicted by normal assist?) ; or my brake booster relief valve is shot.

Brake master cylinder not leaking.

Ideas? The brake booster is super expensive at over $800 USd and only available at dealership - So I want to diagnose with certainty. At $35 USD replacing the relief valve may be in order just to see is a cheap ficx works.

Ideas would be appreciated.

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Anonymous Poster
#37
In reply to #36

Re: How to Tell if Brake Booster or Master Cylinder is Bad

03/05/2010 10:39 PM

Usually that sound that you are describing is a booster with a leak. You'll want to replace it before it goes completely out. My question is about the price of the part and availability. Someone lied to you....I just went on Autozone.com and checked for both the 4wd and 2wd models and a booster is available for both at only 102.99 after the 20 dollar core. Just type in brake booster once you've added your vehicle and it'll come up. Don't waste 800 bucks at the dealer unless you just want the factory part.

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Anonymous Poster
#38

Re: How to Tell if Brake Booster or Master Cylinder is Bad

05/17/2010 10:20 PM

Just a FYI for anyone who may have problems, especially if they are having to pump the brakes to stop, or it will stop sometimes, and then other times it just goes strait to the floor (spungy feeling). I know it sounds dumb, but make sure if you put new calipurs on it, that the bleed valve is pointing up, and not down. If it is not pointing up, the air can't bleed out.

Learned that one the hard way.

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