Very Heavy Clutch Pedal

[Josh]

Hey guys,

My clutch pedal has always been very heavy. I have been through 3 transmission setups (stock, stock with 350z pressure plate, subaru setup) and the clutch pedal is just as heavy as the last.
To me, this rules out the slave, clutch fork, release bearing - anything on the rear half of the car.

I guess my question is can the clutch master cylinder be causing this? I bought it new from DMC 3 years ago.

The clutch circuit is very well bled.

[FABombjoy]

I have one of Grady's "hardcore" master cylinders, and it did seem to help a little -vs- the original master.

I don't usually love the nonlinear feel of clutch assist springs but this car could definitely use one.

[Drive Stainless]

Kink in the line somewhere?

[Josh]

I never knew rob had his own offering. Interesting.
It is certainly worth looking for a constriction in the line, ill take a look.

I should also note I have felt the clutch in stock deloreans and they are much much softer than mine, even when it still had the stock transmission and PRV.

[FABombjoy]

Not sure if these are still available or not. Here's the website around the time I ordered mine:

https://web.archive.org/web/20031104083118/http://www.pjgrady.com:80/lgspec.asp?id=21

[Josh]

Thanks for digging that up!

I also found this, I think Josh is running it in his setups

http://www.wilwood.com/MasterCylinders/MasterCylinderProd.aspx?itemno=260-6089

[David T]

If the pedal is very heavy it is probably not the clutch hydraulic system. More likely the pressure plate, either too many springs or they are too stiff. Talk to the vendors and get a Centerforce or Valeo pressure plate. They have softer springs and centrifugal weights that increase the clamping pressure at higher RPM's so you have a soft pedal at low RPM's.

[opethmike]

If the pedal is very heavy it is probably not the clutch hydraulic system. More likely the pressure plate, either too many springs or they are too stiff. Talk to the vendors and get a Centerforce or Valeo pressure plate. They have softer springs and centrifugal weights that increase the clamping pressure at higher RPM's so you have a soft pedal at low RPM's.

Dave, if you had actually read his first post, you would have noticed that his problem has been consistent across several different pressure plates and transmissions.

[Josh]

I just got guru'd

[PJ Grady Inc.]

If the pedal is very heavy it is probably not the clutch hydraulic system. More likely the pressure plate, either too many springs or they are too stiff. Talk to the vendors and get a Centerforce or Valeo pressure plate. They have softer springs and centrifugal weights that increase the clamping pressure at higher RPM's so you have a soft pedal at low RPM's.
Hate to burst your bubble David but Centerforce ditched the flyweights well over ten years ago when Valeo changed pressure plate designs. I stopped using them after that because you are paying $200- more for a stock Valeo pressure plate and a disc with "improved" friction material. It can't justify the increased expense. I agree it's probably the pressure plate issue but with an LS1/3 or 7 installed a soft clutch pedal is probably wishful thinking and since everything is different/modified I can't be of much help here. I don't sell that exact "hard core" design anymore but could do a one off with my rebuilder. I switched from boring oversize to brass sleeving but could easily do both at slightly higher cost for the larger stainless piston. I don't think it will help enough with the pedal effort but will last farlonger than the normal replacement part and give better disengagement.
Rob

[PJ Grady Inc.]

If the pedal is very heavy it is probably not the clutch hydraulic system. More likely the pressure plate, either too many springs or they are too stiff. Talk to the vendors and get a Centerforce or Valeo pressure plate. They have softer springs and centrifugal weights that increase the clamping pressure at higher RPM's so you have a soft pedal at low RPM's.
Hate to burst your bubble David but Centerforce ditched the flyweights well over ten years ago when Valeo changed pressure plate design. I stopped using them after that because you are paying $200- more for a stock Valeo pressure plate and a disc with "improved" friction material. It can't justify the increased expense.
I agree it's probably a pressure plate issue but with an LS1/3 or 7 installed a soft clutch pedal is probably wishful thinking and since everything is different/modified I can't be of much help here. I don't sell that exact "hard core" design anymore but could do a small run with my machine shop. I switched from boring oversize to brass sleeving but could easily do both at slightly higher cost for the larger stainless piston. I don't think it will help enough with the pedal effort but will last farlonger than the normal replacement part and give better disengagement.
Rob

[David T]

Hate to burst your bubble David but Centerforce ditched the flyweights well over ten years ago when Valeo changed pressure plate design. I stopped using them after that because you are paying $200- more for a stock Valeo pressure plate and a disc with "improved" friction material. It can't justify the increased expense.
I agree it's probably a pressure plate issue but with an LS1/3 or 7 installed a soft clutch pedal is probably wishful thinking and since everything is different/modified I can't be of much help here. I don't sell that exact "hard core" design anymore but could do a small run with my machine shop. I switched from boring oversize to brass sleeving but could easily do both at slightly higher cost for the larger stainless piston. I don't think it will help enough with the pedal effort but will last farlonger than the normal replacement part and give better disengagement.
Rob

If we agree it is a pressure plate issue and he has a very modified set-up, he probably needs to modify the clutch actuating mechanism (the pedal assembly and/or the clutch hydraulics) to try to get an easier pedal. To make the pedal easier you need to improve the mechanical advantage or the hydraulic pressures. Probably both and still have *normal* pedal travel. I did read the 1st post where he tried several different clutch set-ups. Obviously he wasn't happy with any of them for various reasons. Because of what he has done he may never be satisfied. Lotus had a similar problem with the V-8. The very early V-8's used a single plate clutch and they had very high pedal pressures and they still had clutch slippage and difficulty with pedal feel and travel. The way they fixed it was to go to a double-plated racing clutch. As for this particular case, I don't think money is a problem.

[opethmike]

That's some excellent guru-ing

[BABIS]

I guess the problem lies all in the master cylinder, because when I drove the renault alpine (same engine, gearbox, and even slave cylinder) the clutch pedal feel was similar to a modern car..

[PJ Grady Inc.]

I guess the problem lies all in the master cylinder, because when I drove the renault alpine (same engine, gearbox, and even slave cylinder) the clutch pedal feel was similar to a modern car..
This would be the easiest thing to try as I could make up a small batch with the slightly oversized bore and stainless piston we used before we switched to brass sleeving. These could incorporate both for the longest possible life and smoothest operation. It may help with the pedal effort but I doubt it would be the total solution in this particular case. Is there any interest in this?
Rob

[Bitsyncmaster]

I would think a smaller master piston and or a larger slave piston would reduce the effort but also decrease the travel.

I don't find my clutch pedal to feel heavy to press.

[Nicholas R]

Josh are you still running a DMC slave cylinder with the Subaru transmission?

[Josh]

I am running the Subaru slave cylinder.

It is a 3/4" bore, and so is the delorean master so there is no hydraulic advantage at the pedal.

The subaru application that uses this slave cylinder has a 5/8" bore master so I have a new master on order with this bore. There is more than enough disengagement at the pressure plate with the stock setup so I can sacrifice some stroke by going to the smaller bore master cylinder.

In the mean time I took the delorean master apart and found it to have a VERY heavy return spring. I can barely compress the master by hand on the bench. I installed a lighter return spring and the pedal is a little bit better.

I am waiting on the 5/8" bore cylinder before I start chasing other issues as suggested in this thread.

[opethmike]

Huhuhuhuhuh, 'stroke'

[Josh]

Installed the 5/8" bore master cylinder, the pedal is much softer now.

It is amazing how heavy the spring in the delorean master cylinder is.

[kings1527]

This would be the easiest thing to try as I could make up a small batch with the slightly oversized bore and stainless piston we used before we switched to brass sleeving. These could incorporate both for the longest possible life and smoothest operation. It may help with the pedal effort but I doubt it would be the total solution in this particular case. Is there any interest in this?
Rob

I replaced my master not long ago but I love the idea of the longest possible life and smoothest operation. If I don't need to replace it right away, what's the shelf life like on a unit, if there is one? And also, could you do the same thing with the slave?

[BABIS]

It is amazing how heavy the spring in the delorean master cylinder is.

very interesting. I hope that some vendor will offer a clutch master with re-engineered bore diameter and (lighter) spring!