Brake Question

Hi guy's i have this twist over my brake on my cj5.

I have front and rear disk brake using a grand marquis booster (oem four Wheel brake) and a CJ booster. Brake galiper come from a GM 1975 dana 44 on all corner. All reman part.

I have very good brake, so that's not the problem problem. When i drive the jeep, my pedal brake may have a 1 inch travel before getting any pressure.. After some drive and 2-3 stop and go the 1" travel disapear and the pedal get pressure as soon as i press it.

I suspect that it happen when some heat is created by the brake but i just don't know how.

Hope somebody could help.

I did bleed the brake and master the right way, maybe a bubble of air somewhere in the system....

 

Maybe your residual valves leak down when sitting? If you get in when cold and pump the brakes, can you build pressure the same way?

 

No, i did try that yesterday, could pump 10 times in a row and i won't get to that point.

Wheel bearing are brand new, and i check this week-end for any loose and it doesn't have.

 

How many inches of vacuum are you making at Idle?.......need about 19-21 inches........That booster may be hungry for vacuum or perhaps you have a vacuum leak in your supply line.

 

Disk brake systems have a spring assy for the pads and calipurs to distance themselves slightly away from the rotor when no brake is applied. When you apply pedal, the cylinder piston is not fully out due spring action. This accounts for the inch of pedal travel. If the piston does not retract then you will have hard pedal.

 

Walt, on all the disc brake assemblies that I have worked on, I have never seen a return spring as you discribe. Do have a diagram showing the sytem. I would be interested seeing it.

I think the problem here lies in the adjustment of the brake pedal to master cylinder rod.

 

But how would that account for the tightening of the brake pedal when hot?

Next time it's hot and there's no slack in the pedal, I'd try cracking one of the bleeders to see if the pressure is in the hydraulics or if something else mechanically is going on.

 

Good idea i would give it a try.

 

The function of caliper seals

 

one of your calipers has lack of clearance causing the brake fluid to heat. Go drive it and put your hand on the caliper to find the hot one.

 

ive seen hoses fail inside and do the same thing,they act like a check valve

 

Did you try this?

 

I had a similar problem. It ended up being 2 things. 1. Air in the brake lines (front). 2. I did not have full travel on the piston in the M/C. My brake pedal was hitting the firewall.
I am a little confused on your original post. Which M/C?

To fix #1 Tarry gave me a number to call. Here were the instructions to get all of the air out of the front calipers.
Remove calipers
Place a block of wood between the pad that is about the same thickness as the rotor.
Hold the calipers as high as you can.
Bleed brakes normally

I bled the brakes on my CJ over 20 times prior to trying this. With this method I actually got more air out and had great brakes.

 

Well johnnyboy03 have you found the fix yet?

 

Not yet, my alternator give up on me so i'm waiting a new one.

i will give a try to those idea you gave me pretty soon.

Thank's for the help

 

Hope it does help.

 

So i may have found part of the problem. When i come back from my job yesterday pedal was hard (still good brake) when i got in the driveway.

So i jack up front and rear and there's no doubt, all 4 corner i got some brake drag. I was still able to turn wheel by hand but you can feel resistance on each wheel.

I decided to unplug the vaccun line from the booster and the resistance on the wheel (drag) got away. I put i back, got out on the street so i can back with initial sympton.

So this time i decided to give some loose between master and booster (take the nut off), and again resistance and wheel got away.

I remember that 2 year ago i play with the ajusting rod when i change my master.

So i ajust it and the problem seem to got away. But i still have air as i still have a 2-3in of smooth pedale, so i will try the wood block trick as soon as i got some time.

I will give the feedback when it will be done.

Still a big thanks at those who give me some hint , i really appreciate all the input you guy's can provide in this forum.

 

I had the exact same thing happening to my Jeep. The brakes would actually lock up. I would have to release the pressure on the booster like you mention. After I corrected the pedal throw I have never had the problem again.
Let us know if the wood block bleeding method helps.

 

Didn't have time to work on the bleeding. Just did 3 trip to my job and everything seem to be normal.

I'll be back as soon as i'm able to work on it.

 

So as problem goes away without explication i did start to smell burning brake today.

So i give a look over passenger front side anf my chrome wheel was all black inside, something i never saw before.

So i tool the wheel off so i can take a look over the brake. Wasnt able to see anything wrong but removing the brake pad i found that.

Pad did wear not strait but with angle. Now i wounder with the wear if it could have cause the drag problem mentionned before...

Heres some pic of the pad.