Transmission pulls too hard when stopped - PeachParts Mercedes-Benz Forum

Gregory · #1 05-08-2017, 10:23 AM

Is there some kind of adjustment for a 1982 transmission, maybe internally?

When at a stop light, in Drive the transmission still tries to move the car forward too much. It seems like this is hard on the tranny and could result in big trouble.

The engine idles at 800 rpm, so that seems correct.

Many times I put the car in neutral to ease the pressure, especially if it seems like its going to be a long red light.

The 82 trans is on a 83 300DT engine, in an 84 300SD.

mabbonizio · #2 05-08-2017, 07:03 PM

I believe the trans should idle in 2nd gear to not pull the car as much. You should check the 3/2 valves to see if they are leaking on top of the valve cover. When my 3/2 valves we bad, my car would rest in 1st gear.

Additionally your idle sounds high. If your idle is set too high the car will rest in 1st gear as the down-shift from 2nd to 1st when taking off from a stop happens as soon as the throttle is pressed, therefore a lower idle allows some slack in the throttle linkage letting the car sit in 2nd at a stop.

To sum it up, I would check the idle speed and lower it a tad first, then check the 3/2 valves on top of the valve cover.

After making the above adjustments on my 82 240D the car rests in 2nd gear at a stop making it pull less.

Hope that helps!

mark82 · #3 05-08-2017, 11:13 PM

Just to muddy the water a bit;

If you brake lightly to a stop and then do not change your foot pressure on the pedal (just enough to gently stop), and then a couple seconds later the car begins to creep forward requiring firm pedal pressure to hold it, you may have a vacuum leak.

This is a great test when purchasing a car. I had one with a bad brake booster and another with a bad vacuum pump. Both had exact same symptoms.

sixto · #4 05-08-2017, 11:25 PM

x2 on brake problem.

Sixto
83 300SD for sale
98 E320 wagon

optimusprime · #5 05-09-2017, 05:52 AM

You need to do a transmission shift cable adjustment .If the cable is set to tight [no play] it will want to drive off .Or the small micro switch in there for the throttle quadrant is broken inside. And the computer thinks its still on drive settings .Look inside the hood to the place the linkage goes to the fuel flap ,look for a switch see if it clicks on and off as you open the throttle . I will find a picture if i can

optimusprime · #6 05-09-2017, 06:25 AM

This is it gregory Google search in the box -- YouTube then on there put in search - Adjust Mercedes 123 300td Shift cable adjustment . They all operate through vacuum and its the firsr port of call .Any leaks will mean a problem on shift changes . You should have a sticker with vacuum locations on it instde the hood . Also on Google search page look up on the right you will see images .Click on this will bring another search box uo .You can now use tis search as well to find anything you want .It might mean trial and error .The engine may be running to fast let us know how you get on ..

Gregory · #7 05-09-2017, 03:53 PM

Thank you everyone for your helpful suggestions.

I decided to start with changing the injectors to the ones Greaser rebuilt for me a couple years ago. They have been on the shelf since then. The car has been idling rough when cold lately, so that seemed like a good starting place.

I have to order the injector heat shields, so its a couple/three days until that job is completed and I can work on the tranny issue.

sixto · #8 05-09-2017, 11:24 PM

Quote:

Originally Posted by optimusprime

You need to do a transmission shift cable adjustment .If the cable is set to tight [no play] it will want to drive off .Or the small micro switch in there for the throttle quadrant is broken inside. And the computer thinks its still on drive settings .Look inside the hood to the place the linkage goes to the fuel flap ,look for a switch see if it clicks on and off as you open the throttle . I will find a picture if i can

I'm confused:

'84 SD with '83 engine and '82 transmission = what computer?

Control pressure cable tension doesn't affect TC stall so it can't affect how much the car creeps in D while idling. Neither does modulator vacuum. The transmission doesn't know the brakes are applied.

Maybe the tachometer is reading low. Way low.

Sixto
83 300SD for sale
98 E320 wagon

Gregory · #9 05-10-2017, 06:44 AM

Quote:

Originally Posted by sixto

I'm confused:

'84 SD with '83 engine and '82 transmission = what computer?

Control pressure cable tension doesn't affect TC stall so it can't affect how much the car creeps in D while idling. Neither does modulator vacuum. The transmission doesn't know the brakes are applied.

Maybe the tachometer is reading low. Way low.

Sixto
83 300SD for sale
98 E320 wagon

I changed the 84 tach to an 83, because there was a changeover at that time. I also installed the proper tach amp under the hood.

Diseasel300 · #10 05-10-2017, 09:02 AM

I'd find someone to verify your engine RPM. Even in 1st gear you should be able to easily hold the car at a stop if the engine is idling. In fact, if your brakes are good, you can hold the brakes and stomp the accelerator to the floor and the car shouldn't move off.

Keep in mind, the later diesels (not sure what year they changed over) all did 1st gear starts anyway, and they have more torque and more cylinders than yours does.

Gregory · #11 05-10-2017, 09:23 AM

I found an android app for my phone, Strobily. It uses the camera flash as a strobe light to measure engine RPM. When I get the injectors changed out, I'll see how well the app works, and compare it to the tach in the dash.

The brakes hold the car just fine. My primary concern is the loading on the transmission while stopped. There is significant relief to the tranny when putting it in neutral while stopped.

I just want to avoid destroying the transmission, like the last one. The only symptom the 83 trans showed was the same, pulling too hard while stopped.

97 SL320 · #12 05-10-2017, 06:58 PM

Fix one issue at a time, check idle speed before changing injectors as it is probably too high.

Also, if you are putting the trans in neutral at every stop, this will actually cause more wear because clutches need to disengage then reengage. Leaving it in gear only builds heat in the torque converter but given stopping is a shorter time period than driving is isn't much of an issue.

Gregory · #13 05-13-2017, 08:53 PM

Changed the injectors, it runs better. I tried using the android app, Strobily, to verify the RPM. It did not work, the LED flashing is no where near as accurate as a xenon strobe.

The car does come to rest in 2nd gear, I can feel it downshift when taking off again. I think it is operating as it should.

sixto · #14 05-14-2017, 11:01 AM

In my exerience, the Bowden cable is too loose if waits to move away from a stop to shift to first. But if there's too much creeping force idling in second, it'll get worse idling in first.

Sixto
83 300SD for sale
98 E320 wagon

Soxto
83 300SD

Gregory · #15 05-14-2017, 11:50 AM

It doesn't wait, it instantly downshifts into 1st as soon as the fuel pedal is pressed.