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Old 18-12-23, 15:10
Retsarge Retsarge is offline
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Join Date: May 2009
Location: Oak Forest, Illinois, USA
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Default M38A1CDN2 Brake System

Hi,
I was just working on me jeep's break system. I had to replace the Master Brake Cylinder. My jeep still has the tube that is connected to the top of the master cylinder cap. This tube goes over to the jeep's air filter canister., I assume as part of the vehicle's water fording system. With this tube attached to the brake cylinder cap, it makes it very difficult to do a quick break fluid level check.
If I replace the brake cap with a non-fording equipped cap, this would allow for a easy fluid check. But what about the tube, should this be plugged? Will this have any side affects? Thanks Richard

1967 M38A1CND2
7105 96879
CFR: 67-07832
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Old 18-12-23, 17:35
rob love rob love is offline
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Join Date: Feb 2003
Location: Shilo MB, the armpit of Canada
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The vent tube is required. If you go with a civilian cap (like the one that came with your master cylinder) it will have a small hole that achieves the same thing. If you were to simply remove the brass fitting on top of the existing cap, and put in a plug, then as the fluid heats up and expands from either the heat of the engine, or the heat of the braking, the pressure in the master will build up and cause the brakes to either drag or lock on.

Wile it is a good idea to check the master cylinder occasionally, you can also watch the most likely spots on the jeep for signs of leakage. That would be the back of the wheels where the master cylinders will leak, and the boot of the master cylinder where the fluid will leak if that cylinder is failing.

One thing that has become popular, although will be non-original to the jeep, are the remote reservoirs. This will be a plastic reservoir which you can mount on the firewall somewhere, and will include a bellows type diaphragm in the cap of it to prevent contact with the outside air. Brake fluid is hygroscopic: that is it will absorb moisture from the air. This way, your brake fluid will remain pure, and you can check and top up the fluid without having to be a contortionist. As well, there is less chance of you dropping dirt and debris into the master, which will cause premature failure.
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Old 19-12-23, 05:39
Retsarge Retsarge is offline
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Hi Rob,
After reading your reply, I am going to leave the master cap exactly as it was designed to be. We checked all the wheel cylinders when we bleed the brakes after installing new master, no leaks there. Thanks Rob
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Old 19-12-23, 05:44
rob love rob love is offline
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Since the fluid is subject to atmpshphere, it is a good idea to flush the system every 2 or 3 years. Note that if you use silicone it is not hygroscopic, but if water does get into the system, it can collect in a low spot in the lines and freeze.
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