1981 928S AT Transmission Problem

[fkassim]

Hi there,

I am writing in hope that someone can help me find a solution to a transmission problem I have on my 1981 928S. Last week I got my radiator serviced (reconditionned). They said it wasnt in that great shape and to make a long story short we had it fixed. I installed it myself. Filled the transmission fluid and connected everything back. Everything seemed fine. Went for a drive and after about 2 miles the transmission was no longer working...slipping and transmission fluid pouring under the car from the back. AUTO Transmission. Took it to the mechanic and apparently there was water in the transmission fluid. Apparently from before the radiator overhaul was done.

So we drained the fluid and opened the transmission pan and saw some fiber build up. They suggested a transmission rebuild. We went ahead and did it without replacing the torque converter. We assembled it again last night and put it into gear....and nothing no forward no reverse..simply nothing. The transmission people suggested may the control valve was the problem. We replaced that and again nothing. So the only logical thing to do was to go ahead and change the torque converter. We did that today and were excited to get the car on the road.

To our surprise the car did not budge ! Are we missing something here ? Could we have overlooked something ? I honestly dont know were to start now. Without actually having to open the transmission again and go through the whole job again. They dont have a way to check the transmision before it is fully installed on the car ! I have already taken down the entire gear twice and am getting sick tired of the process.

Do the electrical lines coming out of the transmission case have anything to do with the car running. My understanding were they were just for the speedometer.

When I put the gear into reverse I hear the car going into gear as if it were going to move but the wheels dont spin at all ! The torque converter is engaged as the flywheel is spinning. Help please....

[Danglerb]

WOW, did a childhood enemy give you the name of this mechanic?

I don't think under any normal or even abnormal condition would coolant leak from the 12 psi radiator into the 100 or so psi transmission fluid lines. My guess is that maybe some water was left inside the radiator cooler from testing or something, and the lines reconnected without first blowing out the cooler.

Wild guess on the transmission, junk of some kind was also stuck in the cooler.

WOW, I don't have much of a clue about the auto transmissions, but it sounds like your mechanic messed up awfully basic stuff.

Maybe post your location and somebody can recommend a different shop.

[fkassim]

Its probably my wife's curse not wanting me to have that car I'm in Jordan and just got this car last week ! I dont think we have any qualified mechanics around. Its an endless trial effort.

Never had a 928 before....when I lived in the states I owned a 1971 911 T, then a 1991 911 C2 Cabriolet and in 2000 moved back and bought a 2000 911 Carrera (996). Then got married and had to sell So I'm not familiar at all with 928s.

Now it seems I have a problem with this car and not sure which direction to take. One thing I do know is that the AT is pretty much a Mercedes 450 Transmission.

[Danglerb]

I'm not sure which model specifically, but its the same as some mid 80's MB sedan, a good MB shop should be able to sort it out.

I recommend proceeding slowly, and running each step past the forum. Everything so far is kind of bizarre, odd events followed by extreme actions.

What exactly is reconditioning of the radiator?
The core can't be repaired, and the end tanks and cooler can be replaced cheaply as a unit.

They said the radiator or the transmission wasn't in great shape? What was wrong?

Actually, start from the beginning please and explain what was going on before anything happened, and then each step of what was done.

Thanks.

[MPDano]

Here is what I would do being the cheapskate that I am. I would loop those 2 tranny cooler lines (hoses) at the radiator, flush and drain the tranny and put a new filter and fluid. Making sure all looks clean before you mount that filter on.

This way you not dropping the the tranny for this test. Give it a test run and if it works, the issue is your radiator coolers. Unless you can get it correctly rebuilt. Trash it and either get a good used or new. If I were to do it over again, I would have gotten new aluminum one since I now see they are only a couple hundred $ more.

Now, if this test doesn't produce results, then you may have to drop the tranny for further inspection. IMHO

[fkassim]

The guy I bought it from had just sent the radiator for a yearly service in which they open it up check the condition and repair anything if needed. When he received the radiator he called me up to reinstall together. The guy's an aircraft service engineer who likes to work on his cars. So indeed we installed the radiator. Connected all the proper hoses back and got under the car and filled up with transmision fluid. Let the car run and topped of more transmission oil until the level seemed fine.

We got in the car and went for a test drive. He actually drove for the first 3 miles or so. Then I got in the drivers seat and not even 20 seconds later the gears started slipping. We stopped the car turned of the enginefor a couple of minutes and restarted and it drove off. A couple of minutes later the gears slipped aagain. We got under the car and fluid was no longer red it was PINK !

We managed to drive the car to the mechanic stopping on the way several times. The transmission prior to that had no problems apparently.

We openned up the transmission lower case and it was full of foamy pink oil which had left a trail in our tracks. Leaking out of the back. Also we found that there was a lot of fiber sitting on the bottom of the pan. The mechanic said we needed a rebuild.

He sent the transmission out to get it rebuilt for the next couple of days without changing the torque converter. WE then reinstalled everything back together (the mechanic that is and not us). Put the car in reverse and nothing. We called the transmission people and they said it was either the valve body, torque converter or the filter. He said if it was the filter then when you start the car the fluid in the reservoir would not go down when you started the car and go back up when you switch it off. We tried that and the fluid level did go down and then back up. So we didnt change the filter.

He sent one of his guys to our location and changed the valve body without lowering the transmission ... started the car and nothing. The only thing left was the torque converter. So we had to drop the entire transmission again and change the torque converter. We changed it and finally managed to get it done by 9pm. Started the car and put it in reverse and nothing at all !

When you put it in gear it feels like it goes into gear ...you here an engaging sound and then like the transmission is spinning but no wheel movement. I have a feeling that the problem is from his rebuild job inside the transmission case.

This is were we stand today...........

MPDANO:

Your idea about connecting the transmission hoses outside the radiator sounds great...but how will that stop the gears from going into place....does that mean if there's no fluid circulation the gears wont engage ??? I thought the fluid circulation was just to cool of the fluid...nothing more.

[MPDano]

I was trying to rule out issues with the radiator and coolant leaking into the oil coolers or whatever. It is just a test and yes, if you loop the lines, then there is still circulation. Just no cooling, which you don't need if your just "testing."

[fkassim]

But what would happen if there's no circulation in the lines ?

[MPDano]

Ok, I'll bite. Explain why you think there would be no circulation in the lines if you loop them?

[fkassim]

There would have to be circulation in the lines if looped if everything is in working order...my question was what would happen if there's no circulation in the system ?

[MPDano]

Gotcha brother! Since I am unfamiliar with the internals, I would have no clue. Isn't there some sort of pump inside? Also, something could be clogged? Most of which requires a tranny drop. Like I was saying, I would do what I could before a tranny teardown.

[fkassim]

Hey dude its a great idea and I'm gonna try it first thing .... you never know it might just solve the problem (keeping my fingers crossed)

[Danglerb]

My crystal ball says .... tranny shop gets to rebuild it again (maybe try a flush and refill first), mechanic needs to pressure test radiator and the coolers.

***** My two cents ...

Radiator was out for annual service (not likely opened up as the tanks can only come off a few times before the tabs start to break, my guess its was a flush and pressure check). Is it a factory Behr radiator?

You added AT fluid? How much and no sign of any leak or contamination?

I'm having a hard time imagining how water got into the system if it didn't happen when the AT fluid was added.

Tranny operated normally for 3 miles, then started to slip, and you stopped the car to check it? Any leaks?

Guessing as soon as the AT came up to operating temp the water started to boil and the resulting steam and pressure blew out seals.

Drove the slipping tranny a few more miles to assure destruction, and found a trail of leaking fluid, and fibers inside the pan.

Sent the tranny for a rebuild, but decided to keep the torque converter.

Was the torque converter drained and lines flushed to remove all the contaminated fluid and fibers before the rebuilt tranny was put back in?

Rebuilt tranny doesn't work. Any idea what problems the shop found, or what they did or did not replace?

****
The electrical stuff is more than just the speedo, but not sure how critical. Everything should be reconnected.

****
MPDano is suggesting you bypass the radiator cooler, and connect the AT lines together, "loop", for testing. That might be a good time to pressure test the coolers and radiator.

[fkassim]

Your crystal ball was right ! The car is now at the tranny shop were they will drop the transmission and do it all over again...I'll find out more tomorrow. Hopefully I'll have a running car then. Whats a simple way for me to flush the system myself without damaging the transmission.

[Danglerb]

Originally Posted by fkassim

Your crystal ball was right ! The car is now at the tranny shop were they will drop the transmission and do it all over again...I'll find out more tomorrow. Hopefully I'll have a running car then. Whats a simple way for me to flush the system myself without damaging the transmission.

Let the tranny shop do it.

If the shop is expected to be responsible for their work, I don't see how they can do less than 100% of the work.

[MPDano]

Sorry, I thought you were doing this stuff yourself. Yeah, Mike it right. If the tranny shop has to rebuild your tranny, then let them flush and refill. Just mention that the coolers might be leaking. "Might" is the key word.

[928 Go Go Joe]

Hi,

Sorry you are having so much initial trouble with your new Shark. I'd definitely think about a new or good used radiator to prevent all this happening again. Here is what I see happened:

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They over pressurized the radiator when they "serviced" it and blew out the seals in the side tank or there was a internal crack created, allowing coolant to mix with the trans fluid. A very common occurrence at radiator shops not experienced with 928's. We are talking about a twenty-something year old radiator. Most shops pressure test to 20-25 psi. The most you should test a 928 radiator is to 18 psi. Even better is to just flush them out, do a visual external inspection, and reinstall and check for leaks. "If it ain't broke, don't fix it!!!" You'd be surprised how many good used radiator that aren't leaking start leaking after coming back from radiator shops. Best thing is to reinstall them and then leave them alone!!!

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-Contaminated trans fluid, raised the fluid level causing seals to fail. Water in fluid reduces compressibility- trans starts to slip.

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-Trans at this point was probably still salvageable. With a trans flush, fluid change and new filter, plus solving the radiator mystery with a new radiator, You would have probably been OK. The 928 uses the same Mercedes trans from the 300 class in the 1980's. It is a very robust, solid and reliable design. Nothing you mentioned, so far indicates the trans was finished. I know from experience that these transmissions are very sensiitve to incorrect fluid levels. Too little, they slip. Too much they leak. That doesn't necessarily mean that the seals are"blown out". I would have taken these steps and gave it a try before agreeing to a rebuild.

Now that it is rebuilt, it's the trans shop's job to make it right. Also, did they check out the differential, final drive, CV joints and Torque Tube to make sure there is no problem there?

Anyway, good luck with the car, hope it works out. I'm sure once you get it on the road, running correctly you are going to enjoy it.

Joe

[Danglerb]

I still have a hard time imagining how water got into the tranny. Even if the cooler was full of water, how do you reinstall it without spilling some and noticing, hey thats water?

How much water does it take to fubar a tranny?

[Danglerb]

A little google and here is what I found.

http://www.quality-trans.com/faq/faq6.htm#31
31- I have water in my automatic transmission. Can it be flushed out?

In a word, no. When water gets inside of an automatic transmission, the friction lining of the clutches absorbs it and dissolves the glue that attaches the material to the clutch plates. Usually, some amount of water will come out of suspension and form white gummy masses in various areas of the unit.

Simply put, this is why the unit cannot be flushed to remove all of the water.

In addition, the presence of water will start rust forming on the ferrous metal parts throughout the unit. The amount of water and the length of time that it is inside of the unit will determine the extent of the damage, but the resolve to the problem will be to overhaul the transmission.

There is no shortcut that will "repair" the situation! It's only a matter of time before the unit will exhibit abnormal operating characteristics and fail completely.

FYI, water usually gets into the transmission in one of two ways. First, all transmissions have a vent to maintain equal barometric pressure inside of the transmission. If the vehicle is driven through water (as in a flood) and the water level is at or above the vent, the water will cool the unit lowering the internal temperature and water is drawn inside of the transmission.

Also, virtually all modern transmissions (some were air cooler in the old days) have two cooler lines that route from the transmission to a special tank the radiator to cool the transmission fluid. If this special tank ruptures, transmission fluid can enter the radiator and water can enter the transmission. In this case, the cooler tank in the radiator will have to be replaced as well as rebuilding the transmission. One of the common indications of transmission fluid in the radiator coolant is the "strawberry milkshake" appearance of the coolant.

Abstract from a SAE paper.
http://www.sae.org/technical/papers/961917
A bench scale apparatus and accelerated test protocol were developed to evaluate the effect of contamination of automatic transmission fluid by mg/kg levels of water on cellulose frictional clutch surfaces. The testing indicated that water added at levels as low as 600 mg/kg migrated to the surface of untreated paper frictionals and contributed to loss of the paper coating and erratic torque transfer properties. Treated, "high performance" paper frictional surfaces showed less physical damage but the same torque transfer effects from water contaminated ATF. A mechanism of water coating, swelling and weakening the hydrophillic cellulose fibers, with subsequent destruction due to hydrodynamic shear was proposed.

[MPDano]

Mmmmm Strawberry Milkshake. I am thinking this is what happened. Looks like that tranny get's pulled. That was also probably the lining that you guys were seeing in the fluid.

I am still betting on the coolers in the Radiator.