Rear Caliper Adjustment Screw Allen Key Size?

:
2002 Mazda Protege5
Hey Gang,

What size Allen key should I use to turn the adjustment screw on the rear calipers? Feeling pretty defeated after I spent almost 2 hours replacing the pads and rotor on one wheel only to basically feel like I stripped the adjustment screw. I had undo everything and install the old pads/rotors for the time being. I was using a 4 MM Allen Key and it keeps skipping/slipping when I try to turn the adjustment screw. If I try to insert a 5 MM Allen key then it wont fit at all. Do I need to purchase a 4.5 MM Allen Key?
 

pcb

The Diagram Dude
:
2002 MP5
It's a 4 mm.
I just checked my rear caliper from my parts car (it's disconnected from the car).

I played with it for a bit and realized that turning the adjustment screw doesn't pull the piston in.
You still have to push on the piston after turning the screw. The adjuster just adjusts the stopping point of the piston.
Try backing off the adjuster a bunch of turns then push in the piston.

Sometimes the whole mechanism is messed up and doesn't work but, you can also rotate your entire piston and screw it back in.
If you try to screw in your piston, make sure your piston boot is free to rotate and not stuck on the piston or it will rip.
 

pcb

The Diagram Dude
:
2002 MP5
The adjustment screw just floats in the hole, you can pull it out with a magnet and see if the teeth look stripped.

 
:
2002 Mazda Protege5
Thanks for the photos pcb. I finally around to messing with the caliper again and it definitely needs to be replaced now. The adjustment screw feels like its seized in place.. The car has 150,000 miles on it so I guess it was time for that caliper to be replaced.
 

pcb

The Diagram Dude
:
2002 MP5
Your brake piston might be seized so the adjuster can't move it.

This is what mine looked like...

 
Reviving a really old thread here since I am having the same issue. I see brake fluid when I take the bolt off to expose the hex key but it will not turn. The piston doesn't look rusted/seized like the photo.

Worse, when I put everything back together (the old rotor and pads), the emergency brakes no longer work! What did I do wrong?

Thank you so much for the sage advice.
 

pcb

The Diagram Dude
:
2002 MP5
You did nothing wrong.
Your calipers may be shot.

You may still be OK though.

The seal is leaking around the adjustment screw, but it shouldn't matter, because the bolt and washer should provide a seal. (although, you get air in your fluid,... bleeding the brakes should clear that.)


Your self adjustment mechanism may still be working.
Instead of using the adjustment screw to move the brake piston out, you can use your P-brake handle.

Sit in your car (engine off), push the brake pedal hard and hold it.

Then grab the P-brake handle, push and hold the button in, and pull the handle up and down about 4000 times (+ or - a bit, lol)

Each pull of the handle will rotate the adjustment gear one tooth at a time.
It may have to do 3-4-10 full rotations, one tooth at a time to push the piston out until the P-brake starts to grab.

If your P-brake was working before you did the work, then there is a good chance that this will work.

The adjustment screw is not necessary.
 
Will try this once there is daylight.

Just to be clear, this procedure is to save the handbrake and not to push the bear brake piston back to complete the rotor and brake pads change. I will need to buy a set of rear calipers ?
 

pcb

The Diagram Dude
:
2002 MP5
Will try this once there is daylight.

Just to be clear, this procedure is to save the handbrake and not to push the bear brake piston back to complete the rotor and brake pads change. I will need to buy a set of rear calipers ?
It does both.
Activating the hand brake pushes the brake piston out.

Once the brake piston is set, the handbrake will start grabbing.

You may not need to buy new calipers.

As you drive your car and use your handbrake after your brake job, they will keep self adjusting, keeping the piston set and the handbrake grabbing.
 
Sorry for being so slow, if this method works and my hand brakes are saved, this still wouldn't help me with the brake/rotor replacment job that I would need to do since I won't be able to install the pads with the caliper piston pushed out right?
 

pcb

The Diagram Dude
:
2002 MP5
Oops, my bad, I forgot about that...

You can work around that too.
You can simply screw the piston in by rotating it.

Make sure that the dust boot isn't stuck to the piston before you thread it in, or it will tear as you rotate the piston.
Use something like a dental pick to free the boot from the piston, around the circumference.

You can grip the outer edge of the piston with a pliers to rotate it, but be careful not to scratch the surface of the piston that goes into the bore.

It takes quite a bit of force to rotate the piston, you're not just threading it back in, you're pushing all the brake fluid back though the lines, and back into the master cylinder reservoir.
 

pcb

The Diagram Dude
:
2002 MP5
In case you need new rear calipers, you may need to buy new OEM calipers from Mazda.

There have been huge problems with remanufactured calipers.
All they do to remanufacture them, is replace the piston and seals. They don't inspect, test, or replace any of the self adjusting mechanisms.

Some guys would get a new caliper and the adjustment screw was stripped, seized, or there would be no adjustment screw at all.

One guy brought an Allen key with him to the store and they had to bring out three calipers before they found one that worked.

This is part of that weird ass adjustment mechanism...
20210113_104559.jpg



This is where the P-brake cable attaches and goes into the caliper.


20210113_104224.jpg
20210113_104224.jpg


That pin is completely wobbly in the bore.
It doesn't matter if you replace the seal, because it will get completely mashed and start to leak.

To rebuild the calipers properly, you would need to bore out the hole and use an oversize pin to stop the wobbling.


The remanufactered caliper issues were about 5-10 years ago, and things might be different now.

I just checked RockAuto, and the remanufactured rear calipers are about $110 CAD each and up.

The OEM calipers are about $300-$400 each.
 
Thank you for that information PCB, I'll see if I can get the hand brake to work and try to manually push the piston back in.

Just to have my bases covered, the rotation should clockwise to push the piston back in?
 

pcb

The Diagram Dude
:
2002 MP5
I'm almost sure that it screws in clockwise.
You'll be able to see if its going in or out with a rotation or two.


What all have you done so far?

If all you did was remove the bolt, try the Allen screw, then replace the bolt, then I don't understand why your P-brake would stop working.

Did you disconnect the P-brake cable from the caliper?
 

pcb

The Diagram Dude
:
2002 MP5
Oh, OK, I didn't know you got that far.

Yeah, you have to unhook the cable to swing up the caliper.

Make sure you reconnected it properly.

Get someone to pull the P-brake while you watch the cable connection point for movement.
 
Update: I was able to push back both pistons without the need to twist it. I'm not exactly sure what happened to cause the hex key inside the calipers to become unstuck. It may be possible that leaving the hex key cover screw off and gently tapping it help loosen it up.

It was a bit tricky to get both wheels to have the same amount of 'grab' when doing doing the 1/3 hex key turn after tightening the brake pads.

The handbrake issue also fixed on it's own after pumping the handbrake about 15 times.

Thank you for everyone's help as always!
 
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