Brake Issues, Revisited...

OK. I know most of you know the issues I have been having with brakes. I got new springs and installed them, bled the brakes and drove the Jeep for a while and things seemed to be ok. Today, I put it through its paces and the brakes started to drag again, but not nearly as bad as they did originally. You could just tell there was a drag on the system as the jeep did not roll freely.

Since it seemed to be heat related, I wondered if the extra work being done by the system was heating the brake fluid to a point where it was hot and expanding to the point that it was acting as if the master cylinder was overfull. So I pulled some fluid out and today I drove it hard and there was no binding, until I let the jeep sit in the driveway with a hot engine. I went outside in about 5 minutes and the brake shoes were tight against the drums. My driveway is on an incline. I put the Jeep in neutral and it did not move.

I felt the brake lines coming from the master cylinder and they were hot enough to burn my hand if I stayed in contact with them. There was still a lot of heat radiating from the exhaust manifold, which in within a few inches of the lines. I am not sure, but maybe my exhaust runs hotter because the engine/carb system have been slightly modified for more torque and hp.

So I plan on doing the following and will let you all know how it works.

I am going to re-route the brake lines to be further away from the exhaust system and install a heat shield between the two systems.

I am going to run some hose from the front of the jeep so that when I am moving down the road, it can cool the master cylinder. I am not using the large air intake that is just behind the front grille for intake air, but I am thinking of making up a housing that will run fresh air to my air filter on the Weber carb and split off of that with a smaller hose to cool the master cylinder.

Any other ideas you all might have would be appreciated. I can actually drag the 31" tires with the 9" drums. Did it today, just to see, but it still might be a bit much for the 9-inchers to handle 31" tires.

Have a good "rest of your day"...

 

Glenn, I am using off the shelf standard brake fluid. I never use old fluid in new systems. I originally replaced all the wheel cylinders, shoes and lines blocks and hoses to hook them up to the new master cylinder. All brakes are even across the board and work very well. When I parked the Jeep in the driveway this afternoon, the heat under the hood caused them to stay locked up. So a few minutes ago, went outside and hit the clutch, just to see if the brakes were locked up and they were not. The jeep rolled freely. So this tells me that the master cylinder is getting too hot and allowing the pressure on the top of the brake fluid to build enough to push the wheel cylinders outward. I think this will be an easy fix, now that I know what is going on. I will do the items I mentioned in the original post and let you know how it works. I also wonder if it would help if my master cylinder was not painted black... Thanks for sticking with me on this and giving me ideas to work with. You and others in here were great as usual. Have a good "rest of your weekend". I have a short workweek coming up. I am working on Thursday of this week and the rest of it is paid leave. Gotta love it!!!

 

Glenn, one last thing...

Is there a special brake fluid I should be using?? Do you know something I should know?

Thanks....

 

Brake fluid in itself is designed to sustain high temps, if it is not contaminated, since the heat of friction at the wheels can be extreme. But lines in the master cylinder area should not be hot.

Is your master properly vented? Is there an inappropriate non-return valve on it? Was it designed for disc brakes? Drums need return flow, discs don't.

 

A few questions;
1- was the master cylinder over full when you removed fluid?
2- does the master cylinder lid have the correct gasket?
3- does the pedal have free-play before it contacts master cylinder?
4- is the master cylinder correct for the brake components, drum/drum, disc/drum etc?
5- brake adjustment too tight?

 

The master cylinder has been working fine, until the temps out here got hot. I had driven the jeep for several hundred miles when it was cold and never had any issues until temps started hitting in the 90's. That is when it first showed up. There is plenty of return flow.

I am thinking that if I get larger drums/brakes for the tires, this will help keep the temps down and heat shielding the master cylinder and providing better airflow around it will make the issue go away.

The fluid and all parts are brand new. Thanks for the interest. I will post what I end up doing once I get this taken care of. My little experiment today kind of let me know what is going on.

 

86,,,

Thanks for your post. The amount of heat generated in the master cylinder was originally causing the fluid to expand to the point where it was pushing against the lid, but the gasket was in good shape and creating pressure in the brake lines, and as such, not allowing the springs to pull the shoes back away from the drums. This, plus the fact that the original springs were weak. Should there be a vent in the lid for each reservoir? It seems to me that this would be a cure to my problem.

Just out of curiosity, how full should each reservoir in a dual reservoir master cylinder be? Once I pulled some fluid out of the master cylinder and changed the brake shoe springs in each wheel, everything seems to work as it should. It was only after I was traveling slow and using the brakes in an "unnatural" way, did the shoes started dragging a little bit again. Once I let the jeep sit in the driveway and cool off, I hit the clutch and all four wheels were rolling freely.

 

Glenn, see the answers I wrote above. I will let you know what I do to get this working the way it should. I am thinking it would be better off going to larger drums -- 10 or 11 inch. Where do you guys get your 10 and 11 inch drums? Apparently my 31 inch tires are too much for my 9" drums, even with power brakes. Will these work on a '62 cj-5 without a lot of problems?

I already have a vacuum booster and different master cylinder installed...Let me know what you know. Thanks....
View attachment 34028

 

Your MC should have residual pressure valves that retain a tad bit of pressure to keep your pads/shoes near or at friction to prevent half of your pedal travel being used up in slack removal. Over a few PSI of back pressure, and the fluid should bleed back into the reservoirs. You need to find out what is preventing your fluid from being able to release the pressure by returning to the reservoir.

If you can get this to repeat the symptoms, crack the bleeder valve at one of the wheels when the brakes are tight. If fluid shoots out and your wheel frees up, you definitely have a fluid-return issue. If that doesn't make a difference, you're having a friction-related problem, where the shoes are adjusted too tightly and have no leeway for expansion.

Do you have the original single cylinder master cylinder?

 

Since this is a power brake conversion, I'm wondering if somehow the vacuum assist is activating when not required.

 

Herm the orverdrive guy, the Jeep Guy are both great people to work with in getting 11" brakes!

Just search there names and you will find their web sites.

rick

 

We have discussed this again and again and again and ...

site:earlycj5.com 11" brake conversion - Bing

 

Man…. this is why I like to keep things stock. Once you mod, it introduces all kinds of variables.