Newbie hydraulic clutch question

[moparrob]

I recently bought a 1975 911 that someone custom fit a high HP twin turbo 3.8 (based on a 964 motor) which is mated to a G50 6 speed trans (likely from a 993). The car is awesome but the clutch is acting very strangely.

I know these high HP clutches are very 'grabby' and this one is certainly no exception. The problem is that it does not engage until the very last bit of pedal travel (last inch or so) and has a tendency to cause a violent shudder of the rear end if you use too much throttle while trying to launch from a stop.

Based on my experience working on old, cable based clutches on VW's I would assume the cable did not have enough slack and/ or the engine and trans mounts were shot. However, the engine mounts in this car look very good and I checked the bolt torque settings - which were ok.

Also, I did not see any means to adjust the clutch engagement point. Is there anything I may have missed?

Is this simply the sign of an over-worked twin turbo clutch which needs replacing?

Thanks

[boyt911sc]

Are you aware that the G-50 transmission is hydraulic operated and does not use a clutch cable? You probably need to bleed the hydraulic clutch saver using a power bleeder. Keep us posted.

Tony

[moparrob]

Yes, unfortunately I left that out of my original post. There was no means to adjust the engagement point of the slave cylinder.

Also, the pedal did not feel spongy at all so I don't think it needs bleeding - or is my problem generally a symptom of a clutch that needs bleeding?

[Jcslocum]

Bleeding is just the first step and cheep to do. The slave is hard to get to so it isn't really done much. You will need a 7mm box wrench cut off to be about 3" long so you can get it in there and have enough swing to open and close it. A partial drop of the engine makes it easier but is not really needed.

[911Freak]

I'm working on a similar set up.
Unfortunately in order to get a 6spd G50 in an early G series 911 there are compromises and a lot of machining that's needed. First off the bell housing of the G50 is machined down 2", an early turbo pressure plate is needed, a custom machined ring gear and spring centered disc are also needed. And finally the early style cable style pedal cluster needs to accept the hydraulic set up needed for the G50 slave.

Long story short, the high engagement of the clutch is the result of these cobbled parts.

You can call Brent at KEP and buy a complete new clutch kit (reasonable $) including the ring gear (consumable part but that's another story) ready to install.... This will move the clutch engagement back to a mid level release.

Hope this helps!

[RedCoupe]

Originally Posted by 911Freak

I'm working on a similar set up.
Unfortunately in order to get a 6spd G50 in an early G series 911 there are compromises and a lot of machining that's needed. First off the bell housing of the G50 is machined down 2", an early turbo pressure plate is needed, a custom machined ring gear and spring centered disc are also needed. And finally the early style cable style pedal cluster needs to accept the hydraulic set up needed for the G50 slave.

Long story short, the high engagement of the clutch is the result of these cobbled parts.

You can call Brent at KEP and buy a complete new clutch kit (reasonable $) including the ring gear (consumable part but that's another story) ready to install.... This will move the clutch engagement back to a mid level release.

Hope this helps!

The OP's car has a 964 engine. Is the special ring gear and the special pressure plate required to put a 993 transmission on a 964 engine?

[911Freak]

Originally Posted by RedCoupe

The OP's car has a 964 engine. Is the special ring gear and the special pressure plate required to put a 993 transmission on a 964 engine?

Yes, same set up.
964 motor with 6spd (only from 993)

The special parts only come into play when installing this setup into a preG50 911
Or in otherwords retrofitting a G50 6spd into an early torsion bar car

[911Freak]

Btw. Im not performing this mod. Im fixing a no start-hard and high clutch pedal via installing a new clutch and ring gear. The body mods, trans case machining etc has all been done already.

Lots of threds on this.

[moparrob]

911 freak - I would love to talk to you more about this over the phone or in person. I live in the Valley and would appreciate finding out more about this setup I inherited. Please PM me if you are amenable to this. Much appreciated.

[911Freak]

Sure. Shoot me a PM and i can respond with my contact info
You could come by the shop and take a look.

[moparrob]

PM sent. Looking forward to getting this problem resolved.

[Quicksilver]

If the engagement/disengagement point is with just a small movement of the pedal that means that all the rest of the pedal movement is wasted disengagement travel. You have a lot more clutch travel then you need.

One thing you can do is add a bit of slack in the linkage from the pedal crossbar to the master cylinder but that doesn't address real issue of abruptness but it might make it release/engage more where you are expecting it. That might solve it so you are comfortable with it.
To make it more gradual you would need to change the ratios in the system. Either come up with a smaller bore master or a larger bore slave. This would also decrease the pedal effort. I'm not sure if the later cars had different sized cylinders that could be swapped in.

The extreme grabbyness may just be the clutch though. High performance clutches tend to be more toggle switch on/off situations. If it has glazed (possibly from misuse because of the release setup) it may require replacement to make it go away. Unless you are "going in there" anyway, I'd be inclined to live with it and see if it improves after some normal wear.

[SoyRacer]

It may just be the combination of components. We used to do a ton of R+D with clutch setups (by default, the clutch companies were just starting to develop high HP setups) on 993 turbos, 996 turbos and GT3s. The common error was to either use an unsprung disc with an aggressive plate or to use as soft disc with an overly aggressive plate. Most all setups used a lightweight (cup-car) flywheel so they used those tolerances as their starting point. Again though, unsprung disc was not a wise choice for street use. They've clearly learned a lot since those early attempts but you may just have a cup-car clutch in there (on/off switch)

[moparrob]

Thanks again for all the replies. I did bleed the clutch last week and there was no change in the problems with the pedal. It still does not engage until the last one inch of travel and then comes on with a bang, so to speak. If you do not rev the engine pretty high before engaging the clutch it will either buck the trans wildly (chatter) or stall the car. If you do rev it highly, and execute the launch perfectly, you achieve a race car start across the intersection (not great if police are around).

I would love to find a shop in the LA area that is competent to work on this setup and make the clutch more streetable. Does anyone local have any suggestions?

[911Freak]

Which G50 do you have? 5spd? 6spd? G50/20 etc?

Sounds like the clutch disc is worn beyond usable in that setup. We discovered they are tempramental due to the compromised pressure plate set up when putting a shortened bell housing G50 in an earlier chassis.

Try ProMotorsports in Burbank. Its Tyson's new shop.
Considering he helped Jack Olsen spoon a 3.6 in BB he is well qualified to help you.

Also call Brent at Kennedy Engineering (KEP) in Palmdale. He hooked us up with a clutch package for the 3.8/G50 6spd we have in a G body.

Hope this helps.

[moparrob]

Thanks 911Freak, I will follow up with Tyson as several other people have recommended him as well.

My setup is the same as yours - 3.8 twin turbo with a G50 6 speed in a G body
(1975). I can't wait to get the clutch straightened out as this car is going to be a ball once that problem has been solved. Much appreciated.