Brake Bias/Proportioning Spring/O-Ring

[Achilles99]

I have done numerous searches on this topic, and have not found a consistent answer. Some people say that removing the o-ring combines the front and rear systems. Others say that they aren't connected.

Some have bad experiences removing the spring, because it locks up if not disables the rear brakes at times.

My questions is this: what is the stock brake bias on a Viper, and what is the bias after removing the o-ring and/or spring? I locked up the front brakes this weekend during an auto-x, and would like to try and increase rear bias. Yes, I have taken a driving school, and I have my SCCA Regional Competition license. I realize that this is not a novice modification, so don't worry about giving me a disclaimer

Also, I haven't seen a tech article on how to remove the o-ring. Other threads keep suggesting to "check the archives." I have, using several search terms. Can anyone point me to a thread that has been accepted as the "correct" one, please? I just purchased the car last Sunday, so I'm trying to learn it with the new brake bias from the beginning. Thanks!

 

[JonB]

Attorneys keep us from writing tech articles on this controversial (and potentially fatal) subject.

'ie despite great past articles, sime guys still do it WRONG.

 

[RockyTop]

I have done this to my car. Bob Woodhouse and Dean Word have at times done this to their cars as well. My uneducated understanding is that the removal of the O-ring (& spring) removes the combination valve's built in threshold/knee point past which it delivers less line pressure to the rear brakes. On non-ABS cars I think it was at around 800 lbs of line pressure or something like that. The result is that you get more rear line pressure past the knee point so the rear brakes work harder. They are, however, very constrained by the size of the rear rotor and a host of other factors.

The negative side is that the stock combination valve also has the safety feature of retaining some brake pressure at one end if the system fails at the other. Removing the O ring destoys that feature. Ask Sam Kelly what it's like to lose your brakes at 120 mph.

It is a cheap way to increase rear braking, but it doesn't make a huge difference. At the end of the day the stock Gen II Viper really needs a brake upgrade - - like it got in 2003 !

 

[GTS Dean]

As clear and concise an explanation as possible:

The proportioning section can be "fixed" by *either* removing the spring, or pulling the seal ring at the base of the proportioning spool.

The combination valve will continue to function in its fail-safe mode when the proportioning section is "fixed." The hydraulic fluid path is past the safety valve section, then to the proportioning/metering sections. If one circuit fails, (either the front or rear) the spool in the safety valve section is displaced to the front or rear by higher line pressure in the good circuit. This plugs the fluid leak from the master cylinder and illuminates the brake warning lamp.

 

[J.D. Farmer]

Here you go Achilles99, straight from the Viper Manual:


At 800 psi the hydraulic pressure is split by the preportioning valve front to rear with the rear brakes receiving 43% of the front brake hydraulic pressure.

 

[Tom F&L GoR]

From personal experience:

Remove proportioning valve O-ring - fronts lock up first.
Increase rear brake caliper piston from 36mm to 38mm - fronts lock up first.
Increase rear brake caliper piston to 40mm - fronts lock first with clutch engaged, rears lock first with clutch disengaged (i.e. really good balance, I think.)

 

[99 R/T 10]

Anybody have pictures? This would make a great addition to the illustrated upgrades.

 

[Marv S]

<FONT size="-2">save it when you can as it may not be there tomorrow</FONT s>

 

[Mike H]

Achilles.

You said the fronts locked up....Is that just one time? Did maybe you just stand on the pedal way too long? Ususally that is why fronts lock up, we tend to be too heavy footed if we take into a corner too fast ....
What brake setup is on your car? What pads do you run? Many times more aggresive rear pads will help if you are heavy footed, which in many cases is the answer.
I was at Watkins Glen a few months back and a guy in a street Viper told me he was having brake fade and wanted to know what I was running and if I had any brake fade. We were doing testing on our car one weekend. He had 6 piston fronts, 4 piston raers, had Porshe deflectors, Archers brake ducts and he had brake fade. I had 4 piston Brmbo fronts, 2 piston PBR rears. My ducts were disconnected and my deflectors off. I had no fade problems. We followed one another for 4-5 laps. On the long straight He would begin braking at the 450-400 ft mark, riding the brake all the way to the turn in around 100 ft. That was from near a 155 mph speed at the 450 mark. He followed me, we hit the brakes around 225-200 mark.....That was 200 feet less of heating up the brakes. The guy said to me no way he could brake like that, yet he had WAY MORE braking power than I did....get the idea?

 

[GTS Dean]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Mike H:
He followed me, we hit the brakes around 225-200 mark.....That was 200 feet less of heating up the brakes. The guy said to me no way he could brake like that, yet he had WAY MORE braking power than I did....get the idea?

<HR></BLOCKQUOTE>

Bingo Mike!