Clutch preload question with KMC unit

I agree, it's almost comical how often it comes up in the forums, that people can't get their hydraulic clutch setups fully bled. It seems like the usual advice is, when you think you're done, you're not!

The method for setting preload that McLeod puts in its hydraulic TO bearing instructions, is to have the car on a slight incline and set the preload so the car will roll when in gear when you declutch, with the engine not running. Makes sense.

blkfrd said:

I had trouble at first too. Then did the following and it bled in minutes:

You need a helper to press the pedal

Open the bleeder screw while pressing on the piston and push it slowly until it seats. Tighten the bleeder screw. Pull the piston out slowly with something that can hook onto the inside edge of the piston until it is flush with end of the cylinder and don't scratch the cylinder. Loosen the bleeder screw while pushing on the piston and push it slowly until the piston seats. Pull the piston out again and re-seat it using the previous steps. This procedure will draw fluid out of the master and resevoir and help a lot to bleed the system. Refill the resevoir and do it a few more times if you want.

Reseat the piston and refill the resevoir and have the helper press on the pedal and see if the piston moves all the way until its just about flush with the end of the cylinder. You can push on the cylinder while the helper depresses the pedal to be sure the piston feels solid and not spongy.

Your done.

Click to expand...

Blkford I am a little confused on your instructions. I need help too, because everytime I think I have it bled properly it turns out that I don't. Are you saying to have someone push on the pedal from inside the car, open the bleeder, then push into the slave by handwhile someone is pushing on the pedal? I am just putting the image together in my head incorrectly. Care to clarify on the part on the hydraulic slave unit? I don't know what the piston is, sorry to hijack, but I have been driving with an improperly bled clutch which is probably frying my clutch.

Guys, how much travel do you get at the clutch fork? I am struggling to get a hydraulic setup going and need to know how much travel is needed.

Thanks.

Can you tell how desperate I am by how far back I have been searching?

Ahh crap I have nowhere near 1.5in.

I knew I should have just gone with the jmc kit instead of cobbling it together. I could have paid for it about 50x over by now with wasted time & parts.

If anyone else knows for certain how much travel there is please post!

Yep I've seen it. I am using compeltely different parts due to availability.

Using a tilton 75 series 15/16 master with 1.1 in stroke (first mistake)

I have tried a 3/4 slave (really heavy clutch actuation, gives quite a lot of stroke) from a local falcon

Also tried a 1 1/8 slave from a peugot 505 to restore the hydraulic ratio to what it should be stock. This made the pedal feel quite good, but the short stroke of the master seems to have left me without enough disengagement travel.


I haven't been able to find anywhere that says definitively how much travel is required which leaves me guessing as to what the dimensions of everything need to be.

I haven't had time to swap back in the 3/4 to measure the disengagement distance there yet, as I have to make up new hard lines (again).

Hello guys,

i have the jmc system too. First i had the same problem to disengaging fully the clutch.
So i take a guestion at jmc. Here is the correspondence:

> Dear Sir,

i use your hydraulic clutch kit for my 67 fastback with a tremec tko.
Now my question. In the installation instruction you say, i must set a
slightly preload at the throw out bearing.
I use a new tob from centerforce. My clutch is a centerforce dual
friction.
Other clutch manufacturer say, don´t set preload to the tob because it does spin permanetly and does not last long.
The tranny shift only perfect if i set a light preload. I set the preload with my fingers not a wrench.
Is that ok? If not, what can i do?
Markus Becker <

The answer:

Hello Marcus,

Thank you for using our hydraulic clutch kit in your vehicle.
First, we will need to measure the stroke of the slave cylinder to see
if you have properly bled the hydraulic system. The maximum length
the slave cylinder will travel is 1 1/4" (1.25"). Have someone in
the vehicle and press on the clutch pedal. If you are getting the
maximum travel, then call Centerforce and see if you can put some
pressure on the clutch fingers. If you need more travel from the
slave cylinder, we have an upgraded slave cylinder that has a maximum travel of 1 3/4" (1.75"). This slave cylinder is priced at $139.95.
If you have any more questions, please give us a call or send us a
message back. Thank you for your time.
Steve @ JMC Motorsports<

So i take a question to centerforce:

>Dear Sir,

i use a centerforce dual friction in my 67 mustang (5.0 engine). Also i
use a hydraulic clutch linkage. Now my question. The shifting with my
tremec tko is only perfect, if i set a slightly preload on the throw out
bearing. The tob i from centerforce too (#N1714). Is that a problem?

thank you very much

Markus Becker<

The answer:

>Hello, Markus.

When using hydraulic linkage they are designed to apply (preload) to the
clutch assembly. I do not for see a problem with this install.

Sincerely.

Brian Hankla
Tech Support
Centerforce Clutch
928/771-8422 X-36<

Now i give a little preload and the shifting is very easy. But check the
correct travel from the slave cylinder.

I hope that help a little.

Markus

Swapped back to the heavy clutch setup. Looks like I need about 5/8-11/16 of throw to disengage the clutch with no linkage. I am getting a little over 1 1/8 in throw in total.

Hopefully I can tweak the bore ratios a little to take this into account. Also working on the idea of using a bell crank to get more mechanical advantage.