I'm sorting out a new-to-me 1987 300D with a 722.317 transmission. It has had shifting troubles of the 'not wanting to go into 4th gear' sort.

Here's what I've done so far...

1. unplugged, removed the kick-down switch (result: no change)
2. replaced and 'tuned' the modulator. I found the thrust pin to be broken. (result: shifts were softer but 4th gear problems remained)
3. adjusted the Bowden cable (result: no discernable change to the 4th gear problem)
4. drained tranny fluid (including torque convertor), replaced filter and refilled fluid with DexIII. Spent a lot of time making sure the fluid level was correct. (result: transmission shifted great! 4th gear was back! For about a day!)

The fluid I drained in step 4 was really dark and the filter looked very old (should have done that as step 1). Once I got the fluid level dialed in it started shifting beautifully. I took it for a long drive, both city and freeway, and all gears were working as expected.

Today I drove the car to work and it continued to work as expected. On the way home it was working great as well. I stopped for about 1.5 hours at my son's baseball training and when I started driving 4th gear was basically gone again. It seemed like it was on occasion trying to go into fourth but was slipping instead. When I got home I checked the fluid level and it was still right where it should be.

Can someone who understands transmissions better than I advise on why it would work so great for a day and then suddenly go back to losing 4th gear? Am I probably dealing with a dying tranny or might there be some other fixes to try?

I don't understand trannys but it sounds like it could be fluid related. IMHO you might benefit from draining some new fluid out and putting in a can or two of trans-x. General concensus is it can help but not hurt.

After that IMHO I would drive for a week or so then drain and replace the fluid again.

Could also just be worn out if it's a high mileage car. The fact that fourth came back for a while sounds promising though. Good luck

Fourth gear places the greatest demand on the hydraulics, because both clutch packs are engaged. If there are internal leaks, pressure drops and fourth won't engage. A good shop would put a gauge set on and determine the working, modulator, and governor pressure. But bottom line, your transmission is likely on the way to a rebuild. About all you can do is throw in a bottle of snake oil and hope for the best. Look for something that includes both friction modifiers and solvents.

I'd be interested in the color smell of the fluid removed and what was found in the pan

3rd gear is using the K1 clutch (and B2 band) - but 4th uses the K1 and K2 clutches. Your problem sounds like a K2 clutch problem. That narrows it down a bit.

That you had an improvement after the fluid change is promising. If the fluid is already dirty then I'd be tempted to gamble a second time with another fluid change. I know fluid is expensive these days but ...

...I don't know exactly how similar the .317 is to the .315 and .303 transmissions which share the same valve body but this thread might give you some encouragement to have a look in your valve body =>

722.303 in bits photo shoot

(Positions of the valve body parts are shown for .315 and .303 valve bodies)

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

Would a leak due to a worn Bowden cable seal create shifting problems? I'm pretty sure I have a slow leak coming from around the Bowden cable. That or one of the other items on the passenger side is leaking (B1 or B2 piston cover, dipstick, oil cooler line).

The fluid I took out was quite dark compared to the fresh fluid I put in. I didn't catch any smell other than typical transmission fluid smell.

Also, I did put in a bottle of trans-x. My intention was to drive it for ~1000miles and then re-service it again.

External leak could do it, but it would have to be substantial enough to reduce working pressure. You'd have a major mess.

Changing fluid again can't hurt.

If the leak is big enough to change the fluid level then that could be the problem. Correct fluid level is seriously important for the correct operation of these transmissions.

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

The leak isn't very big, I've been keeping an eye on the fluid.

Last night I took the car out again and now third gear is gone as well! It just keep revving and doesn't shift. If I rev it up high and then take my foot off the gas it feels like it might shift as the revs drop, but if it does it immediately shifts back down to second as soon as I give it any throttle at all.

Without starting a long 'what oil is best' thread, can I ask whether I should consider a different fluid if I drain and refill again?

When I serviced it a week ago I used relatively inexpensive DexronIII/Mercon off the shelf of my local FLAPS.

Has anyone ever used TrickShift, which is supposedly just re-branded Type-F fluid? I've read in other, possibly less reputable, non-Mercedes forums that Type-F can help the clutch grab better.