Back to clutch basics - pedal pressure

[DanEC]

Maybe fighting a non-problem but I would like make another stab at getting a balance of reasonable pedal pressure to throw. I have a small input toploader and I'm running a McCleod pressure plate #360821.

McLeod Racing - Diaphragm Pressure Plates

I have a McCleod small input throw out fork I got from Brent.

I have the Quicktime bellhousing and I installed the 1/4 inch spacer under the fork mount to maintain the fork towards the front of the bellhousing opening.

The car came with a 3/4 Tilton master but when the throw seemed long I switched to a 7/8 master. The 3/4 master looked like it had some scoring although I had only cycled it a few times. The pedal pressure was heavy before and I didn't notice a large increase. It did disengage with a shorter stroke but some of my initial problems may have been from pedal placement and adjusting the slave cylinder rod clearaces sufficiently.

Not sure what ERA is providing for a Slave Cylinder size with a 3/4 inch master - hoping Bob P. will weight in on this for clarity.

Couple things I'm pondering:

1. I had ERA splay my pedals out for me.



I have a hard time just stabbing one pedal at a time even with this setup (size 12s) but as a question for Bob again - I wonder if this splayed set up has been associated with any higher clutch pedal operation? It obviously puts a pretty good eccentric load on the pedal shaft bearing.

2. I have a spacer under the slave which is probably necessary for the bent finger clutch and fork positioning. I have what appears to be, pretty good alignment with the clutch fork when the clutch is let out. But as the clutch arm is pushed back it will pivot out and the alignment will become more off-center. I'm wondering if I should shim under the slave spacer to angle it slightly to the outside so that it won't experience quite as much side loading as the clutch is pushed in?

It's a bit strange that my fork clears my master cylinder with no problem considering that many have had to trim their fork on the end to clear cleanly. Maybe something to do with the small input fork????? I guess I will get my little camera scope out and look around in the bellhousing to see if anything is amiss.

Right now I'm thinking about ordering another 3/4 inch master cylinder (original was scored and leaking a little) and see if I can manage the longer throw and hope for lower perceived leg pressure.

It's not like I'm not use to a clutch. I drive a Mustang GT as a daily driver and have a 427 Corvette (also with a McLeod diaphram clutch).

Any thoughts, recommendations, suggestions on this would be welcome.

Thanks

Dan

[DonC]

Dan:
I'll let the experts weigh in on the pedal pressure end of the problem but for hitting more than one pedal at a time, get a pair of driving shoes for your outings in the snake. I've been wearing Puma Speed Cats for years and they work well for me. The problem with most casual athletic shoes today is that they're made for people who want a very wide supporting platform for the sole of the foot. Not needed for driving.
I've had any number of people sit in the car and remark on how close together the pedals are.
DonC

[mickmate]

Dan just an observation, with the large offset done to the same pedal arm you have lost a lot of length on your pedal arm which is leverage or in this case pedal ratio. I have changed several clutch set ups by 1/16" at a time on the bores to give just what you need to release and no more. It did make the pedal noticeably lighter. You can get pretty close mathematically measuring it all. Stroke at clutch and at pedal, pedal ratio, bore sizes.

[DanEC]

Originally Posted by DonC

Dan:
I'll let the experts weigh in on the pedal pressure end of the problem but for hitting more than one pedal at a time, get a pair of driving shoes for your outings in the snake. I've been wearing Puma Speed Cats for years and they work well for me. The problem with most casual athletic shoes today is that they're made for people who want a very wide supporting platform for the sole of the foot. Not needed for driving.
I've had any number of people sit in the car and remark on how close together the pedals are.
DonC

Don - thanks. This is on my list. I looked around last week for something with a narrow sole locally (I do have a narrow foot but usually have to wear a medium width) and bought a pair of Sketchers (nice and comfortable even if they don't work out) and need to try them out. But, I think a pair of driving shoes is in my future.

Dan

[DanEC]

Originally Posted by mickmate

Dan just an observation, with the large offset done to the same pedal arm you have lost a lot of length on your pedal arm which is leverage or in this case pedal ratio. I have changed several clutch set ups by 1/16" at a time on the bores to give just what you need to release and no more. It did make the pedal noticeably lighter. You can get pretty close mathematically measuring it all. Stroke at clutch and at pedal, pedal ratio, bore sizes.

Thanks Nick. I know it will be a compromise - throw versus effort - no magic bullet. With the pedal raised I have plenty of room for stroke to go back to the 3/4 master I think.

I think the pedal ratio is unchanged - but with the offset there are no-doubt, some eccentric loading that may be contributing to pedal heaviness. The pedals have roller bearings so it remains pretty smooth, but - well you can see the offset.

Just seaching for some possible contributing factors like this that may be adding effort to the pedal.

Dan

[strictlypersonl]

Loss due to the offset of the pedal to the pivot bearing support in the frame is negligible. It's all pivoted in needle bearings - very little friction. All the components are stiff enough that there is very little lost motion (and that wouldn't translate into a loss of efficiency anyway).

You can change master cylinder diameter, but there is no such thing as a free lunch. Easier pedal > longer throw for disengagement. You always have to translate the pressure plate force/distance into what happens at the pedal.

[DanEC]

Originally Posted by strictlypersonl

Loss due to the offset of the pedal to the pivot bearing support in the frame is negligible. It's all pivoted in needle bearings - very little friction. All the components are stiff enough that there is very little lost motion (and that wouldn't translate into a loss of efficiency anyway).

You can change master cylinder diameter, but there is no such thing as a free lunch. Easier pedal > longer throw for disengagement. You always have to translate the pressure plate force/distance into what happens at the pedal.

Bob - OK, I will forget about the pedal layout. The spacing is nearly the exact same as my Mustang

Can you tell me what size slave cylinder ERA is providing. I don't remember seeing any identification on it. I'm guessing it's a 3/4 or 7/8 inch unit but would like to know for sure.

[strictlypersonl]

The slave ID is 20.5mm (0.81"). It's in the Maintenance section of the manual.

[DanEC]

Thanks Bob - I missed that.

Fiddled around a little more with it today. I took all the slack out from between the pedal arm and the master with the arm against the front of the floor opening. That brought the pedal back about 3/4 inch further. Double checked the slave adjustment and decided it was too tight and probably keeping the throwout engaged so I backed off it a little until I could see slight play inside the bellhousing. Looked at both the slave an master cylinder alignment with the pedal arm and clutch fork and decided they were about as good as they could get.

Went for a short ride to the corner gas station and pretty much decided I just need to get used to it and it will be OK. Slouching down in the seat just a little the pedal seemed in a good position now (helps me keep my head below the top of the windshield too). Take up is very smooth and linear. Hard to tell but probably starting to engage about 3 inches or a little more off of the end of the footbox. Haven't managed to stall the engine yet so I guess that's a positive note. I'm probably spoiled by my Mustang GT and it's twin disc clutch that 's about like driving a 4 cyl Toyota.

I'm kind of thinking to let this subject die for now and concentrate on the brakes and getting a good pedal with them.

Thanks

[Jaydee]

Is a booster ever used on a clutch?
JD

[Cobra #3170]

I also have very large feet (size 13) and fabricated offset pedals but mostly to facilitate left foot braking. I have crappy bronze bushings not really nice needle bearings and have never had an effort problem with everything from a stock original 427 Ford clutch to a dual disc McCloed racing clutch. My pedal may be lightly taller than yours but not that much (see photo). Maybe you should have some else try it and see if it feels normal to them.

[ERA Chas]

Originally Posted by DanEC

T
Slouching down in the seat just a little the pedal seemed in a good position now (helps me keep my head below the top of the windshield too).

Dan-before you go:
A good fix for this is to fab (or have Jack fab) a seat lower cushion that is lower (thinner foam). You can probably get 1" lower and still have the stock pleats look.

[Tommy]

As with brake pedals, there are various ways to impact the pedal pressure and throw required for full disengagement of the clutch. BUT, anything you gain in one will necessarily be offset by the other. For example, you can reduce the throw by half if you double the pedal pressure. The only way to change the one without inversely affecting the other with a clutch is to change the pressure required to move the clutch components by changing those components. Playing with the pedal arm length and master cylinder: slave cylinder bore ratio will always affect both the pedal pressure AND the pedal throw.

[DanEC]

Originally Posted by ERA Chas

Dan-before you go:
A good fix for this is to fab (or have Jack fab) a seat lower cushion that is lower (thinner foam). You can probably get 1" lower and still have the stock pleats look.

Chas - I have the reduced cushion thickness in my seats and except for a 3/16 inch steel runner under them to allow off-setting them to the rear from the ERA mounts, they are mounted directly on the floor. They are also shimmed at the front about 1/2 to 5/8 inches. The position is actually quite good. When I said slouching I didn't mean in an extreme sense - just a relaxed position. These things have a unique driving position with the offset seating/pedals and it is my first roadster. It will take a little getting used to but even with the little bit of time in it I'm getting to like it more and more.

Got to rig up something to secure the floor mats however - they like to slide forward. I think some binder spring clips on the back edge and hook to a hole on the bottom of the seat frame might work and be hidden out of the way. I guess more trick would be to get a few more lift-a-dot fastners or snap fastners and install a couple on the back edge. A future project I guess.

Dan