Clutch Pedal not Returning - PeachParts Mercedes-Benz Forum

bhammontree · #1 07-18-2020, 12:30 PM

Hello

I have a 1967 200 Diesel with a clutch problem. I inherited this car and it has been un-driven in a barn for 10-15 years. I was told it needed a clutch so I replaced clutch, pressure plate, throw-out bearing, pilot bearing, slave cylinder, master cylinder, and hose between master/slave. The clutch works great now, but the clutch pedal sticks in the down position. I have bled it several times using a pressure bleeder from the slave cylinder, and I get fluid to pass through the system and overflow the reservoir. As a temp fix I have installed a return spring on the pedal to pull it back up, and that works but I would like to get it working normally. Any ideas of what to try would be greatly appreciated.

Idle · #2 07-18-2020, 02:42 PM

Have you checked your pedal assembly for worn out bushings? Perhaps the bushing on the clutch pedal is binding.

bhammontree · #3 07-18-2020, 02:49 PM

I have played around with the eccentric bolt but haven't checked the bushing at the top of the pedal. Will check it and see if it is binding.

Thanks

Frank Reiner · #4 07-18-2020, 07:31 PM

Quote:

Originally Posted by bhammontree

Hello

I have a 1967 200 Diesel with a clutch problem. I inherited this car and it has been un-driven in a barn for 10-15 years. I was told it needed a clutch so I replaced clutch, pressure plate, throw-out bearing, pilot bearing, slave cylinder, master cylinder, and hose between master/slave. The clutch works great now, but the clutch pedal sticks in the down position. I have bled it several times using a pressure bleeder from the slave cylinder, and I get fluid to pass through the system and overflow the reservoir. As a temp fix I have installed a return spring on the pedal to pull it back up, and that works but I would like to get it working normally. Any ideas of what to try would be greatly appreciated.

If you will examine the pedal assembly, you will find, at the top of the clutch pedal, and oriented horizontally & aft of the pedal, a spring linked to the pedal with a push-rod. It is an "over-center" spring. As the pedal is depressed, the spring first resists the motion of the pedal, and then, when the linkage goes past the mid point (over center) the spring aids the continuing downward motion of the pedal.
If the over-center spring adjuster has been adjusted too tight, then the downward force at the bottom of the pedal stroke will be greater than the upward force of the clutch spring itself, and the pedal will not return.
There are two nuts on the over-center spring push rod; loosen the lock nut, and adjust the nuts to remove some of the preload on the spring.

bhammontree · #5 07-19-2020, 11:43 AM

Thanks I will loosen the spring and see if that helps.

Idle · #6 07-19-2020, 02:49 PM

When I get into something as precise as Frank is talking about I try to find a photo of one off of Ebay. Sellers usually post several views and you can get a good view of what you are supposed to be looking at before you crawl under there.

Benz Dr. · #7 07-19-2020, 05:51 PM

If you have too much free play at the push pin for the slave cylinder it can cause the pedal to drop to the floor and not return. The ecentric inside the car also factors in as previously stated.

dobrodan · #8 07-20-2020, 07:45 AM

Don't mess with the eccentric on the pedal assembly. If it was right before the work you did then it is still right. You have air in the system. As Benz Dr. said, take all the slack out of the push rod and bleed the slave again by pumping the pedal. Make sure the push rod is tight against the lever. You will adjust the freeplay after sucessful bleeding. This can be frustrating, but it is a bleeding issue, not an adjustment issue.

bhammontree · #9 07-20-2020, 07:47 AM

I adjusted the over-center spring last night so that it was as loose as possible and it didn't seem to help the situation. I noticed on the eccentric bolt there is a grove cut in the bolt head. Which direction should this grove be pointing to properly adjust the eccentric bolt? My car has the master cylinder under the dash.

Also, I have adjusted the slave cylinder pin so that it is as long as possible, since it almost seems like the pin is too short. The new slave cylinder I installed didn't come with a pin so I reused the one that was on the car when I got it. Wondering if the car came with the correct pin length? Does anyone know if they shipped different pin lengths for different models?

Thanks

bhammontree · #10 07-20-2020, 07:56 AM

Just saw the post about bleeding the system again. I have bled it several times, but will try it again with the pin all the way extended. I have been bleeding using a garden sprayer pressure bleeder to force fluid up from the slave cylinder until I get fluid out the top reservoir. Is there a better method I should try? Greatly appreciate any tips on how to bleed this system. Also, on the eccentric I had to take it out to replace the master cylinder, so not sure which way the adjustment mark was originally pointed.

Benz Dr. · #11 07-21-2020, 12:56 AM

You need just enough play on the push pin so that you can feel it. If you have a lot of play it could be that your clutch disc is worn.
Try turning the eccentric so that the notch is pointing towards the rear of the car. Not sure if that's the right direction but the notch points to the highest part of the adjustment range.

bhammontree · #12 07-21-2020, 11:24 AM

The clutch disk was just replaced, so I can eliminate wear as a possibility. Also I think I have the pin all the way out as far as it will go, but will check it again. I’m thinking I still have some air in the system so I’m going to try to bleed it again using the method of connecting the brake bleed screw to the slave cylinder and pumping the brakes. Also may try to fab a longer pin if nothing else works. Appreciate all the good advice from the forum. Will post if/when I figure this out.

Benz Dr. · #13 07-22-2020, 07:12 PM

I've had to make longer push pins when it wouldn't adjust properly. That's an OK fix because you only need a little bit of free play. Pedal should have about 20 mm of free play when you push on it and then the clutch should be fully engauged about half way coming back up.

KCM · #14 07-22-2020, 07:32 PM

Did you rebuild the master cylinder or replace the entire unit? I put a new kit in a 240D one time and something about the kit was different to where I had to grind off the master cylinder push rod to get the piston to retract completely. Compare the old and new slave and master cylinders and make sure they are identical. Measure the distance from the piston surface where the rods sit and the mounting holes to be sure they match. I know there were two different slave cylinders in those models.

Make sure the rod pushing the master cylinder has some free play when the pedal is all the way up. If the piston does not fully retract to its free position the return hole to the cylinder can get covered up by the piston cup and not allow you to bleed the system properly. Otherwise I'd say you still have air in the system and reverse bleeding should eventually fit it. They can be a pain to bleed sometimes and a little bit of air will cause the problem you are having.

KCM · #15 07-22-2020, 07:36 PM

Quote:

Originally Posted by Benz Dr.

Pedal should have about 20 mm of free play when you push on it and then the clutch should be fully engauged about half way coming back up.

Benz Dr., are you saying that the pedal should travel 20mm before engaging the master cylinder piston? I set the push rod so there is just a tad bit of free play and so the master cylinder piston retracts completely to allow the clutch and hydraulic pressure to push the pedal back and over center. Has worked for me (as long as there is no air in the system).