RockyTop
Enthusiast
In the never ending search for better braking on my 1997 GTS I began the journey I now describe to you in hopes that others will not make the mistakes I did. No doubt I should have done more homework than I did and less listening to speculation by tuners and salesmen. First, I began by buying used Alcon 4 piston front calipers and installing Porsche deflectors (a so-so band aid I am still using; not a substitute for real ducting to the calipers - - not the rotors !), braided lines, Motul 600 fluid and various pads ranging from Hawk Blues (rotor eaters), Porterfield R4 (nice pad, but perhaps not as much bite as later compounds tried), Performance Friction 90 compound (nice compromise race pad). The Alcon calipers came at a good price ($1,700) and I had no complaints, except that my front lock-up symptom just got worse. I then had my tech pull the O-ring in the stock combination valve (which he damaged or tossed - - be careful !) thereby disabling it. The result of this was I seemed to get better rear braking with my stock calipers, but not enough for my liking.
I then longed for more rear braking and listened to a reputable tuner who, upon my inquiry whether I could install my stock Brembo-make front calipers on the rear, said they had done it to a bunch of cars and it worked fine. He said I would need modified knuckles for the rear and so I bought them. I also bought an adjustable proportioning valve from the tuner which (only) restricts/proportions the line to the rear calipers. I then paid to have them installed using the old front rotors in back. Unbeknownst to me, this required the removal of my parking brake. Not a big deal, but a bit of a surprise. Low and behold, when my mechanic went to put my rear wheels back on, there was not enough caliper clearance fore my stock 17 inch wheels. I guess the tuner had never done this on a car with 17 inch wheels (a fact he later admitted).
I was but two days from my next track day and John Purner came to my rescue machining some 1/2" wheel spacers ($25.00) for me and overnighting them to me. Of course no sooner do we get the spacers and try them out (great fit and finish as usual from Mr. Purner !), but my mechanic informs me that me studs are too short. I call the tuner to complain. He scrambles around and supposedly sent me a set of studs that will work, but we'll never know as they never arrived. I was then unable after a literally nationwide search to find studs with the exact knurl size as the Viper requires. It is not a common size.
Nevertheless, I go to Barnett Performance here in Atlanta and get a bunch of 3" Moroso studs with a slightly larger knurl size and my mechanic hogs out the hubs slightly an presses them in. They are of course too long to permit my center caps to be put back on so each has top be cut at its end appx. 1/4-1/2 inch.
Finally, I have the hubs, studs, spacers, calipers rotors etc. on the car and go to drive it home. I test the brakes and experience rear wheel lock up first. F _ _ K ! I then cajole my spouse and 3 kids out to a nearby parking lot to make sure it's the rears locking first, it is (and I have now flat spotted my old MXX3s). Moreover, I am getting right rear lockup only - - a symptom I conclude is due to slight corner weight differences (my car was corner weighted about 9 months ago - -does this ever change by itself I wonder ?).
I call the tuner again and describe my problem and speak to his chief mechanic who informs me it's the lack of the O-ring and that when re-installed that the combination of the stock prop valve and the adjustable valve will do the trick. I scramble around contacting variious folk and a VCA member who happened to have his form his car (which he had sold) overnighted it to me. God I love the VCA ! I have mechainic install the O-ring and bleed iout the system. Guess what. Rear lock-up first !
I then call the unnamed tuner back and speak to his chief mechanic and he tells me I probably have too much rear brake force and may need 6 piston fronts. No sh _t Sherlock, but why didn't this all get discussed at the outset ?!! Moreover, there's no way in heck that (i) I am going to spend that kind of $, and (ii) I sure as heck am not gonna buy them from the unnamed tuner when I do ! However, I have not yet begun to fight. He goes on to suggest that I try street pads in the rear. I buy a slightly used set ($100) from Sean Roe (who once again comes through in the clutch for me though he's very skeptical it's gonna work). Sean suggests I might also try a more aggressive compound in front like the PFC 01 compound. I call and speak with a PFC rep and he concurs it should help, but he's skeptical in light of the comparable piston diameters I now have in the front (1 7/8" and 1 3/4") compared to the rears (1.65" and 1.5"). He was very helpful though.
I have the pads installed and try my braking test again. D_ _ n! I am still getting rear lock-up first. I call the unnamed tuner again and speak to his chief mechanic who suggests that I chip off 1/2" on each end of each of the rear brake pads thus reducing area. GTS Dean is very skeptical (and to this day has not said I told you so - thanks Dean). You guessed it, it didn't solve my problem. The guy at PFC says it won't since it's a force thing more that a surface area thing. All I probably did was increase the heat on the remaining pad surface.
It's time once again for a day at RoadAtlanta. This time I experienced way more pedal travel due to the larger capacity of the rear calipers. Heel-toe is a thing of the past no matter what in the hard braking zones due to pedal travel. I then buy a bigger master cylinder from Sean Roe and got that fixed fine ! Nice high hard pedal with good modulation ability. The prop valve has been dialed all the way out (to the least amount of line pressure) since the day I brought it home. It might serve as a better paper weight !
As I had boiled brand new Motul 600 the last two times I was out at VIR and RoadAtlanta, I tried the AP 600 fluid at Dean's suggestion. Great stuff ! I won't go back to Motul - which wasn't bad, but the AP is better.
SO, WHAT HAVE I LEARNED ? 1. Let the guys like Roe, Stop Tech, Brembo etc. do your research unless you have more patience than I do. 2. The PFC 01 compound is excellent ! 3. AP 600 is great fluid (but flush out all the old stuff before you change). 4. Don't be afraid of math. Comparing my total piston sizes front to rear I have about a 53.5% to 46.5% front to rear bias. It's not way off with my pad compound band aids, but I still get rear first lock up and flat spotted the heck out of my nearly trashed rear Hoosiers last time out - great James Bond smoke screen coming into 10A at RoadAtlanta though ! It's harder to feel the rears lock up because you do not get the nose-dive visual cue like when the fronts do it. Don't worry, I did all my hard braking in a straight line and still nearly got into two Porsches (I hate them for their brakes) ! 5. I am now left with the choice of going back to the ****** stock rear calipers (or something slightly larger - more $) or going to 6 piston front calipers (way more $). I have concluded to go back to stock in the rear and repull the O-ring. UNCLE !!
I then longed for more rear braking and listened to a reputable tuner who, upon my inquiry whether I could install my stock Brembo-make front calipers on the rear, said they had done it to a bunch of cars and it worked fine. He said I would need modified knuckles for the rear and so I bought them. I also bought an adjustable proportioning valve from the tuner which (only) restricts/proportions the line to the rear calipers. I then paid to have them installed using the old front rotors in back. Unbeknownst to me, this required the removal of my parking brake. Not a big deal, but a bit of a surprise. Low and behold, when my mechanic went to put my rear wheels back on, there was not enough caliper clearance fore my stock 17 inch wheels. I guess the tuner had never done this on a car with 17 inch wheels (a fact he later admitted).
I was but two days from my next track day and John Purner came to my rescue machining some 1/2" wheel spacers ($25.00) for me and overnighting them to me. Of course no sooner do we get the spacers and try them out (great fit and finish as usual from Mr. Purner !), but my mechanic informs me that me studs are too short. I call the tuner to complain. He scrambles around and supposedly sent me a set of studs that will work, but we'll never know as they never arrived. I was then unable after a literally nationwide search to find studs with the exact knurl size as the Viper requires. It is not a common size.
Nevertheless, I go to Barnett Performance here in Atlanta and get a bunch of 3" Moroso studs with a slightly larger knurl size and my mechanic hogs out the hubs slightly an presses them in. They are of course too long to permit my center caps to be put back on so each has top be cut at its end appx. 1/4-1/2 inch.
Finally, I have the hubs, studs, spacers, calipers rotors etc. on the car and go to drive it home. I test the brakes and experience rear wheel lock up first. F _ _ K ! I then cajole my spouse and 3 kids out to a nearby parking lot to make sure it's the rears locking first, it is (and I have now flat spotted my old MXX3s). Moreover, I am getting right rear lockup only - - a symptom I conclude is due to slight corner weight differences (my car was corner weighted about 9 months ago - -does this ever change by itself I wonder ?).
I call the tuner again and describe my problem and speak to his chief mechanic who informs me it's the lack of the O-ring and that when re-installed that the combination of the stock prop valve and the adjustable valve will do the trick. I scramble around contacting variious folk and a VCA member who happened to have his form his car (which he had sold) overnighted it to me. God I love the VCA ! I have mechainic install the O-ring and bleed iout the system. Guess what. Rear lock-up first !
I then call the unnamed tuner back and speak to his chief mechanic and he tells me I probably have too much rear brake force and may need 6 piston fronts. No sh _t Sherlock, but why didn't this all get discussed at the outset ?!! Moreover, there's no way in heck that (i) I am going to spend that kind of $, and (ii) I sure as heck am not gonna buy them from the unnamed tuner when I do ! However, I have not yet begun to fight. He goes on to suggest that I try street pads in the rear. I buy a slightly used set ($100) from Sean Roe (who once again comes through in the clutch for me though he's very skeptical it's gonna work). Sean suggests I might also try a more aggressive compound in front like the PFC 01 compound. I call and speak with a PFC rep and he concurs it should help, but he's skeptical in light of the comparable piston diameters I now have in the front (1 7/8" and 1 3/4") compared to the rears (1.65" and 1.5"). He was very helpful though.
I have the pads installed and try my braking test again. D_ _ n! I am still getting rear lock-up first. I call the unnamed tuner again and speak to his chief mechanic who suggests that I chip off 1/2" on each end of each of the rear brake pads thus reducing area. GTS Dean is very skeptical (and to this day has not said I told you so - thanks Dean). You guessed it, it didn't solve my problem. The guy at PFC says it won't since it's a force thing more that a surface area thing. All I probably did was increase the heat on the remaining pad surface.
It's time once again for a day at RoadAtlanta. This time I experienced way more pedal travel due to the larger capacity of the rear calipers. Heel-toe is a thing of the past no matter what in the hard braking zones due to pedal travel. I then buy a bigger master cylinder from Sean Roe and got that fixed fine ! Nice high hard pedal with good modulation ability. The prop valve has been dialed all the way out (to the least amount of line pressure) since the day I brought it home. It might serve as a better paper weight !
As I had boiled brand new Motul 600 the last two times I was out at VIR and RoadAtlanta, I tried the AP 600 fluid at Dean's suggestion. Great stuff ! I won't go back to Motul - which wasn't bad, but the AP is better.
SO, WHAT HAVE I LEARNED ? 1. Let the guys like Roe, Stop Tech, Brembo etc. do your research unless you have more patience than I do. 2. The PFC 01 compound is excellent ! 3. AP 600 is great fluid (but flush out all the old stuff before you change). 4. Don't be afraid of math. Comparing my total piston sizes front to rear I have about a 53.5% to 46.5% front to rear bias. It's not way off with my pad compound band aids, but I still get rear first lock up and flat spotted the heck out of my nearly trashed rear Hoosiers last time out - great James Bond smoke screen coming into 10A at RoadAtlanta though ! It's harder to feel the rears lock up because you do not get the nose-dive visual cue like when the fronts do it. Don't worry, I did all my hard braking in a straight line and still nearly got into two Porsches (I hate them for their brakes) ! 5. I am now left with the choice of going back to the ****** stock rear calipers (or something slightly larger - more $) or going to 6 piston front calipers (way more $). I have concluded to go back to stock in the rear and repull the O-ring. UNCLE !!
