brakes

[Jona1971]

Hi,

recently in the morning, the first time I put my foot on the brake pedal it sometimes goes to the floor. Its fine after that.

I recently replaced my rear trailing arms for ones with disc brakes and replaced the brake fluid. I've bled the brakes and they're firm and work well.

Could it be the master cylinder? If so, is there a rebuild kit available?

many thanks,

[e30-wheels]

Hi

Could still be air in the system. Try pressure bleeding if you have not already done so, if you bleed the brakes
by depressing the pedal you can pick up dirt on the seals which can give you the problem you have, dont know of a seal kit but at present there are a couple of master cylinders on ebay. Hope this helps.

[Jona1971]

Thanks,
I bled it with a vaccum pump.

I'll give it another go when I replace my front calipers and brake pipes next month. (I thought I'd do the master cylinder at the same time if it could have been that.)

[Jona1971]

Er, I've been having a look at master cylinders on fleabay and there seem to be at least 2 types: 46mm and 64mm. Which master cylinder should I be using with a 51mm front strut conversion with the larger calipers? Any ideas, thanks

[e30-wheels]

Have you looked at The Real OEM, you should be able to get a part number to help identify which M/C you want. What model e30 have you got

[bigbird76]

I fitted a 7 series brake master cylinder to my m3 as an upgrade the m3 has a 23mm and the E32 has a 25mm.

If your after better pedal firmness have a look at that option and if it would fit your car.

Leigh

[jmc330i]

Only fit a 25mm master cylinder to a non-M3 E30 if you're also fitting calipers with larger pistons. A 25mm m/c is too big for standard E30 calipers.

[Brianmoooore]

The OP is describing a faulty brake system, not a modified one.
There is nothing wrong with E30 brakes that work as BMW intended, so no need to consider modifications.
This could be a fault with the MC, it good just be residual air, or it could just be a problem with the caliper pistons or sliders, causing the pistons to retract more than they should overnight.
Clamping brake flexible hoses one at a time and seeing what effect it has on the pedal travel will show up the latter.

[Jona1971]

Thanks for your support guys.

My car is a pre-facelift 318i without ABS.

(Eventually I plan on going the M52 route. So far, I've upgraded the rear suspension and brakes and am currently undergoing replacing the front struts to 51mm with the wider calipers and vented discs.)

I thought all E30s had the same master cylinder so haven't considered this until now. The WIKI actually says all "facelift" cars have the same MC.

I've looked at RealOem and can see the following MC part numbers:
from May 1987 - 34311157206 (22.20/17.46mm) and
up to July 1986 - 34311157273 (19.05/20.64mm).

My car was built in December 1986 so falls between these 2 dates. I'm guessing I've probably got the smaller one, is there an easy way to check?

Forgive my ignorance but are the 2 numbers the diameters for front and back brake pressure i.e. 22.20mm for the front and 17.46mm for the back?

I don't mind the lazy, progressive brake pedal feel, but it scares the cr4p out of the wife. I'm going to a fair bit of trouble so don't want one component to let down a decent set up.

So, which MC do I need?

Thanks again,

[Jona1971]

Thanks Brian,
when I put the new (Old) rear calipers on I didn't rebuild them or strip them down first. So you're saying one or more could be sticking and retracting slowly overnight, needing a first pump in the morning to take up the slack?

I'll try the clamping flexible hose idea this week, thanks.

If it is just the caliper and the MC is not faulty, do you see any benefit in changing to a bigger MC or just leave it alone?

Thanks again,