When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
C2 & C4 use the same 4/4 small Brembos and will have the same brake bias, which is ~1.734 below 55bar line pressure and ~3.310 above 55 bar.
the early C2 w/ 4/2 Brembos have ~1.508 below 45bar line pressure and ~2.793 above 45bar
Bill - if my C2 came with the 4/2 caliper combo but was upgraded to the 4/4, which ratio would I have? I would assume the ratio is the braking torque at the front/rear so my ratio would be 1.734 and 3.310, but that the 3.310 bias would kick in at only 45 bar if the previous owner didn't switch out the proportioning valve to the 55 bar? Is that correct? So switching this valve would get me an extra 10 bar of braking with a better bias before the proportioning valve kicks in and sends the majority of braking to the front calipers - does that sound right?
I assume the general purpose of the proportioning valve is to reduce rear braking torque under heavy braking to reduce the chance of locking up the rears and sending the car into a spin?
if you've gone to the 4/2 caliper setup you need to change the proportion valve (it sits next to the ABS pump and is easy to access/swap.
I removed mine, but I also have a very different braking setup, the balance is (supposedly, I never got the piston areas) the same as the stock later 964. Rear lockup is not a problem. Front lockup was until I fixed my ABS pump.
Thanks for the input Spyerx. I've been reading some old threads about changing out the stock 45 bar PV for either the 55 or turbo's 60 bar PV or removing it entirely. Decisions decisions...
Thanks for the input Spyerx. I've been reading some old threads about changing out the stock 45 bar PV for either the 55 or turbo's 60 bar PV or removing it entirely. Decisions decisions...
If you look at my build thread you can see a picture of the valve disassembled somewhere about the middle of the thread :-)
If it was me I'd go for the 60 bar if you keep it, Bill may have a stronger opinion one way or other.
Bill - if my C2 came with the 4/2 caliper combo but was upgraded to the 4/4, which ratio would I have? I would assume the ratio is the braking torque at the front/rear so my ratio would be 1.734 and 3.310, but that the 3.310 bias would kick in at only 45 bar if the previous owner didn't switch out the proportioning valve to the 55 bar? Is that correct? So switching this valve would get me an extra 10 bar of braking with a better bias before the proportioning valve kicks in and sends the majority of braking to the front calipers - does that sound right?
I assume the general purpose of the proportioning valve is to reduce rear braking torque under heavy braking to reduce the chance of locking up the rears and sending the car into a spin?
Thanks for the education.
Here's my page w/ a lot of specs on stock systems thru 993
the 964 4/2 came w/a 45bar p/v which is more aggressive than the 55bar version used on later 4/4
all 964 w/ stock brakes have more front that is desirable, for street use it does not matter, for track use the fronts are overworked and the rear are underutilized. Particularly w/ a car tha has been lowered and uses a stiffer suspension you want to shift more braking to the rear, to do so you can use less aggressive p/v or do as the 964 Cup eliminate the p/v all together.
911s through '83 have 1.491 w/ no p/v and no issues
993RS has 1.426/2.64 these are the brakes I have on both my cars one w/ and one w/o a p/v no issues
964 4/2 1.508/2.793 w/ 45 bar knee, this is the best balanced 964 and can still do w/o a p/v
964/4/4 1.734/3.210 w/ 55 bar knee, needs more rear
964RS/Cup 1.713/3.171 w/ 55 bar knee, Cups are straight 1.743 no p/v and still need more rear to be optimized.
Thanks for the input guys. Seems like the only downfall of the RS29 is the price.
I use RS29 now. The other downfall is the squealing they make. Not a problem on the track but gets annoying and shall I say a little embarrassing when driving in traffic on the street.
I`ve pagid orange, blue and turquoise for my car... together with RS calipers, the car stops great. Also at RBR, that is said to be one of the most brutal track in europe for braking... it`s a pleasure to use the middle pedal :-)
But the color of pads does not make a huge difference for me
Quick follow up from the recommendations. I removed the internals of my OEM 45 bar proportioning valve per Bill Verburg's advice in preparation for a Sebring track day this past Sunday. Overall the Pagid RS29 pads and brake bias worked great on a track that's known to be hard on brakes. No rear lock-up whatsoever. The only thing I would critique is similar to what others have said about the pads not having a ton of initial bite, but they did hold up session after session and didn't fade at all.
Thanks for all of the great feedback and advice. I had a great time tracking the 964.
4/2 has better bias because there is more rear brake torque
4/4 allows for longer mtbr(at least in back) and using the same pads f/r. Also better availability as these same pads were also used on 930s
Thank you for your reply, sorry about my lack of knowledge on this subject but why 4/2 w/a 45bar has more rear brake torque than 4/4 w/a 55bar? 45 is less than 55.