John_AZ

I followed 12 page thread on clutch discs and the conclusion:
https://rennlist.com/forums/924-931-...ensive-12.html

I purchased the Vertex clutch disc and will install this week. I compared the old and new disc construction and used very basic measurements. I thought I'd post my findings for others.

The construction is similiar but very different in 3 obvious ways. Sachs uses 8 independent spacers/with 2 rivets each between the inner and outer plate-Photo 1. Vertex uses a 1 piece metal plate attached with continuous rivets-Photo 2

The Vertex disc uses 6 identical center springs and the Sachs uses 2 large, 4 small-Photo 1 & 2 again.

The Vertex friction material is 35.4mm wide VS an old/OEM Sachs 32mm wide spring disc. The flywheel surface width max is +-40mm.

The Vertex friction material is Raybestos 1675 stock and is in total 9.3mm thick-Photo 3
I do not have the thickness of a new Sachs disc

I will link this post to the above thread and post my final driving impression when installed. I have had the FW Surfaced ($40/$50) and FW and PP professionally inspected & balanced ($75)

It will be a few days. If you have any other questions, I'll try to answer.
I am reusing a PP with 60K miles and as mentioned, I have had both FW & PP balanced and inspected. New FW bolts/rear crank seal/PP bolts/pinion & fork bearings/new TO glide tube.

John_AZ
1988 924S 60K New Sachs clutch Nov. 2007 + 1987 924S 113K-Clutch in process Apr. 2009
1979 924 + 1977.5 925 + 1970 914 1.7 +++=== gone, past tutors

Mark944na86

It sounds like you had removed the PP and flywheel and got them machined and balanced before purchasing the clutch disk. Is that because you were unsure if you were going to need a new PP? How many times can you expect to remachine a PP, generally speaking?

John_AZ

Mark,
The PP was from my 1988 924S and had less than 60K miles. The reason for removal was the original rubber center clutch fell apart. The friction material on the rubber center clutch was very good and there was no damage to the face of the PP. The shop inspected and only minor surface work was done.

The flywheel on the 1987 924S was resurfaced by grinding and the matching outer ring surface was turned on a lathe for the PP.

The flywheel was first balanced and used as an arbor for the PP. The PP was then balanced. Each piece is actually balanced separately so to speak. Then bolted together for final test.

Sorry for the long answer. Short answer, I was going to use it all along. Normally the PP should be changed if the clutch lasted a normal 150K or longer miles. The PP metal fingers get worn and "aged" by fatigue of the TO.

If you were referring the the FW instead of the PP, the FW is like a brake disc and has a built in minimum/maximum allowable measurement for resurfacing.

Thanks,
John_AZ

Mark944na86

Thanks John. That clarifies much. I realised that machining the FW was standard procedure, but wasn't clear when machining a PP was inicated. So your detailed explanation above is very helpful. My clutch, which (if original) is at about ~100K miles, is a job on the horizon - I've been reading threads on clutch replacement to edumacate myself a bit in advance.

Johnny Player Special

I bought the Vertex brand clutch and pp for a 84 944 over seven years ago the OEM rubber center one died, I did the install myself with some help. I sold the car to a buddy he abused the **** out of it and I just bought it back, broken timing belt and bent valves at no xtra charge. When I drove it last summer the clutch was strong as hell. Whoever they are having it built by did a good job. Not really looking forward to doing it again in the distant future.

Mike C.

I just put one in about 1000 miles ago. So far, so good. The flywheel had 90K miles on the previous clutch but still looked fine. I hand sanded it with 320 grit emery paper and it has been very smooth.

Chads996

I personally am not surprised. Raybestos makes GOOD stuff.

C.

John_AZ

UPDATE--Yesterday I finished the project and many WYAIT items on my 1987 924S.

The Vertex disc engages/releases smoothly with out any noticeable grab or bite, very smooth. With a balanced FW and PP I felt no vibration to 4000rpm-I will go beyond 4000 rpm when I retorque and recheck my work.

This is what is interesting. The WSM says a NEW disc should have 18mm of space in the clutch inspection hole from case to fork. Minimum of 15mm OR "possible" problems with release.

The measurement I have is 11mm. I have adjusted the petal play per WSM and Haynes to have 3mm play at the clutch petal. The clutch fork and operation of the PP is working fine engaging and releasing.

The Vertex disc is larger in total amount of friction area as I mentioned above. It is 9.3mm thick in "relaxed" unmounted state. The WSM measurement states 8.1mm in the "relaxed" unmounted state. This may account for the 11mm measurement I have for the distance from the case to the fork. I am thinking that in a couple thouand miles the new disc will compress slightly and have the minimal 15mm distance from case to fork.

John_AZ