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The VIPER Garage  |  How To Instructions  |  How-to section  |  Adjustable Proportioning Valve installation Gen 1/2 and ABS
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Author Topic: Adjustable Proportioning Valve installation Gen 1/2 and ABS  (Read 663 times)
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Viper Nation - ezine
« on: July 01, 2016, 08:52:10 PM »

Because of larger 4 piston calipers installed on rear of Gen 2 Viper in place of single piston 36 and 43mm rear calipers the brake pressure to the rear of the car needed to be decreased to get the true advantage of the larger brakes.  Installing an adjustable proportioning valve in the rear brake line allows the brake pressure to the rear to be limited to the rear.   With nearly equal (or 4 times the rear caliper) braking in the rear the pressure can be limited to get the perfect brake balance.  Factory settings of the pre-ABS calipers were terrible and even in the rain my 2000 GTS ACR couldn't lock up the rear tires under full pedal pressure.  With 4 piston rear calipers the rear brakes locked up long before the front brakes which could easily cause an out of control skid. 

Perfect brake balance is when the front tires skid then applying more pedal pressure will lock up the rear tires.  An adjustable proportioning valve installed in the rear brake line (or the front brake line in the case of a 3" front drag tire) allows a manual adjustment of the braking forces.  Equal sized brakes front and rear isn't needed or wanted on a sports car because weight transfer put most of the weight of a car during stopping on the front tires requiring the front brakes to do most of the work and requiring the rear brakes to be smaller.  For road racing and high speeds big brakes are required to stop the car repeatedly.  With premium 13" slotted high-carbon steel rotors and Ceramic brake pads my Twin Turbo GTS was running easy 215mphy runs and although I thought I was easy on the brakes it turned out that medium stops from 200+mph caused my new rotors to overheat and once cracked after about 12 high speed runs.  Imagine if I'd used the brakes hard ...  Drag racing and roll racing 1/3 mile with light-weight Gen 4 14" slotted premium rotors and ceramic brakes WITH 40mm rear calipers equalled heat scored front rotors and Blue colored rear rotors!

After the Big Brakes and reshaped wheelwells all I needed to finish my brakes for extreme speeds was to add an adjustable proportioning valve to the rear brake lines of each Viper.

The 1999 Viper was pretty straight forward.  The Hurst line lock solenoid was installed in the front brake line (rear line of master cylinder) so I merely bought 2 4" brakelines and removed the line from the master cylinder to the factory proportioning valve and installed the 2 short lines with the adj. prop. valve in between.  I bled the brakes and after some short testing (I found gravel worked well and didn't damage the tires during test skids) I was satisfied with the prop valve adjusted to the middle.  This adjustment (tighten to cut pressure and loosen/counterclockwise to allow higher pressure). 

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1999 1200rwhp TT GTS - ART, 2001 Roe sc GTS- (4 sale), 440 Duster restomod (sold), 3x Stealth TTs, 92 Daytona IROC with T3, 580whp/1080wtq Cummins pickup.
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Viper Nation - ezine
« Reply #1 on: July 01, 2016, 09:28:13 PM »

My 2001 Viper ABS Big Brake upgrade also needed the adjustable proportioning valve to prevent early rear brake lockup.  The ABS prevents total lock up but doesn't adjust the brake balance so the rear calipers (43mm single piston) received nearly equal brake pressure as the fronts.  Having the rear brakes go into ABS and start skid stop, skid stop would be embarrassing in an expensive supercar.  Proper brake balance is required at lower braking pressures as well as high speed stops.  Therefore an adjustable proportioning valve is also required for the 2001 ABS system once it is upgraded.

Unfortunately the ABS system is not a simple couple short brake lines and fittings job.  The ABS system comes with a larger master cylinder and this one uses "Bubble Flares" instead of inverted flares and a long brake line which goes out of the engine compartment to the ABS computer under the left headlight inside the bumper.  I found the easiest way to add the Prop Valve was to use a small tubing cutter to cut the line just inside of the master cylinder then double flare the line while not touching the ABS line computer end.

After cutting the front line (front of master cylinder is the rear braking system) I removed the master cylinder portion and dut off the excess line with a tubing cutter.  The ABS line uses a stiffer steel than the pre-ABS systems and the line has a plastic coating over it.  I used a drill to remove the metal cutting has squished into the hole of the brake line.  I then used a propane torch to soften the plastic coating on the outside of the brake line for the few inches I was working on flaring the new end.  I scraped and eventually filed the brake line end to remove the plastic and chamfer the end of the line.  I then slid the flare nut over the line and clamped the line into the flaring tool and used the supplied attachment to cause the line to "bubble" the end.  I removed the attachment and used the standard flaring tool to collapse the top of the bubble to the inside of the flare creating the inverted (or double) flare.  The short line was finished after a shot of paint over the clean metal where I'd scraped off the plastic rust coating.


 

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1999 1200rwhp TT GTS - ART, 2001 Roe sc GTS- (4 sale), 440 Duster restomod (sold), 3x Stealth TTs, 92 Daytona IROC with T3, 580whp/1080wtq Cummins pickup.
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Viper Nation - ezine
« Reply #2 on: July 01, 2016, 09:47:56 PM »

Now it was time to flare the car's brake line.  I used a piece of aluminium to protect the wiring  and plastic inner tubs from the propane torch as I drilled, heated and scraped the line.  I again filed the chamfer around the end of the line and clamped it into the flaring tool.  About the only difference from the process I described above was that it was a tight working space.  I used a torx 'wrench' similar to an allen wrench so that I could use the 90 degree end to turn/tighten the flaring tool. 

Once the flare and flare nut was installed I reassembled the brake line, fittings and proportioning valve into the line, then bled the rear system.  I used rags to catch any brake fluid drips and was careful not to allow the brake fluid to touch an painted surfaces.  Brake fluid quickly removes/destroys Auto paint. 

I adjusted the Valve to halfway.  Finished.

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1999 1200rwhp TT GTS - ART, 2001 Roe sc GTS- (4 sale), 440 Duster restomod (sold), 3x Stealth TTs, 92 Daytona IROC with T3, 580whp/1080wtq Cummins pickup.
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