Please help me troubleshoot my brake

Post Tue Mar 22, 2011 10:07 am

The problem is that the wheels are not locked when I fully press the pedal from around 15-20 mph. The car keeps on rolling for a certain distance before stopping.

My brake setup:
- Renault Clio servo
- E32 25mm master cylinder
- Front non-vented stock E30 discs
- Rear drums
- A 20mm spacer is used to fill the gap between the servo rod and the master cylinder.
- The servo is moved to the left 6cm.

I've already bled the brake system. I don't think the weight of the S50 engine has become a problem. I may either have an improperly setup brake system or something may be broken.

Post Tue Mar 22, 2011 10:12 am

Is the pedal stiff when pressing or to soft?

Post Tue Mar 22, 2011 12:01 pm

with a 25mm MC and the smaller booster you will need a lot more force on the brake pedal.

Post Tue Mar 22, 2011 12:41 pm

UweM3 wrote:with a 25mm MC and the smaller booster you will need a lot more force on the brake pedal.

+1,
You are wasting your time with that setup, I tried it myself and you cannot press the pedal hard enough to make the car stop sufficiently.

You either need a smaller bore master cylinder or calipers with larger pistons, dont forget the E30 standard brake setup is biased via the master cylinders stepped bore so you will need to account for this.

I think you need to change those solid discs and drum rears for a start....

Post Tue Mar 22, 2011 1:00 pm

+1

MUCH Bigger brakes needed for that master cylinder and servo set up...

Post Tue Mar 22, 2011 1:28 pm

DanThe wrote:I think you need to change those solid discs and drum rears for a start....

that's meant to be a joke, right?

Post Tue Mar 22, 2011 5:50 pm

I ran a 25mm master cylinder on standard e30 calipers for a day or two and it was shocking. As soon as i fitted e36 m3 calipers it was fine

Post Wed Mar 23, 2011 9:08 am

Thank you all for your inputs. The 25mm master cylinder may be the problem then.

I have a set of E30 M3 suspension on its way. How would the stock E30 M3 calipers perform with the 25mm master? I'll be using EBC plain discs and yellow stuff pads with those calipers if that matters.

Post Wed Mar 23, 2011 11:51 am

RoadHazard wrote:Thank you all for your inputs. The 25mm master cylinder may be the problem then.

I have a set of E30 M3 suspension on its way. How would the stock E30 M3 calipers perform with the 25mm master? I'll be using EBC plain discs and yellow stuff pads with those calipers if that matters.

why don't you improve your brakes a little? E32 calipers (735i, 750i) or E34 540 are the same with a Merc 300x25mm disk?

Needs a little machining but it's much better than the stock E30M3 brakes.

But even with the bigger pistons of the above mentioned calipers I still thing a 23mm MC would be better.

Post Wed Mar 23, 2011 12:48 pm

What cars can I find a 23mm master cylinder from? IIRC, the one on M3 is 23mm. However, it has a different thread on the fittings so it's not ideal for me. What else can I use?

I always want to improve my brakes as long as it doesn't hurt my wallet too much.

So let's me repeat what you suggested.
E32 calipers and discs/ or E34 540 with Merc discs. Correct? Are these for the front? How do I fit them on the mounting brackets? IIRC, the rear ones on E32 are the same as the ones on E30 M3 are they not?

Post Wed Mar 23, 2011 2:03 pm

RoadHazard wrote:What cars can I find a 23mm master cylinder from? IIRC, the one on M3 is 23mm. However, it has a different thread on the fittings so it's not ideal for me. What else can I use?

I always want to improve my brakes as long as it doesn't hurt my wallet too much.

So let's me repeat what you suggested.
E32 calipers and discs/ or E34 540 with Merc discs. Correct? Are these for the front? How do I fit them on the mounting brackets? IIRC, the rear ones on E32 are the same as the ones on E30 M3 are they not?

The calipers I listed are all the same and must be used with the SL129 Merc disk 300x25mm.

THEY DON'T FIT WITH THE E32 BRAKE DISK

Watch out for the E32 530i caliper, these are 302mm as well but for THINNER brake disks and won't work

The calipers bolt up the the M3 struts but must be milled flush at the mounting lugs.
The Merc disk needs the cetre bore enlarged and the PCD from 122 to 120mm.
I have posted a write up on e30.de buti's in german. Look at the pictures and you may get the idea.

Look here http://wp1016621.wp027.webpack.hosteuro ... f00464.htm

Post Wed Mar 23, 2011 2:19 pm

UweM3, thanks for the info!

Post Wed Mar 23, 2011 3:31 pm

RoadHazard wrote:UweM3, thanks for the info!

it works really well, I am going round the Ring with ROAD pads.
(with proper cooling of course and they wear 50% in 15-20 laps, but hey they are cheap!)