manual transmission question
 

Hello,

I have problem with manual 4sp transmission on 240D 1976 I bought one week ago. First I could not engage the reverse - it was making loud grinding sound when I tried, but other gears seemed to work fine. The next day this was the case with all gears.

I looked under the car - the rubber bushings on 3 levers on the gearbox were gone, but otherwise everything seemed fine and the levers on gearbox are moved fine by the rods when engine is not running.

So, my question is: could such severe symptoms result just from bushings or that means that the problem in transmission itself? Is there any way to diagnose it on the parking lot? If the problem just in the linkage I can get it from dealer and replace myself, but if transmission needs rebuild, then this car is probably going to wait on the street untill I get rich...

I would appreciate any advice on how to tell the difference..

Thanks!
Sergey

Could be the clutch or syncros.
Can you change gears at all with engine on? If you can do it only with engine off you have a shot clutch.

Sergey,

I would suspect your clutch is the issue. I have never seen one of these transmissions just die like that. About the only thing I can imagine that would ruin the transmission is running it without fluid, or with seriously contaminated fluid. Have you checked the level and cleanliness? You need a 14 mm Allen wrench. IF you got through the trouble to check the fluid, go ahead and change it. Change the differential fluid as well. I use stuff from RedLine Oil (www.redlineoil.com) and have not seen any issues with a transmission or differential on any Benz I have owned yet.

The clutch is a hydraulically actuated unit and it gets its hydraulic fluid from the brake reservoir. If the the cylinder at the pedal is leaking, you will see fluid in the floor area under the mats. If the unit at the clutch is leaking the leakage is not as apparent, unless it leaks in single area while parked. How does the clutch feel? When you depress it what happens?

I have had to drive my 1975 240D without a clutch before, when one of the springs broke. I started the car in neutral, got it nice an warmed up so it was easy to start in gear. Turned it off, put it in first gear, then started it. The transmission should go into second, third and fourth if you take care to synchronise the engine and driven wheels while in neutral between shifts. Just let off the gas slightly while pulling a bit on the lever, and when the dog clutch on the selector is unloaded the lever will move smoothly, no grinding. Do not force anything. Then, put the lever where the next gear is, push lightly and let the rpms drop to about where they would be if the next gear were engaged, and it should slip into gear. Put it in neutral to stop, and shut off and start the process over to get going. You should be able to do this unless the transmission is shot.

Good luck, and I hope this helps. Jim

Thanks for the advices! I will check the clutch. Jim, I was thinking about starting car in a gear, but was not sure if one can do it with diesel, that is the thing which good to know. Thanks!

Sergey,

If the clutch hydraulics have ingested air, you will get something less than full actuation, which will give you the symptoms you describe with the transmission shifting. It will also get worse quickly. Look at the rear portion of the fluid reservoir. If the back partition is low that is likely your problem.

When you start it in gear, make sure the engine is warmed up, and then make sure you let the glow plugs glow again. If you can arrange to be aimed downhill it also helps, although I have done this on a fully warmed up car going uphill at an airport parking lot toll booth.

Good luck, Jim

Yes, you need to check the clutch hydraulics, however, if the shifter bushings are gone, YOU MUST REPLACE THEM and see that the shifter is adjusted properly. These bushings are less than a dollar each.

Good luck,

Thanks! It was master cylinder fault. There were no leaks, though. I am driving the car again. Took me a while to bleed it. After reading Haynes and forum archives I bought the power bleeder from Motiv products, and it could not push the fluid through master cylinder when hooked up to the slave bleed screw. I bench bleeded cylinder next day and increased the pressure up to 30 psi but it did not help neither. So, after I spent 2 eves of making mess with powerbleeder, previous owner was kind enough to help me out and we did it in 15 minutes by old fashioned two person method without using power bleeder. Go figure.. BTW, what pressure can be safely applied to 240D hydraulic? I am still gonna try that powerbleeder with brakes...

Sergey
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240D '76

I have one of those power bleeders and it works great. If I remember correctly, the book recommended 15PSI. I expect it would work with about any pressure at all, but I pump it to 15. It is most useful for flushing, I have not used one for bleeding dry brakes.

I am not surprised that your trans problem was clutch hydraulics. I went through what you've been through. It was many years ago and I just finally went to the regular bleeding method, works fine. It will work better the next day, because bubbles find their way out over night after the bleed.

Good luck,