Brake Caliper Rebuild

[EvilDonut]

I've just got myself some mondeo calipers in preparation for the 300mm front brake conversion, and I'm gonna replace the seals. I'm just wondering - will standard DOT4 brake fluid be ok to lubricate up the piston and other moving parts? I don't have any grease.

And what should I use to clean the inside of the pistons? I have the usual kitchen stuff - paper towels, cloths, scotchbrite pads, etc. Don't want to damage the pistons/bore or contaminate them in any way!

 

[ElDude at Allison Automotive]

get yourself some silicone grease from ebay..it's not expensive, ..you'll probably never use all of what you get... as you only need a smear..

some wet and dry (around 800grit) is good for cleaning scabby pistons....won't really matter how hard you scrub at the inside.... keep the polished side as smooth as possible tho..

:grin:

 

[EvilDonut]

Oh dear, looks like the old rubber dust shield is fused to the pistol housing - its proving an absolute nightmare to extract

Anyone seen that before and know how to solve it?

The dust shield is the rubber bit that looks like this:

(note this isn't a pic of mine, its someone else's but looks the same)

The bit where the guy's screwdriver is wedged is the bit that is almost completely fused to the housing.

 

[YOG]

Pumped my pistons out with a footpump, then removed the dust seals. You should be using new dust seals when rebuilding, so don't worry about damaging them when removing.

 

[EvilDonut]

Yep the pistons are out and I have a rebuild kit with new seals - the problem is that the old one won't come out.

I even resorted to using a penknife and screwdriver at the risk of scratching the polished caliper bore, but the rubber is such a bitch to scrape off the caliper. It won't just pull out as the rubber seems to have bonded with the metal housing. I'm scraping it off in tiny pieces with great difficulty, and I've only done about 10% of one caliper

 

[madhillbilly17]

you need to blow them out with a airline, if you dont have a airline take them to the friendliest garage you know :grin: and just ask if they would blow them out

 

[yippeekiay]

He has the pistons out...lol.

It's just the seals have beel lfet behind because they've stuck to the calipers.

 

[madhillbilly17]

oh :grin: didnt look at the pic properly

 

[EvilDonut]

The advice I've gotten so far is just scrape it off with a knife, which is what I have been doing....was hoping there would be an easier way but I guess not lol.

I hope it all comes off or the calipers are a writeoff

 

[ScubaSteve]

melt it?

 

[EvilDonut]

Yep the thought had crossed my mind, but I don't have a blowtorch. Also I thought that might just make it worse so didnt want to risk it

hmmm...I could try my soldering iron maybe, but that might not be hot enough...its very heat-resistant rubber

 

[EvilDonut]

OK, I got the left over rubber out with my trusty dremel, now the metal is nice and polished too

But now the new seal won't fit in the piston bore! Has anyone ever rebuilt any calipers and, if so, how hard was the dust seal to push back in? I've tried everything I know...heating the main caliper in the oven to slightly expand it, lubing it up with brake fluid, etc...the seal is just slightly too big.

Is there a trick to pushing the dust shields in? Its frustrating

 

[EvilDonut]

Problem solved - as suspected, it my was my own stupid fault

When 'removing' the old dust shield I left the old shield's metal ring in there. As it was metal, I thought it was part of the caliper housing and not the rubber seal.

I kicked myself when I realised that I was trying to push a dust shield inside another dust shield...lol

 

[yippeekiay]

lol...glad your sorted now k: