You have no problems for 180000 miles, and you think it's engineered for failure? If it ain't broke don't fix it! ...especially if you depend on it for transportation....Have you priced a replacement?...that should be motivation enough to leave it alone....A smooth shift is what an automatic transmission is all about...

haha, true ;) But without that "continuous slip" engineered into it the transmission would likely last double or triple that at least. A replacement is about $4000. That's why I don't want to replace it ;) It is a GM transmission but because it's in a BMW it costs double.

"...would likely last double or triple that at least."

No the harsh shifting would drive you crazy long before that....lol

Actually, I don't think you'd feel the difference considerably. After all, the torque converter is a quite "soft" device to absorb any shocks. I think you'd only feel it between 4th and 5th when the torque converter is in lockup.

I'm just crazy about this car lol. The engine is a beast and lots of people find it working well past 300k miles with no repairs. And that's with crazy people in Germany driving 130+ mph all the time (well, crazy people like me!). It handles better than and is quieter than a modern car of at least $40k. It'll cruise at 120 mph smoother with less noise than my VW Jetta at 70 mph. IMHO it's really a piece of automotive history being the most efficient luxury AND fastest diesel car in the world. There also aren't many left. I read in the entire UK there are only 700 registered.

Just try it--you'll either like it or hate it. Then, if no damage has been done, you can just switch back. It sounds like an uncontrolled experiment, though.

Wow Tornado, over 11,000 posts? That's cool!

I think I should just try it. My only concern is that it might require less pressure during a shift to complete the operation right. My guess is if I can try it while barely moving and slowly add speed while changing gears, there should be little risk of something really bad happening. Rolling at a walking pace should reduce the risk since I suppose there is potential for two conflicting clutches engaging momentarily. It's unlikely, but without knowing how it's programmed you can't know.

What's your background? Do you have much experience with messing around with things like this? ;)

I'm not familiar with this transmission, but it would be interesting to know its exact sequence. I think it would make sense to lock up while in each gear, but to switch briefly to torque converter mode for changing gears. I don't know if slippage in this gearbox means mechanical or hydraulic. The former would involve wear and heat; the latter should be heat only.

My background is in industrial refrigeration design, which includes several trades/disciplines. I imagine we'll hear from some of the automotive specialists on board CR4.

Cool, I still appreciate your replies though :)

I have a solenoid/clutch activation table and it should solely be working without lockup until it's above a certain speed in 4th gear and 5th gear (but also sometimes coasting in 3rd gear for increased engine braking downhill).

Yeah, I wish I knew of some people here to ask. No one knows much about this on the BMW forums.

Do you know if this transmission is used in any other American cars? If so, this path of research may yield better results....

http://www.automobile-catalog.com/car/1999/273455/bmw_530d.html

Actually it was used in a couple V6 RWD Cadillac models. Thanks for the tip!

I'd go to some of these forums. I'll be no technical help. All my vehicles are stock.There are some guys here who will know.

GM V8 Transmission Tuning - HP Tuners Bulletin Board

transmission - Chevrolet Forum - Chevy Enthusiasts Forums ...

Transmission - GM Forum - Buick, Cadillac, Chev, Olds, GMC ...

Good luck.

Thanks! I somehow didn't even think of going to a non-bmw forum. I suppose it is a gearbox used in some Cadillac models as well.

If anyone else sees this thread and might know something about this please still leave a message :) I want to make sure the car survives my potential move to northern Sweden. I'd be driving from the 45th to the 65th parallels

Wow crazy! That's a really cool concept. I'll contact that company and see what they say. I didn't know devices like that existed.

But what do you think would happen if I disabled the pressure control solenoid? Would it likely damage anything? Granted it's a completely different gearbox from what you're accustomed too but I'm talking about in theory. Honestly I want it to be a more sporty feel lol. If it kicked a bit I wouldn't mind. I don't think you'd really feel it much because it's such a heavy car. At my last vehicle inspection (yeah, I guess they weigh it in austria?) it was a bit over two tons of german pride ;)

Normally it shifts so soft you don't feel it. I hate that. I don't want to be driving this slushbox around. Sport mode helps a little.

The GM 5L40 and 5L50 series transmissions are listed on their website as being controllable by their unit.

http://www.powertraincontrolsolutions.com/transcontrol.php

That's a cool unit right there. The problem is it carries a pretty heavy price tag lol. I think it's 700 some bucks. For a few hundred it's probably a good idea but for that price I'd probably be better off putting that towards another used transmission from eBay. Luckily in Germany they are reasonably common as they were on every 6 cylinder BMW of that generation up to the x5. In the near future when I get my job I think I'll invest in that device though ;)

Consider the price relative to something else like the fuel you buy. How long does it take for you to burn up $750 in fuel?

Not saying that a independent controller will save you a dime on fuel but just as a comparison to something you spend a fair amount on all the time for your vehicle without second thought.

BTW for me $750 equates to two fills of the propane tank and two fills of the gas tank on my dual fueled F250 pickup or about an average months driving.

Haha you're right. About 3000 miles or so because diesel here is between 8 and 10 bucks a gallon in Europe. I can get up to 35 mpg but I live in the mountains and only get about 20 with the city or mountain driving I do. I never thought of it like that. Fair point. But still my only goal right now is to decide what I can do to make sure the car makes it across twenty lines of latitude to my new job haha. So generally speaking a faster harder shift gives less wear, right?

Correction... between 2000 and 3000 miles to spend that much depending on the driving :)

B and M transmissions has been in the high performance automatic transmission business since i started racing. they're the biggest and the most knowledgable transmission specialists in the would.

a smaller torque convertor "if you can find one at a auto wrecking yard" along with a b&m shift kit will increase the pressure and lock the cluches up faster, slower, smoother, ect. there's dozen of types available to suit your needs.

it only involves dropping the pan, removing the filter and replacing the plate that controls the valve pressures.

it's a two hour job for a novice.

i should have mentioned that there will be a few springs and check balls above the plate that will fall out. make note of the holes that they need to go back in.. i think the info is in the kit. approx. $50..0

B and M can give you advice on the torque convertor, but it's going to be hard to find with the model of car you're revamping.

That's an interesting idea if it's really that cheap. But why would a smaller torque converter help me? It would most certainly get hotter and transmit less torque. Even stock, BMW gave the engine more torque than the transmission was rated for. Then of course I tuned up the engine ;)

the smaller convertor has a faster "stall speed" meaning the fluid velosity and viscosity in the smaller torque will produce high pressure in a shorter time. large convertors are designed for comfort by making the shifts smoother. it involves the larger internal vanes that move the fluid,. increasing the velosity of the fluid makes it act more like solid due to the fluid viscosity.

This has it's own pump so the size of the torque converter shouldn't matter for pressure. I think the TC is already under engineered for the size of the engine.

Remember that the valve is PWM driven, so adding a resistor in series will, either make no difference if the coil still receives enough voltage, or have full pressure if the voltage drops below operating limits of the valve.

What you need to do is to detach the signal from the valve, connect it to a monostable multivibrator, use the corresponding transition input to trigger it.

Positive or negative transition has to be selected according to the polarity of your PWM pulsetrain, i.e. the type of signal, sourcing or sinking, most likely sinking (from a NPN transistor) due to higher current capacity.

Select your capacitor and potentiometer such that they don't generate a pulse wider than the widest pulse from your original control, but will allow reduction to virtually 0% duty cycle (full pressure).

If you don't get the desired results, you can easily go back.

If you like the performance you might want to instal a slide pot in here:

That's a cool idea, I appreciate your reply. That would be a really cool project for the future. But I realize that putting a resistor there would be only to fool the TCU into thinking that there is still something there (i.e. no warning lights). The solenoid would be disconnected entirely.

I'd want to scan the car to see if the slip (of the gear selection clutches) is really occurring during driving. You should be able to get trans input shaft rpm and output shaft rpm and compare the values at different loads to see if slip is occurring (other than, of course, just after the shift itself).

From what reference did you get the info on continuous gear clutch slip? I agree that this seems insane from both a wear and fuel economy perspective. There have been numerous models of auto transmission in which no slip at all occurs in the clutches (other than immediately after the shift) and many in which prolonged slip (as shown by incorrect input shaft vs output shaft speed ratios sensed) causes an error code to be issued. Given that if the designer wants slip at certain times he can modulate the TC clutch, why have continuous slip in the gear engagement clutches? This would seem to lead to eventual clutch shudder.

This transmission is probably near its limit for torque in the BMW application, and adding shock loading by hardening up the shifts would probably not prolong its life (or the life of related components, such as motor mounts, rear end gears, etc.)

Here's a paper from Luk on torque converters (and TCCs) from the era when your BMW was made, which talks (among other things) about the hazards of prolonged slip and the means to reduce the damaging effects.

As a practical matter, changing the clutching routine from one long established can cause rapid clutch wear, shudder, etc. The plates appear to get "settled in" to a routine, and changing that routine causes different thermal stresses. Sometimes it is best to leave well-enough alone.

I have some tools to scan with but I don't have anything which will find that data. Apparently, the transmission computer calculates slip on its own and will give a trouble code. I suspect though it will only turn on a light if it's REALLY bad.

The only way I know it was slipping is that in 4th and 5th gear above a certain speed (~55kph) the TCC is locked so the engine tachometer should match the speedometer. It was visibly jumping in 4th gear (also it was audible in that the engine rpm was changing) but not in 5th gear (5th gear uses different clutches according to the technical document I found).

The continuous slip thing I'm mentioning is supposed to be highly controlled. It must have quite accurate speed sensors at various points. I know for sure the TCC operates under that condition. Ever notice how on many automatics the engine tachometer will jump like 50-100 rpm and go back down to what it was initially under first acceleration at say 50-60 mph? The TCC is supposedly in lockup, but it's under reduced pressure. This transmission I know for sure does the same thing. So does my uncle's BMW 750i, my parents' Ford F-250 and Chevy minivan. It has a PWM for the solenoid to modulate the pressure. But as the system changes (seals start to leak, tolerances widen etc) it doesn't have the proper feedback loops to compensate. There are NO pressure sensors in this transmission. It just assumes it has a certain pressure with some signal value and only increases pressure if the slip is really high. Stupid design. This continuous slip is supposed to be very little. Not enough to see in the tachometer. I'm an engineer but this isn't really my area of expertise so my educated guess is to make it as smooth as possible. If there is say 0.1% slip all the time, any vibrations or noise in the drivetrain would be reduced. Only a small amount of efficiency is lost and since these are wet clutches, the majority of the slip will be taken care of by the fluid.

That continuous slip thing isn't well documented but I'm certain it exists. I've had mechanics tell me and I read it on some forums. I really don't know why they do it because on my car it used to operate in reduced pressure between 100-120 kph. It would normally do that 50rpm jump in that speed range if you accelerated after coasting. It was slowly becoming more and more (to the point it was a 200-400 rpm jump). Above 120 kph it was under full pressure and wouldn't do that. I spoke with an engineer at ZF (the german gearbox company) and he said they do that to reduce low frequency vibrations and noise. But now I have the TCU mod it sounds no different. That's why I think GM and BMW engineered failure :)

I read they reduce clutch shutter by oscillating the pressure when accelerating in 5th gear. I imagine it could have only been the TCC doing that. I remember when I first got the car "chipped" for more power it was apparent that the clutches were oscillating in pressure. Now it doesn't do that. But I can't find a link at the moment to back up my claims :)

Cool, so in the link you gave it says "The lock-up clutch operates partially with continuous slip, and is, in many cases, modulated, for example during gearshifts or after tip-ins."

So I was right ;) It's translated from a german document by a german which is obvious because of all the extra commas :D But I was also right that it is to reduce torsional vibrations. I don't think it says how much slip there is in a typical TCC but I imagine it's not a huge amount.

Yeah, I was also wondering about the clutches being settled in to a routine as you say. The heat distribution during a shift will be different if it shifts faster or slower than it always did before. But it would always vary the shift speed anyways, it's just going a bit faster than before. But, if the transmission was even a little bit suspect to begin with it's just a last ditch effort to make absolutely sure it makes it several thousand km to my next destination ;)

The guy who modded my TCU actually sent me another different one just yesterday. I got a chance to test it out. Inside the case, he provided several jumpers to give 5 levels of clutch pressure (from stock to as high as it will go I guess) and 4 vehicle speeds to activate the TCC. Naturally, I put the clutch pressure to the highest. I think it shifts kind of like I remember my brother's old honda accord shifting. It's just a firmer shift instead of gliding through gears like it did before. And I don't believe 4th gear slips anymore in TCC lockup! So for now, I think I'm ok :p Hopefully in a few weeks it'll get me to northern Sweden! haha :)

Thanks everyone for the replies! I learned a lot more about transmissions. Hopefully someday I'll get a job at GM, ZF, Ford or any other transmission manufacturer ;) For now though it looks like I'll start the PhD with SKF in Sweden. Working for a huge bearing company, I can then say "We've got balls" hehe