Is my transmission slipping? I can't tell for sure.
 

I finally got my recently acquired 1987 300D to make a full 13psi of boost. It had a clogged CAT and could hardly make more than 5psi with lots of smoke (and 40psi of backpressure). Now I get lots of "go" and no smoke, but I also get 3000-3200 rpm in 4th gear from about 45 to 65 MPH under acceleration. It never revs past 3200 below 65 (in 4th gear), but 3000 rpm at 45 in 4th gear while accelerating just below downshift level ? That seems wrong. The car basically accelerates smoothly and strongly from 45-65 all while the engine only increases by 200 rpm - almost like it's got a hydrostatic drive!

I verified the trans vacuum and adjusted the modulator to give crisp shifts for 1-2 and 2-3, though 3-4 is a bit soft (but *never* flares). I also changed the transmission fluid, but it made no difference. I thought the old fluid smelled very slightly burned, but I could be fooling myself. In any case it wasn't obvious.

So I'm trying to figure out if the torque converter on this model is designed to slip a lot or if my 4th gear clutch is slipping and somehow hasn't burned up yet.

When stopped, if I mash the gas and the brakes at the same time, I get about 2500 rpm and then usually one of the rear tires breaks loose (maybe a stuck caliper - I haven't checked yet). In contrast, my '83 300CD, which has the occasional 3-4 flare, never quite manages even 2000 rpm when not moving (but it runs very well too since I installed Monark Injectors, newTurbocharger bearings and seals, adjusted wastegate to 11.5psi, etc...).

Any thoughts? I'm especially interested in the behavior of other 1987 (OM603 based) 300Ds.

Check that you're getting full throttle action at the IP when you floor the pedal.

Can't help you with stall behavior. I don't have that much faith in this 222K tranny even with Mobil 1 ATF :)

Sixto
87 300D

You know, I am having a similar problem and was about to post something about it but decided to wait..
I have noticed that when I give it over 50% throttle (but not kickdown) it jumps up to 2400 rpm and just kinda stays there until the wheels catch up (from 20 or so to I forget what speed)
I didn't think that the torque converter should be slipping 800 rpm, and I never noticed this when I had "full power".
My last car didn't have a tach though, so maybe this is normal? Yours does seem too high, though.
I'd be interested to know if anyone has any input as well!

Thanks for the reply.
I went through all of the throttle linkage a week ago. I lubed and adjusted it. It wasn't getting all the way to full before but now it does.

I haven't checked the transmission control vacuum except in park with the hood open, but it goes to 0 well before full throttle. That's at the Injection Pump. Perhaps I should check after the vacuum amplifier while driving. Is that what you're thinking?
This car has about 195k miles on it and appears to have been reasonably well maintained (except that the clogged CAT went unnoticed for I don't know how long).

awsrock:

Ahh, that's what I was hoping to hear: similar behavior on the same model. On the other hand yours could have a similar problem. You describe pretty much the same behavior at a lower speed. I'll check mine at 2500rpm and upwards of 20mph so we can compare notes.

Cool, let me know what you find.

I am trying to track down a boost leak myself...I'm not getting the full "blast" until around 2400 instead of 2000 like a few weeks ago, so maybe the trans always acted like this but I didn't notice because I was accelerating past it faster! :rolleyes:

I tried the brake and throttle thing in the garage once, trying to find an engine rattle, didn't expect the tires to "light up". Surprised me. I thought that the tach was around 1900, not going to try it again though.

If you need a trans, I've got a spare, ...

I just did a highway run today, actually, so I am trying to think about what my tach was doing.

Your numbers still seem a bit high, but from what I remember, at 65 I am running 2200-ish no throttle, 2400-2500 at a steady throttle, and if I give it more to accelerate it'll go up between 2700 and 2900. Not too far off.
The only thing that seems off is it being at 3000 if you are going 45. That even seems like 3rd gear territory, to be honest. I can't say exactly where I am turning at 45 in 4th under acceleration, but off the throttle it is around 1300 or so, so 3000 seems off.

Is the acceleration ok otherwise? Or do you feel like you are losing some and revving too high?

Also, FWIW, I watched a few videos on youtube of 87 300Ds doing 0-60, and from a stop they jump up to 2000ish rpm, so yours sounds about right in that aspect. Looks like there's something up with 4th gear

I tried to get more accurate readings today. Basically it seems like my torque converter doesn't firm up until about 3200 rpm. I can get 3000 RPM with lots of slip in 2, 3rd, and 4th gear. If I accelerate semi briskly, I get upshifts at maybe 3000 rpm and after the upshift, I still get maybe 2900 RPM. That happens in 2nd, 3rd, or 4th. The shifts themselves don't take long but the converter seems to slip. If I let off the throttle, the engine revs go down, sometimes 800 or more RPM, but if I give it throttle again, the revs climb right back to around 3000.
On the highway, in 4th, I get your same 2400-2500 with steady throttle at 65, but if I accelerate, I get 3000-3100 at 65, and even at 50. It holds right around 3200 until I reach 75-80MPH.
Power feels good. There's no indication that any gear clutches are slipping. There's never any flare, just this mushy feeling torque converter below 3000-3200 rpm. Above 3200 rpm the converter has very little slip, probably under 100 rpm. If I accelerate hard enough to make it shift at 4200-4500 (so that the RPM after the shift is above 3000), the shifts are firm and crisp, with appropriate drops in rpm.

Hmm. Well, I've offered you the only advice / support I could for my experience level! :o

I read that the torque converters don't usually have any problems, but I also don't know what else it could be. Hopefully someone else will chime in on this.

I'll ponder it some more and try to think of some ideas of what else could cause this, maybe something engine related? (Such as manifold leaks?)

4th gear is direct-drive through the transmission, via a clutch and the torque converter.

It is possible for a torque converter to fail, more common for a clutch to fail or for the pump to fail, or for a seal (or seals) to leak enough to lower the pressure to a point where the clutch isn't adequately engaged.

My friends who own transmission shops won't even open a transmission until they look at fluid level and condition, and test pressures. Usually one of these items will tell them what's wrong.

Today I adjusted the cable to the transmission to make it upshift later and downshift earlier. I think my transmission was shifting a bit early, though I don't think that warrants 1000+ rpm of torque converter slip. Now I have it adjusted so that it won't stay in 4th at 45 if I give it enough throttle to do 3000 rpm. Instead it downshifts and does, well, probably about 3000 rpm. I didn't have to go so far as to make it shift like it's in "sport" mode, maybe it's just slightly more aggressive than normal.
This engine makes good torque well below 2500 rpm, it's a shame my transmission can't do anything with it.

A manual transmission would be so much easier to live with (for me anyway)...

Thanks to everyone for your insights,
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83 300CD (last project, now for sale)
87 300D (new project)
04 Jetta Wagon TDI (excellent)
96 Jetta (a bit beat but effective)