Diaphragm Clutch

[70 Challenger Lover]

I know a lot of people have ditched their borg and beck style clutches in favor of the diaphragm style. Doing so means removing the over center spring. I am wondering what people do for a pedal return spring so the throwout bearing gets fully disengaged.

I have been considering a hydraulic clutch on my project build but if I go with a diaphragm style, it's probably not necessary anymore.

[gzig5]

As I understand the mechanism, that big spring is helping to compress the clutch, right?  At least the A-body setup I have appears to do so.  So you don't need that help with the diaphragm type?  For a return spring, if needed, you would have to rig up a compression spring in place of the current tension spring.  But I don't think I've heard of anyone doing that so probably not needed.

[anlauto]

You still retain the spring on the clutch fork.

[70 Challenger Lover]

I have seen posts of other Mopar guys complaining about throwout bearing failure but not sure what they had for a clutch or what the end result was.

The over center spring does assist in pushing the pedal down but at the 'overcenter' pivot point, it also brings the pedal fully back to the upright position and that would remove all pressure off the throwout bearing. I'm guessing the Chrysler designers engineered it that way specifically to save the throwout bearing. If it didn't matter, they would have changed the pivot point and provided a little more downward assist.

The spring on the fork I believe is only to remove slack from the linkage components and eliminate rattling (as I understand it).

There are some drivers who like to rest their foot on the clutch pedal and we all know this causes the throwout bearing to wear prematurely. It seems to me that without a small spring holding the pedal all the way at the top, the weight of the pedal would drop it down, remove play from the linkage and let the throwout bearing make contact which would let it spin constantly and prematurely wear out.

My corvette has a diaphragm clutch and the pedal assembly has a small return spring at the firewall to bring the pedal fully back to the upright position. It seems to me our Mopars would also need this if we removed the stock overcenter spring in favor of a different design.

I talked to one guy at a show who did add a small spring under the dash for this reason but he couldn't recall the type of spring used or where he attached it.

[Chryco Psycho]

  WHy would you want a diaphragm clutch 

[70 Challenger Lover]

On the build I'm working on, I want comfort in every area. Reclining buckets, power brakes and steering, etc. but I also want a nice comfortable clutch pedal. I was thinking hydraulic but some others have suggested that a diaphragm clutch can achieve the same clamping pressure with less pedal effort.

On a side note, I can't stand the weird pedal feel of an over center spring.

[Mrbill426]

Years ago I installed a diaphragm clutch on my moderately built Road Runner and had no "performance"  issues; it was indeed easier on the foot.  I never got around to fixing it because at that time I did not know the cause, but the pedal not coming all the way back up was a annoyance.

On the build I'm working on, I want comfort in every area. Reclining buckets, power brakes and steering, etc. but I also want a nice comfortable clutch pedal. I was thinking hydraulic but some others have suggested that a diaphragm clutch can achieve the same clamping pressure with less pedal effort.

On a side note, I can't stand the weird pedal feel of an over center spring.

[70 Challenger Lover]

Years ago I installed a diaphragm clutch on my moderately built Road Runner and had no "performance"  issues; it was indeed easier on the foot.  I never got around to fixing it because at that time I did not know the cause, but the pedal not coming all the way back up was a annoyance.

On the build I'm working on, I want comfort in every area. Reclining buckets, power brakes and steering, etc. but I also want a nice comfortable clutch pedal. I was thinking hydraulic but some others have suggested that a diaphragm clutch can achieve the same clamping pressure with less pedal effort.

On a side note, I can't stand the weird pedal feel of an over center spring.

The only thing that would bring a pedal back to the top on a Mopar would be the overcenter spring. And if the pedal doesn't come all the way up, then I have to believe the slack is taken out and the throwout bearing is riding on the clutch fingers making it spin constantly.

Maybe it's nothing to worry about. Even if the throwout bearing wears prematurely, it would probably take 10000 miles to fail completely.

[Mrbill426]

Sadly that car is long gone; I gave it up in 1982 for a song... .. but I would look at that if I still had it.  Yes the clutch disengaged ok but the pedal came a up and stopped a few inches shy of the top of its travel as though it hit a stop.  I had to give it a tap with the top of my toe and it would "pop" up the rest of the way.
Thanks.

Years ago I installed a diaphragm clutch on my moderately built Road Runner and had no "performance"  issues; it was indeed easier on the foot.  I never got around to fixing it because at that time I did not know the cause, but the pedal not coming all the way back up was a annoyance.

The only thing that would bring a pedal back to the top on a Mopar would be the overcenter spring. And if the pedal doesn't come all the way up, then I have to believe the slack is taken out and the throwout bearing is riding on the clutch fingers making it spin constantly.

Maybe it's nothing to worry about. Even if the throwout bearing wears prematurely, it would probably take 10000 miles to fail completely.

[70 Challenger Lover]

That pop up to the top of its travel sounds like the over center spring doing its thing. That's exactly how they work but with a good clutch adjusted correctly, it Should come up without assistance. With the diaphragm style, they want you to remove that overcenter spring so I was wondering how people get the pedal all the way up and off the throwout bearing.

[Mrbill426]

Got it 

That pop up to the top of its travel sounds like the over center spring doing its thing. That's exactly how they work but with a good clutch adjusted correctly, it Should come up without assistance. With the diaphragm style, they want you to remove that overcenter spring so I was wondering how people get the pedal all the way up and off the throwout bearing.

[Chryco Psycho]

I highly recommend a rev limiter be installed with every diaphragm clutch

[anlauto]

  I know we're all getting older and use to the clutch in out new Hellcat or something, but with a muscle car....

With all the four speeds I've restored over the years, I think I only installed one diaphragm clutch (at the customers request)and the pedal felt very mushy to me., like something was wrong, and twice the pedal stayed on the floor while the rocker arms were floating around...

However a lot of people swear by them 

I would try an hydraulic clutch with a Borg/Beck style pressure plate, before I went with a diaphragm clutch .

[dodj]

I've had a Centerforce diaphragm clutch for about 12 years now. I think it's a great clutch. I've never had it stuck on the floor like some of you report. CP's recommendation of a rev limiter is a good idea on any performance car with a 4sp in my humble opinion.
To answer the OP's question, the clutch fork spring along with the force from the clutch brings the pedal back up.
I suspect, but don't know, that the clutches that stick to the floor were not set up correctly. Like something binding because there is nothing in the diaphragm setup holding the pedal down. Unlike the B&B setup. The over centre spring does not lift the pedal for most of it's travel when you have a B&B three finger type clutch, it trys to hold it down - the force of the clutch and clutch fork spring trying to  come up and the over centre spring is trying to hold the pedal down.

[Chryco Psycho]

A better way to lighten the pedal & still hold the power is use a multi disc clutch , you can have lighter pedal feel with 2 or 3 times the surface area