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PBR calipers - Piston won't compress far enough for new pads

Old 02-13-2019, 09:42 PM
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PBR calipers - Piston won't compress far enough for new pads

.....so weird story....many years ago, I tried to change my rear pads on my 89/9bolt/PBR calipers. ....with new pads, the piston wouldn't compress far enough to fit over the rotor. I didn't know much....and I simply reused the old pads.

Fast forward to today. New rear...new everything really, including new PBR calipers, pads, rotors, etc. etc..........-same problem. The caliper simply won't fit over the pads. I even brought a mic' down to the parts store and double checked another set of pads. I MUST be missing something, but there doesn't physically seem to be any space. WTF am I doing WRONG!?!?!!


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Old 02-13-2019, 09:44 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

....and the parking brake lever isn't even engaged, so that would make LESS room
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Old 02-14-2019, 03:07 AM
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Re: PBR calipers - Piston won't compress far enough for new pads

On the last few rear pad swaps I have done, I have noticed the inboard and outboard pads are not the same thickness. The pads in the picture look to be the same thickness. Right off, I do not remember which pad was the thinner one.
Also, have you had the calipers apart to rebuild or are they remans. The inner and outer piston are bad for seizing together.
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Old 02-14-2019, 08:18 AM
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Re: PBR calipers - Piston won't compress far enough for new pads

The red paint thickness!!!! lol J/K. Have you used a C clamp to move them back in or how are you going about pushing on the piston?
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Old 02-14-2019, 08:19 AM
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Re: PBR calipers - Piston won't compress far enough for new pads

The pads are in the correct orientation. I did NOT initially notice they were slightly different, but they are....and in the pic they are correct. One has the wear sensor piece, and an exposed rivet on it. The piston doesn't hit it, but the outboard side of the caliper would. I did NOT notice the thickness being different, but I didn't specifically check the thickness individually. ...and the calipers are reman units and the piston slides freely. I can feel the piston "hit" the back, so I'm pretty sure it's actually fully compressed.
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Old 02-14-2019, 08:20 AM
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Re: PBR calipers - Piston won't compress far enough for new pads

With no line pressure, they easily slide in by hand. I DID put a C clamp on it just to see if it gave me more room....it did not.
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Old 02-14-2019, 08:29 AM
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Re: PBR calipers - Piston won't compress far enough for new pads

Maybe the bore isn't deep enough or the piston assembly is to tall. Might have to pull it apart and check it against a original ?
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Old 02-14-2019, 08:56 AM
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Re: PBR calipers - Piston won't compress far enough for new pads

Well my originals were the same way. ...but of course anything is possible.
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Old 02-14-2019, 09:32 AM
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Re: PBR calipers - Piston won't compress far enough for new pads

....as I sit here at work not being able to think of anything else, my frustration comes in that to the best of my knowledge, ALL these parts are the correct parts. I've measured 3 sets of rotors including the originals and ALL measure the same. The rotors are reman'd PBRs, and I had this same problem with NEW pads in my ORIGINAL PBRs...and I've measured multiple sets of pads....all measure 99% the same, all being too thick. Clearly most of you guys out there aren't having this problem, but I can't imagine what I'm missing.
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Old 02-14-2019, 09:44 AM
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Re: PBR calipers - Piston won't compress far enough for new pads

It doesn't look like the park brake lever is located on the pin that pushes the piston/pads correctly. Speaking of that, are those set screws to far out and holding the piston out a bit? Looks like they are sticking through the caliper body a bit.
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Old 02-14-2019, 10:06 AM
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Re: PBR calipers - Piston won't compress far enough for new pads

I moved the parking brake arm OFF the little pin just to free up a little more room. -same with the set screw. Figured I'd give myself the most room possible. Even then they don't fit.
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Old 02-14-2019, 10:55 AM
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Re: PBR calipers - Piston won't compress far enough for new pads

What is the measurement of each pad including the shim? I am in the process of rebuilding my rear and just happen to have new pads, rotors and my original calipers to measure. Here are pics of the difference in my pads. I checked and mine are fine. Everything fits together. Also my outer piston looks like it sits closer to the inner piston when compressed than it does in your picture.


Last edited by Fullmonte77; 02-14-2019 at 11:05 AM.
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Old 02-14-2019, 02:13 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

Also my outer piston looks like it sits closer to the inner piston when compressed than it does in your picture.
Agree with this. ....can you measure the space between the piston and outside of the caliper?

...also, since yours DOES all work....What is the overall measurement of your pad...rotor...and other pad? All 3 sandwiched together? -Like my first pic. ...I suspect my caliper isn't fully compressed, but can't see HOW to get more compression.
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Old 02-14-2019, 02:15 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

...im gonna look into compressing that piston a little more. Might just flat out take it apart. Your pic definitely looks like the inner and outer piston sit closer together.
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Old 02-14-2019, 02:23 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

Originally Posted by Abubaca View Post
Agree with this. ....can you measure the space between the piston and outside of the caliper?

...also, since yours DOES all work....What is the overall measurement of your pad...rotor...and other pad? All 3 sandwiched together? -Like my first pic. ...I suspect my caliper isn't fully compressed, but can't see HOW to get more compression.


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Old 02-14-2019, 02:49 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

Awesome. Thank you. ....I'll have to look over mine this evening and see what I get. ...

Last edited by Abubaca; 02-14-2019 at 02:52 PM.
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Old 02-14-2019, 02:52 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

I know the outer piston slips into a rubber bushing inside the inner piston. That bushing might be to long or not seated the whole way down into the piston. Hope this helps.
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Old 02-14-2019, 03:08 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

Well I appreciate the help.....will dig into it this evening.
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Old 02-14-2019, 08:39 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

Monitoring this thread, along with my legal team (). My calipers and rotors are all boxed up, but I'm curious if I'll run into the same.

Seems like the rear pads are usually thin, even new. I remember them being thinner than the pics in this thread, but it's probably been a decade since I had a set in my paws. Not sure I've ever looked very closely at the new pads from Rock Auto that I've got set aside for the Big Green Turkey. I need to finish converting and refurbing the 10 bolt for the Green, but I need to swap the 10-bolt in deep storage with the one in shallow storage, and I'm procrastinating. LOL
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Old 02-14-2019, 10:47 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

I took apart the calipers and put 'em back together. Looked like the rubber sleeve on the outer most piston (thats sits down in the bore) wasn't fully seated. Now, Both calipers compress fully, and both can be mounted, HOWEVER......It's still a super tight fit and there's no spinning the rotors. ......might just "cough" rub 'em on some 80 grit to free up a thousandth or two!!!!!
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Old 02-15-2019, 06:02 AM
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Re: PBR calipers - Piston won't compress far enough for new pads

when test fitting My PBRs. all new parts(same stock calipers) cleaned/ coated/chromed. I did notice the pads did drag on mine..more then before.. but with mine Im sure its the Coating on the rotors (zink plate) as soon as its off it will be back to like new.

how tight...it was tough turning wheel by hand..just one side set up..im going to remove the zink in where the pads ride.or cut the pads down just a tad..But.. the pads on the calipers did slide on the rotor overly snug..

Last edited by articwhiteZ; 02-15-2019 at 06:35 AM.
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Old 02-15-2019, 06:25 AM
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Re: PBR calipers - Piston won't compress far enough for new pads

also check your E brake paws..are they on right? should be facing out like this..(cant see yours fully)
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Old 02-15-2019, 11:17 AM
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Re: PBR calipers - Piston won't compress far enough for new pads

I'm a fan of "do it right"....but also of "make it work", LOL. ....It's so close the micrometer can barely see a difference. I think I'm just gonna rub the pads on some 80 like I was taking the glaze off. Should only need a few thousandths.

.....e brake levers are not engaged on the little plunger at the moment, but they ARE oriented the right way on the caliper.

-Artic, I've seen those pics before. Sharp lookin' set up.
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Old 02-15-2019, 11:42 AM
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Re: PBR calipers - Piston won't compress far enough for new pads

I have some NOS PBR rear pads and can measure those sometime if i remember.
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Old 02-15-2019, 01:44 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

I'd be curious to see what they measure.
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Old 02-15-2019, 02:07 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

Originally Posted by Abubaca View Post
I'd be curious to see what they measure.









This is a set of NOS pads & instructions (I'm just not certain it's for your year/model brake caliper, I think it is....) - maybe this will help ??
These came with my 89 Formula
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Old 02-15-2019, 02:08 PM
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Re: PBR calipers - Piston won't compress far enough for new pads



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Old 02-15-2019, 02:13 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

Exactly what I was going to post! Saved me a bunch of time lol
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Old 02-15-2019, 02:14 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

Originally Posted by TTOP350 View Post
Exactly what I was going to post! Saved me a bunch of time lol
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Old 02-15-2019, 02:21 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

Those pads look about as thick as mine....of course 30 years later, aftermarket pads, who knows. I'll measure tonight.

....that's interesting info. I see the shim included in the instructions. I have another diagram showing NO shim on the PBRs until the later years, but clearly it's there on your instructions for 89. Anyone know if it's necessary?

...and the free travel check and procedure looks far simpler than the other procedure I've seen. -I should say it's worded much simpler.
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Old 02-15-2019, 02:22 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

also interesting to see the inboard pad is actually SHORTER than the outboard. My old ones are like that....new ones are not.
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Old 02-15-2019, 02:29 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

Originally Posted by Abubaca View Post
also interesting to see the inboard pad is actually SHORTER than the outboard. My old ones are like that....new ones are not.
Look at the drawing - I think this could be your problem....
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Old 02-15-2019, 02:42 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

Look at the drawing - I think this could be your problem....
Oh absolutely! I totally see that, both in your pic and in the drawing. Now I did confirm that my pads ARE the right part number for PBR brakes from multiple year PBR systems up through 97,but still.....doesn't mean there's not something to that pad difference.
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Old 02-15-2019, 02:46 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

Originally Posted by Abubaca View Post
Oh absolutely! I totally see that, both in your pic and in the drawing. Now I did confirm that my pads ARE the right part number for PBR brakes from multiple year PBR systems up through 97,but still.....doesn't mean there's not something to that pad difference.
IMO, you simply can't beat OEM / NOS parts for proper fit, especially in this example....
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Old 02-15-2019, 06:08 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

Ya know, I've had a few PBR rear setups, and never saw the H shim until looking at replacement parts online. There sure wasn't a shim on any of the thirdgens I've disassembled. I suppose it's a sacrificial bearing surface so the pads don't wear on the caliper.
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Old 02-15-2019, 06:51 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

Check out this diagram drew....Doesn't show the shim for thirdgens
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Old 02-15-2019, 06:59 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

...in other news.. -got new pads!

....so these new pads LOOK a lot more like original pads. The inside pad is smaller in length, like the OE. It's also thinner in width, not sure why, or if that's like OE. Hard to tell from BiJetTechs photo, but mine sure is thinner. Also, it's got the wear sensor opposite on one side, so when installed, but will be in the proper "leading" edge side. The other ones I had were the same piece, so on one side they're on the leading edge, but trailing on the other side. Does this matter? -maybe not, but I'm point it out. BIG news is that they're a good bit thinner overall, which should help ME!

BJT's width appears to be about 1.050"
...my crappy new ones were almost 1.240"
...these NEW new ones are only 1.015"

...haven't loaded 'em up yet as my wife said we're all going to Moe's for burritos.
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Old 02-15-2019, 07:01 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

BTW that instruction/diagram is attached to post 9 of THIS thread:
https://www.thirdgen.org/forums/brak...r-caliper.html
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Old 02-15-2019, 07:23 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

Originally Posted by Abubaca View Post
...in other news.. -got new pads!

....so these new pads LOOK a lot more like original pads. The inside pad is smaller in length, like the OE. It's also thinner in width, not sure why, or if that's like OE. Hard to tell from BiJetTechs photo, but mine sure is thinner. Also, it's got the wear sensor opposite on one side, so when installed, but will be in the proper "leading" edge side. The other ones I had were the same piece, so on one side they're on the leading edge, but trailing on the other side. Does this matter? -maybe not, but I'm point it out. BIG news is that they're a good bit thinner overall, which should help ME!

BJT's width appears to be about 1.050"
...my crappy new ones were almost 1.240"
...these NEW new ones are only 1.015"

...haven't loaded 'em up yet as my wife said we're all going to Moe's for burritos.
There is considerably less meat there than my NOS pads, which were 1.050" but I think you are headed in the right direction now.
Sounds like those should work for you....
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Old 02-15-2019, 07:48 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

Wonder if the thicker set of pads are for turned rotors and the thinner ones are for "new" rotors??
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Old 02-15-2019, 08:54 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

Fun stuff... Just pulled out my new pads and had a look. The inner and outer pads have the same footprint, but one is a bit thinner than the other. The pair of pads stacked is just a smidge over 1" thick.

Seems there's no consistency with these things. Like the manufacturers don't care if the inner and outer pads are the same, or thicker/thinner longer/shorter... It's madness!
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Old 02-15-2019, 08:54 PM
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Re: PBR calipers - Piston won't compress far enough for new pads

We looked at several sets in the store. ALL were the same part number, for various years of cars with those same PBRs. .....I didn't mic every set, but some LOOKED like OE, as described above, and some looked a lot more generic and were thicker. I honestly can't say for certain that the generic ones were all thicker, but it did seem that way. Also, it was NOT a price point issue. The ones I picked up were middle of the road semi-metallic for $25. One set of premiums were double the price and looked generic.

I don't know.
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