Rear caliper dissection

pcb

The Diagram Dude
:
2002 MP5
I was curious about how my rear calipers and adjusters work so I took one off my parts car and disassembled it.

First was the adjuster screw under the bolt.
A magnet works great to pull it out.



The adjuster worked to push the piston out all the way then I could remove it.





This is the threaded screw inside the caliper but it's held in by a c-clip that's hard to get at.
There was grease of some sort around the screw... Must be special grease to be mixed with brake fluid ??





I noticed the spring end wasn't in the little hole to hold it on the outer ring... I assume that would prevent it from ratcheting. I don't know if it was working to begin with or if it was me taking it apart that popped it out.



Then I threaded in a bolt and managed to pull out the gears. The big c-clip just popped out.
That's the inside of the brake piston with the cross in it.





This is the bore that the adjuster came out of... You can see the splines of the screw that the adjuster mates with.



This is the pin that the parking brake connects to.
The pin is really sloppy in the bore and you can see how it would mash a gasket in no time and cause it to leak.
I wonder if that pin and bore aren't cleaned up or replaced during a rebuild.

I can't seem to get it out,.. I may have to remove the c-clip and screw to release it.

I don't have a long reach c-clip tool so I sharpened the points of a big needle nose pliers,... We'll see if that works.



 

pcb

The Diagram Dude
:
2002 MP5
Well, I got the C-clip off... I used a dental pick and a small flathead screwdriver.



The pin at the bottom of the picture attaches to the P-brake cable and only "pivots" about a quarter turn and back.
The hole in the pin has a "wedge" shape that pushes the little pin toward the piston a couple of millimeters when you pull the P-brake handle.



The brake fluid enters at the bottom of the bore at the backside of the piston,... All that fluid pressure needs to be contained by the little rubber o-ring on the threaded screw or it works it's way toward the o-ring/seal on the pin for the P-brake and can easily leak there because the pin is all sloppy so the seal is all bashed to hell.
And even that screw was pretty sloppy.

The brake fluid can also work it's way into the bore for the adjuster but that bore is sealed with the little bolt and a copper washer.

Everything behind the o-ring on the screw is caked in grease. ???
I think the engineers were expecting too much from that o-ring...

A lot of guys said that their adjusters were "stripped".
My guess is that some original owner or mechanic tried to retract a rusty piston into the bore and it got stuck so the just reefed on the Allen key and stripped the adjuster or threaded screw... Then it gets sent back for a rebuild where those parts aren't inspected or tested and just gets sent out with a new piston and a broken adjuster.

The parts may be very hard to find even for the rebuilders because as far as I know, this is the only car that uses our rear calipers.
 

pcb

The Diagram Dude
:
2002 MP5
Nice! I've never taken a rear apart before. I hate our rear brakes.

Yea they kinda suck. A lot of people have had a lot of problems with them.

The worst part is buying a newly rebuilt caliper and it's either broken in the box or starts leaking in a few weeks.
I'm sure a brand new OEM caliper would last but they're about $400 each.
 
:
02 protege5 ES 5dr
Awesome, thanks for the information PCB! If you have PayPal should fire me a pm with it, I would like to buy you a [emoji481] beer.
 

pcb

The Diagram Dude
:
2002 MP5
I have PayPal but I have no idea how to send it to you ??
I hate computers and this stupid phone I'm using.
 
:
02 protege5 ES 5dr
I have PayPal but I have no idea how to send it to you ??
I hate computers and this stupid phone I'm using.
Yeah I hear you. As a former network engineer let me tell you that computers ARE crap. I have tried to like them but just can't. I loathe Facebook... etc

And the phone I use mocks me every time it starts up, with lies and propaganda telling me life's good. If it was so good wouldn't I have a better phone ?

Oh and just pm me with your email attached to PayPal, I send that address beer money. Or that's how it's ment to work I believe.
 

pcb

The Diagram Dude
:
2002 MP5
After getting my caliper apart I didn't know what to do with it. It is in reasonably good shape and I'm pretty sure the self adjuster works.

Then I remembered that I would have to loosen the bleeder screw to reuse it and they love to break off rendering the caliper useless so I threw some flame at it in an attempt to break it free.





It Worked !! Loosened it without breaking it.

A rebuild kit for the rear caliper is available but it only includes the brake piston seal and boot... I'd like to get a new o-ring for the screw and maybe one that's slightly bigger (or fatter) to help take up some of the slack and help stop any leaks.
It has to be a quality o-ring,.. It's quite important but I don't know how or where to find one.


I'd like to cleanup the bore where the o-ring rubs up against it but it's kinda hard to get at.
Maybe I'll wrap some fine sandpaper around a pencil and put it in a drill to make a honing tool ??
 
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