Brake problems on 92 silverado

[WS6]

Ok I know this isn't really the proper forum, but I am hoping I can get some help anyway. 92 Siverado standard cab, 2 wheel drive, 350 V8 high mileage. The truck will bounce when braking and your at 35-45 mph. It does it in this range even if you start above 45 mph and go below 35. I've never seen anything like this. It feels like bad wheel hop honestly. Brakes are new all the way around except the front calipers. They are not leaking either. New shocks all the way around. I thought the old worn out shocks may have been the culprit, but that did nothing. This did not start happening with the new brakes. The brakes were replaced and worked fine and then a few thousand miles later this started happening. Nothing is out of balance and the tires are in good shape. Rear drums and pads don't show any odd wear. My thoughts are towards the master cylinder. It has always felt soft to me but the brakes worked perfectly fine even under hard braking they worked great. I thought maybe Silverados have soft pedals. This isn't my truck and I am not fimiliar with how they are supposed to feel. So I am lost at this point. If you have any ideas for my to test out or any thoughts on what may be the problem I am all ears. Thanks.

*****UPDATE*****
Ok we finally gave up and took the truck into the dealer. The pedal had gotten very soft and would go to the floor with constant pressure. The bouncing was getting worse and happening beyond the 35-45 mph range as well. We tried replacing the master cyclinder and that did nothing. Actually it got worse. The pedal was the same whether a bleed screw was open or not. We firgured there was air trapped in the system some how. I bench bled the MC before putting it on the truck and line bled the system for quite a while. Never made a difference.

So the dealership pressure bled the system and turned the rear drums. No more problems. We will now be purchasing a pressure bleeder. I haven't had any issues with manual bleeding even one person bleeding using a half filed jar with the tube running into it. These methods always worked for me in the past without issue. The drums even though they were brand new needed turning appearently. I wish I had a caliper big enough to measure drums. I didn't notice anything with a visual inspection. I guess I missed something. Anyway it is fixed and now everyone knows the cure incase this crap happens to you.



I still don't see how the pedal became so soft when the bouncing was the first thing to happen. As it continued the pedal became soft. Could the out of round drums have cause the wheel cylinders to push in and out quickly somehow building up air that way?

[ProStreet R/T]

What do you mean "bounce" ? Is the pedal pulsing, or is it actually shaking the truck? Does it feel like a vibration, or is it moving around?


Have you checked the bushings in the front end lately? If it's getting sketchy under braking it could be the front end moving around.

How does it feel at highway speed?

[bobbaganoosh]

I bought a 93 once that was doing that, the front end was shot. After new ball joints, idler/pitman arm, control arm bushings, and tie rod ends it went away. I didn't isolate the particular component that was the culprit because I bought the truck knowing it's condition and that I was going to replace it all anyway.

Aaron

[myclone]

As was mentioned look over the idler/pitman arm. These trucks eat them like tic tacs.....ball joints almost as bad.

Ive had a dozen or so of these trucks from 88 to 97 and worked on a bunch more and it seems to be a hit or miss on the soft pedal deal. Some trucks have it some dont.

Just to give you an idea...and this is just what I remember off the top of my head:

88 FSRCLB 2wd 350/5spd 85k miles=normal brake pedal feel
90 FSRCSB 2wd 305/auto 280+k miles=soft pedal and nothing I did helped.
89 FSRCSB 4wd 305/5spd 140k miles=soft pedal EXACTLY like the above truck.
93 FSECLB 4wd 350/auto 175k miles=normal pedal
94 FSRCSB 2wd 4.3/auto 130k miles=normal pedal

[WS6]

Thanks guys. By bounce I mean bounce. The whole truck bounces as if it has horrible wheel hop. Everything is fine until you hit the brakes and you get in between 35-45mph. You are either driving at that range or you go through it from a higher speed. It starts at 45 and ends at 35 like clock work. I can not tell if it is the front or back. It does feel as if it is the passenger side. Idler arm is on that side. Thanks.

[myclone]

That really sounds like steering parts are on their way out. The last truck I did was the 93 FSECLB that had a worn out drag link. At about 30mph if you were going straight it would start to shake and keep on shaking till about 45-ish. You could stab the brake pedal real hard and it would stop most of the time or yank the steering wheel one way or the other and it would stop (most of the time). IMO at a particular speed one or both of the front wheels are doing the same thing the casters on a shopping cart do when they wobble. Hard to explain in text but it made sense to me once I thought about it a while.

Easiest way to tell is to jack the truck up and sit the front wheels on ramps/blocks so they are supporting the trucks weight. Have a bud turn the steering wheel until he feels resistance then go back the other way until he hits resistance then repeat (engine off BTW). Have him continually work the wheel back and forth while you look over the steering linkage for excessive slop. Id put money on you finding one or more really worn out components.

You wont find bad ball joints this way but I bet you find fragged steering stuff before you get to them anyways.

HTH

[WS6]

Well, we checked the ball joints and the idler according to the service manual and they all showed up as being fine. The truck drives great even when braking the whole truck shakes but the steering wheel doesn't move. So we are lost on this still and the plan now is to take it to another shop and get a second opinion. Besides, I really don't have time to get the work done. Thanks guys I will let y'all know what we figure out.

[Hydratech®]

Your rear drums are setup too tight - back off the rear brake shoe adjustment and it will straighten right up.

Trust me on this!

[WS6]

Interesting. Why would they start doing this thousands of miles after the rear drums and pads were changed though? I would think they would have worn in by now and set themselves. I will give it a try and see what happens. Thanks.

[Hydratech®]

Typically the rear drum brake self adjusters don't work all too well (requiring periodic manual touch up adjustments), though sometimes the brake self adjusters will become too aggressive, especially with drums that have been machined heavily. I'm thinking that the E brake could've also been applied and some point, and that they aren't releasing all the way afterwards per stiff / rusted cables...

On a harsher note, you may be losing an axle shaft bearing, which wreakes havoc on drum to shoe air gaps and contaminates the shoes with sticky goo.

[WS6]

Thanks Paul. We tried backing the rear shoes off a little and that made no difference. We are completely lost at this point. The truck drives fine and steers fine, but with normal braking pressure it bounces from 45 down to 35 mph that's it. The truck does nothing else odd or wrong. Hammer the brakes and the truck stops perfectly fine with no bounce. I dunno

[myclone]

Thanks Paul. We tried backing the rear shoes off a little and that made no difference. We are completely lost at this point. The truck drives fine and steers fine, but with normal braking pressure it bounces from 45 down to 35 mph that's it. The truck does nothing else odd or wrong. Hammer the brakes and the truck stops perfectly fine with no bounce. I dunno

Just out of curiosity have you tried stabbing the brakes really quick and really hard when it shakes? Dont stab them and hold them just stab them and quickly let off like your trying to stomp a rabid bee thats landed on the brake pedal.

I know you say you didnt find anything wrong with the steering gear but what youre describing sounds EXACTLY like what Ive seen on a bunch of these trucks so thats why Im still on the worn steering component soap box.

[mone]

Its the front springs or the rotors on the front are aftermarket too small..I see it all the time with rotors.Compare the size and thickness with some GM rotors and tell us what u see...

[Chad-1stGen]

92 Silverado has anti-lock brakes for the rear brakes only. Possibly somehow malfunctioning and causing this?

[WS6]

Front rotors are the same diameter as the ones that came off the truck. Thickness shouldn't have anything to do with it so long as the thickness isn't too little. The rotors wear overtime naturally. As for the springs in the front rotors, well I have no idea honestly.

Chad are you sure about rear ABS? I have not noticed a reluctor ring or sensor of any sort on the rearend or drums. how would the system work otherwise?

Myclone, I haven't tried that but will next time I get a chance. You may still be right. I just have not been able to find any play or problems in the front end that tell me that's the culprit. The whole suspension is going to be replaced soon enough because of age and not knowing if or when it was ever done before(we're going to lower it then too), but we'd like to solve this problem first before making any changes that could make matters worse. We can't afford money or time wise to throw parts at the truck.

Thanks guys. I do appreciate the input and I will report back as soon as I can about the different findings.

[myclone]

I will report back as soon as I can about the different findings.

Please do as this may turn out to be a diff prob than what Im used to seeing with these trucks. Might save someone else (as well as me) some time and $$$ at a later date.

[WS6]

No problem. Whenever I get stumped like this I always post up the solution if I can find it. I prefer to not do a sweeping parts replacement.

[WS6]

Here's an update on the problem. It must be a brake issue. It is getting worse as far as how hard it bounces and the pedal can now be pushed to the floor. The brakes still work fine, but if you apply brake pressure and continue to hold brake pressure, the pedal will go to the floor. I am thinking the MC must be bad at this point. There are no leaks on the system and I figure a seal must be failing allowing pressure to bleed off. I don't know how it could be the proportioning valve so that's why I think master cylinder. Any ideas? Thanks everyone.

[mone]

new info?Are the rears adjusted right?Also the rear does have ABS...believe it...

[WS6]

no nothing new other than what I posted on the 25th above. We simply have not had time to do anything with it. I finally realized that was the ABS controller right there under the MC. How does ABS work on this vehicle if there are no speed sensors? Could the ABS be applying eventhough we are not braking hard?