Evening gents

I’m having a nightmare time trying to bleed the VAG calipers I have on the rear of my Velocity, I’ve tried everything I can think of but still don’t seem able to get any pressure to push the pistons out!

I have a balance bar setup and had no problem bleeding the AP front calipers with an easy bleed kit.
I thought that I may have had a duff master cylinder so I have swapped them over (just to see) and have concluded that both are working correctly.
I have had the rear calipers off the car whilst bleeding because I thought there may be trapped air in them, there wasn’t!
I wasn’t 100% sure which port should have the bleed nipple in and which should have the brake hose so out of desperation I swapped them over tonight and re-bleed, it seems exactly the same as before!
There are definitely no leaks in the system.
The calipers work fine on the handbrake but for some reason no matter how many times I bleed the circuit I don’t seem to be able to get any piston travel at the rear.

Any suggestions would be greatly appreciated chaps

Thanks for reading this ridiculously long post

Cheers

Thom


[Edited on 25/6/07 by pathfinder]

This has been dug out of the depths of my aging mind but i recall some rear calipers need to wound out manualy to a set distance after they have been retracted for a pad change, have a look at a manual for cars that use those calipers.

I have had absolutely no success with the Eazibleed kit. I have tried it on three separate occasions and each time I found that the only reliable way was to call for swmbo and a jam jar I am not sure what the problem is, but it just didn't shift the air out of the system and the pedal was left feeling very spongey.

Call the missus out from watching Big Brother - you will both benefit from the experience

They are almost identical to these calipers, I assume that the brake hoses goes into the port that has the red plug in???
(mine were second hand and both ports were open when I got them so I made an edjucated guess)
Rescued attachment vag caliper.jpg

A friend of mine was bleeding the brakes on a vw when i was in his garage a few weeks ago and mentioned he had a problem with it but sorted it out eventually. Its too late to get in touch with him but will ask him tomorrow if you don't get any luck. Cheers Ronnie

That would be a great help Ronnie, there must be something a bit quirky about these buggers because I’ve never had a problem bleeding brakes before.

A lot of the one man bleading systems are not very good with a lot of air in the system.

I have had more luck with a manual two person blead when bleeding a new sysytem for the first time.

Silly question, but have you checked that you are actually getting any fluid down the pipe, and its not blocked somewhere. Ray

Something I just remembered, years ago a mate had a similar problem, and it turned out that the feed hole had not been drilled into the caliper cylinder, so nothing would go in.

[Edited on 25-6-07 by Chippy]

i know this may sound silly but are the calipers on the right way up ie with the bleed nipple at the top?

Have u tried bleeding using someones foot on the pedal rather thatn the easy bleed?? Sometimes a new sytem needs an extra kick to get the fluid through. A couple of good stamps on the pedal usually gets it through.


Is the any fluid coming out of that end and is the pedal spongey after bleeding??

May sound silly but you havent got the fronts open at the same time as trying to bleed the rears have you?

I’m getting fluid throughout the system with the easy bleed but I just can’t get the pistons to move out at all and the pedal still feels spongy!
My opinion is that it can only be air in the system but I can’t imagine where it’s trapped, (I must have tried bleeding it 15 times or so now).
I will try the manual method this evening. If anyone comes up with any other suggestions please let me know.

I'll wager that the manual stylee bleed sorts out the problem

Another thought to add to the mix...

There's not some kind of manual or automatic adjustment mechanism on the hand brake set-up is there. Could be that the pistons are wound too far back and such a mechanism is preventing them from moving under hydraulic pressure.

Hope you get it sorted - theses kind of things can be a serious frustration

Nick:

That has just crossed my mind, I have now taken one of the calipers apart to try and figure the problem out. because I’m using brand new pads and discs the piston needs to be fully wound in to get it onto the disc.

Does anyone on here know how thick a standard A3, TT or golf disc is, I’m using standard sierra items so perhaps they are thicker???

I may skim a mm or 2 of the discs this afternoon and see if that helps!

Keep the ideas coming chaps, Its starting to bug me a bit now and I don’t want another weekend swearing at it

The solid rear discs for a Seat Leon (should be same for Golf/A3 etc) are 9.0mm thick when new.

This page is from www.brakesint.co.uk

HTH


Edit to say...
According to the same source, Sierra solid rear discs are 10.0mm thick when new.

[Edited on 26/6/07 by nick205]

Thanks for that info Nick.

We have progress, I have long braided hoses at the rear so re-positioned the calipers so that I could get to the bleed nipples whilst semi sitting in the car and manually bleeding the system, the pistons now move and grab the discs, but the pedal is still a bit spongy.
I will have to wait until later when I get an extra pair of hands to do the job properly but at least it’s a start.

My only quandary now is:
I changed my master cylinders over to test if they were working but I didn’t swap them back.
I know have a .7 cylinder for the front and a .625 at the rear, should I swap them over or just forget about it????

It really depends on your caliper piston sizes but I would match the 0.625 m/c with the front calipers to get a front bias.

Job done!

Thanks for all your help chaps.

I drained the whole system, switched the master cylinders back, took both the rear calipers off the car whilst I bleed the rear circuit (first with the easy bleed and then the manual method), Then I bleed the fronts and all seems fine.

Happy days

Great - always good to get something like that sorted out