AX - failed foot brake.

[Jaf]

Hello. Went to drive the car but the foot brakes are gone, pedal goes right to the floor. Pedal comes back up with pumping and engine OFF, pedal immediately goes to floor with engine running. Handbrake works better than the foot brake!

Took wheels off. No obvious leaks, but didn't take rear drums off to look at cylinders. Bled the brakes, surprisingly not too dirty. Did have trouble getting much out of rear left brake.

It's a while since I've looked at dot4 brakes instead of LHM. Normally the brake pedal sinks a little when starting the engine cos of the brake servo/ master cylinder? I'll get the rear left drum off at the weekend. If it's not that then it'll be the master?

Thanks.

[mickthemaverick]

When you bled the brakes did you achieve a hard pedal?

[xantia_v6]

If the pedal goes to the floor with no external leaks (check all the brake pipes for corrosion), then it is fairly certain to be a failed master cylinder. It is likely to be filling the servo with DOT4, which is not a good thing.

[MattBLancs]

Normal servo brakes:

Engine off,
pump pedal till goes hard,
foot on pedal firmly + start engine
= Pedal should drop as the servo receives some vacuum.

Note brake drums could hold a fair quantity of fluid so need to be sure that's not giving a false impression of "no external leaks"

Agree with others judgement, sounds like failed master cylinder

[Jaf]

Thanks.

Erm the brake pedal came up a bit with the bleeding, but only a bit. There wasn't much air bubbles. Lost the harder pedal when I started the engine.

I've just had a look a prices. Blimey! 25euros for a brake master. 10 for a brake disc. I know it's a teeny tiny car with 3 wheel bolts...but blimey. Brake discs are ok, but will need changing with next set of pads. Might want flexi front pipes too, looked a bit old.

[Jaf]

Had a look at the left rear brakes. Drum and shoes look fine, cylinder dry. Bled the brakes again, this time it bled normally so I must have done something wrong last time (though I bled all 4 brakes twice).

I'll order a new brake master. Sadly the parts shop isn't open Saturday afternoon.

[CitroJim]

It is likely to be filling the servo with DOT4, which is not a good thing.

I've had this happen - not on an AX but on a Volvo. I had to remove the servo from the car and drain it. No way it could be done in-situ in that case.

Once all the old brake fluid was drained the servo continued to work fine until I scrapped the car - for other reasons!

If the servo contains any appreciable amounts of brake fluid then performance will be compromised...

AX rear brakes can be a bit fun to bleed. I find it's best done using a vacuum bleeder for the initial bleed and then finish of in the traditional way.

[Jaf]

Ah I hope the servos OK. I went to the spares shop yesterday, they can't get a brake master. Odd as autodoc has some. Only thing is they list 19mm and 20.6mm. Would anyone know which one is correct?

[wheeler]

I've just had a look a prices. Blimey! 25euros for a brake master. 10 for a brake disc.

Are you sure you are not looking at a parts catalog from 1995??

[Jaf]

Update: fixed.

I took the brake master cylinder off to see if I could measure something to figure out whether it is a 19 or 20.6mm. Don't know what the measurement refers to, but there is a blooming great 19 printed on the side! Actually can see the 19 on the car.

Ordered new brake master through autodoc. Been a few weeks but finally fitted it, bled the brakes, and all good.

Thanks for the help.

[CitroJim]

That's excellent news Jaf