Could it be the brake master cylinder?

Post Mon Sep 12, 2016 1:22 am

So I got a D reg 325i auto cab and the brakes are very very weak....
I've bought new discs pads and shoes as well as braided hoses and handbrake cables. Since the car is going on my mates ramp next week so I can get it all done. Front pads are low and the fluid has gone down slightly however when I brake the pedal goes quite excessively low to the floor could that be a sign of a worn master cylinder or is it just a case of low pads?

Post Mon Sep 12, 2016 1:37 am

There is a rod running across from the brake pedal to the master cylinder which can be adjusted to alter the height of the pedal, see http://www.e30zone.net/e30zonewiki/index.php/Brakes under'pedal'

Post Mon Sep 12, 2016 1:44 am

sounds like you got air in the system , when the pads get done i would bleed all the brakes at the same time .

leave the brake bar alone. it is set in the right position from factory and does not need to be altered !

Post Mon Sep 12, 2016 3:17 am

magpie wrote:sounds like you got air in the system , when the pads get done i would bleed all the brakes at the same time .

leave the brake bar alone. it is set in the right position from factory and does not need to be altered !

How do you know it is in the original position after so many years? My brakes felt like cr*p till that rod was adjusted.

Post Mon Sep 12, 2016 7:51 am

The above points are all valid, I replaced both Master and slave late last year as a matter of course.. Neither that expensive. Unless you have some evidence that they were replaced within the last few years I say just replace them.

Post Mon Sep 12, 2016 9:22 am

Brake pull rod is one of the few things on a RH drive E30 that does need periodic adjustment. A small amount of wear in the associated bell cranks and clevis pins results in a considerable drop in the brake pedal.
There's nothing in your OP that really indicates what the problem could be, but worn pads, on a working system, does not affect the pedal height. Worn pads do lower the fluid level in the reservoir though.

Post Mon Sep 12, 2016 2:08 pm

A worn master cylinder was the reason for my excessive pedal travel. Remember the master cylinder can wear internally and lose its efficiency without any sign externally.
As Brian has pointed out already, worn brake pads will not result in a different pedal hight, only a lower fluid level.
If you think about it, as the brake pads wear the piston will have to sit further out of the cylinder in the caliper. This will increase the volume of the cylinder of which the brake fluid has to fill, therefore resulting in more brake fluid being needed in the system.
This is why brake fluid needs to be siphoned out of the reservoir when new pads are fitted, because the piston has to be pushed back into the caliper which reduces the volume of the system.