NSW928

I've encountered a weird issue with my transmission - I've spoken to a few experts and no-one has actually heard of this problem before out here, hopefully someone a bit further away might be able to put their finger on it!

First some history - I competed in a 'motorkhana' (time trial around cones) event last weekend. I was meant to do 8 of these (40-50s each in first gear) but i started leaking ATF fluid after the 5th and retired from the event. I nursed the vehicle home without issue and the next day drained the ATF sump and torque converter (yes the ATF which was removed was dark and smelly) and replaced with approximately 6L of new Dex III. The levels appear right according to all the processes described and the leak has stopped also.

Now to the problem - when the vehicle is cool the transmission works fine and gear changes are smooth. Once it warms up and I speed up it will downshift to 3rd and then after a while as I slow down it will downshift to 2nd, and it stays there for good. If I park for a few minutes it will drive off fine again but I have to go slow to avoid the downshifts from recurring.

I'm inclined to think I've blown something in the valve body. There are some things I can investigate from the troubleshooting section of the WSM:

WILL NOT UPSHIFT
Incorrect governor pressure. Defective governor assembly.
Check for stuck kickdown solenoid or for constant voltage to solenoid
caused by a defective fuel pump relay or sticking kickdown switch.
Valve body dirty or valves sticking. Repair or replace valve body.

UNCONTROLLED DOWNSHIFTS OUTSIDE RANGE OF KICKDOWN SWITCH
Remove kickdown solenoid. Check "O" ring on kickdown solenoid
for damage. Check kickdown switch for sticking in pushed-in position.
Replace switch (if necessary). Check for kickdown solenoid stuck in
opened position. Replace kickdown solenoid (if necessary).

One suggestion was to check the Bowden cable and make sure it retracts when the engine is hot. Aside from that I'm not really sure where to start, anyone encountered this before?

1987 S4, Metallic Cassirot

Speedtoys

Greg: Any of that sound familiar?

FredR

Not that it will likely solve your problem but did you drain the torque converter or just the sump?

You obviously understand the ATF condition has potential implications so no point labouring on that. All I can say is that I have done a few autocross type events with tight and twisty 1st/2nd gear driving and had no issues so if something has failed [we do not know this yet] I might suspect it was something where potential for damage had already been realised prior to the event. Do you know the condition of the ATF before you took part in this event and how long/how many miles it had been in the tranny?

Doubtless our experts will chime in with some informed opinions when they wake up.

Rgds

Fred

NSW928

I agree Fred that if something has failed it was possibly pre-existing. I've only owned the car for 6 months and changing the ATF and filter was one of the first jobs I did, that was 4000km ago. I haven't had any issues with the transmission in that time. To answer your other question I drained the torque converter as well as the sump. A possible clue is that only a total of 4.5 litres came out this most recent time and 6L went back in.

I'll attempt to go through a process of elimination of possible minor causes before I tackle the bigger possibilities. Any suggestions/input would be appreciated though, auto transmissions aren't my specialty!

I budgeted for a moderate catastrophe when I bought the car, perhaps this is it!

FredR

Allowing for deferred maintenance is a necessity for these cars- the amount to allow does not get smaller with the passage of time sad to say. Folks have had icky looking ATF and a good flush "cured" the problem [as in removed the symptoms] but ATF is the lifeblood of these things and very important to have the right amount of fluid in there and in good condition. ATF is relatively cheap but new transmissions anything but.

Once you get crud in the ATF then the valve body becomes susceptible to passages being partially or totally blocked- whether such would explain your symptoms I would defer to the auto tranny experts but it has to be a suspect. Beyond that the real question is whether you have damage to clutch plates and the like.

Just keep an open mind until further analysis proves there is something that needs intervention.

Greg Brown is the guru when it comes to automatic transmission trouble shooting and rebuilding- hopefully he and some of our other heroes will give you some pointers

Rgds

Fred

WallyP

The first thing that I would do would be to pull and check the kickdown solenoid.

Marti

I very much doubt you will find something has broken in the valve body. As part of an autobox problem I was having I had to flush the system 5 times before I was able to remove the contaminated fluid caused by a broken radiator. Each time I flushed the problem reduced slightly. I did remove the valve body and thoroughly clean it (it was quite dirty/high miles). It was quite easy to do with pictures from the WSM.

I see you put in Dex III into it. I used Dex II which was the recommendation I found when looking for fluid, I am not sure if that or the brand could be a factor ?

Also fluid levels are very important, you do need to check and re check. I got the level to the correct amount, took it for a drive and re checked to ensure it was still correct.

potdog

Change oil and filter and add Lucas transmission fix had good results by doing this on mine

GregBBRD

6L for the both the convertor and the oil sump is not enough.

Get the transmssion warm and check your fluid level, before you go too much farther.

On Speedtoy's freshly rebuilt transmission, he was apparently using 1st gear to start, after the rebuild. The secondary oil pump is apparently active when starting in 1st gear (from what I can tell from the literature.) Anyway, the two gears for the governor stripped (apparently a common problem in the Mercedes version of these transmssions.) Once the governor stopped rotating, shifting became...very strange. I'm sure Jeff can elaborate on the shifting problems...I drove it around the parking lot, knew somethng was wrong, and took it out.

NoVector

When I read that you put 6 liters in, I thought, wow that's about a gallon less than mine--is an 87 really that different(?) So I just looked in the 87 owner's manual and your capacity is about 2 1/2 gallons. Low fluid would definitely causes foaming and weird shifting. Or maybe you really only changed 1/3rd of your fluid. Anyway, I would definitely re-check your level. Personally I check it at the "warm" level, take it for a spin, and then check it at the "hot" level. In case you don't have the manual, you can download it here: https://drive.google.com/file/d/0BzC...n&pref=2&pli=1

Charles Parkinson

Call Bruce Buchanan in Balgowlah ... Nobody else in Sydney comes close to his and his son Sean's (JET951 on rennlist) understanding of these cars / transmissions, especially when they are used for club events.
Cheers, Charles

Speedtoys

I dont start in first a lot, but sure..I do some.

My failure mode was one day coasting down the mountain road in rush hr traffic, This would be..for maybe 2miles, and only on the morning side of the mountain, never on the way home at night.

But one day, doing about 15-20mph as usual, the car downshifted to 2nd gear, and would not upshift.

Once I got open area near the highway, I discovered I could start in 1, but would not upshift. I had to go into N, wait, put in D, and I could get 2nd gear, but no more.

What was odder still, was that if I started in 1st, and lifted off the gas, it would free wheel, like I was in N, no engine drag.

Parked, trailered to greg.

Right NOW..I havent found a way to get it to upshift from 1-2 at WOT, it does as expected at non WOT.

Ive losened the bowden 2 turns..did not help so far.


??

NSW928

Thanks everyone for your input, I've been offline for a few days. My understanding is that the fluid capacity overall is about 8L, but that after a change it's only about 6L as there are a couple of litres left in the lines (I don't have the tools to do a complete flush at this stage). I'm about to lift her up now to check/clean the solenoid valve so I'll recheck the level while I'm at it. I've eliminated the relay and switch as the cause.

Will report back.

NSW928

That's it there right? I didn't notice the crack on it until I had a look at the photo just now. Can someone talk me through what I'm looking at there? I can't seem to get it out fully without dropping either the tranny or the suspension, so what do I do now?

Speedtoys

The lines drain with the trans, it is the low point.

If you removed pan, and removed the TC plug, you flushed all you had in it.