Disc brakes not bleeding

[wheelynutz]

So i have just got some lovely refurbed calipers from bigg red as my old ones where seized and past there best but now i have got them all fitted they don't want to work.
I can't get all the air out of them, i have bled front and back (and the fluid in the back was very rusty and horrible) but there are lots of little air bubbles still coming through the calipers.
When i stamp on the brakes the rear wheels lock up and the fronts don't do anything.
So was just thinking is there a certain way i should be bleeding the front calipers (marina set up with no servo) to get all of the air out or could it be something else?

James

[bmcecosse]

Extremely dangerous to have rear brakes locking before fronts. 'Hello ditch' is the likely scenario........ Are the calipers exactly the SAME piston size as the old ones - and are they on right way up - with the bleed nipples at the top???

[wheelynutz]

Don't worry it's not on the road yet just drove it round our little estate, yep the calipers are identical and they are the right way with the bleed nipples at the top.

[lambrettalad]

try jacking the front of the car up as high as SAFELY possible ,leave over night or longer if you can ,and the air may have risen to the top ,every little helps

[M25VAN]

Are you bleeding them yourself or have you got someone to hold the brake pedal down so you can tighten the bleed nipple without letting any air back in?

[wheelynutz]

Nope not just me got a helper to do the pedal

[chrisryder]

Have you tried keeping the nipple closed, and getting the helper to push the pedal down (maybe even pump the pedal a few times) and hold the pressure on. The open the nipple to let the fluid surge out.

It can help to dislodge stubborn air bubbles.

[wheelynutz]

I've got them to pump it a few times then released the nipple but only the once so i'll try that some more but there is not much pressure on the pedal but i'll get there. Where there's a will theres a way, i know that the pedal should be quite tough (tried my mates mini after the disc conversion) but we are no where near that stage yet.

[charlie_morris_minor]

have you asked your friend to slide their foot off the pedal when it is fully pressed down as opposed to lifting their foot up with the pedal under it.. if that makes sense.. the idea is it gives the system a "bang" and helps dislodge any bubbles trapped in the system.

[wheelynutz]

Yeah i get what you mean mate, next time its dry i'll try that and chris' way.

[daveyl]

Has the disc brake set-up been known to be working, at some point, before you bought the new callipers?

Have you fitted new pads? They may need bedding in.

Has the master cylinder had the 'top hat' seal removed?

[wheelynutz]

Yep they where fitted in 1998 I think so have been working for a long time but when I got the mog it was say for four years so they had all seized up and stuck on, so I got a refurbed set.
Yep I've got new pads but it 100% isn't them bedding in as there are NO front brakes so I'll keep on bleeding them and we if I get some where.
Not to sure on the master cylinder but it has a remote resivour under the bonnet so I assume it's all been converted.

[Alec]

Hello Wheelynutz,

you say that the rears lock and that you have no front brake. If there is air in the system you won't have any rears either, or very little and with a very low pedal. I presume that you are getting fluid\air from the caliper nipples?

Alec

[bmcecosse]

Exactly - it does sound like a serious imbalance problem...... But bleeding problems can only be due to air ingress - somewhere along the system. If nowhere obviously else - then either the seals on the master cylinder are suspect - OR the seals in the calipers are not correctly installed........

[lambrettalad]

the pressure is getting to the rear ..... yes

if the pressure is getting to the front it is not working.......yes


no pressure to the front ?

therefore either the fluid isn't getting to the front or it is but it is having no effect on the front so it's either blocked or the callipers are not working

I suggest a strip down and clean of the callipers as both callipers are not working,if it was just one you would feel a massive pull to the other side when breaking hard.

good luck

[daveyl]

If you do strip the callipers then I would suggest you smear a thin layer of 'red rubber grease' on the inner rubber seal that the piston locates into.
This will allow the piston to move freely. If not applied, the piston can stick to the seal, causing the seal to bind and/or stretch and ultimately leak fluid onto your new pads.

[bmcecosse]

The calipers are supposedly 'reconditioned' - so don't strip them down! I would remove the calipers, one at a time, and block the pipe end (use a T piece with a bleed nipple in one leg) - does it bleed out there now ?