Fastmax32168

When I bought my 94 vert I really felt the brakes were pretty crappy for a sports car. They just required way too much pressure to stop the car. I figured crappy pads, old lines, fluid etc. So last fall my rears wore out, and my fronts were down about 1/2 way so I decided to do the J55upgrade while replacing the pads.
I put in all new rotors, calipers, stainless lines, and ceramic pads. Upgraded the fronts to the HD. Flushed out all the lines and bled everything up. To my surprise the brakes werent any different than they were before other than they didnt dust my wheels up like crazy. They still sucked. Had pretty good initial bite and worked OK just driving around but if you stepped on them hard it felt like they lost boost and required both feet to get anything to happen. I nearly rear-ended more than one person in traffic.
So I figure this booster must be bad. I used my mity-vac to try and get it to hold vacum and it wouldnt. Voila! must be the problem. I was a bit confused as to why it didnt appear to have any vacum leak at idle or hissing however.
Ok order a metal booster from hot rod USA and let it sit around for a month or two until I can get a round tuit.
So today I put in the booster. Well now the brakes really suck. Worse than ever. Requires two feet to stop the car.
Now....the website said the rod needed to be lengthened to work on a 94. But....when I put the old and new boosters up against each other the rod appeared to be EXACTLY the same length. So I put it in. However....now that it is in the pedal doesnt return all the way and shut off the brake lights.
So.....I need to take it back apart and lengthen the rod but I dont see how that will have any effect on making it work any better. The rod is at its full travel out of the booster now, and the pedal has plenty of travel to fully activate the brakes. All it appears to me that all this will do is change the position of the pedal about 1/4" and make the brake lights go off. Which I could probably do by adjusting the switches.
Am I missing something? Is there somewhere to screw up on the install? Could the rod being shorter actually cause this problem? About the only thing I havent replaced in the system is the MC.
They dont feel mushy or like they have air in them. Matter of fact there is hardly any play in the pedal before you have brakes. They just require a gorrilla leg to get the car to stop at all.
Suggestions?
Roy

Race Prepared

Sounds like a bad master cylinder...when you replace it, install the brake bias spring sold by Ecklers or Mid-America. Why the master cylinder? When you are standing on the brake pedal - ABS is not popping off...no brake fluid going down stream of the master cylinder.

Not sure of the aftermarket booster - no experience with them.

Fastmax32168

I guarantee my new type of ABS (Antistop Brake System) is working fine.
Roy

Aardwolf

Just a thought, could any of the line be crushed? If I remember right, they run pretty close to the jacking location on the drivers side.

CentralCoaster

Yes, the pushrod is important. It moves the diaphram which turns on the vacuum boost.

You have to adjust it when it's hooked up to the brake pedal. Measure the depth of the m/c piston and adjust the pushrod to match. You should feel the free play in the pedal with the car off, there needs to be a little bit.


It seems the 88-96 are just way underboosted, or the pistons are undersized, you never see any complaints about bite on the smaller 84-87 brakes. Where does the vacuum port hook up to on the LT1? BTW, ceramic pads won't get you more grip than the stock pads.

Fastmax32168

Well coasters suggestion seemed like a good one so I screwed around with the adjustment today. It doesnt make any difference regardless of where I set it. This sucks.
Roy

pcolt94

My 94 had poor brakes when I first got it, and changed everything expect booster but no real change. Not until I installed the J55s and got a huge increase in brake performance and then felt like I was at the point I was trying to obtain. There should have been a noticeable difference when you went to the J55s.


Here is a procedure to help you adjust the actuator rod:
Check the length of the rod. It should be approximately just below the imaginary surface line of the booster. It needs approximately 1/8 inch of clearance to the master due to heat expansion of the parts.

When adjusting the rod end bolt, the rod has to be held and the nut turned, in to shorten. I clamp the rod with thin vice grips VERY LIGHTLY and adjust nut. Depress the brake pedal half way down to get the rod out in the open so it can be worked on easily.

Jack the front up before you start. Then unbolt the master and make adjustments. After adjusting (if necessary) the rod, re-check brake pedal and wheel rotation for dragging. Might take a few tries


You should get a high-hard pedal (no more than 1" of travel) with no sinking with engine off. This would indicte your master is probably good. With engine on, you should be able to press the pedal about 2 1/4 inches of travel pressing hard with your foot. If you don’t get that travel, the booster might be bad regardless if it is new. Try putting the original back in to see if you eliminate the new problems. Also, check the check valve to see if is OK, hose to it, and vacuum pressure.

If the ABS pump had a clog or you had a crushed line, I would think it would effect one wheel and there would be noticeable pulling.

You do need to do the bias spring eventually but at this time it is not your problem, you need to get the brakes working correctly first. And when you do with the J55s, you will notice the front end diving down when braking hard, the spring will help eliminate that.

All in all, if you have got the lines bleed well, you may just have a defective booster.
Good luck

CentralCoaster

The booster pushrod adjustment probably won't be your cure-all, but it should be done regardless.

Nobody's come up with a good explanation on why the later C4 brakes have such a terrible reputation. Some claim they work great, so it's not across the board. If there was an easy answer, you'd know it by now.

Da Mail Man

.......let's hear it for "fred flintstone" brakes! ..mine still suck!

SunCr

No problems with my '89, though the Booster bit it under warranty. Slam 'em on I get ABS and it stops faster than anything else I've ever owned - with or without ABS. As with any "safety" problem, check Bulletins - though I don't remember any for the brakes.

Da Mail Man

.....mine are the worst in any car i ever owned and i have been through the entire system..i keep getting dark brake fluid but, the brakes are not hanging or locking up, no damaged lines, no overheating (to my knowlege)....multiple flushes (dot-3), flex lines changed out, external vac applied to the booster and is holding, new pads and rotors (rotors 2 weeks ago - general mait.)....the only think i have not messed with is the abs.....

SunCr

Well, I don't want to admit it - but my fluid is what came with it. ABS, is flow through; ie, fluid is going through it all the time and the valves only get to working when the sensors send a lockup signal. My guess is that you're not buying/using the right pads, though maybe there is a restriction in the ABS unit. Supposedly, when you bleed the brakes, you bleed the ABS. I've stuck with Raybestos or whatever was on the Discounter's shelf and I did ditch some socalled "Heavy Duty" pads after a couple of hundred miles because they were just friggin' noisy. I've really only had to swap the pads once and if I did it again (I've got 59,000 miles), I'd use Ceramics. I tried them on a '95 Gran Prix I use to own and they were an improvement (and it wasn't bad to begin with), though the rotors only lasted about 12,000 miles.

Da Mail Man

..i hate you! (kidding - grin)....the system bleeds fine and i spent all afternoon on web sites reading about the bleeding issues...i did everything right acording to what i have read...i never did bleed the abs because teh sites don't seem to indicate that.....i get a good strong stream from each line/caliper bleeder each time.....i have a spare set of calipers for my car and since i have to flush the system anyway, i may put 'em on to see what i get.....

cv67

Strange...didthe same thing yesterday- GOt a strong stream through the rear brakes yet pedal feel didnt improve much. Stream in front was very weak yet improved pedal feel. Go figure.

Also curious about bleeding the ABS.

Da Mail Man

i was on a site that ws very detailed and i thought that i sent a link to myself but, i guess not..will look for it tomorrow and send it to you.....at any rate, i have a great stream through both teh f+r and teh brakes are still fred flintstone and can't figure out why......my bedal is a bit firm but, booster shows no vac leaks....

SunCr

As I remember the Gospel according to GM, it says the ABS unit is bled through normal bleeding; ie, it doesn't need to be bled separately. I'm not so sure at this late date I'd accomplish anything - other than mucking up a line - by trying to bleed it separately. Think if I ever get around to flushing anything, I'll leave it alone - or wait until it just doesn't work and hope a boneyard has something half way decent. I do think some around here have deleted it - not because they wanted to, there just weren't any parts.

cv67

I have never heard the 90 do a self check..Was just told to get up to a hundred or so, lean on the brakes and try to activate the ABS. Then go bleed it.
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