Transmisssion Intermittently Slipping '84 300SD

[gasman]

Over the last 3 months, I've noticed on initial startup in the morning that the transmission is slipping, I believe while in 2nd (could be 3rd), on my 84 300SD with 250,000 miles. The car is in central Texas with mornings temperatures 40-55F. This has occurred about 3 times over this timeframe. It is only momentary and like the title states, is very intermittent.

Again, while in 2nd (or 3rd), I notice a loss of acceleration and the engine revs up to 4000, I let off the accelerator, gingerly reapply more accelerator pedal, and the transmission catches and all is well for the rest of the day (and for that matter, for weeks). This occurs within a few blocks of leaving the house.

Otherwise, the rest of the time the transmission shifts fine through all the gears, with no flaring or hard shifts. I do notice that sometimes when the transmission downshifts from 2nd to 1st on hard acceleration, it does so abruptly to the point of chirping the tires. The transmission fluid is red and has no burned odor, and is at the correct level. When shifted into reverse, it takes about 1 1/2 seconds for the transmission to engage. The fluid probably has not been changed in 35000 miles though.

All the vacuum lines under the hood appear intact with none disconnected. All door locks work properly, and the engine shuts off promptly. There does appear to be some oil leaking from around the vacuum pump leaving a drop or 2 on the driveway every morning (Just adding this info, not knowing if it could be related).

[P.E.Haiges]

gasman,

Try adding some TransX to the transmission and after about 1000 miles, change the transmission fluid to Mobil 1 synthetic fluid ATF and change the transmission filter.

If this doesn't work, you my be looking at a transmission rebuild.

P E H

[Hatterasguy]

Try what P.E.Haiges said first. If that doesn't work run it until it blows. The trans might last another 50k miles.

[tesavage]

I would suggest changing the transmission fluid and filter before adding any sort of additive (but I am generally no fan of "miracle in a bottle"-type products, especially when used in lieu of proper maintenance). The fluid may seem fine, but it is overdue for a change, and old fluid and/or an occluded filter can cause all sorts of strange problems. BTDT - Basics first.

Is it only slipping when in gear, or as it shifts? If you get any slip/flare in the 2-3 shift, you may want to change K1 accumulator spring whilst changing the fluid and filter. I'm unsure, however, if a tired spring would account for such an intermittent problem.

Good luck,
Tom
'82 300D 317k
'96 Passat TDI 177k

[leathermang]

There are some great threads concerning Trans-x... (they should be read)
I think I was one of the first to champion it...and have been pleased with the number of good results reported.
I have said this before with regards to the order of use/filter/fluid changes...

The Trans-X has varnish dissolvers in it... so the filter and fluid should be changed once it has had a chance to work..

If you only put new fluid into the trans you do not have any dissolvers to get the burned on varnish to change forms... back into fluid so it can be evacuated from the trans..

[tesavage]

Originally Posted by leathermang

There are some great threads concerning Trans-x... (they should be read)
I think I was one of the first to champion it...and have been pleased with the number of good results reported.
I have said this before with regards to the order of use/filter/fluid changes...

I'm not trying to start another "oil war"-type debate or impugn Trans-X, which may in fact be a great product (I've never used it), but...

The Trans-X has varnish dissolvers in it... so the filter and fluid should be changed once it has had a chance to work..

If you only put new fluid into the trans you do not have any dissolvers to get the burned on varnish to change forms... back into fluid so it can be evacuated from the trans..

Mobil 1 ATF is loaded with detergents, too. To my mind, if maintenance has been neglected and the car's performance begins to suffer, the first step is to perform the required maintenance. Old fluid and clogged filters can create all sorts of odd behavior in a transmission, and if caught before serious damage has been done, fresh fluid and a new filter is often all that is required to correct it. How do we know varnish deposits are the cause of gasman's problems, ayway?

Those slide rule-wielding guys in Sindelfingen built a truly amazing machine, capable of lasting an incredibly long time without the use of any addititves so long as three simple rules are followed: "Maintenance, Maintenance, Maintenance!" Now, if I had a misbehaving transmission that simply would not operate properly after all the standard procedures had been followed (fluid/filter, bowden cable, vac modulator, K1 spring, etc), well, it is likely teetering on the precipice of failure anyhow, and I'd be happy to throw additives at it in hopes of eking a few more miles out of it before a rebuild. But I fail to see any reason to do so before that point.

When I first resurrected the AC in my 300D, it would run unaccebtably hot while charging through the Appalachians at high speed in hot weather. I'd read how RedLine WaterWetter can help lower operating temperatures. So I tried it. No noticable change. Cooling system maintenance had been neglected by the PO, and the only real fix was to correct the resultant damage (descale the engine and rod-out the rad) and refill with fresh MB coolant. 3.5 years later, it still runs nice and cool no matter what I throw at it.

Sorry this has grown to be so long-winded, but as you may have guessed, this is something of a touchy subject with me.

Tom

[Jim H]

Sounds like it's slipping when cold. Possible reasons:

A. Thicker trans fluid takes longer to pump up to holding pressure.
B. Varnish in passages aggravates thicker fluid in A.
C. Vacuum modulator not applying as much pressure as it should.
D. Nothing listed here.
E. Some of all of the above.

My SDL slips more when cold, probably from A, & B above, plus there is a temperature switch to 'soften' shifts when cold that aggravates condition C...

My plan is a fluid change first, perhaps some Trans-X or other varnish dissolver just before the new fluid. Then, probably some adjustments.

If that all fails, I'll drive it until it fails completely and drop in a remanufactured, or good used replacement.

Best Regards,
Jim

[leathermang]

"....fresh fluid and a new filter is often all that is required to correct it. How do we know varnish deposits are the cause of gasman's problems, ayway (sic)?"

All of your objections have been answered in the other threads on this subject.. but it looks like you are too upset to go read them... so I will point out a couple of the most obvious answers... to whit :

We don't know he has a varnish problem... but many of us have used the trans-X on these types of problems and it immediately cured them.

The cost of doing this is WAY LESS than any other plan of action I know of and it does not preclude doing the OTHER things which cost more. It is a low cost attempt to logically correct what many who have taken apart automatic trans valve bodies know can cause problems.

If you have these symptoms putting only new fluid into the system does not introduce anything which would be expected to erase the build up of varnish by the old fluid.. thus the need for dissolvers.

Check the amount of fluid your transmission has.. it may take two bottles ( particularly since it comes in different sizes ) to follow the instructions with regards to strength.

[gasman]

Thanks to everyone for all the good information. I have read many of the Trans-X threads. The transmission fluid, though seemingly okay, is indeed overdue for a change. I'll probably try that first before Trans-X. Would using Mobile 1 synthetic be advisable or is regular Dextron III the way to go?

I'm not sure if the slipping is occurring at the 2-3 shift or after since it has occurred so few times, I'm moving so slowly, and I'm not paying attention until I notice the loss of power and the engine reving.

I like Jim H's list of possiblities and hope that new fluid and filter will cure this. None the less, I am concerned about the 1 1/2 second delay in engaging reverse. Does this along with my slipping symptoms portend imminent failure of the transmission?

It's strange that it is so intermittent, but it definitely has only occurred with the engine completely cold after sitting overnight.

[gasman]

It slipped again a couple days ago, but this time it did it while in 2nd and 3rd and for a longer distance from my house. By about 3/4 mile, the slipping was gone and back to normal shifts since. This slipping has occurs only about once a month on cold starts in the morning only.

Last night, I sucked out a quart of transmission fluid and replaced it with a quart of Trans-X that I had gotten a month ago after the last slipping episode. The slipping this week finally prompted me to use it.

My question now is how many miles do I leave it in. PEH in the first reply to this thread says to leave it in for 1000 miles. Is this a typo or does he mean 100 miles. I've read through most of the transmission/Trans-X threads and have seen 100, 200, 300, and 500 miles; but not 1000 miles.

[P.E.Haiges]

gasman,

I suggested 1000 miles because since the slipping is so intemittant, 1000 should give you enough time to evaluate Trans-X to see if it was curing your problem.

P E H

[d.delano]

When I got my car back in August I changed the fluid and filter. Around January I pumped about 100 ml of fluid out and added Trans-X. I just changed the fluid and filter again today and replaced with Mobil 1. The fluid was maroon, didn't smell burned, but wasn't transparent. The transmission seems to be shifting more confidently. Could it be that varnish was discoloring the fluid?