Frame mounted master cylinder questions

I am planning on keeping my frame mounted master cylinder if possible (with a Herm the overdrive guy's upgrade). But I have a few questions first.

1) Front disc, rear drum, what residual valves do I need if any? I am planning on running a proportioning valve from a TJ with front disc/ rear drums.

2) If the brakes and or fluid get warm, and I suddenly submerged the master (crossing a stream or mud) will it contract and suck in water like an axle will do (assuming the axle is not properly vented)

3) is a heat shield really necessary?

4) are there any better upgrades for a frame mounted master? I have a wilwood master for another project I could use, but it has a plastic reservoir. Would that pose a problem? Or is it just better to use Herms kit? I just want to make sure I have sufficient (good) brakes.

Thanks everyone

 

#1 If any explains it well.

#2 Vent the Master cylinder cap with a hose.
Run 100% silicone Dot 5 in the system to eliminate hydroscopic absorption.

#3 I have a stock engine and exhaust system.
I don't bother with the heat shield and have no master cylinder heating problems.

#4 Upgrade to the 1967 -1971 CJ system (split bore master cylinder)
You will need the stock mounting bracket from a 1967 to 1971 CJ.
It will bolt directly onto any early CJ frame 1949 to 1971.
Not sure if it will directly bolt onto the early 2 A frames (1945 through 1948)

 

I think it would be easier to find Herms kit, than find the parts for the 67-71 stuff.

I am under the assumption that master cylinders are supposed to be air tight. I am hoping that it will survive the occasional water crossing/mudhole. It will by no means be a bogger.

Still looking for input either way. If you have had problems or not had problems please post input

 

The bracket in Herms pic appears to be very similar to the stock CJ bracket for split bore master cylinders.
The stock master cylinders caps are vented whereas the master cylinder in Herms kit is not vented.

 

Herm builds the brackets because of the difficulty in finding the stock dual reservoir master cylinder bracketry. His also work on flatty's, etc. If you buy the mc from him with the kit I believe he has them set up with the correct residual check valves. You can add a simple adjustable proportioning valve for the rear drum brakes so you can dial it in right where you want it. These are available from Summit, Speedway, Jeg's, etc.

Most dual reservoir m/c's are not vented. The cover seal or diaphragm allows for fluid level changes. I'd have to check and see if the Daughter's '70 is or not but I would suspect not.

Edit: Might also try doing a search. Lots of good info as Herm's conversion has been the topic of lots of discussion here since he put it on the market.

 

Mostly looking to find out if anyone has had water/mud anything else enter the reseroir.

 

Ask Herm if his are vented. If not nothing should be able to enter. If so a vent could be run up high to the firewall.


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My 70 has the stock dual M/C under the floor. I've been in water deep enough to get my feet wet, and I havent had any problems with the master cylinder.

 

I have used Herm's kit on my 43 GPW. I had several issues but nothing major. The Stock GPW frames are boxed in the brake location so I had to notch the boxing in order to get the bracket to slide into the frame rail. The MC that came with herms kit did not have a push rod. I used my original however, I had to notch Herms bracket to get full movement of the brake arm.

 

oh ya, depending on your engine you may need a heat shield. I have the 225 with a 231 rear dump exhuast manifold and my brake lines are quite close to the exhaust. The MC is not the issue but the brake lines might be.