Author Topic: 25mm Brake Master Cylinder Info Needed (Read 3507 times)

Wise Old Dog · « **on:** July 01, 2007, 04:15:51 PM »

My oem brake master cyl is in need of a rebuild. It's leaking internally. The kits that I've seen run about $40-$50. I have been thinking of buying one of the 25mm masters from the m3. I saw a post from D. Clay where he used a master from a 92 750il that cost about $125. Sounded like it worked good. Do any of you have experiences with the 25mm master? Good or Bad? I just use mine for a DD, no track.

bmwman91 · « **Reply #1 on:** July 01, 2007, 06:30:02 PM »

I used one that was like 24.xx mm. I found it on an E28 5er.

My recommendation is to stick with the stock one. I removed the bigger one eventually. The rear brakes are on a smaller plunger than the fronts, and rightly so. The rear needs to have a lower bias. When I had the bigger one, both the front and rear were the same size and I found myself locking up the rear wheels a lot, which is very unsafe. Rebuild the original.

D. Clay · « **Reply #2 on:** July 01, 2007, 07:39:06 PM »

I haven't noticed the rears locking up but I have ABS. I don't know if it has separate front and rear circuits for the anti-lock but it has four sensors. The pedal is quite a bit firmer which I like.
The only size given for the E30 master cylinder that I've seen is 22 mm.
Where can you get a kit for the master cylinder?

bmwman91 · « **Reply #3 on:** July 02, 2007, 02:49:29 AM »

I think Bimmerworld has the kit. They highly recommend getting the $50 Wilwood bias adjuster, and I think it is a good idea. Maybe everyone is a little different with their experience in this. When I had qual size plungers for the front and rear, the rears locked up before the fronts, and it was quite unnerving!

Wise Old Dog · « **Reply #4 on:** July 02, 2007, 05:08:13 PM »

Well, I took the plunge and bought the Bimmerworld kit. $141+ shipping. I guess I'll find out about the performance and report back. I needed to go one way or another SOON. I had seen some rebuild kits on e-bay recently that included the shaft and all the seals in an assembly. I remember them only costing about $50, but I looked yesterday and the only one I could find was $95. So, I opted for the upgrade.

Wise Old Dog · « **Reply #5 on:** July 07, 2007, 01:54:31 PM »

I like my new master cylinder. Nice hard pedal, very little pedal travel. But, it will lock up the rear wheels if I didn't have ABS controlling it. Looks like I will be getting an adjustable proportioner. More toys for my toy. Thanks yall for the info.

D. Clay · « **Reply #6 on:** July 07, 2007, 05:38:26 PM »

Does anyone know if the OEM E30 master cylinder has different bore sizes and what they are? Are there any problems with letting the ABS do the work with the 25 mm MC such as extra wear? Did you deactivate the ABS to find this out. What happens if you deactivate the ABS with the OEM E30 MC?

Wise Old Dog · « **Reply #7 on:** July 07, 2007, 06:43:05 PM »

Good questions. Stomped on the brakes several times and the rear wheels locked for an instant then the ABS kicked in to control it. Didn't think to try it before, but I don't recall it ever locking up like that before. It's drivable like it is, but I want to fine tune it for best performance. Looks like the Wilwood valve should do it. Maybe someone can check out their braking performance without ABS and let us know?

romkasponka · « **Reply #8 on:** July 07, 2007, 08:35:01 PM »

It is posible to connect wilwood adjuster instead of original pressure reducer? What type adapter is needed to connect wilwood adjuster? All bmw brake lines connections are metrical (M10) and willwood connections are imperial.