Leaking caliper bleed valves?

[Jpich85]

I've been trying to sort my slabside brakes out, I got them so powder coated with new pistons and seals, I bled them up and thought that was job done but the bleed valves keep leaking and also one of the o rings that join the calipers together keeps leaking too,

I've tried a few different sizes o rings but I can't get it to seal properly, has anyone had this and managed to solve it? The surface on the inside of the calipers isn't great as they are so old but I was hoping it would seal.

Does anyone know how to fix my leaking bleed valves too? I've tried OEM bleeders but they seemed worse?

I'd like to keep them if I can repair them if possible as I've spent a bit of money on them already.

Thanks

[Swiss Toni]

Try PTFE tape as a last resort?

[coombehouse]

PTFE tape on the threads of the bleeders has worked for me in the past although they really should seal on the taper on the bottom body.

For the caliper halves, the o rings are normally a square section seal. Are you using these or a generic normal o ring.

[Jpich85]

16 hours ago, coombehouse said:

PTFE tape on the threads of the bleeders has worked for me in the past although they really should seal on the taper on the bottom body.

For the caliper halves, the o rings are normally a square section seal. Are you using these or a generic normal o ring.

Thanks mate, i read somewhere that you can use a valve and some grinding paste and sort it mature a new seat, also if you hit a ball bearing in the seat it can create a better seal, do you think there's any true in those?

If tried various o rings and the oem ones but they still leak, I think the surfaces are slightly pitted so it's not dressing sealing fully, I thought about trying to smooth it down slightly to create a flatter surface but not sure if that'll work.

[Swiss Toni]

You can only tap a ball bearing on a seat if that seat’s meant to seal with that particular ball bearing. I think if you tried it with a bleed nipple seating, you’d round the seat out, make it worse! As for trying to grind the seat with valve paste … yes, it would work, if the hole wasn’t threaded! As it is, the nipple would bottom out, and you’d have to over tighten to get a face to face grind. Stick with the tape!

As for the half to half seal, try a sheet of 400 wet & dry on a mirror. Don’t go mad. Give it a rub and see where the high spots are. 
And, tighten the bolts evenly to spec. on re-assembly!

Inside to out!

Edited October 24, 2022 by Swiss Toni

[bluedog59]

Are the bleed nipples leaking up the thread or out the hole at the top ?

I would have thought tape would only stop a leak via the thread ( which then raises the question of how if it's not coming out the bleed hole as well ? ).

Tape may seal it but do you want to trust it when you're hard on the brakes ? It's your life at risk at the very least.

[Dezza]

I would be trying to answer the question: why are the bleed nipples and caliper seal leaking? Faffing about with PTFE tape, if successful, masks the underlying problem. When you had the caliper halves powder coated, did someone go beserk with abrasive blasting media and fuck up the surfaces where the seals go and the threads for the bleed nipples?

[Jpich85]

2 hours ago, Dezza said:

I would be trying to answer the question: why are the bleed nipples and caliper seal leaking? Faffing about with PTFE tape, if successful, masks the underlying problem. When you had the caliper halves powder coated, did someone go beserk with abrasive blasting media and fuck up the surfaces where the seals go and the threads for the bleed nipples?

Yes I was thinking that too dezza, something must be up for them so to be like it, I had a different bloke do them this time so maybe he did go a bit crazy with the blasting. 

[Jpich85]

2 hours ago, bluedog59 said:

Are the bleed nipples leaking up the thread or out the hole at the top ?

I would have thought tape would only stop a leak via the thread ( which then raises the question of how if it's not coming out the bleed hole as well ? ).

Tape may seal it but do you want to trust it when you're hard on the brakes ? It's your life at risk at the very least.

They are leaking out the hole in the top on two of them bluedog, I'm not sure how to fix it, I've seen some nipple repair things you can get for them or even fill them in and maybe bleed from a banjo bolt bleed bolt, I was thinking that grinding paste method but if turn the threads off so it would screw it the hole and fix the bleed valve to a piece of stainless bar and put it in the drill and spin it up a few times to try and create the seal back. It's not ideal but maybe worth a try, those slabside calipers aren't the best.

[Jpich85]

3 hours ago, Swiss Toni said:

You can only tap a ball bearing on a seat if that seat’s meant to seal with that particular ball bearing. I think if you tried it with a bleed nipple seating, you’d round the seat out, make it worse! As for trying to grind the seat with valve paste … yes, it would work, if the hole wasn’t threaded! As it is, the nipple would bottom out, and you’d have to over tighten to get a face to face grind. Stick with the tape!

As for the half to half seal, try a sheet of 400 wet & dry on a mirror. Don’t go mad. Give it a rub and see where the high spots are. 
And, tighten the bolts evenly to spec. on re-assembly!

Inside to out!

Thanks Tony, I was thinking about turning the valve down so it turns in the threaded hole and hopefully use the grinding paste.

[Swiss Toni]

27 minutes ago, Jpich85 said:

Thanks Tony, I was thinking about turning the valve down so it turns in the threaded hole and hopefully use the grinding paste.

By the sounds of it, the seat’s the problem then. Your idea might work. Give it a go. 

[bluedog59]

45 minutes ago, Swiss Toni said:

By the sounds of it, the seat’s the problem then. Your idea might work. Give it a go. 

But I'd lap them in by hand rather than using a drill.

[TLRS]

The hole in the bleeder might scoop up your paste in double quick time. Something to keep an eye on maybe.

An alternative might be banjo bolts with a bleeder on top. Depending on the sort of brakelines you run.

[bluedog59]

Unfortunately the banjo bolt bleed nipples will only work if he can get the originals to seal fluid tight.  You don't actually need the bleed nipples to bleed the brakes. I very rarely use them, preferring to bleed the air back up the system and out via the master cylinder.

[Jpich85]

Thanks for the imput everyone, I have a few things to try, not ideal but I think it's worth a try before I look at other calipers, I thought maybe I could use a m7x1 bolt and a crush washer to just blank off the nipple and bleed via a banjo bleed valve but I'm not sure if that would work as I won't be able to reverse bleed it completely.

[bluedog59]

If you can get it to seal with a bolt and copper washer you can still bleed it, you'll just have to do it via the m/cylinder. It may help if you do it on the bench or at least, with the calipers unbolted.

[Jpich85]

2 hours ago, bluedog59 said:

If you can get it to seal with a bolt and copper washer you can still bleed it, you'll just have to do it via the m/cylinder. It may help if you do it on the bench or at least, with the calipers unbolted.

Thanks mate, I have a few things a can give a try now then, I thought rebuilding the brakes and bleeding them would be a fairly simple job but it's turning out to be one of those jobs that's a right pain lol