Iam having a nightmare trying to bleed my brakes! Ever since I replaced my rear calipers I have never been able to get a firm pedal like I had before. Does any body have any ideas I could try?

are you using sierra rear disscs and callipers ?? if so I think you have to tilt the calliper backwards when bleeding, something to do with the bleed nipple being too low, MK indy's have this problem when disc's ar fitted

Yeh it sierra rear discs and calipers. I have tryed this but still no joy. I dont know whats going on!

hmm, which way up should they be? got a feeling mine might be on the wrong way

What do you mean when you say the wrong way?

you might have the same problem as i did on my indy
what you have to do it unbolt the caliper and take the disc of and turn the caliper upside down so the bleed nipple is totally vertical pointing upwards
remember to put the disc between the pads when the caliper is in this position and you are bleeding as if you dont u will have to rewind the caliper
next time i am home i am going to make a picture tutorial to deal with this occurrent problem

well, i've got mine on a atlas axle. i think mine are on the wrong sides, and by the looks of things, on a sierra they were mounted at the top of the 'axle' mine are mounted to the rear, with the handbrake cable entering from underneath

think you might need to hold them this way to get them to bleed properly


heres how mine are

Description

[Edited on 31/1/10 by blakep82]

Are you using an EZ Bleed? I only ask as I had real trouble doing it this way and ended up getting my missus working the pedal whilst I bled it the old fashioned way. It worked a treat like this and pedal is solid.

hi blake, no i think you've got it right.

you want the bleed nipples at the top, otherwise you'll end up with a pocket of air in the top of the caliper.

quote:

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Originally posted by cd.thomson
hi blake, no i think you've got it right.

you want the bleed nipples at the top, otherwise you'll end up with a pocket of air in the top of the caliper.

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pretty sure you have the same i had prior i dicovered my front callipers were not square to the disk (thank you british trident)
callipers were too flixible, and drain back cause a spongy pedal.
i had to shimed/"grind", my calliper mounts to get them right.
ally bulkhead on MNR are very bad IMHO as the are way too flexible.i also welded a steel plate where master cylinders are fixed.my english sucks, so here is what british trident advise me to do, i should be easy to understand in his words:
You really have to make 100% sure the caliper is presenting the pad parallel to the disk in in all axes if not you will get lost motion at the pedal. It takes only a tiny amount of movement at the caliper to result in excessive pedal movement.

After market calipers are very bad for this because they do not mount straight on to the standard brackets, longer multi piston calipers make the effect much worse.
If the caliper is to true to the disk every time the pedal is pressed the caliper bracket has to bend elastically (ie it acts as a spring) when the pedal is released the fluid is slowly forced back to the master cylinder.

Because of very clever design of the main rubber hydraulic seals in caliper the It takes a lot of pressure difference to push back the pistons in a caliper, the difference in pressure of having the calipers 100mm or so higher than the fluid level in the resevoir isn't anywhere near enough to over come the static friction.
the seals is the caliper are designed to have a friction characteristic.

If you get lost motion on the first pump of a disk brake system if the mater cylinder is OK it it is a sure sign some mechanical component is flexing.

(1) Check all the pistons in the caliper are moving freely.
(2) Check the caliper body is set a square as humanly possible to the brake disk.
(3) Check for flexing of the caliper body under pressure using a dial gauge --- some alloy multi pot "racing" calipers are no where near rigid enough.
(4) Check the pedal box and its mountings for flexing using a dial gauge.

[Edited on 1/2/10 by antonio]