One Piston more extended?????

Daniel644

Original poster
Member
Feb 27, 2015
573
OK, i'm at a complete loss, about 8-9 weeks ago I replaced the entire front brake "system" (Pads, Rotors, Calipers, Caliper Mounting Bracket) using one of those Powerstop brand kits, everything was fine and appeared to be working fine, then a week or 2 after that I did the rear rotors and pads (just pressing the pistons in without pinching the line or opening the bleeder screw), this is when my issue started, I noticed my front brakes running much hotter, to the point even the driverside brake would smell of burning pad after hard braking and pulling to a stop.

Last Weekend I bled out the whole system starting at the passenger rear, driver rear, passenger front, driver front. this seams to have gotten the temperature of the passenger front down (I pointed a laser thermometer gun at the rotors shortly after driving and the rear rotors where around 134-140* F and the Passenger front was at 160ish and the Driver Front was at 204*) but as you can tell the driver front is still running hot, so I jacked up the truck and it was MUCH MUCH harder to spin the driver front wheel then the passenger front wheel.

Fast forward to today, First thing I wanted to rule out was a bad brake hose not letting the fluid back to the master cylinder, to that end I perform the test I've seen suggested, Pump the brakes so that you can't spin the rotor by hand, crack the bleeder valve and if you can spin the rotor then your problem is in the rubber hose, well I cracked the bleeder and NOPE, still impossible to turn the rotor by hand (which I kinda doubted it was the rubber hose because I replaced all of those after I had a rear caliper seize up in February of 2021). So next thing I do is start testing different scenarios on the caliper, I remove the slide pin bolts and start pulling off the caliper, at this point I notice the lower piston feels harder to slide off the pads, so that inspires me to test something, so I angle the caliper so that only the upper piston of the caliper is making contact with the pad, at this point with only that piston over the pads I can spin the rotor by hand (not as easily if there was no caliper but it will move), then I angle the caliper so the lower piston is on the pads and not the upper, rotor then won't turn. So I then assume the possibility of a frozen piston on this caliper and decide to try some things, I use my C-Clamp to hold the upper piston from moving then step on the brakes causing the lower piston to extend (as it should), I then press the lower piston back into the caliper using the c-clamp, which it compresses as expected for a good piston that isn't binding up, so the piston appears to be functioning as expected when the pedal is depressed and when pressing in the piston (like you where installing new pads). At this point I assume there is an issue with the caliper and decide to swap back in the caliper I removed when I did the brake upgrade 8-9 weeks ago, only problem is this Caliper is behaving EXACTLY THE SAME, same lower piston making rotor not spin, same upper piston allows rotor to spin, all the same behavior I described of the new caliper is happening with the old caliper, even the cracking the bleeder and still not being able to turn the rotor

I'm at a complete loss of what to try next, the slide pins aren't frozen up, they both move freely, I went ahead and re-greased them just to be safe at the beginning of today's troubleshooting. It doesn't make any sense to me that 2 different calipers would behave exactly the same and releasing the bleeder screw should rule out pressure being held on the brake due to an issue in the brake lines.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Maybe contact Powerstop for some technical assistance and possibly getting a warranty replacement. I wouldn't mention the same thing happening with the old caliper as that would assume a problem with the truck.

Since compressing the other side seemed to have fixed it, maybe try doing that several times to see if it will loosen up. I'd take the caliper off and use a block of wood instead of the pads to let the pistons come out more. I don't know what Powerstop does when they rebuild calipers but hopefully they use new pistons since they are phenolic.
 

Daniel644

Original poster
Member
Feb 27, 2015
573
OK, I know it's been a minute, but some updates, first I took it to a mechanic, they couldn't find anything wrong with it and didn't drive it long enough to get the brakes hot enough to see more then an 8 degree temp difference, I took it back home, went ahead and did the Rubber Line just to rule it out, contacted Power Stop, told them the lower piston was not retracting and I had even replaced the line to rule it out, they sent out a whole new front kit, both rotors, pads and calipers and provided me with a shipping label to return the rotors.

Well finally after a a week and a half I found the time to install the new parts, problem still happening, has got to be something further up in the brake system, but even that doesn't make sense because if it's further up then cracking the bleeder should relieve the pressure and allow the piston to retract.

i'm at a loss, I don't know what else to try at this point.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
So only the right side is still hard to turn? And opening the bleeder doesn't release it? That is just strange. And the pistons compress back in without issues? I dunno. Maybe Powerstop has an issue rebuilding these? But you put your old caliper back in and same thing. I'm also at a loss. Cracking the bleeder would allow it to retract if it's something up the line is holding pressure on.
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,045
Brighton, CO
I am wondering if when he pressed in his rear calipers, if some debris didnt get stuck in his ABS unit..
 

Joe_67

Member
Aug 9, 2022
56
Central Virginia
Not knocking you, but just as a way of prefacing, the way you wrote up the initial post with that huge block of text made it hard for me to follow...so I'm really just apologizing in advance if I missed something. What I'm understanding is that you've got one of the pair of pistons binding - regardless of which caliper you're throwing on there (old/original / new #1 / new #2).

I too find the whole thing to be way weird, but it would be hard to imagine how a "upstream" problem would do that. What I'm wondering is whether or not the bracket might not have gotten distorted somehow. Or if some rust-jacking isn't going on - not under the pads, but at the bracket mounts. If that bracket got offline - even by a little, everything could remain slightly cocked in relation to the rotor.

It's the best thought I've got, but I like puzzles so I'll be thinking on it.
 

budwich

Member
Jun 16, 2013
2,027
kanata
my best guess is you have a pad / disc problem which is causing one of the pistons to not seat correctly and as a result it binds. I don't recall what "notes" are on brake pads (ie. front side / back) but you could try switching them around "temporarily" or swapping one side for the other (ie. right / left).
 

Daniel644

Original poster
Member
Feb 27, 2015
573
OK, now i'm even more confused, after months of just letting the truck sit I decided to get back on trying to trouble shoot this issue, I pulled the caliper off the bracket to "cycle" the piston out and back in a few times (locking the other piston in place with some blocking) and I managed to position the caliper where I could see it while pressing the brake pedal, I can see the piston retract when I let off the pedal, but when I put it back on the rotor its still seizing up.

I am leaning towards the "something is binding" theory but not sure what it can be, when Powerstop sent out the new parts they sent new Everything, Pads, Rotors, Caliper/Caliper Bracket, if it was simply a improperly installed pad or a warped rotor those issues should have gone away with the parts swap.

And even then that really doesn't make sense because of the one constant, I can UNBOLT the caliper from the bracket and it's definitely the lower piston still gripping the pads as it's much harder to slide the lower half of the caliper off then the upper half.


Edit: OK, I tried one last thing, I compressed the pistons again, then set the caliper in position and started the slide pin bolts just a few threads, then I mashed the brake pedal several times and I was still able to spin the rotor, it wasn't seized up (still had drag, not like when pistons are fully compressed) and then tightened the 2 slide pin bolts and took it for a drive around the block then jacked it up and spun the tire by hand, feels much more like the level of resistence I get from the passenger side wheel when I spin it.

Gonna take it to town and back tonight and see if it gets any brake pad smell.
 
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