Different caliper and brackets. I rebuilt a set of used calipers and it used the same kit as standard from memory at least so I think piston sizes are the same too. I also have stainless lines DRM bias spring flushed the fluid with th brake fluid the FSM speced and do not remember what it was to be honest DOT4 I think as it was common and backwards compatilble with everything else. Checked the booster and it passed all the FSM checks and the pedal feels right. It is due for an oil change at my local dealer and will have him check and reset codes that are beyond the ones I can get. I was hoping for at least to set off the ABS with better pads etc..

 

No, it's not a night and day difference.

The JL9 12" brake system works very similar to the J55 13" brakes on a stock street driven C4 Vette, I've had both.

It's only during very hard continuous braking (when racing) that the 12" brake system will begin to fade and the 13" brake system will perform better because of the larger and thicker calipers and rotors.

I could easily activate the ABS with either the 12" or 13" brake systems.

 

I think C4s just have sucky brakes. My '84 had new slotted / drilled rotors, calipers and really premium pads and it still had a hard time stopping. This '92 has new pads, rotors and calipers and has a hard time stopping. But, my C5 could stop on a dime.

 

Well, I can't comment on the J55, but the C5 with the larger pistons and brakepads is a huge difference, so if the J55 is similar to the JL9, then upgrading to the J55 is a waste of time.

 

ran my car down to the shop today, and i got a clean bill of health on the brakes and ABS system (no codes, and the ABS does engage). so i guess it's as good as it's going to get... next off to the shop to get some minor paint touch-up done on the front bumper cover. i'm pretty much done with everything i've wanted to do to the 90 - just waiting for my new timing light (w/built in digital tach) - going to double check the timing, and check the idle speed. i'm thinking my idle speed is a little high - showing about 700 on the instrument panel, but i can't rely on the IP accuracy.

 

My 91 goes into the shop this week for an oil change and check for chassis noises located in a different post. While it is there I think I want to have them pull the ABS codes that can not be seen from the other easy ways to check codes. Does anyone know and want to share exactly what they need to do this? It is a Pontiac dealer as they seem to more on top of things and the service manager made comment the guys really hate to work on Corvettes and the service manager at the Pontiac dealer is a gearhead old enough to actually get it so to speak and the mechanics there as well.

 

Hello Gents,

I’ve seen many a post about C4 brakes being sucky over the years! I’ve got an ’89 6-sd w/ J55’s and PFZ pads. Day to day driving my C4 requires more pedal effort than my other vehicles, I suspect this is due to the bore size of the OEM master cylinder. Once heated to optimal temps these brakes have shocked/scared people with near 100% forward passenger weight transfer! When up to temp, I can suspend people in their safety belt on soft compound street tires!

Years ago I had a fellow Forum member’s Ex-wife in my C4 on the track, was only doing about 7/10th to make it uneventful. Within the first lap she was screaming, when she got out after three laps, she was a greenish/white color & her legs were slapping together at the knees! This was mainly due to the constant late corner/ABS threshold braking style.

Based on my ’89, I think that one of three conditions exist for all these C4 poor brake comments.
1. Owners have low coefficient of friction pads installed.
2. The system has air in the ABS unit somehow; I’ve read that once this happens, it’s a b1tch to bleed it out.
3. People are too used to modern production car brakes, which exhibit low pedal effort, and are design to be very forgiving. They are just not used to mashing their foot into the brake that hard. Mash that thing like you hate it, pretend your tying to crush an empty beer can, you’ll engage the ABS!


Warning: the following contains a little story about cheap Pads!!!

Back in the mid ’90’s I cheap’ed out on the pads on my Iroc because I was using it as a commuter. Went from PFZ’s to mid-line Raybestos (tried the brute-stop pads once, eat up a set of rotors on <10K miles on the street). The sh1tty mid-line Raybestos severely let me down at the worst moment! It was on very familiar Hwy off ramp, 270 degree high bank tight twister in Sunnyvale CA, going in around 80MPH. Going in late braking, these pads just started to produce the mother of all pad out-gassing (yes they were broken in & thermally cycled), the friction went negative and the Iroc did an awesome attempt of outdoing the General Lee at about mid-apex off the ramp! It shot out about 35’ in the air, landed drivers-side nose down at about +/-45degrees.

That one hurt a little!:o