G50 SBC wont release clutch all the way.

[cstreit]

Hey guys,

I'm completely out of ideas here.

Ive got a Short Bellhousing G50 gearbox that we've installed in the racecar. Everything went in fine, however the clutch doesn't seem to be disengaging all the way. At first I discovered I had the wrong ring gear and needed the 76 turno one with the holes for the pins that protrude from the pressure plate.

Reassembled and same issue.

I've verified that the clutch fork is moving quite a bit. There is no leakdown (held in pedal for 5 minutes, fork did not move... ...and bled the crap out of the system through both conventional and pressurized methods.

Taken all the free play out of the pedal adjusting the clutch master rod adjust. Same issue. Clutch seems to disengage as much as it's going to after about the first 4 inches of pedal pressure, then it gets no better. I can move the wheels in gear somewhat, but when running the car cannot be put into gear because the clutch won't release.

Any ideas anyone has would be GREATLY appreciated. I've got 2 weeks before a race and I'm dead in the water.

Thanks,

Chris

[911quest]

Chris,

I ran into similar experience the other day on a 930 clutch I couldn't get it to release all the way and once I removed the gearbox I noticed the pressure plate springs where pushed in toward the crankshaft, and not flat like they should have been. I had to get a replacement clutch kit from the manufacture (centerforce) not sure what clutch setup your running but....


Another thought was it a new flywheel or had it been machined?

[cstreit]

New flywheel, new clutch, new pressure plate. It's the Patrick Motorsports 76 Turbo setup on a 3.0L engine. It's almost as if the clutch disc is too thick....

[burgermeister]

Not too much clutch experience here.

Any significant clearance between the slave cylinder rod and the fork cup?
Bent release fork (not sure if this is even possible)?
Mismatch of small release fork shaft bearings/bushings and bored out for bigger release fork shaft bearings tranny case?

That's my 3 dumb suggestions ...

[911quest]

Chris,

PM sent

[dean]

I had the same problem with my KEP PP. (who makes the PP for Patrick)

It turned out that KEP forgot to mach reliefs in the PP for the bolts so the clutch couldn't release. So check that out

[cstreit]

Dean,

Not sure I understand what relief's you are talking about... Can you elaborate?

I have the case update with the updated guide fork, TO bearing, and guide tube, so it's all new stuff. When the slave is installed you can only move the throwout bearing fork a mm or 2 so there isn't too much free play. We installed the slave while the engine was on the ground to watch it, it moved about 1/2 the distance from rest position towards the pressure plate, maybe 3/4" or so?

The pressure plate is an Alum. Sachs model with extra clamp force. Flywheel is Patricks lightened version. Everything APPEARS to be working properly, had a Master Porsche Tech come buy the shop and look at it, he was stumped as well. Jim Patrick spent a fair amount of time on the phone with me and doesn't have ideas as well.

[dean]

Chris,

I thought you had a KEP PP. The reliefs are for the bolts that hold the steel part that grips the clutch disk. On the KEP PP there needs to be reliefs so the steel part can move away from the flywheel so the disk can release.

I would take the clutch disk out and reasemble and see if it is releasing. That would eliminate a bad tranny for example. Then I would get a powerpack and check with a mirror to see what is happening in there. That would eliminate a bad master.

It does sound like the fork is moving enough but I am not sure the TO bearing is moving enough.

Are you sure you have the correct parts? It was a long time ago that I did it but I think KEP builds a special PP for this app. It is an early 930 plate with G50 springs or something like that.

Good luck
Dean

[cstreit]

The sachs clutch also needs those reliefs. The early turbo ring geat has them though.

I assembled without the Pressure Plate to ensure there wasn't something dragging there and everything turned freely. I don't think I can assemble the PP without the clutch disc as then the pressure plate spring wouldn't be in the correct position.

I'm going to re-verify the parts with Patrick today.

[cstreit]

I do have the correct fork and the TO bearing/clutch/PP came from Patrick directly.

There is very little free play on the fork when everything installed, meaning the slave cylinder is acting upon the fork as soon as it begins to move. I'm going to use some modeling clay to test clearances between the fork, guide tube, and case....

[cstreit]

#$(*&@#(*$&!!!!!!!

Put it together with the clay and the pivot pin boss snapped... It just keeps getting BETTER!!!

Off to the welders this afternoon.

[KTL]

Well it sounds like there's your explanation? If the bell housing bores/ears are cracked, I suspect the shaft was rocking in it's mountings and reducing the amount of travel the fork could make. Here's some pics in case some people can't picture what's going on here

Cracked bellhousing mount



Picture courtesy of California Motorsports to show how they repair this problem

[cstreit]

Heres a picture of mine...

I wonder though... Would they flex at all before cracking? Seems with alum like that it wouldn't really flex much, just break.... I wonder if the breaking is a symptom not a cause...

[cstreit]

Figured it out.

The limit springs/straps on the pressure plate were installed backwards by Centerforce! They should pull the friction surface of the pressure plate AWAY from the clutch disc, instead they are pushing it TOWARDS the clutch disc.

(*&#*#!!!

[KTL]

What a load of crap. Centerforce should be ashamed.

[cstreit]

Indeed,

The good news is that Jim Patrick is standing behind this 100% and has gone well beyond the call to make it right. It's nice to see that my expectations of resolution are being met and even exceeded. I'll have a good replacement tomorrow in time to install this weekend!