fuch

Brake pressure valve 928.355.305.02 is this the one I need for my early c2 running c4 rears all you part number guru's before I hit the big button... I need a 55 bar as I understand it & I think the 55 in the number above denotes its a 55....thanks fuch

berny

Yes I fitted the 928 one when I changed to the 4 pot rears. Big improvement!

Vandit

I removed the guts of the stock valve when I went w/ the '92+ 4-piston rear calipers on my '91.

fuch

Thanks gents...ive locked the rear end up a couple of times under heavey braking so pushed my luck
running the original one!!

Vandit

I don't remember the specifics, but from what I recall, running the 2-piston caliper bias valve w/ 4-piston calipers means you're underdriving the rear calipers, since the 2-piston calipers are more efficient, hydraulically, than the 4-pistons. So when you upgrade to the correct bias valve for the 4-piston rears you're actually adding more rear bias than if you kept the original valve. Gutting the valve would add the most rear bias.

Silvertarga

I have the 964 355 305 10 on mine..probably same part as the 928 numbered one..just a different label on the package.

ja78911sc

Why not just install the 55 bar valve which is OE with four pot rears? Do you have any info that would suggest that gutting would be the same bias?

Curious because I am also upgrading to four pot rears.....thanks.

Vandit

Read through my 2nd reply. The gutted valve results in more rear bias than any bias valve setup.

There's a bunch of mathematics to calculating the piston sizes and hydraulic pressures, but that's for technical people like Bill Verburg or other members to explain.

Vandit

Here's your technical data. It's very technical.
https://rennlist.com/forums/964-foru...lp-needed.html