Diaphram clutch pedal adjustment

Hey All,

When using a diaphram clutch in our old mopars what is the best method to adjust free pedal play and the pedal stop?

Thanks,
nd65

The only adjustment is on the rod underneath. That is a variable to a lot of people. Most important thing is that the throw out bearing in not spinning when disengaged. As far as a stop there is no adjustment the over center spring pops the pedal back against the rubber stop.

I recall in a Rick Ehrenberg article he said you need to install a pedal stop when switching to a diaphram clutch. He stated you can over extend and damage the clutch.

The over center spring should be removed when a diaphragm clutch is used.

I adjust by measuring the clearance between the disc and pressure plate/flywheel. I shoot for .060"" and let free plat at the pedal be what it is, after all what is important is that the disc is disengaged when the pedal is down, not how much slop there is at the pedal with it up.

Remove the clutch inspection cover, have someone floor the clutch pedal, measure the gap between the disc and flywheel, .060" is what I go for. Adjust the rod as needed to get into spec, cycle the clutch pedal a couple of times and recheck, adjust if needed and you are done.

So your want to put a stop to prevent over engagement? You would have to devise some sort of travel limiter. Not sure why as almost all mopars had a diaphragm style clutch.

That style of pressure plate does have a shorter stroke so a down stop is a good idea.(actually a good idea for any clutch)
I have seen some pretty nice adjustable stops that people have fabricated. I used a chunk of 2X4 under the carpet for years.

Nope

I should correct what I was trying to say. Mopars that run a diaphragm style may or may not need the over spring or stop . Follow the manufacturers instructions.

Determining the pedal stop's travel limit is done in combination with setting the full clutch release free play. You can adjust it so that your feeler gauge will just fit in between the pressure plate, clutch disc and flywheel when the clutch pedal is all the way on the floor. I used to start with the feeler gauge not being able to fit between the clutch disc etc when pushed all the way to the floor , and then increase the adjustment using the clutch rod until I got the desired release clearance. That way I would have the correct clearance when the pedal is fully depressed when fully on the floor.

In a lot of cases, this will mean that the clutch pedal will not come up enough for the over center spring to lift the pedal past the over center point of the spring's top-of-travel resting position. I used to have to use my toe to bring the clutch pedal the rest of the way up. This is another reason why some people remove the over center spring.

Spend the time to make sure all the connecting points in the linkage are square to each other where they connect. I have always had to straighten out linkage parts when assembling the Z-bar components.

Another trick I learned while trying to set-up my clutch release mechanism is to lubricate all the parts that contact each other with synthetic disc brake grease. It outlasts and outperforms any other lubricant that I have found and won't attack rubber or plastic.

As my old autoshop teacher used to say, the only time clutch parts wear when set-up correctly is when they are being used, so keep your foot off the pedal, hand off the shifter(to reduce wear on the shift forks and synchros) and use the clutch's "slip" as minimally as possible to reduce wear and keep the heat down in it.

I cringe when I see how much some people unnecessarily over slip and ride the clutch when they drive a manual transmission car, and learn how to heal-toe the brake and gas pedal to start moving on a hill start if you don't know how to do it yet..

Problem with that is, if there is a lot of pedal free play you get into the over center spring which will pull the pedal down. Above works OK if the OC spring is removed.

I appreciate the comments. The over center is removed and an adjustable pedal stop in place.

Thanks
nd65

The standard recommendation when running a diaphragm clutch is to remove the over center spring regardless.

FYI, when designing my hydraulic clutch linkage, I contacted Centerforce tech line about the Dual Friction 10.5" disc & diaphragm pressure plate.

This was their reply: "The disc will be released with an 0.030” air gap. Linear travel at the bearing is 3/8” to release. Bearing load is 500 lbs."
May be useful to someone

Same .030 here. That was the recommended back in the 60's and 70's by Schieffer and Zoom on their diaphragm clutches. Much more than that would cause the pedal to stick to the floor on shifts above 6000 rpm.

My CF has been in for years Its been beat on and still works like new,Center spring removed and just the spring for the fork.I adjust all my clutchs so that they just engane Reverse easily.Ive had to adjust y Cf once in years.Only like 1 turn or so on the rod.With a scatter shield its just about impossible to get to the disc to check clerance.Rocky

Sure like to hear the reasoning for this

Go read John Kunkel's post

Because the over-center spring helps to bring pedal down not up. It's only needed with a 3 finger design to help your leg push down that race-style design. Generally when left in place with a diaphragm style your pedal will stay to the floor with high RPM's.

Ron

Actually it does both; at the top of the pedal travel it pulls the pedal up, after traveling over center it pulls the pedal down and reduces the leg effort.

So leave it there if it ‘helps’ pushing the clutch. The diaphragm clutch stays on the floor because the ‘fingers’ go past center and centrifugal force pulls it in. That’s an adjustment issue, stop travel before it gets to that point. Major problem on Chevys, Been there done that. I want that over spring on there to keep the throw out bearing off the fingers (thats not not the little spring on the bell’s purpose) (keeps pedal from rattling too). If to much travel change the ratio on Z bar, pedal or make a pedal stop. I certainly don’t want the clutch pedal setting below the brake pedal. Seems like you all are looking for a fix for no problem.

Sounds like you have it just the way it's supposed to be A pedal stop is always a good thing to have if you plan on banging the gears with gusto. I adjust my clutch so I have about 1" of free-play at the pedal.

Gus

You should explain that to centerforce then. Or to the guys who put those diaphragm clutches in cars that I fixed by taking the over center spring out.

Seen it all my life, someone says it’s the best thing since sliced bread then all the rest jump on the bandwagon thinking it’s the gospel. In reality it’s a bandaid to make their product look great since the majority cant fix it the right way. But then maybe the centerforce guys are smarter then the Chrysler engineers. So tell me what do you use to keep that throw out bearing off the fingers? Take out a spring, then add another?

https://static.summitracing.com/global/images/instructions/CTF-I97CH002.pdf

There’s still the small spring on the fork. The travel on the pedal is much smoother and doesn’t get sticky with the overcenter spring taken out. You do what works for you, the rest of us will stick with what is recommended and works for us. You should try it and compare. Your stated reasons for keeping it don’t mesh with reality. It won’t rattle and the pedal will sit even, at least on a manual brake car. The over center spring isn’t keeping the TOB off the fingers either. When the pedal returns to the top without one, I’m not sure what you think is different with one.

Well that’s just wrong. So is Eberg, me and all the rest who take them out. Can’t wait to have pedal problems again so I can say I do it the right way next time. If I’m lucky I can put one back into a car.

You tell use because it sure ain't the over center spring.

Right out of the 70 FSM.

Look again where the spring is attached on both ends. Clutch fork and lower arm of the z bar. It keeps the rod from falling out (been there) and it has nothing to do with keeping the bearing off the clutch fingers. The over center spring does that, like I said the clutch guys say take it out to idiot proof their clutch. Adjust the ratio for less travel and install a stop

Hydraulic clutch out of a Ram/Dakota anyone?

Guess you missed that spring was 6 cyl models only, on V8's the fork return spring is hooked to the bellhousing. the overcenter spring does not keep the throwout bearing off the clutch fingers. The fork return spring does and without that fork return spring the linkage would pull right out of the fork because there is nothing else holding it together when the clutch is released. Here's a pic out of the 73 FSM showing the fork return spring setup.