Brand new clutch slipping; is this test valid?

[moroza]

E46 Valeo single-mass clutch/flywheel conversion with an E46 trans, in an E34. The car hasn't been on the ground or started yet, but the driveline is assembled.

After bleeding the clutch, I found the pedal very light. Research showed that E46 clutches are quite light, with a heavy spring on the pedal assembly to compensate (multiple reports of E36 clutches in E46 feeling very heavy, one report of E46 clutch becoming extremely light when the spring broke). Still skeptical, I decided to test the clutch before installing the exhaust.

Trans in fifth, standing on the brakes, bigass cheater pipe turning the crankshaft bolt, and at somewhere around 150-200ft-lb, the clutch slips. The pressureplate and flywheel were thoroughly cleaned with brake cleaner before assembly, but I didn't bother scuffing them. Is this test valid, and my pressure plate is weak/defective? Or is this to be expected until it's broken in?

[jclausen]

Typically you would drive the car to verify

[bmwdirtracer]

+1. You need to complete the job before you can evaluate it.

That said, E34 vs E46 isn't a valid way to describe the mating of transmission to car. There are clutch master and slave cylinders with different throws - different amounts of fluid moved. You'll want to make sure that the two items are compatible. The throw needs to be appropriate to the transmission being used, not the bodyshell of the car.

"Hard pedal" vs. soft also very much depends on the pressure plate itself. The E34 535i has a light to normal pedal, the E34 M5 has a MUCH stiffer one; same hydraulics and pedal apparatus.

[moroza]

Yeah... I was hoping not to risk having to redo the exhaust in particular, for it is a hassle.

Cylinder bores are the same size on E34 and E46, at least non-M models - 19.05mm master, 22.2mm slave.

Hydraulics on the E34 M5 are all different from the 535i, and use 12mm pipes where all other BMW I've seen use 10mm.

[bmwdirtracer]

You're right about the M5's hydraulics being different parts than the 535. I hadn't checked. I was basing my comments on the fact that I've worked on several E34 M5's with 535 clutch kits, and very light pedals. When swapped to the correct M5 clutch assembly, the pedal became a real workout. The M5's clutch is rated at 400 lb/ft of torque, so it's been commonly used in various BMW's when they are subject to extreme use.

All that said, I still think you're going to have to have the car running and driving to evaluate the clutch.

[ross1]

My thoughts; If you are applying 200# on the end a huge bar then of course its way more torque applied. Having said that it does seem suspicious that you could by almost any means slip the clutch by hand.
Is there any free play between the TO bearing and clutch fingers? You see what I'm getting at.

[moroza]

Updating this after putting ~1000 miles on the swap, the first 400 of which never exceeded 50% throttle. I don't know how much my tired old M50 makes, but the clutch holds its WOT output just fine in all gears. My takeaway is that the test I did is *not* valid until clutch friction surfaces have bedded into each other.