Factory Five Racing Forum banner

1 - 16 of 16 Posts

·
Registered
Joined
·
672 Posts
Discussion Starter #1
I m having an issue with the right front caliper sticking. It is a twin piston PBR caliper. I got it loose a while ago flushed the fluid real good, and it seemed fine until today and it is locked up again.

Thinking of just trying to rebuild it, but I have read where people had issues with rebuilding, so should I just replace it? Best place to buy one? Thanks.
 

·
Registered
Joined
·
672 Posts
Discussion Starter #2
i decided to pull the caliper and take it apart. I think the plastic pistons must be swollen or warped. They were very hard to get out. Inside was perfect. No gunk or anything. Very hard to get them back in. I ended up going to Autozone and got a reman PBR for $50. Easiest route. If anyone has any pearls about the calipers, I would love to hear them.
 

·
Registered
Joined
·
206 Posts
I had the same with used ones I bought for my build. They Bothe stuck when I got them installed. Ended up swapping for reman ones like you.
I’d take a min and measure to see it the pistons are square to the “fingers” that hold the outside pad.
Mine aren’t square on one side and the outside pad doesn’t sweep the whole rotor.
 

·
Registered
Joined
·
192 Posts
Same here 2 weeks ago,traded mine for a rebuilt at NAPA up here in Canada.
Seems to be quite common with those calipers...
 

·
FFCobra Craftsman
Joined
·
22,146 Posts
I have a brand new pair I was going to install to replace the heavy cast iron calipers I have now. Bought them last winter. There has been a resurgence in sticking caliper threads so I've decided to forget that 'upgrade'.
 

·
Registered
Joined
·
672 Posts
Discussion Starter #6
During my internet search, I found some metal pistons and considered trying to rebuild mine and getting rid of the phenolic pistons. . Once I added up parts and it wasnt much more to buy the rebuilt caliper with a warranty and I wasnt sure a rebuild would evn work. I bet there is a lot of good info on the Mustang forums. I may keep digging.
 

·
1st RFM/FFR Legacy Winner
Joined
·
21,369 Posts
Mine were sticking from the donor. I got decent rebuilt ones from rockauto about 4 years ago and so far they are ok. The phenolic pistons do eventually swell.

Greg
 

·
Premium Member
Joined
·
1,042 Posts
Mine were sticking from the donor. I got decent rebuilt ones from rockauto about 4 years ago and so far they are ok. The phenolic pistons do eventually swell.

Greg
I just went thru this on my 2008 vintage Mark 3.1, about 10,000 miles on the PBR brakes, left front starting sticking. I track this car so they have seen some high heat, but I bleed the brakes at least once a year.

I took them apart and measured the old pistons versus new pistons and there was only a couple thousandths of an inch difference. Not much swelling but maybe enough. I checked the rubber seals versus new seals and they were identical, no swelling. Hmmmm...thought i would find a bigger issue.

Ok, so put new pistons, new seals, put back on the car....pads won't even come out!!! Really....so pull it apart again, put caliper on the bench, compressor set to 100 psi....after pulsing the pressure for a minute it finally moves out. Ok, so I have a lathe, I remove .005" off the diameter where the rubber seal sits ...reassemble...reinstall....ahhhhhhh...they work now.

I think the tolerances are just not right for the pistons to the bore in the caliper block and the size of the rubber seals, maybe it crept this way over time, can't believe it was designed this way.
 

·
Registered
Joined
·
1,879 Posts
I've had these on my race car for 8 seasons. I've resealed-rebuilt them several times. I think the difference is mine have steel (stainless steel) pistons. They don't swell.
 

·
Registered
Joined
·
24 Posts
Emac,

Not sure how much you're looking to spend, but I am selling the full front brake set for $275 + shipping. They've never been installed and will include both calipers, mounts, rotors, brake pads, pins, and clips.

PM me if interested.

- Flip
 

·
Registered
Joined
·
672 Posts
Discussion Starter #11
Emac,

Not sure how much you're looking to spend, but I am selling the full front brake set for $275 + shipping. They've never been installed and will include both calipers, mounts, rotors, brake pads, pins, and clips.

PM me if interested.

- Flip
Flip, Thanks for the offer, I am hopefully good to go. That should interest someone with a new build for sure.

ernest
 

·
FFCobra Craftsman
Joined
·
22,146 Posts
I've had these on my race car for 8 seasons. I've resealed-rebuilt them several times. I think the difference is mine have steel (stainless steel) pistons. They don't swell.
Steve do you have a source for the steel pistons. I had no luck looking.
 

·
Registered
Joined
·
1,879 Posts
Craig, No help here. They had the SS pistons in them when I got them. I bought them used (very slightly used). They are powder coated red and say "Cobra" in white letters so maybe they are from one of the after market performance brake suppliers. The rears are also red powder coated. Was probably an un-grade kit someone offered.
 

·
Registered
Joined
·
672 Posts
Discussion Starter #14
I spent some time searching the internet and found a thread on a Mustang forum about the phenolic pistons. Several people searched various other cars trying to find a steel piston to replace them. No one ever seemed to come up with a match. Most people just went to another caliper. Others just flushed fluid annually or kept spares. Too bad as it seems such a waste.
 

·
Premium Member
Joined
·
1,042 Posts
seal groove

One thing I didn't mention about machining the groove deeper for the seal to sit in, was the groove is actually a "V" shape. Not a square shape that you would expect with a square cross section seal. So I machined it only a few thousands deeper, but created a flat surface for the flat side of the seal to sit on. Does anyone know why the seal groove is a "V" shape?

I also machined the square groove about 20% wider then the seal itself, rubber is incompressible so you need to leave some room for it to grow sideways when it is compressed radially. I guess the V groove allows for that, but just doesn't seem right to me. The V groove would be perfect for a round O-Ring, but seems weird for a square cross section.
 

·
Registered
Joined
·
38 Posts
I had the same problem. Check the brake bias. My brake bias bar was catching and not releasing completely. This only happened for the front brakes. Hope this helps.
 
1 - 16 of 16 Posts
Top