AT MY WITS END!!!!! :mad:

[24V Renshaw 0]

I HAVE HAD IT WITH THESE DAMN BRAKES!!!!!! :mad: :mad: :mad:

 

As many of you know I have installed the complete brake system from the MK4 4motion. Literally everything. I cannot get them to work properly. Whatever I do, as soon as I start the engine and the vacuum comes on the servo the pedal just sinks, not all the way to the floor, but quite a way down. The brakes do actually work, but just right at the bottom of the travel. I have bled the system in every way possible, manual bleeding, pressure bleeding, using VAG-COM, not using VAG-COM, gravity bleeding, cracking each union off in turn, bleeding the master cylinder everything!! even down to leaving a block of wood holding the pedal down over night. I resigned to taking my car to VW for the first time ever and they had two attempts and could not get it to work.

I have had a few more goes, but still it does not want to know....

 

I have run out of ideas, I just don't know what to do now.....

 

Ideas please.............help me!!

 

Jay

[G60Jet 1]

have you got a faulty slave or master cylinder?

[24V Renshaw 0]

There is no "slave cylinder" and if the Master cylinder was faulty I am pretty sure I would not get a firm pedal at all. I do get a pedal it just sinks when the servo gets a vacuum from the engine running, which suggests an air lock.........

 

Jay

[Andy Brookes 0]

James.....you say "Whatever I do, as soon as I start the engine and the vacuum comes on the servo the pedal just sinks, not all the way to the floor, but quite a way down."

 

Have you tried bleeding them with the engine running? Maybe a very stopid idea!!!

[24V Renshaw 0]

No, I haven't actually, not that stupid an idea, but I have never heard of it being done..... could there be any possible problems?

 

Jay

[dr_mat 0]

Have a word with PhatVR6. I think he had similar problems with a mk4 abs setup and it took a significant loss of hair before he sorted it. Don't remember the details though..

[24V Renshaw 0]

dr_mat, cheers for the suggestion, everyone says the same thing but, Paul has not fitted the MK4 brake system, wiring loom etc.. just the engine. He had similar problems with the Corrado ABS system, but I have done everything he did as far as I know.

 

Jay

[biggerbighugo 0]

have you tried pressure bleeding at the same time as manual.

20 pumps on each caliper with the pressure bleeder.

[Kevin Bacon 5]

Jay, Stealth bled my Brakes with the engine running mate....after I'd had the full MK4 front and rear caliper conversion. You most definitely need to adhere to the VW ABS specifics when bleeding....

 

A few more basics....what Servo, MC, and calipers are you using? Might be some pressure differentials.....too big an MC will give you a sh1t pedal....you don't want anymore than the VR's 23mm tbh..

[24V Renshaw 0]

Kev

 

I have had VW do it, but they got nowhere, so VW specifics are not working here!!

 

I have absolutely everything and i mean everything from the MK4.

Servo, MC, pipework, ABS unit, Front calipers, Rear calipers, wiring loom absolutely everything!!

 

So I will try it with the engine running tomorrow then....

 

Jay

[Kevin Bacon 5]

Have you got the 288 front and 239 solid rear setup? Some MK4s have a 256 vented rear setup.

 

Just trying to build a picture of what you've got.....

 

The ABS units are sensitive to servo pressure (does the MK4 servo have a pedal position sensor in it? Are you drive by wire or coilpack?), hence bleeding with the engine running. If you really can't get it to work, speak to Stealth as they've bled all manner of things over the years and they seem VERY clued up on VAG ABS quirks.....

 

As you've no doubt run through your mind, if it's ALL MK4, then it should work as a MK4....but something minor is putting a spanner in the works.....

 

good luck

[24V Renshaw 0]

Keep em coming Kev, this is all good stuff.

 

It has 312mm 4motion fronts and 4motion calipers. It has 239 solid rear discs with MK4 calipers.

The MK4 brake pedal servo setup has a brake light switch and a brake pressure sensor, neither of which are throwing up any fault codes on VAG-COM.

It is fly by wire throttle, (not sure what that has to do with anything).

I may give Stealth a ring tomorrow, but I am getting some good ideas from various forums I have posted this problem on tonight. The Corrado Forum once again comes up with the most though!! :)

 

Jay

[Kevin Bacon 5]

I was thinking the FBW might have an influence on the braking....but I guess not if the servo has a BPS like the normal Corrado brakes have.

 

All the MK4s I've driven have VERY sharp initial bite compared to C brakes....so something is amiss. I take it you have the MK4 ABS ECU too?

 

I'm wondering if the ECU you got was perhaps from a MK4 that had the 256 rear vented setup, which would have a different brake bias pressure I suspect (MK4s don't have an axle regulator IIRC?).....

 

Dunno mate...tis all guesswork!! Speak to the Vince man....but he won't have experience of all MK4 onto Corrado either, but I'm sure he'll have some nuggets of useful info up his sleeve...he usually does.

[rmn 0]

with abs your meant to bleed with the engine running

in 9 out of 10 cases it will work fine with the engine off, but this seems to bhe that 1 case

Engine running is the way to go!

[CoxyLaad 0]

wasnt horrocks' problem something to do with his brake discs not sitting right?

Anyways if you are really struggling I have another mk4 abs/esp unit that you can have.

[VEEDUBBED 0]

Have you tried clamping off each brake hose in turn?,it has been known to happen that the hoses look fine but under braking they may bulge slightly because the inner wall of the brake hose is damaged,give it a try.

By the way,if you don't have a brake hose clamp you could use a pair of vise grips with 2 sockets on the jaws to protect the hoses,good luck mate.

[24V Renshaw 0]

Unfortunately I have braided hoses so that is not an option.

 

Jay

[Blown 0]

:?: Dunno if this'll help,(not very clued up about mk4's tbh)but I remember someone with a very similar problem on their mk4,which turned out to be something along the lines of a rubber grommet at the top of the brake pedal getting a hole in it-whether it was a hydraulic unit or something,I don't know,but the VAG dealers said that it was a common problem on MK4's and that they were replaced with an uprated one.

[24V Renshaw 0]

They apparently have a weak master cylinder, but its not that as otherwise I would get no pedal at all. I get a pedal but I lose it when the vacuum comes on.

 

Jay

[Blown 0]

Airlock in the ABS pump,if it has one?

May shift with bleeding whilst the engine's running......

[G60JAY 0]

Something else that might effect it is that your using the abs unit from a 4-motion but without a haldex connected to it. Might be telling the abs unit somethings up. Can you rig up a cable from the abs ecu to the haldex ecu temporarally.

[sciroccotune 0]

I read a thread about some on using mk4 callipers and having to shorten the throw of the peddle buy adjusting where it connects to the semester cylinder. Worth a look!??

[aki 0]

hi justa thought (i do have them from time to time) you say that mk4s have a poor m.c. and your pedal only sinks when there is a vacum does the pedal sink very very very gradually without the servo assistance? try putting an even pressure on the pedal without the vacum and hold a steady pressure for a few minutes and see if the pedal sinks if it does the m.c seals are shot! also it doesnt do the seals much good if they are moved out of there normal operating range.you can still have a firm pedal when the seals are shot the test is to apply pressure over a period of time not just a few seconds!

to check for air in the system push the pedal to the floor and then pump the pedal if the pressure builds chances are theres air in the system!

good luck!

andy