Hydraulic clutch questions
 

Hey guys, just finishing off the clutch system install on my marlin and all is not well. The clutch works but the bite point is right on the floor, and only takes a fraction of a movement to get the wheels to turn. I have used a 0.625 universal master cylinder and all is bled as it should be. I started to think that Im not actually moving enough fluid to fully stroke the slave cylinder. After looking into it the m3 uses a 3/4 bore master cylinder. Could this be where my issue is? I guess the bigger bore will move move fluid but make the pedal harder? The problem is the 0.625 felt hard enough and was making the mounting bracket flex. What master cylinder sizes have others used? Any input would be greatly appreciated!

I used whatever Marlin supplied. It works fine but the clutch pedal is very heavy. The original BMW clutch arrangement features spring assistance. Several people (including me) have re-enforced the pedal box to overcome flexing.

Cheers, Robin

My M20 engine Cabrio uses a .750 Master cylinder. Original Marlin pedal box now done 22000 miles and no sign of failure! Sure it flexes but it ain't broke yet.

Well at the end of the week when my parts arrive I am going for clutch attempt number 2! I have blasted all the powder coat off the pedal box and welded on additional bracing. The box should no longer flex when in the car! I have also moved the mounting hole the master cylinder push rod connects to. This should make the clutch easier as the hole is closer to the pivot point giving around a 6:1 pedal ratio. I have also bought a new slave just to eliminate the old one having any issues. A new 3/4 master cylinder and a braided stainless line to replace the rubber one that goes from the slave to the bulkhead as on the m3 this was known to balloon, causing a low biting clutch, they actually did a recall to change this hose! If the clutch does not work now then it's engine out and changing the clutch assembly on the flywheel! Not what I want to do!

I used the 0.75 ore (I think) that Marlin supplied for our M3 E36 Sportster. Then got a hose made by HEL for it, and it works OK. It is a pretty hard push (you do get used to it), and the bite point is in what you would regard as a 'normal' position. Haven't reinforced the pedal box, but think after reading other comments maybe I should have done! This can be a winter project, whilst the panels are off getting painted.

Hope that helps maybe!

Rob

I found that the whole bulkhead top, to which the pedal box is bolted, flexes. Rather than weld bits onto the pedal box itself, I reinforced the bulkhead top by bolting a substantial steel angle widthways across it. The pedal box is bolted through the bulkhead and the steel angle. Works a treat....

Robin