Question on clutch free play

[DanEC]

For those with ERA supplied hydraulic clutch components (3/4" master and hydraulic slave cylinder) and a single disc clutch - about how far off the floor is your clutch beginning to engage and about how much free play do you have at the top of the pedal before you feel good resistance from the pressure plate?

I switched to a 7/8" master early in my build as it seemed I could barely get full disengagement with the 3/4" After a few miles it seemed the fuzzies wore off the disc and engagement was over a shorter travel, but the 7/8" master is notably heavier on pedal effort. I thought I might try the 3/4" again.

So, I finally got around to switching back to the 3/4 master this week but after extensive bleeding and adjustment my clutch is still disengaging maybe about an inch off the floor and I probably have about 1" or so of free play before pressure at the top. It works but I would like to have a bit more distance off the floor for good disengagement in case I get a little sloppy on foot action when shifting. It's difficult to judge free play at top of pedal with a hydraulic system and I don't like the ideal of the TO bearing having any contact with the clutch fingers.

I adjusted the link between the clutch pedal and the master to where it has a slight preload on the master cylinder so there's no slop in the pedal at all. I've clocked the arm on the clutch shaft so that it starts slightly forward, goes over center and then back to maximize it's stroke on the master cylinder. I'm getting a full 1" stroke on the slave cylinder and I'm running a QuickTime bell housing and Ford fork. I do have a return spring between the fork and master to try to keep the TO bearing free when the clutch is engaged but it's not much stronger than the spring inside the slave cylinder.

Could be my McLeod Street Pro clutch but in the vintage Corvette world they have a reputation of being pretty short throw which is necessary as old Corvettes have limited clutch pedal travel while the ERA is fairly long travel.

Thinking of taking a bit more free play out of the top at the clutch fork/slave and calling it good and hoping I adapt. Just curious as to what type of clutch action others are experiencing with a single disc set up?

Thanks - Dan

[patrickt]

I walked down and measured it for you. My clutch pedal sits 6" back from the wall. It has a little over 4" travel before the top of the pedal hits the back of the wall. It begins to engage with an inch, or slightly less, of travel off the wall. When fully engaged, it has an inch or less of free play before it starts to disengage. This is just a plain old Centerforce dual friction clutch with a plain old National TOB and the same fork that's been used for 75 years or so on a Lakewood bellhousing. I do have the larger Tilton 7/8" master cylinder. It all works like a charm... knock on wood.

[DanEC]

I haven’t measured to see where my clutch rests from the foot box end and overall length of stroke. I’ll do so and see how it compares. Mine with the 3/4 MC seems to be about the same as yours with the 7/8 MC. With the 7/8 MC mine didn’t start to engage until quite a way off the floor.

Thanks for checking. I see what my pedal stroke is compared to yours and report back.

[patrickt]

Here's a video of my slave and fork in action, for comparison sake.

[DanEC]

Not easy crawling in there with a tape measure, light, and my arm/shoulder but here’s what I got. My pedal is about 8” from the foot box wall and at full stroke it’s about 3-1/2” to 3-3/4” from the wall. As near as I can judge and measure I have 1” free play at the top of pedal - no way to really measure start of engagement at bottom but I would guess about 1 to 1-1/2” off of where the pedal bottoms - probably closer to 1”.

I have my pedal clocked a little further back than you do but you’re a couple inches or more taller than I am from memory. It sits about 1” higher than the brake. But at full stroke my leg is pretty extended as my seat is mounted back pretty good.

But it looks like we have about the same pedal stroke overall and with a 3/4 MC I seem to be getting pretty close to the same engagement range that you are getting with a 7/8 MC. So, may be time to call it good and just try to adapt. My other two manual transmission cars have f airily short clutch pedal strokes so it’s always a bit of adjustment when I climb into the ERA.

Thanks Patrick

[t walgamuth]

I concur that 1 to 1.5" free at the top is a good idea.

[DanEC]

I took a bit more free play out as I like a little room off the floor before the clutch starts to bite. But I did work up a concentric, dual spring for the fork return that seems to do a better job countering the spring in the slave cylinder and should keep the TO bearing off the clutch fingers.

Thanks

[patrickt]

Originally Posted by DanEC

... and should keep the TO bearing off the clutch fingers.

We may have already discussed this, and I think maybe we have, but if your throw-out bearing is of the “self-aligning” type then a light preload is acceptable. The Federal Mogul #614038 that is in my car is clearly labeled as "sealed and self-aligning," so a little bit of preload is just fine. But I have a vague memory of you having a funky TOB that had zerk fittings on it. Maybe I'm imagining that.

[DanEC]

It’s a McLeod TO bearing Patrick and I think I got it from Blykins but right now I can’t remember much about it. It’s been quiet so far.