Brake proportioning valve delete/new valve installation

[NDW]

Gang,

I am locking my front tires up very easy (flat spots) with the 4 wheel Stop Tech brake upgrade and slicks. I have purchased an adjustable proportioning valve for my pre-ABS '99 GTS and need some help from someone who has knowledge of how to install this item. I have the '99 service manual, and reading it brings up more questions for me than answers. The car is driven only on the track.

My questions are:

a.) Do I take off the stock proportioning valve or leave the stock valve on in addition to the new valve?

b.) If I leave the stock valve on, which line (front or back) would you put the proportioning valve on?

c.) If I take the stock valve off, which line (front or back) would you put the proportioning valve on? Also, how do you eliminate the brake warning light if you delete the stock valve?

Thanks for your help.

Newt

 

[JGarrett]

Howdy Newt,

Which pads are you running? Could it be too high an initial bite? What have the Stoptech guys said in regards?

Cheers,
Jim

 

[dblankenbaker]

My questions are:

a.) Do I take off the stock proportioning valve or leave the stock valve on in addition to the new valve?

b.) If I leave the stock valve on, which line (front or back) would you put the proportioning valve on?

c.) If I take the stock valve off, which line (front or back) would you put the proportioning valve on? Also, how do you eliminate the brake warning light if you delete the stock valve?

What many call the stock prop valve is a combo unit (aka brake distribution block) with two different valves in it. One activates the brake warning light if pressure is lost in half the system. The second valve is the prop valve.

Your options are:
a) Completely remove the stock prop valve (shuttle, spring, and o-ring) and plumb your aftermarket prop valve in-line with the rear system. You will retain the brake warning lamp and have adjustable rear braking up to 100% pressure (no reduction).

b) Always the rear.

c) You can plumb the (rear brakes!) aftermarket prop valve around (completely by-pass) the brake distribution block, but doing so triggers the brake warning light. Pulling the electrical plug at the block turns the light off. This option gives the same performance as option A.

 

[NDW]

David,

Thank you for the answer. I found out that the brake warning light is activated by faulting to ground, so unplugging the wire would cure the problem. I believe I will go with your solution to a, it sounds like the best way to go. Thanks for your help, I can always count on the Viper nation to pull through with the answer.

Jim,

Hope you are feeling better, I met a frind of yours, David at MSR last week. The pads are Brakeman 3's all the way around. Maybe a less aggressive pad in front would help. I haven't contacted Stop Tech as of yet, I will give them a ring. The rub is that when I go back to DOT tires for Viper Day's, I will have to make adjustments to ease some of the back bias to keep them from locking first.

Hope to see you soon,

 

[ViperRay]

Hi Newt,
Sorry we didn't get more time to chat at MAM this weekend. I wanted to find out how you made out with your brake setup. Did you remove the o-ring from the stock prop valve and install an adjustable one? Did you switch out the brakeman 3's to something else? I still have the stock calipers and rotors with brakeman 3's. I had hoped the Cone brake cooling ducts, fresh motul would help with the brake fade but I lost the brakes Sunday after only 8 laps. I notice (based on the lack of brake dust on the rear wheels and remaining pad thickness) that the rear brakes appear to be just for show. I wonder if dismantling the stock prop valve would allow the rears to participate more and take some of the "heat" off the fronts without risking rear wheel lock-up. I briefly locked the fronts on Sunday so I know it's not an issue as is. I was running Sport Cups. Do the Stoptechs solve this problem? What about circulating the brake fluid as some have done?
I would appreciate feedback from anyone with personal experience on this issue. Thanks.

 

[James Bell]

I am using the Stainless Steel Brakes adjustable proportioning valve (with gauge) in my 1994 RT. Their tech guy said to always install the adjustable valve on the rear line, after the factory proportioning valve. If it is installed between the master cylinder and the stock proportioning valve, the rear brake pressure may feel softer or spongy.

 

[Tom F&L GoR]

ViperRay,
From personal frustrations and experience, I can recommend you read this: http://vca2.viperclub.org/forums/showflat.php?Cat=&Board=UBB14&Number=326009&fpart=&PHPSESSID=

I have also installed the brake recirculating valve, let me know if you have any questions about that. But the bigger issue is the "non-participating" rears. I will have several 40mm calipers back from the machine shop this week, so if you are interested, I can send them fairly soon.

 

[Janni]

All,
Installing a brake proportioning valve on the rear will really do nothing, as it can only serve to further REDUCE brake pressure there (in it's fully OPEN state it's the same as you have now) and then each turn reduces the pressure.

I'd recommend a couple of things -
1. Think about corner weighting the car. There's always going to be a tire that's light - usually the right front. If you can get more weight on it, the brakes will work better and you'll have less chance of lockup. Finding someone that can do it may be tricky, but a well balanced car is a good payoff.

2. Tom's rear brake upgrade. It's simple and safe. It seems to be a good complement to the StopTech fronts brake upgrade that starts to reduce the piston size of the fronts to accomplish more rear braking. Tom's upgrade will do this in a more direct manner.

3. I'd still remove the o-ring from the stock valve if you haven't - it's a small difference, but works pretty well.

4. As an investigatory move, you could measure brake pressure at all four corners to make usre you don't have a pressure issue.

5. Fluid - if you are running Motul - especially at a track that is ******* brakes - you MUST bleed every day. I've seen folks that bled every session. While Motul has a great DRY boiling point, as soon as it heats up (esp. if stock lines) and takes on water (which it does quickly) the wet boiling point falls like a rock.

6. Pads - I wouldn't go any less aggressive on the fronts that the BM3s - they arep retty forgiving. I would consider going more aggressive on the rears. But do be aware that with different tires, your brakes will react differently, as there are different levels of braking torque based on grip.

My overall advice is to use the least invasive braking system mod you can get away with. Adding proportioning valves and other systems IMO just adds a level of complexity that a street car / challenge car doesn't need. And I don't think that you want to be to the point where you are adjusting the prop valve based on how much gas you have in the car. To do it right - it needs to be in the cockpit so the driver can adjust based on changing conditions. Too complicated. Play around with the stuff above first.

 

[ViperRay]

Tom and Janni,
Thanks for your responses as you are two people on this board whose information and advice I value. I will e-mail you Tom as I am interested in your rear caliper upgrade. I will plan corner weighting but understand that I must upgrade the (currently stock except for adjustable front sway bar from Woodhouse to decrease push) suspension system to allow this (?). Does running the Sport Cups as I currently am affect the brake decision? If I go 40 mm in rear, should I remove the o-ring from the valve and put in an adjustable one? I would plan to adjust it only according to tires and not "fiddle" with it all day. I'm just afraid the 40mm without prop valve might cause rear wheel lockup.
What about the recirculating system for cooling ?
Thanks again.

 

[Janni]

Ray,
If you car currently has stock fronts(?), I think that Tom has studied the effect of both the 38 mm and the 40 mm rear calipre upgrade and neither one should produce rear lockup. You do want your fronts to lock first - it's just a matter of "how much first"....

My guess is that the tire change should maintain the balance as long as you are going with like sizes. Increasing the fronts by 30 mm would change your brake proportioning I would htink, as your increased contact patch would provide even more grip to the fronts.

Suspension is a huge one - keeping the car level and more weight onto the back end will help your rear brakes do more. Springs and adjustable shocks are key here. You CAN cornerweight a stock suspension, but it involves shims and shaving springs, etc. Lots of work, but if you are bound by some rules, then it's doable. Otherwise, it's better to look at dampers that adjust for ride height, rebound, and mess with spring weights. Also, aero - we added a HUGE HONKING WING over the winter and it's amazing how much more work the rears can do now - Henry's been dialing in more rear brake at each event.

Personal opinion - I'd avoid a brake proportioning valve on a street car. Talk to Tom about the 38 vs the 40mm and go from there. There's a ton of stuff you can do with compounds, too.

As for brake fluid recirculating - we've never had the need for it. Henry's as tough as anyone on brakes and we've never boiled fluid. Conbination of cooling and fluid.

 

[Janni]

Newt - sorry - my reading comprehension is pretty poor - I reread and now see that you have a Stoptech 4 wheel upgrade. Scratch my Tom's increased rear caliper upgrade recommendation...

However, StopTech should help you on this. While you do want front lockup prior to rear, it sounds like you are not getting the pedal modulation you desire and that it's being "grabby". You could go ot a softer / less initial bite front pad. We've always used Brakeman #3's as the best "forgiving" pad for ease of brake modulation on the non-ABS cars. We then changes to PFC01 (03 now, I think) as we got better with our driver training for increased pad life and higher temps - but they are "grabbier".

A proportioning valve is still out though - as it never increased the pressure to the rears - it an only dial in less pressure than stock.

I'd also ask someone with a similar system to your what they are running or maybe ride with them. You may also talk to Archer's - as they ahve hte most real world track experience with the best pad compounds for the entire StopTech line.

Hope this helps - and sorry for my irrelavent post earlier. Doofus.....

 

[ViperRay]

Janni,
Sorry to confuse you by starting a separate thread within Newt's original one. I DO have stock brakes other than Brakeman 3's all around and intend to talk with Tom about his 40mm rear calipers. Thanks again for sharing some of your wisdom.

 

[Rich Wesorick]

Hey Janni:

While we're hijacking threads, did you change the front aero on the car when you added the huge honking wing???

Rich

 

[Tom F&L GoR]

>Scratch my Tom's increased rear caliper upgrade recommendation...<

Ouch! Actually, Newt and I had talked about 40mm calipers and he wanted to go racing big time, so he appropriately went full StopTech. [So far, I can't do trackside assistance ]

I just wanted to ask those with the 38mm or 40mm versions what they thought about pedal modulation. In theory, the larger rear piston volume should increase pedal travel ever so slightly, and I thought probably imperceptibly. I recently drove a stock '94 (only difference from mine is rear caliper) and was surprised how hard the pedal was and how little feel there is.

 

[ViperRay]

Tom,
I guess one could calculate the additional pedal travel by knowing the additional volume required to cause the pistons to travel the required distance and the diameter of the lines...but that's more math than I care to ponder.

 

[Tom F&L GoR]

Math?

OEM rears are 36mm, which is 1018mm^2 area, and there are two of them. Assume 1mm clearance to make contact and volume needed is (1018*2*1) = 2036mm^3. Change to 40mm rears, and new volume needed is 2513mm^3.

Master cylinder is 27mm diameter, or 572mm^2 area. To push the extra (2513-2036=477mm^3) volume, the MC piston travels 0.8 mm. If the pedal ratio is 3.5 (I'm guessing) then the extra distance your foot travels is 3mm, or 0.11" This seems small, but would "grow" with more pedal application. Please check my math...

 

[Janni]

Hey tom - not an "ouch" - all I menat was that I thought he had the stock rears - but since I reread and he had already done the "full 4 wheel Stoptech" recommending your caliper upgrade wasn't appropriate.... Believe me - if we still had our non-ABS GTS's - they'd both have your rear caliper upgrade before any big $$$ brake system.

Hijack on
Rich - we're running a modified GTS-R type front splitter. We've had for a few events, but the downforce difference with the new wing is UNBELIEVABLE. I talked to Ben the other day and offered our cheap solution for a front splitter that eases the pain of the $$$$$$$$ wing.... email me or call.
Hijack off

 

[ViperRay]

Looks like a small change in pedal travel indeed Tom.

I guess it is really the amount of force that we apply to the pedal that gives us the feedback we need to modulate the brakes and not really the amount of pedal travel. I would go as far as to say that I would prefer a pedal that didn't travel at all for brake modulation.

I am looking forward to trying your rear caliper modification in conjunction with disabling the stock prop valve. I still can't help but believe that an adjustable prop valve would be useful though. One of the reasons my fluid boiled this past weekend (and not last time) I'm sure is because I ran with Cup tires this time which caused more forward weight transfer which was harder on the front brakes.
At the same time, this would have made the rear brakes easier to lock theoretically (though they didn't which means they are REALLY underbiased).

If I upgrade the suspension (which is planned now that I am saving money on the brake system!) this will put more pressure on the rear brakes again.
If I add a wing, that would put additional pressure on the rear brakes.
If I add a front splitter that would decrease rear brake requirements, etc., etc., etc.

My point is, it's hard to believe that one static ratio of front to rear brake torque would be optimal for all these conditions.

In any of these cases, as long as the rears do not lock first, I feel safe with the mod.