Bleedin Brakes

[confusionhunter]

Tried posting on other forums but no luck....as yet

Bleedin Brakes....
Its a curse not a request on how to bleed brakes!!

My brakes are knackered and I dont know whats wrong..... but there is a bit of a story.... The issue is on a an 98 A3 SE Tdi 110, I have a 2000 Bora SE 1.6 16v too and as far as I can tell the brakes are identical....

Anyway, I suffered catastrophic brake failure on the passenger rear caliper, so I changed that and the flexi hose..... but ever since then the brakes have been spongy and with the engine running the pedal slowly sinks to the floor...... I fitted new front discs too and thought just incase I managed to get air in the M/C I though I might bleed the brakes through. I have VAG com so I bled the ABS pump, all four corners and the 2 on the Master Cylinder......but I did this manually using the age old pumping technique.....

No difference pedal feels great until you turn the engine on and it slowly sinks to the floor.....

So I read up on the usual brake issues on uk-mkivs.net and thought Id managed to flip the seals on the MC.... SO...I bought a new MC and an Eezibleed kit...... fitted it and bled the system all 4 corners and the 2 nipples on the MC as well as the clutch cylinder too..... No difference.....

Ive checked for leaks in the servo system, cant see any and even if there were I dont see how that would cause these syptoms. The only thing I havent done is bleed the ABS pump again....

.... so I'm a bit stuck really.....Help....!

I can apply HARD pressure on the pedal with the engine off and it will stay solid for as long as I can apply the pressure, but with the engine running it slowly sinks to the floor every time even if you pump it up..... ive checked the 4 corners for fluid leaks too...and dont appear to be losing fluid from the reservoir.....

It went through an MOT on Sat and failed on this sinking pedal(I knew it would)....so there I bled the ABDS pump again 8 times as ELSAwin instructs you to(seeing Ive changed the MC)

No difference....
I suppose I could check for leaks properly by jacking the car up and getting underneath......... I tell you, if I find a leak i'll be Very pee'd off with the MOT place wasting my money on an MC.......as they should have spotted any leaks. and pedal sinks so many times there would be fluid everywhere!

Also reading on ross tech: http://www.ross-tech.com/vag-com/cars/absbleeding.html

that when bleeding the ABS pump all 4 wheels need to be off the ground.... Why?

as far as I can tell there are no load sensors or anything so I dont understand why that is.... I did it anyway last time but Im confused as to why..... my wheels are big enough I dont have to take the wheels off to bleed the brakes, so getting it the the air seems an uneccessary pain in the bum.... unless anyone here knows different?

Any one have any ideas on this? The problem doesnt happen when the servo doesnt have a vacumm either.....

any thoughts would be appreciated.....

Any one have any ideas???

Cheers.
Mark.

 

[nwhiteley]

first of all, clamp all 4 flexi hoses off, (useing hose clamps) and start the engine, check the pedal again. reason i say this... i have had a similar situation, with a pedal that only sinks when a vacuum is applied to the M/C. it tuned out to be fluid leaking past a seal on one of the calipers.

if the pedal is ok with the clamps on, release them one at a time, taking note as to which one causes the pedal to sink.

if clamping them off doesnt make a difference, the new M/C could be faulty.

you do nead to get it on a ramp though.. just to see if any of the pipe joints are leaking under pressure.

 

[confusionhunter]

Thanks for that, but arent the front flexis like the rear caliper ones that if you clamp them the lining inside will kink?
Given that the problem still occured with the rear clamps in place I'll go check the front calipers now...... Excited at the prospect of a solution!!!

 

[nwhiteley]

Thanks for that, but arent the front flexis like the rear caliper ones that if you clamp them the lining inside will kink?
Given that the problem still occured with the rear clamps in place I'll go check the front calipers now...... Excited at the prospect of a solution!!!

do you mean that they may get damaged? if so... they will be fine

you do nead to stop the flow of brake fluid getting to the calipers, if only to eliminate the calipers as a problem

 

[confusionhunter]

Hmm.... OK... Front calipers looked ok, so jacked up the car and I put dry paper towel under the MC, and both front calipers etc..... PUmped the pedel and it sank to the floor 10 times......

No fliud in the towels, non on the floor. and resevoir level looked the same........Id already clamped the back ones before So I clamped the 2 front hoses still the same problem. I guess that leaves the MC and the ABS unit???

 

[nwhiteley]

Hmm.... OK... Front calipers looked ok, so jacked up the car and I put dry paper towel under the MC, and both front calipers etc..... PUmped the pedel and it sank to the floor 10 times......

No fliud in the towels, non on the floor. and resevoir level looked the same........Id already clamped the back ones before So I clamped the 2 front hoses still the same problem. I guess that leaves the MC and the ABS unit???

shame. i dont think it will be the abs, so i think it will be a faulty M/C.

have you had a garage look at it, other than the mot station?

 

[confusionhunter]

No, no other garage has looked at it..... ALthough Ive spoken to a mate who said he spend 2 days bleeding a mk4 golf and still couldnt get the air out it....
Ive already put 4 litres of fliud through it and bled the ABS pump properly all using the pressue system at below 1 bar.......

Anyway I gave it another bleed ... I took the car for a drive and the brakes seem fine when driving, ABS works..... But if you stop and pump the pedal it does sink quite far down..... My mate says it sounds like there is air still in the system..... which sounds plausable but Ive followed Elsawin instructions to the letter..... Never had these problems on my old cars.... if the MC was knackered you knew about it!! lol

 

[confusionhunter]

Hmm. OK... well I bled the whole system again and the pedal felt better and didnt go to the floor..... So I resubmitted it anyway and it passed the MOT.... but they still arent the same....

Everyone Ive spoken to that works in the trade say these cars are a nightmare to bleed..... Even with the proper equipment........
I'll do it a gain ones evrything beds in.....
Cheers for your thoughts.
Mark.

 

[nwhiteley]

glad your getting there now.


neil