Finally came up with a solution for the over-center spring with a diaphragm clutch.

With a diaphragm clutch in my 66 and the over-center spring installed, I had a hitch point in the pedal movement about 1 to 1-1/2” from the top. The pedal would rest there unless I adjusted the clutch to where it was fully engaged just above that hitch point so the clutch fingers could push it over the hitch point, or I put my foot under it to lift it past the catch. That meant the clutch didn’t even begin to bite on release until the pedal was about 4” or more off the floor. If I adjusted the clutch below the hitch point, the pedal would just stop its return at the hitch point way off the pedal top, and felt like it was letting the TO bearing ride on the clutch fingers.

I have the spring in down at the fork but it’s just an anti-rattle spring that pulls the fork together with the push rod and the Z-bar. It does nothing to return the pedal. From the forum many suggested that the over center spring should be removed with a diaphragm clutch but they admitted that will increase the pedal stiffness and I like the pedal effort just fine just as is.

So I got to looking to see where I could mount a second spring to return the pedal over the hitch point. No room under hood as the z-bar is so close to the firewall and it’s crowded enough under the dash already and besides the pedal has such a long travel, tying another spring to it would probably increase the pedal effort due to the amount of stretch. So that left down by the shift fork and I got an idea from looking at it and possible anchor points forward of it.

The Hemi exhaust manifold to H pipe bottom bolt was in reasonable good alignment and distance from the fork. So I made a little bracket up out of bar stock to fit under the bolt, with a small hole to hook a spring into. On the fork, it looked like actually bolting a short bracket on to the push rod stub behind the fork would give me a better alignment and allow using a longer spring for tension. So I took a washer, drilled it for hooking a spring to, and double nutted it on the section of threaded push rod extending through the fork. I cut a spring down to 6” - started out with 7” which worked but I thought 6” would give a little more positive return. Parts were simply this.



Installed the whole thing looks like this.




I readjusted the clutch to let it start to engage now about 3-4” off the floor and leave a couple inches or maybe a bit more freeplay at top which feels much more natural. The spring pops the pedal all the way to the bumper and since the fork and rod cycle is pretty short the spring doesn’t have to stretch much and I can’t tell any difference in pedal effort. Feels great now - no more having to ease off the pedal for 4-5” off the floor before I start to feel the clutch bite.

On a wedge someone who wants to try this will have to find another anchor point if one of the manifold to H-pipe bolts isn’t aligned similarly.

I removed the over center spring under the dash.

I did too. Clutch pedal comes up just fine without it. Clutch took some getting used to BUT ... I hadn't driven the car in 40 years !!!

Well, as I finally lowered my clutch engagement point down to where it felt natural to me and I increased free play, the hitch in return of the clutch pedal cropped up again despite the return spring. After playing around with it, it looks like a lot of the problem is just loose, sloppy fit of the clutch linkage pieces. Even with the fork end pulled forward tightly against the rod and Z-bar, the linkage slop doesn’t return the pedal to where it can return over the hitch point. So, I ended up adding a second light spring under the dash, hooked to the pin for the over-center spring and running to a point on the dash bracing. This is working OK - the bottom spring is positively pulling the fork end forward to keep the TO bearing off the clutch fingers, the over-center spring is still keeping pedal effort low and the spring under-dash is returning the pedal to its resting bumper. The 2 added springs are so light I can’t feel them.

But ultimately I need to pull all the linkage out and see what can be done to fix all the slop, replace worn pieces or bush just plain sloppily designed connections.

451Mopar said:

I removed the over center spring under the dash.

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Getting rid of all the slop basically boils down to replacing every connection with a hiem joint. The z-bar pivots are usually ok as they are.

The problem with keeping the over center spring on a diaphram clutch is at high rpm the clutch may not engage. The pressure from the spring and the centrifugal weight of the high rpm keep the pressure plate disengaged.

I cobbled together my own linkage years ago when I changed over from an automatic. I never knew if it really worked the way it should.

So a couple years ago I decided to get the right parts. Bought repops from the most reputable vendor. Hahaha all those years my stuff worked better.

I ended up redoing it with heim joints and new custom stuff. Much better.

A little play here, a little play there and the gap between the throw out bearing and pressure plate fingers all ads up to the free play at the top of the pedal stroke. Ever wonder why some holes in the ends of the rods are oval shaped? All that play ads up.

Just get rid of the spring and be glad that you did. I fixed two cars people had left them in when they installed a diaphragm clutch. I didn’t know about this deal and found out when I wanted rid of the non returning pedal.

I don’t want the higher pedal pressure without the spring. And I like to keep the TOB firmly off of the clutch fingers when the clutch is released and I don’t see how that’s possible in the absence of a linkage/pedal return spring. All the lower spring is for is to cut down on linkage rattles between the Z-bar and fork.