RPM slips 300 or so with throttle application- problem? - PeachParts Mercedes-Benz Forum

jfowler · #1 11-16-2008, 10:01 PM

When I am driving my 1985 300TD, I can alter the RPM 300 or more simply from throttle without effecting car speed. In other words, when driving on the highway at 65mph, my RPM is 2750 up a hill and 2400 on a low-grade downhill and maybe 2600 on the flat. This seems to me like there is clutch slippage. This appears to happen in all gears and speeds and I believe it has driven this way since I bought it six months ago (it took me a while to notice) My shifting is quite nice..firm but smooth. Should I be bracing for a rebuild?

-Jeb
Austin, TX

jfowler · #2 11-16-2008, 10:06 PM

I should mention that I tried searching the forum regarding this problem but I'm wondering if I don't have the proper terminology for this issue. No love on "clutch slipping", "transmission slipping", or "RPM slipping".

#3 11-16-2008, 10:17 PM

Thats the nature of a non-locking torque converter, there is always a few hundred RPM of play.

jfowler · #4 11-16-2008, 10:23 PM

Good to here. I didn't question it for the first few months but as I started to think about it, it seemed strange. I clearly need to learn about torque converters. Thanks for information.

pawoSD · #5 11-16-2008, 10:24 PM

Yep, perfectly normal, its just the liquid coupling of the torque converter slipping. On a steep hill I've seen mine slip as much as 400rpm if I give the engine enough fuel/power. It happens more in the upper gears as there is more resistance from the drive line when the engine pushes on its end of the coupling.

jfowler · #6 11-16-2008, 10:31 PM

That's fascinating. I just wickied "torque converter". Some cars are such complex feats of engineering! Anyhow, I'm relieved that the car is doing what it's supposed to after having replaced everything rubber forward of the firewall. I'd like a little peace.

-Jeb

Brian Carlton · #7 11-16-2008, 10:32 PM

If you had a manual transmission, it would be time to worry about it..........

Actros617 · #8 11-16-2008, 10:58 PM

Quote:

Originally Posted by Brian Carlton

If you had a manual transmission, it would be time to worry about it..........

If your lucky enough to get a manual transmission

pawoSD · #9 11-17-2008, 12:04 AM

Quote:

Originally Posted by Actros617

If your lucky enough to get a manual transmission

I still a firm believer that the auto trannies can outlast the manuals when treated and serviced properly along the way.

Or at least last equally as long. None of our auto's have had an issue except mine had a modulator failure (diaphragm) which I fixed in about an hour with a new one. Easy. No clutches to fix...no endless shifting in city driving.....no worries taking off on hills.....ah, autos.

Manuals are fun to drive....but I'd not want to use one in my daily commute.

#10 11-17-2008, 12:13 AM

Quote:

Originally Posted by pawoSD

no worries taking off on hills

There are no worries. All you need is a quick brake-throttle transition, if you're good enough you can do both with one foot at the same time. Although having size 13 helps.

pawoSD · #11 11-17-2008, 12:33 AM

Quote:

Originally Posted by ForcedInduction

There are no worries. All you need is a quick brake-throttle transition, if you're good enough you can do both with one foot at the same time. Although having size 13 helps.

Its probably easier in a diesel manual than in a wimpy gasser manual.....gassers have no torque. On a steep hill you need to lift the rpms quite a bit to get going in our Rav4....or it will flat line and die.

#12 11-17-2008, 12:39 AM

True, I have more torque at 1500rpm than most g@ssers have at 3000rpm.

Caduceus · #13 11-17-2008, 01:46 AM

On this note I have been comparing specs of mercedes torque converters and there is one from a 722.6 tranny that will bolt in place to my 123's tranny. Only difference is the new one is a lockup

If I ever come by one I will definitely try it...Any thoughts on why it would be bad? Other than stall speeds maybe being a bit off.