13 replies to this topic

[Scruffs]

Hi Guys

Car: 1986 mini (no servo) with Mk2 Fiesta calipers & braided lines...

On Monday I had the FL brake bind on on the way to work. Rather hot it got indeed . So called the breakdown out to tow me home. I figured it was just an accumulation of crap from all the ready salted roads so I'd strip it, clean it, regrease the sliders and clean the carriers out. An hour's worth of work no problem. I ing wish!

Job so far has entailed: (to both sides, not just the FL)

*Stripping, cleaning and greasing sliders - No change, still binding.
*Cleaning and copperslipping carrier channels - no change
*Removing shims from the back of the pads (just in case) - no change
*Pulling out caliper dust seal, some light surface rust in there (originally assembled with brake fluid only), so clean out, grease and reassemble - no change
*(getting frustrated now) Wind piston in and push back out. fifteen times. in case it was a piston/seal/friction issue - still no change.
*(language now getting foul) Make it bind, then crack bleed nipple and retighten (in case of any crap in pipes acting as one-way valve) - no change.

Note the grease for the sliders and piston is the proper stuff - red rubber grease, NOT LM, Cu slip or anything else...

The brake is not locked - it needs about 2-3 x as much torque to get it turning as the FR wheel. I'm sure it's a piston/pressure seal issue as the inboard pad DOES NOT back off the disc when released (I can slide a 0.05mm gauge into this gap on the right side). The car has covered probably 6/7k miles (over the course of 6 months) with this conversion on with no problems other than this so far.

Oh and it was DEFINITELY binding, by the time I got out, walked round and took a peek it was still glowing dull red. luckily I got it slowly moving again and the disc hasn't warped.

The only thing I can think of - when I rebuilt these calipers, the pressure seal had a four-stripe colour code around the outside. I assumed this indicated direction of fitment, so I called the supplier but they said it didn't matter...so in they went, no particular direction...I'm just worried I was given duff advice and it's not manifested itself until now...

What do you think? Could the pressure seal have hardened with the lack of lubricant on the air side of it? If I get no further on this I'll have to rebuild the hydraulics (again) as I'm at a dead end...no idea how this could have gone tits up after 7k though...

Thanks for reading this far, if nothing else!

Al

[bmcecosse]

Hmmmm - I ran MKI Festers a while back - and they were perfect - absolutely excellent brakes - and the BIG advantage to me was the absolutely 'no sticking' compared to the standard calipers which were giving me problems much as you describe. Have you established if there any hydraulic pressure holding the pads on ? Try releasing the bleed screw - do you get a spurt of fluid - and the pad releasing ? If there is - can only think the feed pipe may be twisted/kinked/collapsed inside - this has never happened to me - but others have reported it. If it's not that - you seem to have covered all the possibilities! I really don't know what else to suggest - I think it MUST be hydraulic related.

[jameswhiles]

Do they have automatic adjusters in the calipers? it could be one of those playing up?

[Scruffs]

Thanks for the replies guys

bmce - Yeah I cracked the bleed nipple, was the last thing I did, made no difference! to be honest it had all new kunifer lines and goodridge 600 hose with the fiesta conversion so I'd be very surprised if it was them playing up!

James - fair shout, but they don't have any handbrake mechanism so no need for any adjusters, the pad back off *should* be taken care of by the square section seal pulling back when the pressure's removed. I'm starting to think more and more it's this seal that has hardened where I didn't have the red grease to hand when I assembled.

I'm clutching at straws really but I'll swap pads over tomorrow see if it makes a difference...

ta!

Al

[jameswhiles]

If swapping the pads makes no difference I would be looking at those seals next then!

[Major Burkenshaw]

Are the slide bolts dead straight and sitting at a right angle to the mounting? I had this problem with one of my slide bolts being slightly bent and cause the caliper to bind as it travelled along them.

[Scruffs]

Hi Major,

Yeah I'm pretty sure they're straight. As part of the head scratching I undid them so they had the play in the thread to realign themselves and that didn't help. I will go have a double check though as it's a good possibility.

I'll also try and block up the calipers with any chunks of metal I have lying around, if the piston still doesn't retract then it's seal ordering time.

Cheers

al

[MRA]

probably rusty pistons..... causing the piston to stick in the bore..... and as it normally occurs just outside of the fluid seal but below the dust seal it doesn't cause a leak just binds up tight restricting the action of the seals to "pull" the piston back in to the caliper thus releasing the gripping forces etc.........

[Scruffs]

Thanks MRA

I took the calipers off, shoved a thick bit of steel between the pads and hit the brakes. The FR released fine, the FL wouldn't give me the steel back for love nor money. So off they came and although the piston was fine (was new when I rebuilt them) the bore outside of the pressure seal was corroded, which I assume, as you say, was restricting the piston movement.

It's all cleaned up now, I've got red grease coming out of my ears and just awaiting the rebuild kits.

I'll update when it's all back together.

Cheers

al

[MRA]

Red grease is a little concerning ??? when rebuilding any of the hydraulic piston assemblies used on the Mini you should use brake fluid only, using grease can cause the seals to fail as most greases "eat" the material that brake and clutch seals are made from ....... try one dipped in a tub of grease and see what happens

[bmcecosse]

Red grease is seal-friendly - designed for use with brake pistons and seals.

[MRA]

Not all red greases are seal friendly.......

[Scruffs]

Thanks for the concern, I know there's issues with some greases and hydraulic seals, so I did look into it...

For everyone else's info...from the Castrol 5900 data sheet:

Rubber Compatible Grease
DESCRIPTION
Castrol Red Rubber Grease is a medium consistency grease based on a vegetable oil and a synthetic gelling agent. It is fortified with additives to improve its resistance to oxidation and corrosion.

APPLICATION
Castrol Red Rubber Grease is formulated for rubber to rubber lubrication where any effects such as hardening or swelling of the rubber must be avoided. It can therefore be used on automotive hydraulic brake and clutch components where compatibility with natural rubber and SBR seals is involved. It may also be used to assist assembly of natural and synthetic rubber components for automotive brake and clutch systems and suspension units.

BENEFITS
S Compatible with natural and synthetic rubber
S Good anti-corrosion properties


When I assembled these in the summer I used plenty of brake fluid, making sure I got some in between the dust and pressure seals, and this still resulted in this area corroding...so the rubber grease is going in and at this point, based on what's happened here when I didn't use it, I would reccomend others use it too..

al

[Scruffs]

All back together and running SO MUCH better. Both sides had a lot more friction than they should have had...Roll on the MPG increases

The whole reason for the problem was - as MRA said - corrosion between the pressure and dust seals. I've cleaned it all out, replaced seals and packed behind the dust seal with Castrol 5900 so, for the moment, it's all good...

Cheers for all the help

al