Clutch Master Slave Cylinder Question

[patrickt]

Originally Posted by Gaz64

Sounds like the clutch is stuck to the flywheel, but will release when the engine starts if clutch started.

OK, how 'bout if he starts the car up with the rear wheels elevated off the floor via jacks under the frame. Then, with the clutch pedal pushed in, he revs the engine good and hits the brake pedal hard at the same time. Seems like that would bust it loose.

[Gaz64]

Originally Posted by patrickt

OK, how 'bout if he starts the car up with the rear wheels elevated off the floor via jacks under the frame. Then, with the clutch pedal pushed in, he revs the engine good and hits the brake pedal hard at the same time. Seems like that would bust it loose.

Yes, that should work, if this is the cause.

Gary

[patrickt]

Originally Posted by Gaz64

Yes, that should work, if this is the cause.

Gary

Alright, I want it on video. Somehow I think it will go down in Club Cobra history.

[Jim Coleman]

Only two problems - the motor doesn't even have oil in it, and the wiring harness hasn't been installed.

However, there's something I did notice. On a mechanical clutch the pedal goes all the way to the floor to engage.

On a brake master cylinder, the pedal doesn't go all the way to the floor to engage.

My clutch master cylinder is going all the way to the floor. Is this normal ?

Thanks,


Jim

[Gaz64]

Originally Posted by Jim Coleman

Only two problems - the motor doesn't even have oil in it, and the wiring harness hasn't been installed.

However, there's something I did notice. On a mechanical clutch the pedal goes all the way to the floor to engage.

On a brake master cylinder, the pedal doesn't go all the way to the floor to engage.

My clutch master cylinder is going all the way to the floor. Is this normal ?

Thanks,


Jim

How long since the engine and trans installed?

Clutch pedal should go to the floor, regardless of type of operation.

Gary

[Jim Coleman]

Engine and trans were installed 8 months ago.

Thanks,

Jim

[Gaz64]

Well you need to get the engine running first, then the clutch might "let go" from the stuck condition.

Newly machined surfaces and heavy clamping force invites the clutch plate to get "stuck".

Is the clutch plate organic?

Gary

[Jim Coleman]

Yes, the disc is organic.

Thanks,

Jim

[Gaz64]

Originally Posted by patrickt

OK, how 'bout if he starts the car up with the rear wheels elevated off the floor via jacks under the frame. Then, with the clutch pedal pushed in, he revs the engine good and hits the brake pedal hard at the same time. Seems like that would bust it loose.

So this what we will end doing, we think Jim, would you agree?

When I build my cars, the engine goes in last, and is driving within a few days.

Gary

[joyridin']

Just to make sure you have all this set-up correctly:

Nearly every clutch master cylinder is matched for size to its connected slave cylinder for a 1-to-1 relationship. So, a 3/4" bore master cylinder should only connect to a 3/4" slave cylinder. A 1" master should have a 1" slave cylinder. A master cylinder that is larger will yield a rather spectacularly blown out slave cylinder and a master cylinder that is smaller will yield a rather disappointing lack of travel for your left foot's efforts.

The pressure plate must move about .100 to .120 of an inch to RELEASE THE DISC and provide .030 to .050 air gap between the disc and the flywheel.

A 9" clutch has about a 4.5-to-1 arm or diaphragm ratio.
A 10.5" clutch has about a 6-to-1 arm or diaphragm ratio.
An 11" clutch has about a 6.6-to-1 arm or diaphragm ratio.

The release bearing must move away from the fingers or diaphragm sping at least 1/16"
(.0625 rounded off to .06) for freeplay.

The release fork ratio is determined as described in the release fork section.

Example: A 10.5" clutch and a #RAGM GM release arm (2.17 ratio).

So, 0.120" required movement multiplied by the ratio of a 10.5" clutch equals .72" plus .06" movement of release bearing for freeplay equals .78 of an inch. Multiply .78" by the ratio of the release fork (2.17") equals 1.69" (or 1-11/16") of travel required where the linkage attaches. It doesn't matter if the linkage is mechanical, cable, or hydraulic, it must be able to move the end of this arm with this pressure plate the above indicated amount in order to properly release the clutch disc.

For comparison, using the same release arm with a 9" clutch only requires about 1-5/16" movement while the 11" clutch requires almost 1-7/8" of movement -- nearly 9/16" more. It is the ratio of the pressure plate that makes this difference.

[RallySnake]

Joyriding hit it on the head. Both cylinders need to be the same size. Years ago, I used a Nissan pickup truck slave cylinder. These have a very nice mounting plate, are cheap and easily adjustable. They wear out about every 50,000 miles. I am on the third one and keep a spare handy.

[Jim Coleman]

I just ordered another clutch master cylinder in 7/8" to match the 7/8" slave.

Thought the one I have was 3/4" -- it is 5/8".

Sure hope this fixes it...….

Thanks,

Jim

[AC Ventura]

Originally Posted by Jim Coleman

I just ordered another clutch master cylinder in 7/8" to match the 7/8" slave.

Thought the one I have was 3/4" -- it is 5/8".

Sure hope this fixes it...….

Thanks,

Jim

Jim

I recently did what you are doing. My clutch is a 12” McLeod Super Steet Pro, 75236 I think and the actuating slave is 1” bore. It’s operated via a conventional external Ford (FE) Fork, which is around 2:1 ratio. The clutch fingers need, upon contact 0.500” movement to release the clutch. You want some free play finger/bearing for clearance and to accommodate wear over time, you should bank on 0.625 travel at the clutch bearing end. That means 1.25” travel at the slave due to the ratio. My master cyl in the pedal box gives 1.25” max, so I couldn’t use a smaller master than slave. Hence both my masters and slave are 1” bore, which I was pretty unhappy about. When I first pressed the clutch, I thought I had damaged my back, but now the car is in the road it’s not problem at all. There’s a lot of drama in driving a Cobra and a hard clutch you get used to quick.

To test the clutch works, as others have doubltless said, first check the fork is moving when you depress the clutch. Then put the car in top gear with the rear wheels raised. Remove the plugs, drop a little oil in the bores if you like, a tablespoon max and turn the motor in the right direction with a wrench on the crank pulley nut. If the wheels turn, clutch is engaged. Then do same with somebody depressing the clutch pedal all the way down.The rear wheels should not turn. If they do clutch isn’t releasing. Whether it’s external fork or internal HTOB it either isn’t near enough to the clutch fingers of something has failed.
In that case make it easy on yourself. Drill a 5/8” inspection hole in the bellhousing that you can plug with a plastic grommet. Then you can shine a torch and see what’s happening. You should do this in line with the flywheel face. Then you can alternatively insert a feeler gauge to check the clutch release. You should have a measurement in the instruction for this. I think mine was .050”

[Jim Coleman]

See next post...……..

[Jim Coleman]

The 7/8" master arrived, got it installed and bled and now the clutch works when the transmission is in gear.

Thanks to everyone that responded, I got the help needed.

Jim