930 Brake upgrade; bias valve stays or goes?

[newms]

I have 930 brakes with new 23mm mc on my '82sc track/ax/street car. Should the factory proportioning valve stay or go? Does the valve reduce rear pressure or what exactly? Thanks.

[javadog]

You'll get all sorts of opinions on this but the chances that the stock valve will be correct for whatever setup you have are small. I'd remove it and make provisions for adjustable brake bias. What you want is for the front brakes to lock up a little before the rears. The proportioning needed to accomplish this depends on a whole host of factors:

Calipers used; did you do 930 calipers on the front or both ends?
Rotors used.
Brake pads used; cooling used.
Wheel and tire sizes; tire compound.
What sort of weight distirbution you have.
What fuel level you run.
What rear diff you use.
Shock valving.
What track you run.
Yada, yada, yada.

In other words, if you want to get all the braking you can, you'll need to adjust the bias.

JR

[KFC911]

I'm going to respectfully disagree with JR on this one. At least on my Carrera, the PV is eliminated, but I can't speak for the SCs. The difference in front/rear braking bias is built in to the 930 calipers due to the differences in front/rear pistons. I sourced mine from Steve Weiner (Rennsport), and followed his advice...can't go wrong there !


edited: Upon rereading JR's post, he is probably right. If you want the ultimate control, ditch the stock PV and go with an adjustable one. However, imo, that would be only for achieving 'ultimate control'...the 930 calipers alone will absolutely do the trick by themselves for most...

[beepbeep]

Remove it. Brake bias is built into 930 calipers (rear pistons are smaller) and as far as I remember, there is no proportioning valve installed on 930 either. Most of the time there is a slight front bias margin built in, so I assume you aren't going to brake faster by increasing front bias even further with extra valve.

[javadog]

True, but the Turbo look Carreras had one....the plot thickens.

JR

[KFC911]

I did not know that JR...very interesting indeed!

[DW SD]

Bill Verburg has posted numerous times to go without a proportioning valve with 930 calipers. I'm sure he'll chime in. I'm with BeepBeep on this one.

Doug

[Wil Ferch]

Brake Upgrade Clarification

- Wil

[89911]

Remove it. I have 930 brakes on my 89 coupe. I ran them for a while with the valve on and noticed all most no rear pad wear. When I removed it, I had more stopping power but it was a little tricky. I spun at the track when I was trailbraking. Since then, I have gotten use to it and they work great. If your really concerned leave them on, but your giving up some braking ability in the process.

[newms]

My interest is to take some bias off the front as the fronts locking up/wearing down way too fast.

I have 930 calipers front and rear. Coleman front rotors, oem rears. Performance Friction 01 pads. '82SC euro non sunroof coupe, RS interior with Euro 3.2, SSI, Mass flow, SRP susp., etc. I'd guess 2600lbs and 240hp, conservatively.

Thanks to all for your responses.

[kycarguy 935]

Originally posted by javadog
True, but the Turbo look Carreras had one....the plot thickens.

JR

I never did understand why the 89 speedsters/turbo look cars have a PV and the 930 and 911 turbo's didn't.

Anyone know the answer?

[Steve@Rennsport]

Because the 930's (Turbo) had a MUCH heavier engine and moved rearward with the 930 transmission and thicker clutch package.

That said, 930 brakes do not need a PV and in fact, work much better without such things (except for Tilton adjustable ones).

[kycarguy 935]

Thanks Steve.

[Bill Verburg]

I agree w/ Steve and will add that suspension, tires, lsd etc. also affect how much rear bias you might want.

Leave it off, but be open to the possibility that an adjustable one might be wanted

[GrantG]

I have a 73RS replica with the 930 brakes (205/15F and 225/15R tires) and I find the bias to be just about perfect without any valve. I do use Pagid RS19 Yellow pads in front with RS44 Orange pads in rear though...

[newms]

OK then, Part II -
When the factory bias valve is removed, will the brake lines need any kind of adaptor or connector to fill in?

[Bill Verburg]

Originally posted by newms
OK then, Part II -
When the factory bias valve is removed, will the brake lines need any kind of adaptor or connector to fill in?

Well, assuming that you have an '82 SC, there is no p/v to remove(unless someone added it after original delivery)

[newms]

Well then why am I asking all these brilliant questions?

[javadog]

Because if you really, really want to get the most out of your new brakes (that is why you put them on the car, right?) you want an adjustable proportioning valve.

They aren't much money, in the big scheme of things.

JR