19 replies to this topic

[daveeeeee]

Hi, sorry this isn't about a mini but I'm trying to help a mate with his BMW and I know there are some technical wizards on here.

Problem: loads of travel on the brake pedal, travels 3/4 to the floor then gets firm, but with engine running (servo action) it pretty much gets to the floor feeling spongey. He's had no loss of fluid.

He's got a servo, tandem master cylinder front back split, with ABS, discs all round, aftermarket calipers and steel flexi hoses.


I've checked for leaks on all lines, bled full system, checked calipers for leaks, also had mastercylinder off and servo side is also dry.

I made the assumption one piston wasnt sealing in the master cylinder letting the pedal atleast half way without doing much, swapped master cylinder with one off of a friends car who's brake pedal was high and firm (same car by the way lol).

Problem not resolved.

I've also adjusted out all the slack in the pedal mechanism, so where's the travel coming from?

Thanks in advance.

[Saxo-Fiesta-Mini]

either there air in the system, or the abs is being painful sorry cant be more help are the wheel locking or not

[MRA]

a BMW ? well there is a special garage that these have to go to....... when you get there ask the kind man with the "special car lifter" (magnetic crane grab) to correctly place your BMW so the correct gas torch oops sorry I mean tooling can correct this issue

No really, it does sound like air in the system, give it a good bleed use a pressure bleed (about £20) and see if this helps

oh and don't worry about my sense of humour

[Saxo-Fiesta-Mini]

thats just random fella your normally fairly serious makes me want to get in my matchbox go cart with 4 wheels and do 90 sorry mini hahahah

[Chris_9866]

Yea i would go along with air in the system, make sure you bleed it in the right order away from the master cilinder, and that is it under pressure using a bleeding kit, not just a mate pushing the pedal. What year car is it. possibility that there is a leak inside the DSC modulator, but this is unlikley, as this doesent usually just occur. have you made sure that the master cylinder is not leaking into the servo.

[daveeeeee]

ha i like bmws!

thanks for the replies though, i'll try pressure bleeding
i've not bled a system with ABS before, i've been giving it 13 pumps per corner starting furthest away etc.

what's a dsc modulator? inside abs?

yes i've checked for a leak into the servo.

thanks again

[Chris_9866]

Yes it is the hydraulic unit that controls the stability control, if this car has it, i dont know how old it is, but yes it controls the ABS, depending on which model it is it should be just visable in the engine bay or under the plenum cover. But i really think the probelm is probably with the bleeding.

Good Luck

[Major Burkenshaw]

You might have got air traped in the abs pump. Try using a pressure bleeder rather than doing it manualy.

It could also be possible that the internal walls of the rubber pipes have clapsed, try checking all the rubber pipes to see if they are bulging when the brakes are on?

[daveeeeee]

oh it doesn't have one of those chris thanks for the explanation

think most of the flexis have been replaced but i'll double check for rubber pipes.

thanks guys, i'll let you know how it goes.

[minimat]

Have you replaced any of the discs or pads?Reason i ask is that if you are not careful when pushing the caliper pistons in you could reverse the seals in the master cylinder meaning you will never bleed the system properly and get a good pedal
The safe way to push the cylinder in on any car is to clamp the flexi hose,undo the bleed nipple push the piston in then do the nipple up again before removing the pipe clamp,you will obviously lose a tiny bit of fluid but you will not damage anything this way.

[daveeeeee]

Had the pads out to check for leaks before, but I've swapped the master cylinder since. I've not heard of that problem before though cheers for the advice.

[Boycie]

A long pedal on a system like this (that is poperly bled) is normally down to a master cylinder fault.

[daveeeeee]

Right what I've done today is, set up an E Z bleed system at 15psi and bled the brakes, pressure wasnt moving alot of fluid so had the pedal pushed too, got a constant flow. I also had the engine running.

My Dad's been trying to read up on it, the reason I had the engine running was something to do with getting the abs to activate or something, but I got no warning light or anything.

Apparently you can get gadgets to activate the ABS whilst bleeding?

Cut a long story short, no air bled out of the system.



Boycie I just changed the master cylinder for one that was working nicely on another car.


Any more ideas? Still don't want to send the poor guy to BMW at £90 an hour.

[MRA]

You might have got air traped in the abs pump. Try using a pressure bleeder rather than doing it manualy.

It could also be possible that the internal walls of the rubber pipes have clapsed, try checking all the rubber pipes to see if they are bulging when the brakes are on?

If you are going to do this make sure that you wear the correct Personal protection equipment, high pressure fluids can damage your health....

[daveeeeee]

bump