Front calipers keeps locking up

[fanopj1]

The piston on the PBR calipers ( both sides ) does not retract all the way. I cannot spin the wheel with two hands, its so tight. I removed the calipers and reset the piston, and than soon as I press the brake down, they locked up again.
Is this as simple as bad calipers or am I missing something? its weird that it is happening to both sides.
One day I will get this car back on all fours and down the road.
Any suggestions or tips would be great. Thanks

 

[HISSIN50]

Do the pistons push back pretty easy with your hand?

Do we assume there are no issues with the MC piston displacement or adjustment.

Any chance you have a line(s) that is collapsing?

 

[fanopj1]

The pistons do not go back in easy, I used a c-clamp. Is that a good thing or not?

I have tried different adjustments on the booster which is a 1993 cobra mc/ booster.

No colapse on the brake lines. They are MM stainless steel braided lines that are new.

 

[hotcobra03]

brake

hission hit most of them..here is a dumb one...the new calipers are bigger and take more fluid..yes?the mc ,,is it full to the top?maybe the pressure is building up when fluid is returning back to mc... and did you do anything else other than just change calipers and hoses? if yes all details,and why did you try push rod on mc?was something changed thier?

 

[hotcobra03]

brake

as to brake line ..a twisted line will do that also..but with both doing that than both would have to be twisted...a steel brake line can also be crushed,,,the proportioning valve could be bad,,,also how about the back wheels?are they doing the samething?

 

[hotcobra03]

brakes

was helping a guy out last week with a brake problem after doing conversion...he had hydrboost..i did a search for a seal kit to rebuild it and came across this web site..looks like it has alit of good stuff to read .go to home page,than scroll to bottom and thier you can search by manuals..than when in manuals go to bottom and you can search like google ...brake system

 

[HISSIN50]

It's not unusual to need a clamp to retract caliper pistons. If they sat for a bit, I'd consider rebuilding them. They're pretty easy to take apart and clean up. You might have pitting in the bore which is holding things up.

Chances are right now that if you put a bleeder kit on the bleeder fitting (so you dont spray brake fluid all over), and you open the bleeder, fluid will whiz out and your wheel might turn.

 

[fanopj1]

hission hit most of them..here is a dumb one...the new calipers are bigger and take more fluid..yes?the mc ,,is it full to the top?maybe the pressure is building up when fluid is returning back to mc... and did you do anything else other than just change calipers and hoses? if yes all details,and why did you try push rod on mc?was something changed thier?

Fluid is filled. Basically the whole brake system was upgraded. New booster/ MC from a 93 cobra, new adjustable Prop valve, gutted stock valve, new lines.
Rear brakes seem to be fine, just the fronts are having the problem.

 

[fanopj1]

It's not unusual to need a clamp to retract caliper pistons. If they sat for a bit, I'd consider rebuilding them. They're pretty easy to take apart and clean up. You might have pitting in the bore which is holding things up.

Chances are right now that if you put a bleeder kit on the bleeder fitting (so you dont spray brake fluid all over), and you open the bleeder, fluid will whiz out and your wheel might turn.

That is what I was thinking, with the possiblity that they have sat for a while. I was thinking rust on the pistons.
I will try to see if they release with the opening of the bleeder. I did not think of that.
How do you remove the piston from the caliper? that sounds like something that will not hurt to do either way.
Thanks guys

 

[hotcobra03]

lock uped

how about the back wheels?are they ok before you go further,,if they are locking up too thiers no need to rebuild yet....i cant see your set up..how are the calipers held on ?are thier guide pins?

 

[fanopj1]

The backs are fine.
The fronts are off of a 1999 GT. I bought new caliper brackets for the front and the rear. They are held on by 2 12mm bolts to the caliper bracket.

 

[hotcobra03]

upgrade

The backs are fine.
The fronts are off of a 1999 GT. I bought new caliper brackets for the front and the rear. They are held on by 2 12mm bolts to the caliper bracket.

Special Edition PBR 2-Piston Calipers - '94-'04 Ford Mustang


is this the upgrade you did? ist says you need 94 spindles...did you use something else? im thinking the caliper bracket is holding caliper in the wrong spot maybe,and thats stopping the pistons from retracting? i find it hard that both calipers are stuck just from sitting...im assuming you havent drove the car and its still up in the air...i havent done an upgrade but maybe if you loosen the caliper bracket alittle to see if brakes release..after pushing on brakes,,,sounds crazy but when you use c-clamp to push in pistons ,when its reinstalled its not centered untill you push on brakes?