14 replies to this topic

[MB1380]

i have an 89 city with a servo and after bleeding all the brakes the pedal still feels spongy and when the engine is running the pedal goes straight to the floor unless i pump it a lot so i changed the master cylinder and to feels less spongy but still wont work unless pumped alot when the engine is working.?? Must be something to do with the servo. would it help to disconnect the vacume hose when bleeding?

Any suggestions welcome, im also using metro turbo calipers if that helps.
Thanks

[Jammy]

Is there any difference between braking when the engine is running and when its not?

Have you bled the rear brakes in the correct order according to Haynes?

[MB1380]

yea they have all been bled as per haynes. when the engine is off and i pump the pedal it holds its pressure. however when i start it up the pedal will travel to the floor on the first attempt

[Jammy]

I'd say its a nackered servo then, since the servo uses the vacumn from the engine to work, your not getting any smoke when the engines running and your pumping the pedal are you?

[MB1380]

Now that you metion it, i am getting a bit of smoke. but i tought that the master cylinder does not actually exchange any fluid with the servo??

[Jammy]

Ok, I've never taken a servo apart to know exactly how they work, but I believe there is a diaphragm that can split, so I'm guessing, if there the engine is on, theres a vacumn present which could be pulling the fluid through into the engine and causing the loss of brakes.

One sec and I'll do a touch of reading...

EDIT: Also, just thought, check for any splits or leakages in the lines and fixings from the servo to the engine.

[MB1380]

ya but i think the diaghphram only separates the vacume air and atmospheric air and from what i can see from the master cylinder, there is no way of fluid transferring to the the servo but i donno.....?

[Jammy]

Hmmm, your probably right, a search on here didn't really turn anything up, and I haven't got my books around me since I'm at work...

[MB1380]

i just drove it there with the vacume hose off of the servo and taped it up and it was more or less the same. it myt just need more extensive bleeding maybe?

[miniboo]

i would give it anoither damn good bleeding if i were you.

I think you need to have the servo hose connected to the manifold though.

[minislapper]

Take the cap off the master cylinder and jam a piece of wood between the pedal and steering wheel (so the pedal is pushed to the floor). Leave it overnight and see if it makes a difference. Don't forget to put the cap back on when you've done!

[Jammy]

Take the cap off the master cylinder and jam a piece of wood between the pedal and steering wheel (so the pedal is pushed to the floor). Leave it overnight and see if it makes a difference. Don't forget to put the cap back on when you've done!

Won't that just introduce a load of moisture to your brake fluid??

[The Matt]

...........
Any suggestions welcome, im also using metro turbo calipers if that helps.
Thanks

I am not familiar with the 4 pots, but isn't there two bleed nipples on them and aren't they always a pig to bleed? I know there are two pipes that go into em on the metro aint there? Do you use a link pipe when fitting them to a mini? I am guessing that could be the issue?

Anyone got a piccy of some 4 pots?

I am assuming you are not loosing any brake fluid anywhere either? Rear cylinders OK and everything? Are the brakes in a generally good condition?

[pikey7]

Read this!

Its a good diagram on how a brake servo works. Basically, if your servo splits then you will just get no servo assistance on the brakes, but it will not cause you to not be able to stop.

Second, no, there's no hydraulic system in the servo.

You just have a brake bleeding issue. Make sure you bleed them properly in the correct order. use new fluid and only complete the bleeding when you see new fluid coming out of the cylinders. (to make sure you don't have contaminated fluid). If you think you won't be able to tell new from old, get some coloured fluid (ATE do a good grade Blue fluid).

DON'T leave the cap off overnight. You'll only encourage more moisture into the system (Brake fluid is hydroscopic). by all means use the plank of wood trick though, but I don't see it helping.

Also, have a good look round the components of your system. Do you have any leaks, any bulging flexible lines, any bad corrosion, are the components bolted to the car properly etc etc.

[minidaves]

you have the calipers on the right way around?

dave