930 brake upgrade: Removing Carrera proportioning valve

[Will]

I've just upgraded the brakes on my '87 Carrera to 930 brakes. All is well except that I forgot to have the rear proportioning valve removed. How is this done? My mechanic says that all new lines will have to be run, but I've heard that simply splicing in some line where the PV used to be will work. Anyone done this themselves? Any advice on how to do it would be appreciated.

On a related topic, I'm considering putting in a Tilton 7-way proportioning valve into the front brake circuit. If any of you have done this, I'd love to hear about what you think of this setup, as well as how you did it.

This is a track-only car.

Will

[91C2wrencher]

I think you'd be wise not to "splice" in a piece of tubing. Could be bad if it came apart at just the wrong moment Using a manifold block would be a better idea, the best for a track car would be to run new lines my $0.02.....

[89911]

Two responses: I've done the 930 brake upgrade and still have the proportioning valve in. The company I used for the machining does not think you need to change from you stock set up. After using these for the past year, I've had no problems. If anything, you may want to further decrease the amount of fluid going to the back calipers because the 930 upgrade is much larger in the back then the front compared to the original car. No bias may mean too much rear brake. I've installed the Tilton on my brothers car with Big Reds. This is advised because of the size and amount of stopping force will need fine tuned. It simply replaces the proportioning valve once it is removed.

[Bill Verburg]

Mike is correct, the original Carrera hyd. bias was 1.306 the mechanical bias is difficult to put a # on, but stock is also front ~1.5. To correct for the total bias which is too far back a very aggressive 33bar p/v was used to move bias back to the front when it was needed as in an aggressive stop.

Keep in mind that all previous 911/930 used a hyd. bias of ~1.5-1.6 and a mechanical bias of ~1.5-1.9

now w/ the 930 brakes f/r your hyd bias is back to the more front 1.6 and the mech. bias is also a more front 1.9 You no longer need the additional front bias of caused by using a p/v

There are situations where even more front bias may be wanted, it depends very much on the suspension, wheels, tires, course, driver preference, aero and even the lsd action. No p/v was used on a 930 til '82. So no p/v is a very good starting point but if you wish to experiment a click stop Tilton won't hurt and may help.

You will definitely find that the 33bar oem is way too aggressive and not at all desireable.

[KFC911]

Hi Will, If you're opting for the no p/v solution (as I did), here's what worked for me. Since the p/v (approx. 3'' in length), and the line from the p/v to the m/c (approx. 11"...if I recall correctly), are hard to source (in any combination), I opted to use a 30" length (metric & bubble flared...available at any good auto parts store), and shaped it to replace the p/v, and the two lines the p/v was connected to). In other words, the 30" line connects to the m/c, then is bent to follow the contour of the other 'removed' lines...down through the smugglers box to where it attaches to the 'front coupler' (replacing the p/v and the two short lines).

[89911]

Bill I read you post several times (even slowly ) Are you saying I should remove my stock bias valve? I've locked up the fronts briefly several times on the track and have never locked the backs up yet.

[Bill Verburg]

I've locked up the fronts briefly several times on the track and have never locked the backs up yet.

Absolutely!! The 33bar oem Carrera 33bar p/v is way too aggressive for the 930 caliper/rotor setup. Any p/v on the rear circuit only moves bias forward.

No p/v would be best for most setups.

If you have drastically increased the grip at the front then you can experiment w/ an adjustable, likely only using the gentlest end of the range.

[ChrisBennet]

I've done this (twice) this summer. Simply get a piece of premade brake line 12" long (I think) and bend it to replace the line going from the master cylinder to the where the PV is now. Unscrew the female/female adapter from the PV and join the lines using that.
This setup has one fewer part than the factory setup. Personally, I would leave off the adjustable bias until you identify a problem with the "no PV" bias setup. Simplify, simplify...
-Chris

[Will]

Thanks, guys! I did a hybrid of KC911 and Chris' approach, and it worked fine.

For those of you wanting to do this, here's a description of what I found in my car: The brake line exits the MC, travels about 6" to a coupler that mates the brake line to the proportioning valve (it's a female/female coupler). The line exits the PV and ducks down into the smuggler's box straight down towards the ground, where it enters an elbow fitting. It then continues into the passenger compartment for it's trip to the rear of the car.

So... one could: (1) replace the entire line from the MC to the elbow (done by Chris), (2) from the above mentioned coupler down the elbow (what I did), or (3) take out the PV, screw the longer line into the female/female coupler, then run a new line from the coupler to the MC (Chris' approach).

So I bought a 2' piece of ISO/metric/bubble-flared line, removed the PV and the line that goes down into the smuggler's box, and replaced these two pieces with my new line. The advantage of this approach is that I didn't have to fight the mess around my master cylinder. The disadvantage is that I had to spend a bit of time under the car and had to remove the underbody tray that protects the steering rack. A 2' piece of line works well; it's only about an inch too long, so I just made a few S bends on the long section that goes down through the car.

Off to the track on Sunday to try it out. I'll delay the decision on the Tilton valve until I see how I like this setup, although I was talking to my mechanic today about it (he's a long-time Porsche racer), and he thought the Tilton in the front brake circuit was a great idea, since it would allow me to find the point at which rear brake lockup begins, then back off a click or two to restore a slight bias toward front lockup, thus having maximum braking power. Another advantage of this is that the rear rotors on the 930/Carrera setup are MUCH cheaper than the fronts (which are custom rotors), so you may as well get them working. The downside is that braking while the car is turned, as in trail braking, will require a bit more finesse. To me it sounds like a great experiment. I'd love to hear from anyone who's actually tried this.

Again, thanks everyone!

Will

P.S. to 89911: You mentioned that it may not be necessary to remove the PV because the "back calipers because the 930 upgrade is much larger in the back then the front compared to the original car. No bias may mean too much rear brake." Don't forget that the rear calipers on the 930 upgrade have smaller pistons inside than in the front, which automatically alters the amount of rear brake that you get when you hit the pedal.

[89911]

Will, I will be removing the valve today. I have been using my front rotors and pads up heavily. I just recently got custom Brembo's from Rennsport and at that price, I want as much life out of them as possible. I'll take a look and see what method I'll use. Thanks, Michael.

[89911]

I used Will's method and just replaced the whole piece. Here is a pic of the entire tubing intact.

[DJB]

Interesting thread as I am about to commence my upgrade to 930 brakes. Removing the PV now sounds easier than anticipated, Will what mods did you need to do to the rear calipers to make them fit. I have heard conflicting reports that some calipers have to be machined whilst others don't kind frankly I am a bit confused.

[alfizzo]

did 77's have a rear p/v valve? i have a 930 mc with big reds front and back and the fronts lock up. the rears dont look like they are doing anything.

[Bill Verburg]

did 77's have a rear p/v valve

No, only '84 on

big reds front and back

There are several different big Red combos out there the 993tt used very small 28/28 pistons on the back circuit , this will cause the fronts to lock prematurely on a 911 or 930

The better rear caliper for the Big Red front/322 combo is the 30/36 993RS rear calipers w/ 322 rotor

[alfizzo]

i got the brakes from race technoglies. did all 993tt rear calipers have 28/28 pistons? should i add a tilton adjustable p/v to the front circuit to help balance it out?

[Bill Verburg]

993tt rear calipers have 28/28 pistons?

Yes, all the ones I have seen, but I have talked to several owners that swear they have 28/30, I only trust what I see, owners are often incapable of understanding what they are looking at.

Again every Racetech kit I have seen uses a 993RS rear caliper, which is 30/36. You should have no issues what so ever w/ front lock up w/ these calipers, if you do there are other issues.

Never use a p/v on the front these devices are non linear and reduce line pressure just when it needs to beincreased.

[alfizzo]

could be that my rear pads are falling apart with 400 miles on them got them from performance products in 5/03. the fronts look great . go figure.