300TE Auto trans slow shifting

[Leylandp76]

Hi,

The auto trans on my 300TE (87 model, 170K miles) shows a tendency to be very slow on the upshift between 2nd and 3rd gear (usually), and while between gears the engine revs will rise a lot unless I back right off the throttle. Once in gear it doesn't slip at all, ever. The problem occasionally gets better, occasionally worse, but I can't tell if there's a pattern.

I haven't had the car long and I don't know its service history (maybe that was foolish of me ). I do most stuff myself and will change the trans fluid soon in the absence of a better idea. I'm wondering if I have worn clutches (seems unlikely as it doesn't slip once in gear), or else something awry with the valve body.

Any ideas, known problems, fixes etc?

 

[sunil sood]

i would check the following

the control cable that connects the fuel injection to the autogearbox-too much slack in this cable could could lazy/delayed shifts as i once experienced when i previously owned a high miler 123 series 280e.

there was a perished vacuum hose which was causing lazy shifts.

and finally,your suggestion of a gearbox oil and filter change if that has not been done and is due.

good luck.

 

[Andy]

Hi

Sounds like the clutches to me. I have had gearboxes which when you strip them you think how could they ever of driven as there is not clutch lining on them.


Sorry to bear bad news.

Regards

Andy @ www.mercedesservicing.com

 

[Leylandp76]

Oh dear, I hope I can coax a little more life out of it, I can't afford a rebuild at the moment. I'll check that cable adjustment - assuming the W124 has it as well. I'll read Haynes and find out if it has anything useful in it. Fingers crossed, but I'm not feeling very lucky on this one. Every time I fix something something else goes instead.

 

[Leylandp76]

Actually on reading the thread about the 300D box and snatching upshifts, I understand the vacuum reference better now. My upshifting is worst under hard throttle, if I back off it can sometimes be absolutely perfect. I'm guessing that this could imply a bad vacuum pump (or is it drawn from the manifold on a petrol engine?) or else a leaking vacuum pipe. At least I have something to check, although I admit the clutch wear is probably still most likely, maybe I can reduce the symptoms.

 

[sunil sood]

on the 123, 280e car,the vacuum hose was from the inland manifold on this petrol engine car.

do not know if this the same on your 124 car.

hope it is!

 

[Leylandp76]

yup, I read up in Haynes and it is indeed apparently connected to the inlet manifold. I haven't looked yet but it gives me (once again) cause to gripe at Haynes :roll: and ask for help.

I get really irritiated at Haynes the amount of times they say 'this is too complicated for the Home mechanic so go to a dealer'. Well I'm sorry, but I'd still like some information and make up my own mind. I notice the vacuum hose is connected to a 'vacuum unit' on the side of the trans. Haynes gives absolutely no indication what this does, yet it looks like something that could possibly be removed, tested, cleaned or even replaced, if I knew (a) what it does, and (b) how to test it.

From the above posts I understand that it helps in gearshift changes, and if there is insufficient vacuum, poor changes may result :idea: . Could this also apply if the unit is faulty, and if so, how to test? I will check that mine is propoerly connected and that the hose is airtight, and if I find nothing wrong there I would want to check the unit, but can I do this, and how is it tested?

Any help appreciated.

thanks,

 

[Leylandp76]

Solved!!!

Would you believe it, my car was previously owned by gremlins :evil: . I have found so many things mis-adjusted it's not surprising this was one such case. I checked the cable which runs from the throttle to the box and it was out of adjustment - too LONG by 1/2". Going on the assumption that this cable tells the box where the throttle is and therefore how quickly/slowly to engage the clutches at gearshifts, the car could be on full throttle and the box would think it was only slight, so the gearshifts were so slow that the box could slip between shifts.

The other downside (which I assumed was a characteristic of the car due to the stump-pulling torque of the 12v 300 engine) was a tendency to go up to 4th gear very rapidly and stay there, even up hills. Without manually selecting lower gears it did make the car quite sluggish.

The cable is now correctly adjusted and the box shifts like it should, no slippage and a significant performance increase. Needless to say I'm so happy I'm going to give it a trans oil and filter change. What is the best oil to use on the 4-speed auto box (1987 vintage)? The book says Dexron II which I think is mineral based. Is there a problem in using Dexron III which (I think) is synthetic?

Alistair

 

[steve kane]

Hello, I wonder if any of the above applies to our 1996 C250D? its a lovely car but the only gripe is a sluggish first change (ie 1st to 2nd) it seems that the change does not take place untill the revs are quite high when it then goes in with a bit of a jolt, the following changes then happen quite quickly (and smoothly) I dont know the arrangement of Vac hoses etc but Im guessing that a leaky hose could cause these symptoms, does anyone have any ideas and perhaps what hoses etc I should look at?

 

[woodturner-fran]

dexron II is what spec'd for it and new filter ---- don't forget to drain the torque converter... look for a thread a while back where I gave some tips on how it went for me. You'll need 2 x 4L dexron II for about 15 euro and the filter from MB for about 28 euro I think and a sump gasket for 8.

Messy job so don't do it on the front drive!


Fran