Please help, I need the collective expertise of the members of this forum.

I am presently stumped by a seemingly very unusual transmission problem that neither my indie nor myself can quite figure out. Any help would be appreciated.

I have recently purchased a very nice 87 300SDL with 240K miles as a stablemate to me 92 300D with 380K. Driving it home from New Jersey to Michigan I noticed a slight problem at the start of the trip that seemed to resolve itself after a while: Approaching highway speeds, the transmission was very reluctant to come out of passing (3rd?) gear. Eventually it did and I drove it home and for several weeks with no problem.

I took it to my mechanic for a laundry list of repair and maintenance items and mentioned the shifting problem to him - he subsequently changed the very dark tans fluid and filter and suggested that the problem seemed to be alleviated - and it was, for a couple of more weeks.

Recently, about 8 miles into a freeway trip cruising at 75 on cruise, the trans dropped to passing gear and was coaxed out by tapping accelerator to hit the kickdown switch. This worked more and more reluctantly for 1-2 more miles until it stayed in the passing gear at ~4000K on the tach. A few moments later, the trans decoupled from the engine completely and I coasted to a stop, the engine able to uselessly rev. the whole time. After shifting to park and back to drive, the car was able to go again, but would not shift past 2nd gear.

When the car cools off, the problem goes away and starts over again on the same cycle. It seems to be related to the trans running for 6-8 minutes at freeway speed (60-70 mph) and goes away after it cools down.

My indie is checking out a possible stuck kickdown switch, though that wouldn't explain the repeated delay in failure. He has checked thre vacuum lines that control the trans and they appear to be operating normally and the trans fluid pressure also seems to be OK.

Has anybody experienced anything like this? If so, how was it corrected? If not, what would you suggest? I don't want to replace this trans in order to get my car back and running, especially if it won't correct the problem.

I understand it to be a 722.321 transmission.

Any help would be profoundly appreciated.

pete

Kickdown switch would be a good place to start. Sounds like something in the transmission is overheating at highway speed and causing slippage?

Easy stuff to check:

Check fluid level, per the Owner's Manual.

Check the Bowden cable adjustment, it should not be under tension at idle. (Do a search on bowden cable if need be...)

Check kickdown switch, see if it's jammed, or loose. You could try disonnecting it...

Nastier stuff that may mean spend $$$:

You mentioned dark trans fluid, that might mean "internal stuff gone wrong..."

Best regards,

Jim

As redundent as it may seem try replacing the fluid and filter again...

Seems like the old tranny fluid was [gnarly?] enough to contaminate the newer/fresher fluid...

Have vacuum checks performed on the modulater valve and vacuum supply line...

Just trying to help, thanks.

Also if by chance your tranny has fluid disappearing it could be the modulater valve...

I had something similar happen with my 87 SDL, wouldnt shift into 4th unless I first shifted to neutral then to drive. Turned out the fluid was a little low, after topping it up, it was fine. Need to adjust the cable though, as it does hold into all gears a little too long. Was shifting too soon and I adjusted cable but probably tightened it too much.

The kickdown cable on the 603/722 tranny works "backwards" from most -- it is all the way out of the housing at idle and all the way back in at full throttle, should be all the way out with a tiny bit of pressure on the spring at idle. If you screw the aduster to move the cable "in" you will get later shifts, not earlier.

As for the actual tranny problem, I suspect you have a clogged cooler, and the tranny is overheating. By now, it's time for a new tranny, the old one is toast. Most likely the clutch packs are worn out from the low pressure resulting from running too hot (and possible frothing fluid), and there is a possiblity it has gotten coolant from a bad cooler in it -- this will both strip the lining off the clutches and foam the fluid when it gets hot.

Failure to stay in 4th is usually a sign it's time for a rebuilt tranny.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Ahh, that explains it. OK, will adjust it oposite from what I am used to. I was not the one with the major tranny problem, mine just wouldnt shift right when it was low on fluid, when I corrected that, its fine except I was adjusting the cable wrong.

Thanks

Thanks for the info, I'll keep working on it...