Excessive Brake Travel

[jay77]

Hi everyone,

I'm new to the forum - I'm after a little bit of help, and I'm hoping you might be able to help me.

I have a MK4 VW Golf 1.6SE 2002 plate it’s only done 27K, I have just changed the brake pads and bled the brakes due to some travel on the brake pedal prior to changing the pads.

In stead of improving the travel in the brakes its seems to have made it worse, so Ive put 5 ltrs of brake fluid through and bled it now 4 times...The brake pedal has deteriorated to the point brakes really only kick in about 2 inches from the floor and full braking is almost an inch from the floor. Which is a lot of travel!

I used a one way valve bleed kit and a mate helped me bleed the brakes...some air came out initially, but 4 bleeds later and now its just fluid.

Any ideas what it could be or what I could do to improve the feel of the brake pedal so its not 2 inches from the floor before braking?

Any help would be appreciated!

[guyg]

Sounds like the reservior might have run a bit low, drawing some air into the system. If this is the case, it may have entered the ABS in which case I think you might need VAGCOM to cycle the pump - anyone know a bit more about this?

I did once damage a master cylinder by pushing the brake pedal too far whilst bleeding. The cylinder can build up a ridge where the normal range of travel for the seals in the bore ends. If you then push the pedal completely to the floor when bleeding, it's possible to damage the seal by making it travel past the ridge.

Does the brake pedal have less travel if you press it very quickly? If this is the case and it sinks slowly under light pressure, then the master cylinder seal is probably damaged.

Again, I don't know if this is a problem with the Golf and maybe unlikely for a car manufactured in 2002.

I use a pressurised system to bleed brakes - I've never trusted the one way valves as they encourage you to leave the bleed nipple open during the upward stroke of the brake pedal. This can cause air to be drawn past the seat of the bleed nipple and back into the system.

Hope this is of some help.

Cheers

Guy

[jay77]

Thanks for replying...

I did once damage a master cylinder by pushing the brake pedal too far whilst bleeding. The cylinder can build up a ridge where the normal range of travel for the seals in the bore ends. If you then push the pedal completely to the floor when bleeding, it's possible to damage the seal by making it travel past the ridge.
Guy

After doing the 2nd set of bleeds the travel was still low, on the two subseqent bleeds the pedal sofened and the travel got a little worse.
I did push all the way to the floor when the nipples where open.

Does the brake pedal have less travel if you press it very quickly? If this is the case and it sinks slowly under light pressure, then the master cylinder seal is probably damaged.
Guy

I will give this a try and see, is this while the engine is running (Sorry if this is a dumb question)? when the engines off its hard after a few pumps and when the engine is started and the servo kicks in it softens

Do you think its worth trying a pressurised bleed? after 4 sets of bleeds there is no air coming out just fluid..

[guyg]

I will give this a try and see, is this while the engine is running?

It shouldn't matter much, the pedal will soften with the engine running as your effort is being assisted - this is normal. What I was trying to determine is if fluid is getting past the seal in the master cylinder. If you apply a gentle but steady pressure to the pedal, does it continue to sink?

If you press the pedal abruptly and it initially stops some way from the floor but then slowly travels further, the seal may be damaged.

Do you think its worth trying a pressurised bleed? after 4 sets of bleeds there is no air coming out just fluid..

Does the pedal feel spongey? Is there any possibility that the reservior ran low at any time [perhaps before the pad change?]

You may have bled the mainstream system to death, but there could be air trapped in the ABS unit - I read somewhere that this can only be fully purged by using VAG-COM to cycle the pump.

I'm not sure that a pressurised bleed will resolve this once air has been introduced, it is more of a preventative strategy. Hopefully a VAG tech will read this and advice further...

Cheers

Guy

[Col]

I'm no expert but have read about the seals being inverted in the bores if you do it the old fashioned way.

The best method I've found to bleed manually is as follows (with assistant);

1, Pump pedal until hard and hold.

2, undo nipple and let pedal sink to floor and hold until nipple is closed.

3, release pedal and repeat 1 & 2.



As Guy does, I use a pressure bleeder these days, perhaps you should give one a try.

As for the ABS system, unless the level has fallen and air has entered it is supposed to NOT be a problem. However if you can access vagcom, it certainly would be worth a try.