8 replies to this topic

[bluesprite]

Hi All,

I got some minisport caliper seals for 8.4" disks last year and they have recently failed and leaked fluid.  When I took the pistons out (they were tight) I could see that a ring of rubber from the seal had torn off either during use or when I fitted them.

 

I've come to fit a new set (also from minisport) and the pistons are really tight when I'm putting them back in.  Even with red rubber grease I have ripped a ring of rubber from the the seals just fitting them.

 

How tight should the pistons be when fitting them with new seals? should you be able to press them in by hand? I've been having to use a vise they are so tight!

 

It seems as though the seal is slightly the wrong size - has anyone else had similar problems? or am I doing something wrong?

 

Thanks!

[wile e coyote]

I've always reassembled them lubed with plenty of fresh brake fluid and never had a problem...have you got any corrosion - in the piston bore or worse on the piston itself???

 

They should be a tight fit but I think the key to pushing the pistons in is consistent even pressure with an eye to perfect alignment- to that end have always used a G clamp and the odd bit of scrap timber..

[bluesprite]

I don't think there is corrosion in the bores, and the pistons were new stainless steel pistons that I put in last year when I changed the seals then.  I think even with a g clamp it would rip the rubber off because it's such a tight fit.

where do you get yours from?  I might try another source and if it turns out that another set go in easier then I'll have a better reason to be able to return the set that got torn up.

[dklawson]

Don't worry so much about the caliper bores, look at and worry about the grooves in the bores where the rubber seals sit.

 

The seals don't work on the bores.  But to work properly they need to sit in good, clean grooves without extensive pitting or corrosion.   If there is corrosion in the grooves, not only will the seals not seal well, they will also be held up and out, as if they were too big or the groove they are in is too small in diameter.  Take a close look at the caliper bore grooves and let us know what you find.

[wile e coyote]

Yep - DK is right there....

 

Got my last set of pistons from Min-Its - stainless ones and very good they are too, the seal kits came from local partco / Unipart...my calipers are "S" ones but for all intends and purposes all the same...

[AlexMozza]

I had this same problem. In the end I just ordered up some seals for a Cooper Monaco Race car. Fitted fine! And no leaks!

They are standard square section seals. This was with brand new pistons and fully cleaned calipers.

 

Edit - I got them from BG Developments 

Edited by AlexMozza, 22 December 2013 - 01:13 AM.

[MrBounce]

I've just done my calipers - as stated above the most important thing is to make sure EVERYTHING is clean. Take the old pistons & seals out and throw them away. Spend a LONG time cleaning - if there's any dodgy looking parts or dirty bits the best thing I have found is to give them a going over with some light wet & dry (I used about 400grit) then make sure you give everything a really good flush out with brake cleaner. Then leave it to dry and do it at least twice more. If you can't get some rust and/or marks out of the bores after that much cleaning it may be worth chopping them in for a recon pair.

 

Patience is the way forward for this.

[tiger99]

I scrub them with a nail brush, toothbrush and Fairy liquid and hot water first, till scrupulously clean, and then dry off by washing at least twice with methylated spirit, including through the hose and nipple ports. Done that since long before brake cleaner became generally available, and typically after an overhaul and filling with silicone fluid (high temperature silicone grease where needed, not that red muck), my cars did well upwards of 100k miles without further attention to the hydraulics.

[bluesprite]

Hi All,

Thanks for the advice - I'll check the grooves where the seals sit. 

Can I just check that I'm not being an idiot:

There are two seals for each half of the caliper, one has a square cross section and one has a 'C' cross section (it has a groove along the inner edge).

One of these seals is the main brake fluid seal, and the other is just the dust seal that sits under the metal retaining ring.

Which is which?

 

thanks again!