Clutch adjustment: 1-1.5" of pedal play or 1/8" fork play?

[robroy]

Good evening!

My clutch assembly is complete and works wonderfully. Thanks for all the great advice!

One remaining question I have is regarding clutch linkage adjustment.

In the 1972 Ford Truck Shop Manual, on page 16-03-3, I read this:



The 1 to 1.5" of free play they're talking about there is in the clutch pedal itself, not any other part of the linkage. And according to these instructions, 1.5" is really better than 1".

I messed around for a while with the adjusting nuts and finally achieved a position where the pedal free play was about 1 and 1/8". With this in place, I measured the play between the tip of the clutch release rod and the fork (with the fork already positioned so it was just touching the T.O. bearing to the P.P.). The play there was about 1/4".

If I remember correctly, I've heard from several Fordification members that with the T.O. bearing just barely touching the P.P., I should have about 1/8" of free play between the tip of the clutch release rod and the fork.

So, which amount of play is best? Is it better to follow the Ford shop manual with my 1 and 1/8" of free play in the pedal, or reduce the play so that I have 1/8" of play between the T.O. bearing the the P.P.?

Two more questions:

1. Is it true that the free play decreases as engine RPMs increase? Does this mean that I should adjust the clutch differently if I plan on doing >4k RPM shifts?
2. What's the big deal with this free play anyways? Why not have the minimum free play that would keep the T.O. bearing from touching the P.P. when you don't want it to, like 1/16" of play or even less?

Thanks very much for the truly superb guidance!

Robroy

[70_F100]

Free play is necessary to keep the release bearing from being in constant contact with the fingers on the pressure plate. Nothing more, nothing less.

By keeping the bearing away from the pressure plate, the bearing is not constantly turning. It is NOT designed to be a "constant-contact" bearing. It's only purpose is to spin while the clutch pedal is depressed and the clutch disengaged.

As for higher RPM movement, it's possible that the fingers on the clutch move outward at higher RPM, just because of the design of a clutch assembly. Some of the pressure plates are designed to "tighten" against the driven disc as engine RPM increases.

If you've got free play of 1"-1.5", you should be in good shape.

And, by the way, a 4000 RPM shift is NOT high RPM!!!

[robroy]

Hi 70_F100, thank you for replying!

Maybe I should have added to my original post that I'm motivated to reduce the free play, since I like the way the clutch pedal feels better when it "kicks in" sooner in the travel. But I don't want to risk messing up my T.O. bearing by reducing the play too much!

Thanks again,
Robroy

[convincor]

your good were you are. if you have the return spring pulling the fork forward you could take up a little more freeplay if you want. won't hurt unless the T/O bearing is making contact with the PP.

[70_F100]

Keep the free play at 1"-1.5", regardless of what you like. That's the proper adjustment for a mechanical-linkage clutch.

A hydraulic clutch on a later model vehicle will have a different feel. DO NOT try to emulate that, or you'll create problems.

If you adjust it with the proper clearance (free play) you'll be able to tell when the driven disc starts to wear, as the clearance will decrease as the lining wears.

Proper clutch adjustment, as originally engineered, is based on free play, not the distance from the floor to the engagement point of the clutch.

I know it sounds like a cliche, but "Trust me" on this.

[fordman]

i was thinking this last night but wanted to look first. i put my fork rod on tonight it was the correct length. it was already adjusted to the proper length for the pressure plate and clutch disc i took off the other engine. the fork rod also came off of that engine.

ok so what i was thinking is this. i could move the clutch fork a little with the fork rod and spring installed. how do i tell by that gap how to adjust that rod. i dont want it falling out but i dont want it tight either is that right. how much slack should i have between the clutch fork rod and the clutch fork? i know that i should make the proper free play between the pressure plate fingers and the throw out bearing.

but how loose should that rod be to get the free play i want?

[robroy]

Hey Fordman!

Through trail and error I noticed that while pressing gently on the clutch fork just enough for the T.O. bearing to touch the P.P., 1/4" of play between the tip of the clutch release rod and the fork yielded about 1 and 1/8" of free pedal play. Since the book says I should have 1 to 1.5" of free pedal play this 1/4" of free play at the push rod seems OK.

I also noticed that when I had about 3/4" of play at the pedal (not enough), I had about 1/8" of play at the pushrod.

I'm not sure if that information helps or not, but I'm not sure if there's an official answer to your question, at least as far as the Ford shop manual is concerned--it seems to only talk about measuring the pedal free play, not measuring the push rod.

Robroy

[fordman]

i'm close then. i have abotu 1/8 to 3/16 between the rod and the clutch fork.

[70_F100]

Actually, Ford engineers did the calculations for you many years ago.

Based on the travel of each of the components, radius of the circle traveled by all of the pivots and mechanical advantage gained, 1-1.5" at the top of the pedal translates to the correct clearance at the clutch fork.

No need to overanalyze this.

Nearly every car and truck ever made that had mechanical clutch linkage specified the same free travel at the top. That is the quick, easy, down-and-dirty way to tell if a clutch is adjusted correctly. You'll never see a mechanic check the clearance at the clutch linkage underneath the vehicle unless it's on a heavy-duty truck with a pull-type clutch. No need to. If it's within specs at the pedal, it will be right at the release bearing.

[robroy]

Interesting, thanks for emphasizing this 70_F100!

[fordman]

my main concern was the rod falling out of the clutch fork. the rod just seemed too loose sitting in the fork.

[70_F100]

The return spring on the clutch fork pulls the fork in such a way as to keep it off the release bearing while keeping it tight against the linkage (rod). As long as you have the correct spring, there is a VERY SLIM possibility that the rod will fall out of the fork.

If the spring is missing, you need to replace it, because there is definitely the possibility of the rod falling out if the fork is not held snug against it. Also, without the spring, since the rod is pointed and the recess in the fork is tapered, gravity pulls the rod down and the taper causes the fork to move away from the rod, which could cause the release bearing to ride against the pressure plate. This will cause premature failure of the release bearing and/or pressure plate.

[fordman]

so then since i have the spring in there i shoul droll the rod out to where it touches the fork better and get rid of that gap there?

[70_F100]

Worry only about the free play at the top of the pedal.

If you've got a return spring on the fork and the proper free play at the pedal, just drive it.

[pelesl]

The 1 to 1.5" of free play they're talking about there is in the clutch pedal itself, not any other part of the linkage.

Am I understanding correctly that this "play" refers to how much travel there is in the pedal before the clutch actually starts to disengage from the flywheel?

I'm not sure on my truck I can feel when the pedal is actually "doing" something to the clutch. Perhaps it's way out of adjustment (I just got it; a '68 F100 with a 3-speed with overdrive).