rbender52

92 C4 LT1. Brakes very weak. Can't get ABS to pulse or brakes to lock. Have replaced booster, Baer slotted and cross drilled rotors, Hawk HPS pads, braided steel hoses and new booster. No abs warning lights when driving but abs does not self test. Any thoughts???

ChumpVette

Checked to see if the ABS is getting power?

rbender52

Sounds like a great thought. That could explain why no warning light. Looked in owners manual and couldn't find ABS fuse. Wanted to try checking that. Thanks

fake

Use both feet! Thats why God gave you two!

MatthewMiller

If you can't get the brakes to lock, then ABS isn't the problem. It's not supposed to come into play unless/until the brakes lock. Pull the ABS fuse and verify that you really can't lock the brakes even without ABS connected. If that is the case, you have a very serious and shouldn't drive the car until it's fixed. Assuming you still have pads at all four corners and the calipers aren't stuck, and assuming you have a firm pedal (I'm assuming you'd have told us if the pedal was going to the floor), then I'd start looking at the replacement booster. Here are a few questions that could help in diagnosing:

• Was the car braking like this before you replaced all those parts?
• Why did you replace all those parts?
• What is the pedal like?
• Can you really not lock up the brakes with the ABS disconnected?
• Can you verify that all four brakes are getting some braking force? (Jack one side up and have someone apply the brakes, and check to see if both wheels on that side can be turned by hand; repeat for the other side).

rbender52

This is my first Corvette. I have had it 3 or 4 years now. Before that I always had Euro sports cars. The brakes never measured up to my previous cars but not dangerous either. Before I purchased I even had a friend who drives a '96 LT4 test drive it. his assessment was simply that the brakes weren't as powerful as his. I drove the car for about a year without doing anything to them. It is mostly a weekend car when I wasn't on my motorcycle. I don't drive it as I would on a track so pretty easy on brakes and never tried a full panic stop or real deep braking into corners so no reason to bring the ABS into play. After dealing with several issues that came up due to age I decided I wanted better braking. That's when I replaced the rotors and pads. No noticeable improvement even after bedding in pads according to Hawk instructions. So now braided steel hoses. No improvement. Then the booster failed so I had that replaced. Other than the brakes the car is fully sorted and really nice to drive so I really want to get the brakes squared away. That's when I decided to take it out and try some full on panic stops and found that ABS wouldn't pulsate nor would brakes lock. I have a shop manual and according to that the ABS is OK as all the ABS and ARS lights go on & off when they should. The ARS does work as it should. I gather from my reading, that they are related systems.
* The pedal is firm but feel is wooden
* I am still looking for ABS fuse. The owners manual doesn't list an ABS fuse. Haven't been able to find it's location in shop manual yet.
* I'll try to verify all 4 wheels getting some braking force. It does brake evenly in a straight line with no pulling.
I should note that all work has been done by a very good local shop as I have gotten too old and lazy to do a lot of my own work any more. In fact the service writer, an avid local canyon racer who has an Evo with Baer brakes spent an afternoon driving the car and did not say anything about the brakes. I have gut a feeling that the replacement booster isn't very good but just a guess. It's going in to the shop this week to get sorted out. Now I at least have some direction. Thanks so much for the feedback.

MatthewMiller

Something does sound wrong. C4s actually have pretty good brakes, especially with good pads like you installed. They should easily be able to lock the tires up. As you do some more digging, let us know what you find.

jefnvk

Did you rebuild calipers when you did all that? I would expect a shop to catch if they were corroded or seized and not fully actuating, but that would be my next suspect item.

Are you losing brake fluid at all?

bosshog8

There is only 1 elephant left in the room regarding the brake system. The ABS pump/valve.

rbender52

Thanks for all the advise. I'm certain the front calipers are OK as I personally inspected them. I would think the shop would have caught any problems with the rears. Definitely not losing brake fluid. Sure hope it's not the ABS pump. Don't even want to think what one of those costs. Actually, probably could live without ABS easily. Never really was a big fan. Just practice threshold braking, haha. It's going into the shop Thursday with a mandate to find the problem. Fingers crossed.

MatthewMiller

As I think about it, even if the rears were not working at all, you'd still be able to lock the fronts (which are more prone to lock without the ABS anyway). So if you can't lock them then it's something else. I'm not sure how the ABS pump could cause this without also causing a soft pedal, but maybe there's a way. I don't want to douse the flame of hope here, but I am skeptical that any normal shop is going to have the diagnostic chops to track this problem down and fix it. Before I took it in, I would definitely disable ABS and test out the system.

Also, I'm not a proponent of disabling the ABS. It actually works well on a C4, and I guarantee that you can't outbrake it.

85WHITEZ51

Drawing at straws here. If the system wasn't properly bled after changing the brake lines wouldn't that cause this issue? By properly, I'm talking about the ABS system being bled. If air got in their would it effect normal braking? Always thought normal braking would be about the same but would suffer once you get to the point of locking things up as the air would only then be compressed.

I'm not expert thus why I state I'm drawing at straws here.

cv67

Do you have a way you can measure the pressure at each wheel, that ought to tell you something.

Had a set of J55s that drove me nuts for a long time couldnt get that car to stop right. Tried every method of bleeding, still did it.
Got some speedbleeders from Summit racing, makes it a quick 1 man job. Car stopped like it should.

You say you got a firm pedal so it might rule out air...perhaps not. Keep us posted, Id want to know how much pressure each caliper was seeing first

rbender52

First thing I am going to have them do is flush fluid and BLEED ABS> Pretty simple on '92. I also discovered a couple suspect vacuum lines. I am hoping they can check pressure at each wheel. Then will see what happens when ABS disabled. It concerns me that the ABS doesn't sound like it goes though the 4 MPH self test. I understand you should be able to hear it. Right now the pedal feels good but stops like it ran into a big pile of mashed potatoes.

Red Sleeper

I just went through exactly what you are going through. My pedal was also low.
I replaced the master cylinder also along with everything you changed. I decided my ABS/ASR unit was bad so I blocked it off and removed it. I still had a low brake pedal and very poor braking.
All that is left are the brake lines and wheel cylinders. Brake lines can balloon. My wheel cylinders do not leak and I don't know why they would cause a low pedal but this spring I plan to replace all the cylinders and the brake lines. BTW, my brakes are so weak I cannot even skit on gravel.
One thing I did was block off my new master cylinder to verify it was working properly by plugging the brake line ports and I had full pedal. So, I'm pretty sure the problem are the lines or the wheel cylinders. Good luck to you!!!

rbender52

So frustrating

MatthewMiller

I've never heard a 4mph ABS self-test in my 96, FWIW. And my brakes are just fine. Also, to both the OP and Red Sleeper, even one of four corners was totally disabled due to bad lines or a bad caliper (wheel cylinders are for drum brakes!), the car would still be able to lock up the other three wheels as long as the pedal wasn't going to the floor. I strongly suspect your problem is upstream of where the lines split to go to each individual corner.

Red Sleeper

Yes sir right after you start it up and start to roll it does its ABS self test. Sounds like it's growling at you. It does it forward or reverse. In my case there is nothing up stream except a master cylinder because I removed my ABS module behind the drivers seat. I have bled my brakes about 100 times trying different techniques. I bled the brand new master cylinder on the bench. So this spring when I get it out of storage I plan on replacing the brake lines then if necessary the wheel cylinders. Then if that doesn't do it, I give up.

MatthewMiller

You learn something new every day! I just looked it up in the FSM for my 96 and it confirms what you're saying. I've never heard that in my life, and I know my ABS works and it isn't setting any codes. I'll have to listen closely next time.

Red Sleeper

The 96 is a little bit different animal. Maybe they quieted the growl.