Rear brake adjustment gear works, but piston stuck. Seized?

6

616Nickel

:
2002 Mazda Protege5
I posted on this issue in a different thread yesterday, but after reading up on this it seems like most people have a different brake-seizing problem to mine.

Other people find that the little allen-socket adjustment gear seizes or strips--mine turns fine in both directions, but the piston doesn't move. I removed the adjustment gear, and both it and the mating gear look to be in good shape. I can feel very slight wobbling movement with my fingers while turning the adjustment gear, but no in-out movement. Bottom line is I can't retract the piston to get the caliper over the new pads. Is this another variety of seized caliper, or is there something else I can do?

Details
  • This is the driver-side rear caliper. The piston on the passenger side retracted fine.
  • Over the past couple of weeks, I had noticed that the RL rotor was cooler than the other three after driving some distance: The RL rotor was hot to the touch while the other three were too hot to touch for more than a second or so. Plus, the e-brake needed to be almost at the limit of its travel to hold the car.
  • Both sets of rear pads were worn unevenly, with the outer pads more worn than the inner (~3.3mm on the outside vs. ~4.5mm on the inside), which seems odd. The rotors are both at ~9.2mm.
  • I removed the cap from the brake fluid reservoir before trying to retract the piston.

The fact that the RL rotor was cooler may indicate that the piston has been stuck for some time, keeping the pads in contact with the rotor but not applying much braking force. This may also explain the e-brake not working well. It may be that the RR brake has been doing all the work.

Thoughts?
 
I've had this happen, the caliper is on it's way out but for the time being you can use a big c-clamp to push the piston in while turning the gear counter-clockwise. The piston is most likely rusty and getting caught on the outer seal. You could try removing the piston (see the service manual for full instructions on how to do that) and see if you can spot any problems. If it is rusty you might be able to fix it by simply sanding and polishing it.
 
Honestly, I would just replace the caliper. The rears are so finnicky, once that allen gear strips or seizes, it's tough to get the caliper back working again. Swapping a caliper isn't a really big deal, so I would just do that if I were you.
 
agree with using the c-clamp while rotating the gear. the gear is should only be for hand-brake adjustment although as you've found out its a frustrating piece of equipment.

word of advice: if you get a rebuilt caliper, inspect the adjustment gear of the new caliper!!!!! i replaced a caliper from Napa (rebuilt as well) and the teeth on the damn adjustment gear was stripped. had to use 1 gear back and forth between both calipers. thats the worst case scenario if you didnt keep the good adjustment gear from the old caliper.
 
No disrespect meant to the above poster, but the service manual states that rotating the gear is the procedure for retracting the piston. Certainly you can use the c-clamp to put pressure on it so that the gear will turn, but if the caliper is already having issues, I would just replace it. There's no guarantee that you'll be able to readjust it back out with the gear once you have the pads installed.
 
C-Clamp will simply Eff Up the rear caliper .

Not a helpful suggestion..

The correct way to slack off the piston is to rotate the gear all the way off.
Install the new pads
and Adjust the gear as per the manual

1/4 to 1/2 turn from tight. Then check the Park Brake position.


If the gear isn't doing anything then Core the Old Caliper and replace it with a new one. (Not From Mazda, they will poke you in the Bum... $$$)

Go to NAPA or whatever store is near you like NAPA
 
Thanks for all the advice, guys. I ordered a World Brake Resources caliper from Autopartsway and it should arrive tomorrow. I have to send the old core back to recover my $100 deposit, but I think I might disassemble the piston mechanism beforehand just to get a sense of what went wrong. If it's interesting enough, I'll post pictures.

In this case, since the adjustment gears appear to be in good shape, I expect that the piston has frozen due to rust or something like that.

And now I'm a little worried about the other caliper, even though its piston seems to be moving freely. I'm going to flush the brake system, of course, but are there any early warning signs of a piston seizing, or do you just have to wait until it happens? Fortunately, in this case, it seems to have seized in the non-clamping position, so I haven't destroyed my rotor.
 
BRIAN_MP5T said:
Go to NAPA or whatever store is near you like NAPA
Click to expand...
i replaced a pair of rear calipers from NAPA that were bad. had to use a c-clamp as the adjustment gear was not going pushing or retracting the piston. why use a clamp? once you've installed the caliper and positioned the piston, the fluid does the rest of the work. the gear is to make sure the spring loaded handbrake makes proper contact. so i agree the clamp is not the correct method, but really as long as youre turning the gear as you push the piston you're just assisting the work.

NAPA also paints the calipers black, they call it "exclusive protective coating" when in reality its a pain in the ass cuz they also paint inside the bolt holes. we had a hell of a time bolting it back up cuz the threads now had to fit in a tighter space. got new bolts cuz we were afraid the old ones were stripped.

i exchanged for a 2nd pair which weren't much better. rotating the adjustment gear took quite a large amount of force, but at least it was working. the old leaky stock calipers were much easier and smoother. they and all the other auto parts stores send off the cores to a big warehouse somewhere where it all gets rebuilt by some john doe with a couple rubber seals and a socket wrench. good luck with the install.
 
All right, so I replaced the caliper on the weekend, and took the old one apart to see what had happened:


The piston had grown rust, which caused it to seize up.

I flushed the brake fluid in all four calipers before doing the replacement, and a fair bit of crud and maybe even water came out of this one.

Aside from the rust, the actual mechanism seemed fine once I had it apart. Interesting to see how it all works:


Mazda Protege5 Rear Caliper Piston Mechanism

For those who don't know how it works, the whole six-piece "star" assembly in the middle snaps into the piston, and the shoulder nut (with the wave washers still attached) threads onto the gear bolt. When you turn the allen-socket gear (not shown), it causes the gear bolt to turn, which moves the piston in or out. The little round-ended pin at right is the linkage between the external parking-brake actuator and the piston mechanism.
 
Sorry to revive such an old thread but I have a question relevant to the calipers:

We are rebuilding a caliper and I am wondering how the piston moves under hydraulic pressure? Does the adjusting screw engage into the "stuff" that is inside the piston or does it just push on the piston? Does the "stuff" inside the piston move with the piston or does it stay "stuck" to the adjusting screw and the piston moves independently?

Inquiring minds want to know...

Thank,
mark & Woody
 
When the brake pedal is pushed, the hydraulic fluid pushes on the piston, moving the piston forward. This is different from how the e-brake engages the piston.

When the e-brake is pulled, it turns the screw mechanism, which pushes on the piston.
 
The adjustment gear needs to be operating properly to adjust for the slack due to brake pad wear.
It also prevents the piston from retracting too far after applying the foot brake to allow for even braking on both rear calipers.
It's the application of hand brake that turns the gears to "self adjust" the brake.

If your brake piston is rusted, the brakes will engage but not release fully and will drag.
When the pads are worn,the piston extends further and can rust at the exposed part. Then when it is pushed back in (to make room for new pads), that rusted ring jams inside.
 
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