I have a '94 E320 wagon that has suddenly started downshifting on its own. It usually starts happening after the car is warm, maybe 10 - 15 minutes into driving. I'll be cruising along at 65 and suddenly it shifts down from 4th to 3rd and the RPM's jump from below 3k to between 3k and 4k. It has also on occasion downshifted to 2cnd after downshifting into 3rd.

If I shift into neutral then back into drive it will go into the correct gear, but then downshift again after a few seconds.

I've checked the fluid and it is clean and at the correct level.

I disconnected the kick-down switch under the gas pedal without any effect on this problem.

The shifter bushings are good, no slop in the shift selector.

This morning I disconnected the Bowden cable thinking that perhaps it was out of adjustment. No change in downshift problem.

Additionally, this car has an updated (non deteriorating) wiring harness and throttle body. The engine idles and runs smoothly.

Can anyone advise what I should try next?

Looks like you are having a similar problem to this guy.

http://www.peachparts.com/shopforum/tech-help/393874-e320-94-limp-mode.html

Loss of governor pressure will cause uncommanded down shifts. This was common on GM TH 350 / 400 trans due to governor bore wear. I'm not sure if this is possible on your trans.

While driving at lower speeds last night, ie not the freeway, the car was downshifting on its own all the way into second. I found that if I accelerated hard it would eventually upshift, but well above 5K rpm

You disconnected the Bowden cable but maybe it’s sticking in the sheath. Does it movement freely when you tug on it? Do you feel the springiness on the far end.

Sixto
98 E320s sedan and wagon
02 C320

This is happening to me also. A friend said there is a switch, forgot the name by the wheel hub. He said he took it out and cleaned it good, put back in and the car drove great again. Not sure of the name of that part.

Three possibilities basically: Either the valve body is dirty and some passages are clogged OR a valve is sticking in the valve body OR the K2 clutch pack seal is leaking/damaged.
Take out about 10 oz of transmission fluid and pour in a bottle of Lubegard 60902 transmission fluid protectant (red bottle). Give it about 150 miles and see if it goes away. If not then you may have to open up the transmission for repair.

Tried the Lubegard suggestion below and took the car for a ~70 mile drive. The trans shifted fine getting to the freeway which is about 10 minutes of normal city driving. Once on the freeway it did well too, it shifted without issue into the highest gear. At several points during the trip I manually downshifted then shifted back into into 'D' and it always shifted back, although a few times not quite as quick as I would expect.


At the end of the long drive coming back into town it started acting up again. Once I was off the freeway and back to city driving it started downshifting two steps (I think into second) and wouldn't upshift. I could put it into neutral then back into 'D' and it would go into the right gear, but then a few seconds later it would downshift again.

One thing I noticed is that the ATF I dropped to make room for the Lubegard looked pretty dirty, i.e. I didn't see any metal in it but it was murkier than I would have expected it to be. I haven't changed the fluid since owning the car so I'm wondering if just having old fluid could be causing problems. I plan to change the fluid asap and re-add a bottle of Lubegard to see if it makes any difference.

How many miles on the car? These transmissions are not known for longevity. My 300TE had a destroyed 2nd gear band at less than 138,000miles (when I bought it, fixed the engine issues and found it was skipping 2nd). If the fluid hasn't been changed at the proper intervals, you may well be looking at a rebuild.

I had a similar issue with my '94 E320T when I first got it - fine around town but would start dropping to lower gears and eventually losing drive after extended highway driving; pulling over and letting it cool down would let everything return to normal.

Not having a high level of confidence in the maintenance habits of the previous owner, I drained the transmission, replaced the filter and refilled with correct fluid to the proper level, and it's been fine ever since.

Your original post said that you had good fluid at the right level, but it can be difficult to get a proper reading on these transmissions, so starting with an empty transmission and putting in the correct amount will at least give you a known baseline. Plus, it's easy and cheap and can't hurt.

I figure mine was aerating, and stopping the car to cool let the bubbles come out of the fluid. Don't let anyone tell you these transmissions are fragile - both my wagons have/had mileage well into the 200ks and work/worked perfectly fine.

__________________
Robert Fini

'12 ML350 BlueTec, 100k
'06 E320CDI (x2)
'05 T1N Sprinter 2500/Pleasure-Way Plateau TS, 70k
'97 C36AMG, 319k (son's)
'94 E320T, 249k
'93 190E Sportline LE, 168k (daughter's)
'84 190E-2.3/5spd (Stage Rally Racer)
'66 230 W110 Sedan (Barn Find, Vintage Racer build in progress)

In my experience it needs about 150-200 miles to really see the benefits but if you saw some improvement it means that there is hope...
It seems that your existing fluid is worn out so like you said, change the dirty existing fluid with some new Dexron III (don't forget to drain the torque converter too it has a allen plug screw to drain it) and add a bottle of the Lubegard and it looks as if it may solve your problem. These 722 series ZF transmissions are actually garbage, they rarely go beyond 100K without problems (i am on my 4th one...) but that additive has been very helpful in my experience.

I hate to possibly jinx it by talking about it, but I changed out the fluid and filter this last weekend and so far I haven't experienced any of the symptoms I was having before the change. The fluid was exceptionally dirty and murky, so shame on me for not changing it sooner.


I didn't empty the torque converter, so I'm thinking I will drain the pan again in the near future and refill again with fresh fluid.

Also, I somehow managed to break my speedo cable while changing the ATF and transmission filter. http://www.peachparts.com/shopforum/tech-help/394076-whats-cable-hanging-down-my-transmission-speedo-cable.html