HOT REAR BRAKES

[3b a runnin]

I'm still having some problems with my rear brakes getting tight and hot on my 3B. This all started when I changed to the flanged axle and dual Wilwood master cyl. 11in. brakes with no integral park brake. As I'm driving I can feel the brakes getting tight. It is building up pressure in the rear only. No issue with front brakes. I can bleed the rear at either wheel cylinder or at the bleeder on the master cylinder to relieve it. Once that's done it is fine again for a day, a week, or a month, no real pattern. If it was a bad rear hose from the chassis to axle, how would bleeding at the master cylinder help? If the plunger in the master was not returning all the way, why wouldn't I also have problems with the front brakes?
I'm sure there's something simple that I'm missing, but I'm kinda stumped.
Any help appreciated.
Link to the master cyl I'm using https://www.wilwood.com/MasterCylinders/MasterCylinderProd?itemno=260-7563

EDIT
I used this unit on my cj6 for a couple yrs until I changed to hanging pedals and vacuum boosted brakes, with no problems at all.

 

[Howard Eisenhauer]

Check to make sure there is some slack in the push rod without the pedal applied, there should be an inch or so of pedal travel before the rod hits the piston.

 

[3b a runnin]

There is definitely some travel, probably not an inch. But wouldn't it also affect the front brakes if that were the issue?

 

[Howard Eisenhauer]

There is definitely some travel, probably not an inch. But wouldn't it also affect the front brakes if that were the issue?

I think it depends on the exact placement of the ports between the reservoir chambers and the cylinder, maybe one piston isn't moving quite far enough back to open the channel. it's something to check, even if it's not the issue you'll have eliminated a possibility.

 

[47v6]

There is definitely some travel, probably not an inch. But wouldn't it also affect the front brakes if that were the issue?

Back brakes are supposed to engage slightly before front brakes .

Also, how hot are your drum brakes getting to expand the brake fluid ? I would assume smoking. I had this issue with disk brakes, but the wheel cylinder is farther away than a caliper. Check that rubber hose to see if it’s acting as a check valve. Any release of pressure may fix the internal hose issue, should there be one.

 

[3b a runnin]

I'll go back and check the plunger in the master cyl. to make sure it's returning and has slack between it and the pushrod.

 

[3b a runnin]

Since the rebuild kit consists of 2 separate plungers, is it possible that the rear brake plunger is sticking in the bore but not the front brake plunger?

 

[Rich M.]

Bad rpv valve (should be 10lb)?

 

[Daryl]

How old is your flex line that drops to the rear axle? Quick $10 fix if that hose has deteriorated inside and is acting as a check valve.

 

[3b a runnin]

Bad rpv valve (should be 10lb)?

Possibly
It’s internal in the master cyl

How old is your flex line that drops to the rear axle? Quick $10 fix if that hose has deteriorated inside and is acting as a check valve.

Probably 10 yrs

I may have found it, maybe.
The plunger was pretty cruddy. The pic is of the front brakes, rear plunger not hardly as bad.

I’ve got a rebuild kit on the way

 

[OzFin]

Hopefully the rebuild kit will solve the issue, even if it doesn't that needed to be addressed anyway.
You might consider disconnecting the brake lines from the wheel cylinders and flushing / blowing them out just in case there is more crud down stream.
X2 on Daryl's recommendation on the flex line.

 

[3b a runnin]

Welp, I got it all put back together. I rebuilt the master cylinder, blew out all the lines and replaced the rear hose. I drove it to town tday, 20 miles or so round trip and all seems good. Brakes did not get hot,I guess time and miles will tell.