I have been having a heck of a time with the clutch on my w123, manual trans swap. First I assembled everything and could not get the clutch to fully disengage. I tried everything I could think of, bleeding it over and over, trying both lengths of clutch master cylinder push rods at all adjustments. Nothing worked.

I have a machine shop and decided to make my own clutch master cylnder rod, but longer. This worked and I drove the car around the block a few times. all gears worked great, and reverse. The problem with this, is because the push rod was longer, it moved the piston inside the master cylinder too far, and would allow brake fluid to leak. So basically the car drove, but it leaked under the dash.

I then read and read as much as I could on the subject and everyone suggested trying the thinner version of the throwout bearing, because they had the same symptoms and it had worked for them. Well i Just got done installing that bearing and now I have less pedal than what I had before with the larger bearing. I was afraid of this.

So neither throwout bearings work with the stock MC push rods, and the MC leaks with the large bearing, and custom long push rod. How is my setup any different than every other manual trans out there?

It's almost like I need a thicker bearing. I really would like to figure this out, I have now pulled the trans twice and its getting old fast. All parts are brand new, quality stuff. Please help!

Flywheel may be to thin .Is it the right one for the gearbox? Make a fixture plate to bolt the cylender to, so it moves less .

What was the source of the flywheel, manual transmission, and all the clutch hydraulics and pedal and master cylinder? If you took them all from one car, and they were working fine, then you must have done something wrong in your installation.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

Not sure if it would be enough to matter, but has the flywheel been resurfaced? And if so, was an equal amount taken from the outer surface where the pressure plate attaches? The height difference between the friction surface and pressure plate mount flange is 22.5-22.6mm. And even if you did it correctly, who knows what has been done to it in the past.

I bought the flywheel, trans, linkage, and trans from a guy on CL. Pretty sure they all came from the same car. The flywheel was resurfaced by a local shop near me, they did take equal amounts off each surface. The tech also asked what the flywheel was for, looked up the spec and said it was within spec.

The master cylinder is an ATE brand I bought from pelican parts.

I'm guessing the flywheel is too thin now and this is what is causing me grief. That would certainly make sense.

Re: "too thin"

The minimum distance, after machining, from the friction surface to the bolt flange of the flywheel-to-crankshaft attaching bolts is: 17.5mm.
(New dimension: 18.5mm)

In practice, the clutch can be moved forward twice (or more) the spec of 1mm. The available travel of the throwout bearing will accommodate quite a bit more than a 1mm relocation of the pressure plate.

A leak from the clutch M/C, especially a new one, is an indication of a fault in that area. The M/C is constructed such that even at full stroke, all fluid ports are inside the cups.

For hyd clutches in general.

With the clutch pedal up, you should have free play at the MC push rod. RE: the MC should not be depressed at all while the pedal is up.

The clutch MC should not leak even when fully depressed, this needs to be fixed. Are both of the clutch lines tight?

If you have a miss match between MC and slave cyl bore sizes, ( small dia MC / large dia slave ) you will get a feather light pedal and not a total release of the clutch. Going the other way you will have a hard pedal and possibly too much release trael.

With the pedal up, does the release bearing contact the clutch pressure plate fingers? If you have a non adjustable slave cyl rod, the bearing should lightly touch the fingers. If adjustable, do you have the bearing just off the fingers?

Did you put a clutch fork / slave cyl pull back spring on a non adjustable rod setup? If so, this will cause a non release of the clutch as you are compressing the slave cyl and not allowing it to self adjust.

I don't see a possibly too thin FW as an issue unless the way too thin is cause by a mix match of parts. In this case I've added a thick washer under the fork pivot to move everything forward.

The master cylinder is an ATE brand, just bought from pelican parts.

The slave is also ATE brand, from pelican. I was under the impression the slave was not adjustable.

The master cylinder was only leaking when I used the longer custom pushrod that I made. The rubber boot was filling with fluid and would squirt every time the pedal was pushed. I didn't take anything apart, just made an identical rod that was longer.

How do I check if the bearing is touching the fingers with the trans in the car?

Only an idea,, but some gear boxes had a spcer .

It may or may not be as I don't know this car specifically. Look at the rod between the clutch fork and slave. You also need to measure actual bore sizes and make sure the master is proper size for the pedal assembly you are using ( not necessarily the car ) , slave is proper size for the MC and clutch fork.

Given this info, there is a chance that over stroking the MC will uncover the supply port but this isn't common in general. For now we will go with stroking too far caused the leak. The MC boot will need to be removed and brake fluid cleaned out. Brake fluid absorbs moisture and this will lead to bore rust at the end.

In general, look through the clutch fork opening, vent holes or grab the fork and move it in the direction of slave travel. If the fork moves more than 1/8", the bearing is too far away from the fingers.

Gotcha, thanks for the replies everyone. I actually have bought another new ATE master cyl and swapped it out with the one that was overstroked/leaking just to rule it out.

I will try to check the bearing clearance today. If there is more than an 1/8" gap, can I just make a spacer for the bearing?

If the slave push rod is adjustable, use that to reduce bearing clearance.

If the slave rod is fixed length, as long as the slave piston isn't near fully extended, it will self adjust. And actually. . .typically the slave piston isn't retained by much of a clip / boot so if you did over stroke the slave, the piston should pop out.

Does your slave cyl bolt on like a brake master cyl or are the bolts 90 degrees to the bore?

If the slave bolts on like a brake MC, there is a way to measure rod protrusion that infers clutch disc wear. If you were able to measure this it would give you some sense as to if your flywheel / clutch was the proper height. I don't have the measurement, the factory tool was a u shaped gauge.

Making a bearing spacer might not be possible so spacing the clutch fork towards the clutch might be better.

I agree in theory with what's been written. However, as a practical matter I'm running a Chevy S-10 master and the Mercedes slave in Mutt the Race Truck with no issues. The pedal a tad closer to the floor than I would like when the clutch engages but it works fine. I made no effort to "match" the master bore size with the Mercedes bore size - didn't even look with the idea that I'd try it this way first. Oh, and I'm running a BMW disc with a Mercedes pressure plate (Sachs, IIRC). So my mash-up of clutch bits is working and can hold almost twice the stock HP of a OM617.

Dan

I agree with Frank.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

In your case the master cyl is too small a bore relative to the slave. Overall, we want a certain clutch pedal travel to pressure plate departure ratio. Changing bore sizes is the most direct route to adjust ratio as the mechanical portion of the system is more difficult to change.

You ran across the street without looking and didn't get hit. ( Although with the low pedal you got a blast of wind from a passing car. ) That might not work in another situation or with the guy at the top of this thread.

For your truck, I would have given bore size / pedal ratio a quick look but likely used parts on hand to establish a design floor then make changes from there as needed.