Changing to a 1 inch clutch master cylinder

[jhv48]

I currently run a 7/8 inch Wilwood slave and master cylinder in my SPF.

Have problems with the clutch completely disengaging when very hot. Tends to drag just enough that first gear at a stop is hard to engage. I have replaced the slave, changed to Wilwood 570 hydraulic fluid, bled the heck out of the system (it was brown) installed heat shields over the clutch lines that run close to the headers and every part of the clutch and trans has been examined and found in excellent condition.

Only a problem after sitting in traffic for a long time.

Would the larger master cylinder give the slave a longer stroke? Might be just enough to offset the heat problem.

What would the downside of using the larger M/C be?

[cdnus]

Do you have a travel stop on the clutch pedal?
If so a little more travel may cure your situation.
Is your master traveling full stroke? If not a pedal ratio change may be the solution.
If neither will solve the problem then you may have to up size the M/S, that will increase the pedal pressure somewhat. Depending on the clutch you are using that may or may not be a problem if your left leg is out of shape.

Craig

[carmine]

Do you have a slave mounting plate coming off the transmision made of aluminum, if so replace it with a 1/2 inch thick steel plate.

The aluminum tends to flex just enough under load that you lose that little bit of slave travel.

Also make sure that the slave rod is pushing in perfect line with clutch fork.
If not pushing in straight line you will lose slave travel from there as well.

[jhv48]

The floor is my travel stop on the clutch pedal.

I have an aluminum mounting plate for the slave, and it is at least 1/2 inch thick.

The slave push rod is not perfectly straight out of the cylinder. It is angled a few degrees upward. I have tried to make it straight but would have to fabricate a completely new mount.

This setup works fine on 99% of the SPF's so far. I'm leaning on the psssibility of an internal M/C leak or needing a slightly longer stroke due to some type of heat cause. Would the seals in the m/c be fine until good and hot and only then bleed off pressure? But then return to normal after driving speeds (and air circulation) have resumed.

And remember, the only time there is trouble is when everything is good and hot. Always in stop and go traffic.

[jdean]

The 1" master cylinder itself may have a shorter stroke (esp. if Wilwood), and will likely have a significantly harder pedal. I think you should see if you can adjust to get more stroke from you current MC if possible before going to a 1".

Of course with larger bore the same stroke pushes more fluid so you should get more movement on the TOB.

I just changed from 1" to 3/4". The 1" needed only about 2" of pedal stroke to work. Be careful you don't over extend the TOB and break the seal....once you get the distance figured out put a pedal stop in place if you dont have one.

[Michael C Henry]

I have a traditional cast iron slave cylinder. the tipical OEM thing. My car came with a 7/8" Tilton master cylinder. Just barely enough volume to get the littlest free travel and barely clutch release. Went to 15/16" Tilton master cylinder. Takes a little more reffort but now can be more generous with free travel anf still get clutch release.
Had the old OEM slave cylinder start getting stuck inside the bore itwouldn't return back beyond where the pressure plate would quit pushing. I ended up getting a new disc full 12" a new OEM style slave cylinder came with a better cylinder all bright plated, a little more travel capacity, and a better fitting rubber boot. And during the coarse I installed a 1' Tilton master cylinder I had. It take even more effort but allowed for evan more free travel and absolute full clutch release. I now need to get off the dime and get rebuild kits for all the used Tilton master cylinders I have now.

[shawnpreston]

Jim,
I've also had some problems with my slave-cylinder for my tranny. I bought a replacement part from NAPA and installed it on my TKO tranny. Unfortunately, I installed it so that the rod going to my transmission was at an angle that pushed the piston inside my slave-cylinder at an unusual angle. This caused the piston inside the slave-cylinder to lose fluid because of the unusual angle pressed upon the piston inside the slave-cylinder. I had to grind off a tab on the slave-cylinder to make it adapt to the TKO tranny. I've been problem-free since then.......knock on wood.
Shawn Smart
Component Craft #18
1966 427 with a 390 FE bored over .40

[mpanten]

I just went through this, It will give you more travel, you will not notice the pedal difference. I didnt notice much between a 3/4 and a 1 inch master. Im not sure it will solve problem but it shouldnt hurt at all.