weak servo... UPDATE: + ABS failure!

[gareth]

my brakes 'feel' significantly weaker then any other E30's i've driven. it feels as if the servo is not amplifying the pressure to the required extent...

i have ABS, mintex M1144 pads and ATE disks on the front, new genuine stuff on the rear.

i recently swapped the servo for another used one and it feels exactly the same.

even when i heat the brakes up (we're talking blue disks here!) it just lacks bite and power. my wife had a E30 320i at the same time as me having this fault and her car (abs and standard disks all round) would outstop mine by a stretch! the brakes took a lot less foot pressure and had a lot more bite and available power.

any ideas?

what does the valve inline with the servo hose do?

[ian332isport]

Gareth,

The valve in the vacuum line is a non return valve. It basically makes sure that the vacuum stays in the servo. If you didn't have the valve, the vacuum level would go up and down depending on the engine revs/throttle opening.

If you still suspect the servo, I have a very good spare in the garage. Your welcome to it if you don't mind collecting (Hastings isn't that far from me)

Have you considered the flexible brake hoses ? If one of these is a bit tired, it may be swelling up under pressure and taking the bite out of the brakes. Could also be a master cylinder problem (probably got one of those somewhere as well).

Ian.

[gareth]

hi mate.

that's a cool offer! ta! you're horsham area aren't you?

i know the hoses would make the brakes a little softer but they wouldn't necessarily reduce the power..?

even though i can get the ABS to cut in, i need to strain my leg to do it.

would anything as simple as air in the system be to blame?

[kam-325i]

I have a similar problem with mine, but i am changing the vacum lines and Non-return valve this weekend, i will let you know if it has a positive effect.

[gareth]

cool!
ta!

[ian332isport]

hi mate.

that's a cool offer! ta! you're horsham area aren't you?

i know the hoses would make the brakes a little softer but they wouldn't necessarily reduce the power..?

even though i can get the ABS to cut in, i need to strain my leg to do it.

would anything as simple as air in the system be to blame?

Yeah, Horsham (or just south anyway).

Any problems with the hoses or air in the system will tend to make the pedal a bit spongy with extra pedal travel. It would certainly take the bite out of the brakes, but don't think it would give symptoms like you describe.

Is it possible that a previous owner fitted a larger bore master cylinder. This would reduce pedal travel and cause you to have to press harder to get the same braking effect. Is there any 'sponge' in the pedal, or is it really firm ?

Ian.

[gareth]

there is (at present) some sponginess to it, this arrived when i got the brakes so hot they were smoking! i boiled the fluid and it's spongy now...

before that, it wasn't any firmer than anything else i've driven and has never really had any decent bite.

[Andy335Touring]

Did you change or bleed the fluid after it boiled ?

[gareth]

not yet, but it was like this before i cooked the fluid, just a little firmer.

[gareth]

UPDATE!!!!!

the brakes have been feeling consistently weak but have always 'worked'...

on the way back from work earlier, my ABS failed! it now merrily locks its wheels and there is none of the usual ABS vibration though the pedal.

there is no light on the dash, however, there never has been one, even when starting! i assume there's either no bulb or it's blown.

any ideas on how to diagnose the ABS fault?

[Jon_Bmw]

Hmm sounds like the bulb has been removed or it has blown. It should come on when you turn the ignition on and go off when you start the car iirc.

You can check the sensors with a voltmeter, the readings should all be the same, a certain resistance-but it slips my mind, i'm sure brian moore will have the answer.

Other than that i'm not sure as i've never had any further problems since removing the faulty sensor that was causing my problems.

[Brianmoooore]

ABS sensors are about 1000 ohms each.
First thing to do is replace the ABS bulb and see what it does. With sensor failure the bulb should go off when the engine is started, and only come back on when the car starts to move.
Air in the ABS unit can be very difficult to bleed ouit.

[gareth]

hmmm.. air...!

there's some in there i think... i boiled the fluid a while ago and it new needs a flush though/bleed.

i'll give that a go asap i reckon!

would this still stop the ABS system attempting to do something? eg, i can't even feel any action from it.

[bigkev]

whether there is air or not shoul'dnt effect the ABS as it only detects when a wheel has stopped moving and then releases pressure to that wheel it sounds like you have air in the system

[bigkev]

cheap pads will also give you a spongy pedal i go for genuine every time its worth the extera dosh

[gareth]

mintex m1144's. not cheap or nasty!

there is some air in the system as mentioned above, however, the air has been there for a month or two with the ABS working fine. this fault has just happened. the ABS is not reacting at all.

[Jon_Bmw]

Have you checked the sensors it is a 5 min job? Unplug the yellow connectors put your volt meter probes in there(sensor side obviously) on ohms setting see what you come up with.

[gareth]

not had a chance yet...

[Martinaston]

Unplug the ABS (if it's working) and put the car into a skid and the wheel that doesn't lock will show which line has the air in it (not very helpful with the rear i know)

[gareth]

the ABS is not even attempting to work, on all wheels. the ABS pump is not doing anything, at all!

if i try and lock up, i succeed, with all four wheels! no ABS pulsing at all.