Brake servo problem ?

Hi, I've just had the brake master cylinder replaced on my 300tdi abs Disco.

The brakes are now worse than before, I've read a few of the old threads and this seems to be quite common !

I'm trying to work out what the problem(s) are.

Under pressure, the brake pedal will go down to the floor when I start the car. I can then pump the pedal a couple of times and get a good hard pedal.
I can't get this when travelling though, the pedal is really soft.

There is a lot of travel to the pedal and I can hear the servo venting. In fact, I can now hear it inside the car down by the pedal !

I reckon the system needs further bleeding, but what's with the loud venting ?

as you said, air still in it.
not sure with the venting noise tho.
if a garage changed it, take it back to them.

Cheers for this. I was thinking it might be a split diaphragm in the servo, I can't get to have a look at it until the weekend.

park facing up hill and wedge a stick inbetween the drivers seat and break pedal forcing i all the way down and the air will slowly rise to the resivoir, do this till the weekend or tillyou have a chance to bleed them

Lyndon said:

park facing up hill and wedge a stick inbetween the drivers seat and break pedal forcing i all the way down and the air will slowly rise to the resivoir, do this till the weekend or tillyou have a chance to bleed them

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how will air get to the resovoir if the brake is pressed?
and how will trapped air get out of the calipers as the bleed nipples are at the top?

Davee said:

Cheers for this. I was thinking it might be a split diaphragm in the servo, I can't get to have a look at it until the weekend.

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press the pedal with the engine off.
keep it pressed and start the engine.
if the pedal travels down an inch or two, the servo's working.
(this is assuming the pedals not gone to the floor due to the air in the system)

pump pedal hard and then start engine. it will then probably drop to the floor.

try to get a pressure bleeder on it, see if that works.

was it a new servo??

I've got the identical problem - had thought it was just the system needed bleeding. I'd be interested to know how you get on.

Cheers guys, I checked the servo the other morning. The pedal does go down when the car is started.
It was the odd air venting noise that you can hear down by the pedal that confused me.

We didn't get a new servo, it was just a master cylinder change.

It went back to the garage and the missus collected it. She reckons it's a lot better now.
The guy rebled the brakes a couple of times with an auto fill machine, he also changed the flexibles for some stainless braided ones that I bought.

I'm going to swap the pads for some EBC Ultimax next, see if things get better. I think it's probably got a set of aftermarket Mintex or similar at the moment.

SteveBLandy said:

I've got the identical problem - had thought it was just the system needed bleeding. I'd be interested to know how you get on.

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Steve, in answer to your question, the garage re-bled the system a couple of times. They also changed the flexibles for some stainless braided ones.
Result. The pedal now travels a fraction of the distance and has a much firmer feel to it.

It does seem like some of these motors brakes take a lot of bleeding just like the damn water system !!
All I can say is don't be put off if your first attempt at bleeding the system doesn't produce the results.

I think I've got a set of braided hoses that I had originally intended for my other truck. Might be worth me fitting them and bleeding the system before I do anything further (like change of master cylinder). Is it just three hoses that were changed?

SteveBLandy said:

I think I've got a set of braided hoses that I had originally intended for my other truck. Might be worth me fitting them and bleeding the system before I do anything further (like change of master cylinder). Is it just three hoses that were changed?

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Steve, I've got an abs version, so it was 4 hoses. Two at the front and two at the rear on the diff.

Finally picked my truck up from my Dad's house and it turns out I've got ABS on this one too, so my 3-hose set is no good (plus they're really for a truck with 2" lift) so I'm going to try and bleed the system thoroughly without changing the hoses just yet.

I drove it for about 10 miles today, and once you take up the initial slack, the brakes work fine.

I drove the Disco Monday night and the brakes seem to work as they should, once you pick up the first 1 1/2" of travel. Does feel like air in the system somewhere so I had planned to bleed the system with my old man today, but with the weather he didn't come over.

I did manage to swap the alternators though, so the blue ES is working now, but the green 300 is getting more and more poorly!

I'll have a crack at the brakes as soon as I get a second pair of hands on the case.

Thanks for the updates.

Turned out the rear brakes were knackered. Overhauled the rear callipers, new rear pads and a couple of pistons and piston seals, and now everything working perfectly