PMB 914-6/GT - Rear Calipers

[glovebox]

Bought a pair of these awhile back and had problems with them leaking !! Spoke to Eric at PMB Performance who said send them back and fitted new seals again and pressure tested them.
So finally I got the chance to fit them last weekend
Had to fit them offset so the inner Pistons worked with the handbrake?? As the Pistons would not stretch far enough to push the pad to the rotor even with the pads adjusted ??

And now I cannot get the bleed nipples to stop weeping !! I dont think I can tighten then any further with fear of braking something. They are not leaking as in dripping but just wet around the bottom of the threads !??
Any ideas guys or tricks ??
Can or should I use a thread sealer ?? Or can you get a bleed nipple with a O-ring??



Best regards

Mark.

[Darren C]

Bleed nipples have a taper seat on the bottom that should seal off the fluid when tightened firm but not too tight.
I've had refurbished calipers before where the new zinc plating has built up heavily on the taper down the hole and stopped it sealing off when the nipple is wound in.
They can also leak if there is any contamination/dirt under the seat.
Very, very worst case is a damaged thread in the caliper so the nipple cant get a purchase.

I'd put a clamp on your rubber hose (to stop you having to drain the fluids) and then carefully unwind the nipple and take it out.
Have a good inspection of the threads both in the caliper and on the nipple and look at the seat. Until then we're only guessing what might be wrong.
Thread seal is only as good up until you need to bleed again or as an emergency, you need to see what the problem is first. I wouldn't recommend any sealant as the answer.

Good luck, I hope its just a bit of dirt from sand blasting or similar.

[glovebox]

Thanks Darren, problem is they are brand new Calipers and brand new bleed nipples

Best regards
Mark.

[jwhillracer]

Bought a pair of these awhile back and had problems with them leaking !! Spoke to Eric at PMB Performance who said send them back and fitted new seals again and pressure tested them.
I've been waiting over 2 years for Eric to send me a replacement pair of calipers because of leaking around the venting adjustment bolts unless the lock-nuts were done up 'king tight..........
So finally I got the chance to fit them last weekend
Had to fit them offset so the inner Pistons worked with the handbrake??
They have to be fitted with shims (large washers) behind the mounting bolts to centralise them on vented rear discs. I fitted longer bolts to compensate. As the Pistons would not stretch far enough to push the pad to the rotor even with the pads adjusted ??

And now I cannot get the bleed nipples to stop weeping !! I dont think I can tighten then any further with fear of braking something. They are not leaking as in dripping but just wet around the bottom of the threads !??
Any ideas guys or tricks ??
Can or should I use a thread sealer ?? No!
Or can you get a bleed nipple with a O-ring?? No! Try to get replacement calipers.



Best regards

Mark.

The annoying thing is that they are basically superb calipers. Our car already had S calipers on the front, and these balanced and improved the braking immensely. I just keep getting excuses from Eric.

[glovebox]

Had to fit them offset so the inner Pistons worked with the handbrake??
They have to be fitted with shims (large washers) behind the mounting bolts to centralise them on vented rear discs. I fitted longer bolts to compensate. As the Pistons would not stretch far enough to push the pad to the rotor even with the pads adjusted ??

I did the same. Fitted longer bolts and shimmed them so they were equal to the disc. But then I had no handbrake ?? Even with adjusting the inner piston and tightening the handbrake cable. How far should the piston press out ?? I took the pads out and with the cable pulled they hardly move at all even with the handbrake lever on the caliper pushed fully back??

And now I cannot get the bleed nipples to stop weeping !! I dont think I can tighten then any further with fear of braking something. They are not leaking as in dripping but just wet around the bottom of the threads !??
Any ideas guys or tricks ??
Can or should I use a thread sealer ?? No!
Or can you get a bleed nipple with a O-ring?? No! Try to get replacement calipers.



Best regards

Mark.[/quote]

The annoying thing is that they are basically superb calipers. Our car already had S calipers on the front, and these balanced and improved the braking immensely. I just keep getting excuses from Eric. [/quote]

[/I have e mailed him this morning. I wont hold my breath !color]

[jwhillracer]

Have you the correct caliper/disc combination? Just wondering if you have calipers for vented discs, with the central spacer, and solid discs, so the pistons will be over-extended.
Are the pistons engaged on the venting adjuster threads?

Our handbrake is quite good..................................for a 914

JW

[tp_reading]

Have you the correct caliper/disc combination? Just wondering if you have calipers for vented discs, with the central spacer, and solid discs, so the pistons will be over-extended.
Are the pistons engaged on the venting adjuster threads?

Our handbrake is quite good..................................for a 914

JW

That's what I was thinking ! Mine work well although expensive. Eric was quick to respond to email enquiries, never needed to phone him.

[gridgway]

Are they definitely leaking? I thought the bleed nipples on my single seater were seeping so was doing them up tight. Then I found it was actually just residual fluid from the bleeding. So now after bleeding I roll up some tissue and put it into the hole in the nipple and it soaks up the spare fluid. There's a surprising amount!

Graham

[glovebox]

Have you the correct caliper/disc combination? Just wondering if you have calipers for vented discs, with the central spacer, and solid discs, so the pistons will be over-extended.
Are the pistons engaged on the venting adjuster threads?

Our handbrake is quite good..................................for a 914

JW

I have vented calipers and the ones on PMB website.



When I first fitted them I spaced them out so they were central to the disc. At least 4mm packing with washer to get them even. Then adjusted the pads inside and out 0.2 mm and then adjusted the cables . But even with the handbrake calipers levers fully extended, so no further cable travel is possible.. The handbrake was very poor.
So I changed the packing so the calipers are more offset so the inner pad side of the caliper is much nearer to the disk than the other side, with a much much improved handbrake:)

So they were bled one and a half weeks ago. And every night I check the bleed nipples and clean and degrease and compress air dry the calipers. Oh and tighten them up again just so I know it's clean for the next nights inspection [FLUSHED FACE]

B R

Mark

[glovebox]

Just had a reply from Eric!! That was fast.
First step he has offered to send over a bottoming tap for the bleed valves

[Darren C]

Make sure you clean any swarf out that the tap may leave down the hole, otherwise some may be pushed in the hydraulic system when you screw back the nipple or drag and damage the threads.
Dont use any compressed air or pressurised spray like WD40 and the thin red tube, that can push the swarf into the caliper.

A magnet is best. If it wont fit down the hole, just stick it to a screwdriver and poke that down the hole to collect any swarf, then without the nipple fitted, slowly let some fluid through to finally wash it out from the inside.
Good luck.

[jwhillracer]

A magnet is best. If it wont fit down the hole, just stick it to a screwdriver and poke that down the hole to collect any swarf, then without the nipple fitted, slowly let some fluid through to finally wash it out from the inside.
Good luck.

That won't work with an alloy caliper!

JW

[davep]

I do not see the bracket for the rotor shield in place. The bracket or an equivalent spacer MUST be used to correctly place the caliper of the rotor.
Venting clearance (pad to rotor) is 0.004" or 0.10mm; please write this into any book that says otherwise.
The factory manual was WRONG, and the factory instructors that trained dealership technicians stated that 0.004" was correct.
It is best to adjust the outer clearance first, then the inner clearance.

[glovebox]

I do not see the bracket for the rotor shield in place. The bracket or an equivalent spacer MUST be used to correctly place the caliper of the rotor.
Venting clearance (pad to rotor) is 0.004" or 0.10mm; please write this into any book that says otherwise.
The factory manual was WRONG, and the factory instructors that trained dealership technicians stated that 0.004" was correct.
It is best to adjust the outer clearance first, then the inner clearance.

Thanks Dave, I think that's tp's photo . But yes I have the rotor shield fitted. And thanks for the info I'm gonna give it a go later. Much prefer to have a better equal spacing like I first had.

[Darren C]

A magnet is best. If it wont fit down the hole, just stick it to a screwdriver and poke that down the hole to collect any swarf, then without the nipple fitted, slowly let some fluid through to finally wash it out from the inside.
Good luck.

That won't work with an alloy caliper!

JW

Ah, I wasn’t aware it was an alloy caliper body, and different to the stock cast iron one.
In that case, from the description/symptoms I’d be fearful that the thread is stripped and a tap will not cure it. Then you’re in a whole load of hurt as the supplier may say you over-tightened the bleed, as it was ok when it left them after the pressure test.