Slicktop s52 swap clutch heavy

[Wishno87]

Just finished the zf310/s52 swap on my slicktop touring tonight. The clutch is much heavier than expected considering it’s mostly stock parts.

I’m running the e36 m3 16lb chromoly flywheel with an oem e34 m5 sprung clutch disc and stock e36 m3 pressure plate.

The clutch master is new and the slave is a new 22mm unit.

I used a stock pressure plate and disc hoping to preserve the factory feel. Any ideas?

[m60power]

Assuming the throw out bearing isn't binding on the guide sleeve, it must be related to the hydraulic ratio between the clutch master cylinder and clutch slave cylinder, along with factoring in the spring force of that stock e36 m3 pressure plate. What car is your master and slave cylinders stock to? The e34 M5 or the E36 m3, or a mix between the two cars? I'm not familiar with the straight six transmissions - is the ZF310 for an e36 m3 or the e34 m5? Did you install the clutch pedal spring? on the E34 it is an overcenter spring that returns the clutch pedal at the top of travel but also assists with depressing the clutch pedal after it passes the 'center' point, which is only about a half an inch down from the released position of the clutch pedal.

[Wishno87]

The clutch master is stock e34 which is supposed to be common across all transmissions. The slave is stock for the zf310 that is used in the early 525 cars and 95 m3s.

I did install the clutch return spring during the manual swap. I saw somewhere that the m3 came with a slave that compensated for the stiffer pressure plate but when I looked into it I could not find a part number for the m3. Specific slave.

[moroza]

First things first.... your What Now swap?! This I gotta see!

This is related to my issue with an E46 pressureplate being way too light. Anecdotes from the M3 crowd are that E46 with E36 plate feels much heavier than stock E46. Master cylinders are all 19mm. Slaves vary:

E34 M50 clutch slave 21526775924 has a 22.2mm bore and is used on both early ZF 310Z and later Getrag 250G transmissions. E36 M3 used it too.
E46 M54 slave 21526785966 also has a 22.2mm bore and is used on both 5- and 6-speeds.
E36 M52B28 slave 21521159045 has a 20.6mm bore and would stiffen up the pedal. Seems like all E36 use it except the M3.

The only remaining variable is pedal geometry. My previous conclusion was that the E46 is lighter than E36 and prior (including E34). Now I'm wondering if it's just the E36 that's heavier.

[Wishno87]

Hah this is the 95 white slicktop touring that I told you about years ago and just now got around to swapping.

The 924 is the slave that I have installed so unless someone knows something wrong with my clutch/flywheel combo I will have to conclude that something is binding in the bellhousing and I will have to take it apart again to inspect.

My DD 95 touring with manual swap is currently running a g250 with stock e36 328is 240mm clutch and flywheel combo. This also has the 22mm slave ending in 924 and that vehicle feels completely stock.

[Wishno87]

I removed the trans tonight and the slave cylinder slides along the sleeve with ease. Is there any possibility that my use of the e34 m5 disc instead of the stock disc could cause this? It’s the only other thing I can think of because the flywheel and pressure plate are designed to work on that engine/trans combo.

[moroza]

I can't fathom how the friction disk could affect pressureplate/hydraulic effort.

[Wishno87]

I ended up installing the valeo single mass conversion kit that I had laying around today. Everything seems normal with the clutch operation now. When I compared the e34 m5 disc to the one in the single mass conversion kit it was almost twice the thickness. I remember when I first installed the pressure plate on the original setup that by the time the pressure plate bolts were snugged up the fingers on the diaphragm spring were almost concaved in rather that being flat. It seemed that the diaphragm spring was already toward the edge of its operating range so when I was pressing it even further with the throw out bearing it was much stiffer than it was meant to be.

[5mall5nail5]

I ended up installing the valeo single mass conversion kit that I had laying around today. Everything seems normal with the clutch operation now. When I compared the e34 m5 disc to the one in the single mass conversion kit it was almost twice the thickness. I remember when I first installed the pressure plate on the original setup that by the time the pressure plate bolts were snugged up the fingers on the diaphragm spring were almost concaved in rather that being flat. It seemed that the diaphragm spring was already toward the edge of its operating range so when I was pressing it even further with the throw out bearing it was much stiffer than it was meant to be.

This is your issue. I run a ZF 310Z (stock on M50 '92 cars) with a UUC Twin Disc and the clutch is no heavier than stock, really. You had an issue with the spring already being sprung as your stack height under the PP was too high - glad you got it sorted!

[Wishno87]

Thanks! After looking at this thread I was able to start figuring out what was probably going on with my clutch.

https://www.bimmerforums.com/forum/s...er-and-M5-disc

The company that sells that flywheel also sells a disc that is designed to go with it so I will probably buy that and put it in with the lightweight flywheel sometime in the future.

[moroza]

Ohhh, I see. Great, that gives me an idea of what to do for my overly light clutch. Thanks, Jon.