CentralCoaster

Looing for info on the different brake options offered. J55, 12", 13".... were the rears upgraded with the big brake option?

I can't seem to find this info. I need piston and rotor sizes mainly.

Jeffvette

J55 88-96 Dual piston 13.0" x 1.1

JL9 88-94 Dual piston 12.0" x .75 it seems just by going the difference in the caliper throat

All 88-96 cars had the same caliper/rotor Single piston 12.0" x .75" rotor (not sure on the thickness, just going by what I remember being a joke)

84-87 Single piston calipers front and rear. From what I understand smaller rotors as well.

Unsure of the piston sizes, I used to have it written down before I went to the Big Reds trying to figure out fluid displacement.

Corvette Kid

It's always been my understanding that the optional brakes were strictly a front rotor size upgrade, which also takes a caliper with a wider opening. I'm not sure if the piston size in these calipers is different or not. All C4s have 12" rears.

VenkmanP

Some of the info is here:

http://www.superchevyperformance.com.../c4brakes.html

Look at the C5 page also, it has pics of C4 rotors.

VenkmanP

I just measured my rears, since they're conveniently lying on the floor, and they are indeed 12 x 0.75

VenkmanP

Just realized I have a rear piston out also. Don't have calipers here, but it's roughly 9/16"

Z51L9889

I have my brakes torn apart right now also. I'll measure the pistons and post the info later tonight.

CentralCoaster

Thanks guys! I also think there's some specs on brake line pressure w/ 100# force on the pedal. It's in either the dealer specification manual, or the brochure.

HansB

I'm sorry CentralCoaster if I hijacked your thread
Anyone of you gentlemen know the Mastercylinder info aswell? I'm looking for the bore and stroke for a 90/91 brake MC.

Kind regards, Hans B

Z51L9889

J55 front piston size is 1.47" (37mm). The base brake caliper has the same size pistons. Rear piston size also appears to be 1.47", but it's tough to get a good measurement. Just for reference, C5 front piston size is 1.54" (39mm).

VenkmanP

That's odd. I'm pretty sure the JL9 and J55 rears are the same. Never seen different part #s for them.

Here's my rear piston.

CentralCoaster

The stroke is difficult, since there's the primary and secondary piston. I don't know if they have the same amount of travel, the front might have more since the front pistons hold more...

I have the rear stroke, and the bore written down somewhere for my 85.

Z51L9889

You're right -- 88-96 rear brakes are the same for all models.

I don't think that is the primary hydraulic piston -- I believe that is the plunger for the parking brake. I don't have a diagram in front of me, but I think the plunger sits down inside the main hydraulic piston when the parking brake isn't set. I measured under the dust boot right where it meets the caliper body.

VenkmanP

You're right!

I'd never seen a caliper like this one before - now it makes a lot more sense!

VenkmanP

OK, now that I'm looking at the right thing...

Looks like 39mm.

CentralCoaster

How thick are those rear rotors? Seems like the integral parking brake would be a great way to upgrade the rear rotors... since it always involves tossing my drum ebrake.

Z51L9889

Rear rotors on 88-96 are 3/4" thick.

Z51L9889

Thanks for checking the piston by itself. My caliper is still assembled and I estimated the measurement through the dust boot.

VenkmanP

Thanks for pointing out my cluelessness! I thought I had the thing disassembled and the main piston was still in there!

I did think it was a pretty weird looking piston, but hadn't looked closely enough to figure it out. Hopefully I would have noticed my mistake when I went to install the new seals, but who knows.

HansB

Hmm, I haven't taken a C4 MC apart, but since the front calipers has dual pistons and the rear has single (big area differense), I expect that there is a bore differense in the MC between the primary and secondary pistons to compensate for that? However, the stroke should be the same because they are "inline" (or am I wrong here?)

Regards, Hans B