How to rebuild and improve stock rear brakes

[Tom F&L GoR]

The Dodge Viper service manual claims these calipers are not serviceable. Because I'm stubborn, I learned they are. Thanks to Keith Verges and TrueChoice, I now also have the rebuild parts and have come up with directions on not only how to rebuild these calipers, but how to use them to improve your brake balance. It's a 2Mb Word file, lots of pictures, hopefully complete. Please let me know if you have questions or comments.

The non-ABS Viper rear caliper is criticized as being too small. One brake manufacturer reduces the piston sizes in the front calipers in an effort to provide better front to rear brake balance. Using that ratio of front to rear piston area as a target, the same ratio can be achieved by using stock front calipers and increasing the rear caliper size from the standard 36-mm to 38-mm diameter.

Custom Machining in Newburgh, NY (845 562 0880) can modify stock calipers to accept a 38 mm piston and sleeves the stock piston up to 38 mm. They charged me $500/pair to do two pair; although that included making fixtures and jigs, so future conversions should cost less.

This modification appears completely stock on the outside, retains the use of stock brake pads, stock brake lines, requires no modifications to the upright. If you do all the work yourself and use your existing calipers, it's just the machining costs plus rubber parts. If you buy replacement calipers, add another $200 (RockAuto.com and look for 90-92 Monaco calipers.) If you add labor, this project may cost more than buying the smaller piston front caliper, since R&R for rear calipers is longer due to the parking brake, and add in the time to disassemble and reassemble the calipers.

The non-ABS Viper rear caliper with integral parking brake is also used for the rear caliper of the 1990-92 Eagle Premier and Dodge Monaco. The rebuild kit for these calipers is available from AutoSpecialities (a division of TRW) as KC-83017 for about $6. Each kit does one caliper.

For the larger piston, you will need a Brembo 38 mm seal 20.4872.45 available from Truechoice (1-800 388-8783) The conversion to 38 mm pistons still allow the use of all the other standard size parts that come in the KC-83017 kit. A parking brake shaft O-ring is PN 05-595557 also available from Truechoice.

I am not a brake expert, but I did put the modified calipers on my car. It helps a lot, especially in the wet, although eventually the fronts still will lock up first. Pedal travel is slightly longer, although pleasantly so. I'll be at Pocono with the PDA on July 20 if anyone wants to see them.

I will be happy to send anyone the directions. They'll show you how to do a normal rebuild or the larger piston conversion.

 

[Tom F&L GoR]

Dean,
I had previously removed the O-ring, also had changed to the newer power brake booster. You've got mail...

 

[Bill B]

Tom, I'd love to see those instructions.
You could email them to [email protected]
Thanks.

 

[onerareviper]

Tom,

Can you PLEASE mail me all the details. I am still 100% stock in my 1998 GTS, therefore the braking could be waaaayyyyy better. Brake bias is horrible. I TOTALLY agree with your logic about increasing the size of the rear caliper. Thank you for such persistence...

THANKS A MILLION!!!

P.S. - Just received your info. Looks real promising.

 

[FrankBarba]

i am also interested in this information. Just 4 months ago when i was re working my rear brakes i was told by a reputable person that visits this board that rebuilding the rears could not be done. where were u then? Please help.

 

[RoyV101621]

here to Please

 

[GTS Dean]

Tom,

I really appreciate your dogged determination and effort. I'm quite interested in the mod.

The longer pedal is proportional to the additional fluid volume moved against the bigger rear pistons. Did you keep the spring/o-ring in the proportioning valve or had you previously removed them?

 

[GTS Dean]

Outstanding, and I do mean outstanding illustrated technical report, Tom!

 

[JonB]

F&LGoR.....and now RBCs too !

Thanks, Tom: VIPER PIONEER Award.


"The difference between a Pioneer and a Settler is,

Pioneers get arrows in the chest....

Settlers get arrows in the butt."

 

[John Moore]

Very fine piece of work Tom. Thanks a bunch!

 

[99 R/T 10]

Hey Tom,
think I can get that email? If for some reason it does not go through to my hotmail account, try [email protected], Thanks.

Mike

 

[KepRght]

Tom, i could host the directions for you... drop me a message if your interested

 

[Bob Woodhouse]

Thanks again Tom. I am late seeing your post. I can add a couple of alternatives as well.
The rear brake caliper is 36MM on cars up to 99. No need to do the machine shop thing if you want to bolt on some 2000 to 2002 rear calipers. They are 38MM. Yeah I know, sounds easy, it just basically does the same as what Tom did, I remember we priced going this way and it was slightly more.
When Tom gets some track time he will get on here and post his impressions I hope. Tom you need to. I suspicion you are not done tinkering. The pedal travel might become an issue on a hot set of brakes. What may happen when fluid gets hot and compressable, you can find the botttom of that master cylinder. Gets thrilling. Just have to hear what you think.
One solution: the master cylinder on the 2000 and up Gen II is approx 1.5" diameter and all earlier Vipers are 1.1". They swap if you don't mind moving a brake line. This will give you back a rock hard pedal. The change in master cylinder volume, for those of you that do your math; is huge, like 50% or so. There is a difference in boosters also but I don't know what. Suspect you will end up using the newer booster.
One more thing. If any of you have compared the brake pedal feel of the 99's and back vs the 00's and forward you will find a big difference in pedal effort. My opinion is that the plant got tired of hearing about flat spotted tires and raised the pedal effort. The ideal master cyl bore is probably under the 1.5" on this caliper set up. I know people that can do the real math. If we need them, E me.

 

[Big Medicine]

Is this the solution to the brakes? I'm researching archives & all I can find are debates. I'm stuck on the fact that if I can lock 'em up at 70 mph with stock rigs, installing new brakes on the front can't help. (e.g very pregnant & more dead) It's a threshold thing, right?. So I need to look for help elsewhere, like the only other contact patches available....the rears.....w/o overbiasing. I need help.

 

[Tom F&L GoR]

Howdy.

My searching found that the rear caliper of the ABS cars was a 43mm piston, not 38mm? Also, it's completely different, not the old caliper made larger. There's an additional bracket for the brake pads, it's taller, and the banjo fitting for the brake hose hits the inside of a 17" wheel. I bought a caliper to try this, there's no way around the interference, and the bracket or knuckle would need lots of work to mate with the Gen 1 system.

Track experience was really good. With a 40mm rear caliper set, no prop valve seal, no aftermarket prop valve, Valvoline brake fluid, Brakeman#3 in front, Porterfield R4 in rear, no cooling ducts, and Gen 2 pre-ABS booster, I had good balance front to rear at Lime Rock. I could feel the uneveness of the track as each corner would slightly bite more or less depending on the surface - a wiggly feeling depending on which wheel was grabbing more, but comfortable in that it was me causing it. No fade, no long pedal (until the rear pads wore to the backing plate. Replaced them and was back to normal.) Best of all, under braking with the clutch engaged, the fronts will lock first-barely, and with the clutch pedal depressed, the rears lock first, by a noticeable margin.

Pedal travel was barely perceptibly longer when I first installed the calipers, and I honestly didn't think the newer brake booster was worth it; it was free, so for the 20 minutes it took to replace it, no big deal, but I would say to go out and do it.

The added piston area represents a 23% increase in the rear caliper, but it's only a 4% in the overall system, so the brake pedal travel shouldn't be more than 4% longer (I think that's how it would work.)

The ABS cars with the rear 43mm single pistons still use the same front calipers. I assume this system is balanced because while it seems more rear brake than needed, the ABS takes over to keep everything balanced.

StopTech's front calipers use smaller pistons, so they approach things similarly. In fact, the 38mm rear single piston math comes out the same front to rear piston area ration as the StopTech front + stock rear caliper.

I've had mine on the car in track use, autocross, wet weather, dry roads... and while there are a few times that a rear will lock, it doesn't bother me. I believe (and I'm not an expert) that the 38mm rear and rear pressure limiting valve disabled is a goof-proof improvement; the 40mm rear probably needs an aftermarket proportioning valve added to be also goof-proof.

 

[ElDiablo Viper]

I installed StopTech big kit on the front and I'm very happy with it.

 

[NCVCA]

Big Medicine...

I would start by removing the proportioning valve or the proportioning spring. I removed the valve on my 2000 GTS and it made a noticeable improvement.

 

[Nadine UK GTS]

I've been modifying a couple of sets of rear calipers (with Toms help) and now have 'OE' 40 mm rear calipers on my '97 Coupe. It was an interesting project to do once I really got into it especially with a resent research article Tom found in piston seal design. The breaking is very much stronger, and I felt it easier to now modulate the pedal on the point of lock up than before. There is no real notable travel in the pedal than before. If breaking to the point of lock up, I too found the rears will easily lock up first with the clutch in. Without clutch in, I've found it feels like both front and rear lock together! I still have my spring in, and I'm thinking about fitting an adjustable proportioning valve now. Only been able to try them fast road driving so far, but I can't wait to try them on a track. I'm also wondering what they'd be like in the wet, which I will soon find out given the UK climate. Although hard breaking in a Viper in the wet I've always found to be 'hairy'! I'm also hoping to see how they compare in actual stopping distances to a Viper with the big Stoptech step up. After some hard breaking I checked the rotor temperatures at the same point after the caliper with a laser gauge, and all 4 wheels were with in 3 degrees C of each other, impressive I thought. Many, many thanks to Tom for bringing this mod to us, and for all the help you've given me with mine. Well worth doing.