Brake calipers rebuild

[rafikdous]

anyone here rebuilt their calipers? I have few questions I need help with

my calipers are the pin type (M?). I bought a rebuild kit from Bigg Red in the UK. The new pistons are not the pin type. Should I snap the pins and use the new pistons or better to use the old piston which look in good nick and just use new seals?

[LeeM]

Use the old ones Raf. New seals etc. They can be a pig to pull apart if they're seized up, yet once you've done that, make sure they have no scratches or dents (dints to you Victorians) then surgically clean everything! I sent mine to a brake shop to be safe

[LeeM]

 Knew Victorians were weird 

[rafikdous]

Thanks Lee, yes absolute bugger to pop them out. Tried soaking them overnight. Then tried compressed air but nothing working

Everything is off the car including hard and flexible line so couldn't use  them

Ended up having to make a jib using the old master cylinder. Will post a pic later

[LeeM]

 Are you installing a new master cylinder? Upgrade to a dual outlet if you haven't as yet. I didn't with the 912 and regretted it

[rafikdous]

Yep, ditching the crap original MC

[ELSPORTO]

Definitely worth replacing the pistons and cleaning all the gunk in the caliper cylinder too.

I used a grease gun to get my pistons out - if that's what you mean? Standard attachment fit right onto the nipple.

The piston will be the 'pin type' ... they just wont have the female part that accepts the pin (the anti knock back mechanism)

The anti knock back mechanism that sits in the piston and goes over the pin in the caliper, is held into the piston with a circlip - you need to take it out of the old piston and set it into the new piston.

I'm told you can run the pistons without the anti knock back mechanism, but it's not how they were designed and it can create a long pedal...

I can't upload pics .... are we talking about the same thing or have I gone off on a tangent??

[rafikdous]

Yes talking about the same thing

Don't think the new pistons would fit without snapping the pin

[Shady Speedway]

I've rebuilt countless calipers. Did my 930s last year.

You won't need new pistons if they worked when you pulled them out. I'd only replace them if they were severly rust pitted or scored.

I wrap calipers up in a heshion bag and pop the pistons with compressed air.

Hone the piston by hand with 1200 wet and dry. FInish with metho and scotch bright. Metho is the best cleaner as it won't leave any residue.

Reassemble with rubber grease.

When putting them back on the car. set the pistons and pads at just the right point so they hug the disc.

If you set the pistons all the way back at install. You will be chasing a spongy pedal as the new seals will pull them too far  back.

It's all straigh forward. Good luck.

[SteamWolf]

Don't use anything metal to clean out the seal groove. Scratches can compromise the seal area. Scrape it out with some hard plastic such as a cut cable tie or ice-cream lid.  Give everything else a good linish with a green kitchen scourer pad.  Don't use sandpaper.

[tazzieman]

All very good advices!

I use a thin wooden skewer to clean the seal grooves.

Grease gun is messy , but a nice smooth way of pushing out pistons (esp badly stuck ones)

And the pistons need to be set at the right rotational  angle with respect to the disc.

Just in case others are looking to tackle this straightforward , satisfying job! (unless you snap the bleeder screw )