Clutch pedal sticking with high rpm shifts

[Grape]

The car is a 60 Bel Air with a 348 4 speed. The clutch is a Centerforce with diaphragm type pressure plate. I have it adjusted properly and everything works well with normal driving. The pedal will stick to the floor with high rpm shifting. I can let off the gas between shifts and the pedal comes right up. Should I get rid of the Over center spring under the dash? I have read this spring is not necessary with a diaphragm type p plate. I suppose I can just let off the gas when shifting but what fun is that.

 

[scott hall]

Sounds like your over centering the psi plate. The weights are keeping it disengaged at a high rpm when taking over center.

 

[La Hot Rods]

I put some fancy race clutch in a Saab and had the same problem. So I talked to the man that made it and told me to send the flywheel clutch and pressure plate to him. So I did and when I put it in it worked fine but have no idea what he did.

 

[MRHP]

What rpm is this happening at?

 

[Grape]

I believe the clutch over center spring under the dash is there to assist with the Borg and beck type pressure plate. I think GM did away with the over center spring in 62 or 63 and started running a spring from the bellcrank to the firewall.

 

[Grape]

What rpm is this happening at?

The pedal will stick to the floor with only 4500 rpm. I have read about a lot of hydraulic systems having this issue but not much out there on mechanical linkage.

 

[Don Jacks]

The main reason that I've seen cause this is too much clearance between the pressure plate and disc when the clutch is depressed.Adjust to a clearance of .032-0.035 on a diaphragm type pressure plate .It's a 2 person operation,one in the car holding the pedal down,the other adjusting the clutch linkage until the proper clearance is achieved.

 

[La Hot Rods]

Is it one of the pressure plates with the weights on the fingers?

 

[Grape]

Is it one of the pressure plates with the weights on the fingers?

Yes it has weights on the fingers.

 

[Grape]

The main reason that I've seen cause this is too much clearance between the pressure plate and disc when the clutch is depressed.Adjust to a clearance of .032-0.035 on a diaphragm type pressure plate .It's a 2 person operation,one in the car holding the pedal down,the other adjusting the clutch linkage until the proper clearance is achieved.

I will give that a try. Thanks.

 

[La Hot Rods]

Sounds like as Scott and Don have brought up.
The weights are working on a vertical line so what ever side of the line is the direction they will want to go.
At what point in your pedal travel is the clutch disengaged?

 

[Grape]

Sounds like as Scott and Don have brought up.
The weights are working on a vertical line so what ever side of the line is the direction they will want to go.
At what point in your pedal travel is the clutch disengaged?

It is close to the middle of pedal travel when the clutch disengages. I adjusted just about all the free play out of it today. I am afraid another turn of the rod will have the throwout bearing running all the time. It is like the clutch pedal needs a stop under it or the over center spring that assists in holding the pedal to the floor needs to be taken out.

 

[La Hot Rods]

Try adjusting the pedal with a bunch of free play so the clutch disengages close to the floor or just shorten your stroke on your foot.

 

[Grape]

Try adjusting the pedal with a bunch of free play so the clutch disengages close to the floor or just shorten your stroke on your foot.

With a lot of free play in the clutch, the pedal will stick to the floor easily. With the free play taken out, the pedal returns nicely except when speed shifting. The big over center spring under the dash sure seems to be part of the issue. It doesn't look easy to get out of there.

 

[Don Jacks]

For what it's worth,I've always preferred the clutch engauging right[like an inch to inch and a half] off the floor.I.ve shifted as high as 7,000 rpm that way using a diaphragm pressure plate.

 

[Grape]

For what it's worth,I've always preferred the clutch engauging right[like an inch to inch and a half] off the floor.I.ve shifted as high as 7,000 rpm that way using a diaphragm pressure plate.

Do you have the big over center spring under the dash? There doesn't seem to be enough spring tension in the pressure plate or the return spring on the lower arm of bell crank to overcome the one under the dash that helps hold the pedal down.

 

[Don Jacks]

Mine was on much later stuff[64-up,as well as Mopar.You could be on to something about that spring.

 

[Grape]

Do you have the big over center spring under the dash? There doesn't seem to be enough spring tension in the pressure plate or the return spring on the lower arm of bell crank to overcome the one under the dash that helps hold the pedal down.

Oh, the big felt washer on the firewall that acts as a clutch boot doesn't help the
linkage return as easily as it could without it. There is definitely a little bit of drag there.

 

[Grape]

I found this from user Duntov at chevytalk.

The over-center assist spring is designed to be used with a Borg & Beck style three lever clutch. Those type clutches have 12 springs and are difficult to disengage and hold without an assist spring. Shifting without an assist spring and a 3 lever clutch would be difficult without grinding the gears, especially before the fully synchronized transmissions were introduced in 1964.

The assist spring is not required with a diaphragm clutch because both the low cone and high cone diaphragm clutch has low pedal effort.

The 3-lever clutch Borg & Beck style clutch was the HD clutch option until the high cone diaphragm clutch was introduced in 1964. The low and high cone diaphragm clutches are low pedal effort clutches. The high cone diaphragm clutch replaced the HD 3-lever B&B style clutch.

A diaphragm clutch can over-center by shifting at high RPM or by using the wrong release bearing. That will cause the clutch pedal to stick to the floor. The clutch pedal used to operate a B&B style 3-lever clutch will never stick to the floor under any condition.

The Centerforce pressure plate has to be a high cone so I will get rid of the over center spring under the dash or install a Borg and beck type system next time I have the trans out.

 

[models916]

I used to run a piece of wood on the floor to limit pedal travel and still keep the free play for the bearing.