pcolt94,

I started a new thread (87 brakes) before you had answered this one. I have new info shown on that thread concerning psi pressures at the front and rear calipers (900 to 1000 psi) when 100 pounds applied to the brake pedal.

My point is that these vehicles were always poor brakers. I have a lot of history with this Vette, and had driven several other C4's back when they came out. None were great brakers then. In my case, I can safely say it had only gotten better when I put on the J55 fronts.

I don't have the figures, but the original 12" 87 caliper was a single piston, and the J55 are 2 piston. Not having the piston diameters (to calculate area), I cannot say if the J55 has the same (or more) effective braking force as the original (for the same pressure input from the master cylinder).

Plasticman

 

I can not believe this thread, I have been following it because of my braking problems that I seem to share with a lot of you guys.

In the meanwhile I have flushed a lot, actually using ATE Super blue racing, installed Speedbleeders ( really great!!), installed Goodridge brake lines that improved pedal feel.
But, yesterday the pedal went all the way down again! I just can not understand what is happening and I do not have a clue anymore on what to do to correct this.

Maybe it will be time to install the vacuum reserve. But I have no more ideas for that more than spongy pedal!

 

Does the ABS cause it to feel someone hits the brake pedal with a hammer briefly when you start moving after starting the car up?

I sometimes get that too when I first hit a speed bump.

With regards to this post, my theory is that the J55 upgrade does not have anything to do with the crappy brakes. I think it is something else. Though, I'm sure it does improve on what is already there.

 

the vacuum revovoir ("vr") will do nothing for you since the pedal is going to the floor. it sounds more like defective seals in the m/c even though you are not/may not be leaking brake fluid. the "vr" is only used in conjunction with a good brake booster. if you have gone all through your system and bled the master, and the caliper s and you have no leaks, the problem lies in the m/c.

 

it is a "growl" of sorts after moving the car that is a "self check" not a hammering effect and that comes in usually about 4mph when you first start up the car. that is usually heard when the abs is actvated during driving/braking. the j55 upgrade doesn't have anything to do with the crappy brakes, it is only a band aide fix for a yet to be discovered pre-existing problem with the stock brakes. i think a few others have covered this earlier in this post.

 

At first thought I would think you would have a bad master. I have seen seals do weird things in the past and have had similar problems in the past. This suggestions not rocket science but is just basic.

The only other suggestion I have is that air is getting in from one of the calipers. But if you say there is no air in the system then forget this. As said, forget about the booster if the pedal goes to the floor.

 

Whenever I would enter a corner at speed and hit the brake pedal, it would be hard at the very top and "rattle" as if my rotors are extremely warped. You could push past that and they would continue to work normally but it was very dangerous. If you ever had to hit the brakes to prevent an accident, that stupid rattling would probably make you crash.

After reading this thread, I pulled my ABS and ASR fuses and the problem went away. My brakes work normal, possibly even better.

 

Where is the ABS fuse? I have an 89 and didn't see it listed in the fuse box.

 

There are two fuse boxes under the hood of my '93 and they are both near the battery. One of the fuses runs horizontally and one vertically. The vertical fuse box (behind the battery near the firewall) contains the ABS fuse.

 

ttt

 

WOW, what a fantastic thread!!

My daily driver vette is an 88 auto coupe. Brake Bias spring, 12 month old M/C, braided lines and recent new pads - EBC Greenstuff. I've had the vette for 5 years. The brakes have always worked, probably only 85% as good as a normal car, but good enough. Pedal has never been spongy. Booster working well.

3 months ago, the master cylinder began leaking and I had it fixed under warranty.(took the brake shop 3 goes to fix it!!)

My weird problem is that recently I have occasionally hit the brakes and the pedal has gone down a long way, like I've lost all my fluid, very scary, I've immediately pumped it once or twice and it's come back up.

I have no idea why this is happening. No fluid loss, reservoirs are filled to the brim.

Could the ABS cause this? if not then is it the M/C letting fluid past the seals on the piston?

It's a big worry not knowing if I'm about to have NO brakes!!

Also - and possibly unrelated to the above problem, Da Mail man - several pages back you described something that has happened to me, it's intermittent, I nearly ran someone over because my brakes just wouldn't stop- it felt like wet brakes. The pedal was not spongy.

I had new EBC Greenstuff pads on and I decided that they need to be warmer to work and also weren't bedded in enough - though they should have been as I had to bed in new rotors with 20 very hard stops - my eyeballs nearly left my body! The EBC pads work really well when hot but I have to drive much harder than I want to, to get and keep them that hot, they're v poor when cold. I'm going to change them.

Any suggestions on my sudden and intermittent loss of pedal very welcome

S'nut

 

Sounds like the master cylinder is leaking internally and allowing fluid to bypass the internal seals. Get the master cylinder replaced, again. Just my 2 cents.

 

i know da mail man but, it seems he got kicked off of the forum for criticizing a vendor and wanting to start a poll on some product so, i don't think you will hear a lot from him. good guy though as he has helped me in the past.

he apparently did find the cause of the brake problem that he had although i am not sure what it is/was but, w/o him to post it here, it has little chance of being disclosed.

i have reviewed your post and will say that the first think you need to do is completely flush and bleed your calipers and master cylinder and use a synthetic brake fluid but NOTHING with silicone in it. if you are by yourself, then, you could possibly get a set of speed bleeders to assist you in the caliper bleeding process.

as far as the m/c goes, disconnect the lines and get a small simple bleeder kit that consists of a couple of plastic lines and a few plastic adapters that screw into the m/c. the lines loop around and go back into the m/c reservoirs that enable you to bleed it while on the car.

when a m/c leaks at the rear seal at the booster, it should be changed out asap as the brake fluid will take out the diaphragm in the booster leaving you with another pain in the a$$ job to do. if the pedal went down a lot further then "normal", it could be a sign of failing internal seals in the m/c even though there is no leak. do the above and get back to me with your results.

 

Thanks for the replies, but this problem iv very intermittent with hundreds of miles between it happening. If it was the master cyclinder, it would be happening all the time, plus the reservoirs are full to the brim and stay that way - no sign of air in the system.

Where does all that fluid go on the very occasional times that the pedal tyravels towards the floor - the only answer I can see is that it goes into the ABS reservoirs - earlier in this thread Mike says So is there anyway to disconnect the ABS without re routing all the brake lines that go to it?

Because this problem is so infrequent it would probably take 6 months of driving to prove it was the ABS.

I'm sorry to hear Damailman is off the forum, I used the forum email contact to him, but no reply - does anyone know how to contact him?

I'd appreciate anyone asking him to contact me, in case he found the solution - we both have 1988's

S'nut

 

ttt

 

 

ttt

 

I'm about to attempt it myself.Looking at it quickly it seems there are two lines going in(front and rear from the mc) and three coming out(two to the front and one to the rear).I'm going to pull the unit out and leaving the pipes where they are using a brake line tee couple up the fronts and a straight joiner for the rears.This way if I hit problems I can just drop it back in.If it works ok I will replumb it more elegantly at a later date.

 

........ttt

 

The brakes on my C4 are non effective just like everybody else's. why?
is the rotor too small? the caliper pistons too big? the booster not big enough? The ABS in the way of the rears acting fast enough with enough pressure?
Nobody knows for sure.
I had a 96 Olds cutlass Supreme with 16 inch wheels. It stopped like there was no tommorrow.
I still have the calipers for it. I measured the rotors, and they are the same size as the corvette. The calipers need a little smoothing of the castings to fit the factory wheels. The brake lines are the same size. I am going to change the master cylinder to the Olds unit, then check on how I can add the rear calipers to the rear of the Corvette. If the car doesn't stop any faster, I will be trying a Hydro-boost to up the pressures. Something has to be the problem,
It can't just be the ABS, because that's just in the rear, and not on all the time.
It has to do with the clamping force and the friction materials.
Even a 5,000 pound cadillac stops better than this "sports" car.