Brake Problems on my 98 Z71

Recently I replaced the front and rear brake on my '98 Z71 1/2 ton 4wd. For a while I thought that I hadn't gotten the rear brakes adjusted out far enough before putting the drums back on. It just felt like the rear brakes just weren't grabbing. I also noticed that my ABS was acting like I was sliding around on ice. It would make that horrible noise and the peddle would pulsate and the peddle seems a little spongy.

I talked to a guy at Tires Plus today and told them what I had been experiencing. He said that they had had a GM truck that they ended up sending down to the dealership because of the same problems. They were unable to figure out the problem. The owner stopped back in and told them that it was something to do with the ABS computer and the valves/pistons in the calipers getting stuck when the guy compressed the pistons. They said it had been too fast and screwed things up. He told me to take it to the dealer to have them reset the ABS computer and things should be back to normal.

Does any of this make any sense to anyone here?

I would really like to get this problem solved because when I have to brake hard, the ABS kicks in and the truck doesn't stop for crap. A lot of the time if I just press on the peddle lightly, the ABS crap kicks in with that noise and the pulsating. My brakes just don't work worth a damn. What can I do to get this problem solved??? Anyone?

It sounds like a wheel speed sensor signal is dropping out at low speeds.
The best way to figure out which one is to drive the truck with a bi directional scanner attached and watch the WSS signal.
Why did you take your truck to a tire store for a brake problem...that is like going to KFC and asking for a BIG MAC.
They gave you some good advice..go to your local GM dealer and let them DIAGNOSE the problem...do not ask them to reset the computer, this wont fix the problem

It sounds like a wheel speed sensor signal is dropping out at low speeds.
The best way to figure out which one is to drive the truck with a bi directional scanner attached and watch the WSS signal.

Well, the dealership diagnosed just as you thought they would. The left front sensor is dropping out at low speeds. They quoted me about $550.00 to fix it. :screwy: I took it to another local shop and told them what the dealership said was wrong. They said that they'd like to look at it before they would actually replace the wheel speed sensor. They thought they could just clean it and it would be okay. He asked, "When was the last time they [wheel speed sensors] were cleaned?" Well, since I bought this truck last spring, I have no clue if they've ever been cleaned. I don't even know if it's possible.

At any rate, the truck goes in to the shop on Wednesday for them to look at, and possibly replace, the left front sensor. They wanted $177.00 for the sensor and $67 to put it in. That would be over $300.00 savings over the dealership.

Why did you take your truck to a tire store for a brake problem...that is like going to KFC and asking for a BIG MAC.


Tires Plus is a 'full service' service center. They do all repairs, not just tires. Besides, I know one of the guys at that shop and I know he wouldn't steer me in the wrong direction so I'd get screwed.

As for KFC and the Big Mac, they don't find it all that amusing when you pull into KFC's drive-thru and order a big mac and fries... I should know, I've tried it once. They fail to find the humor in it. :grinyes:

Recently I replaced the front and rear brake on my '98 Z71 1/2 ton 4wd.

I wouldn't doubt the existence of a wheel speed sensor problem, but as a Delphi employee that's looked at ABS warranty, I've seen more problems with the WSS wiring than the sensors themselves. Wheel speed sensor wiring is by far the largest problem on ABS systems, and electrical interference due to careless wire routing can wreak havoc on the wss signals. However, it may have nothing to do with your current problem or may only be a minor factor.

You failed to mention the type of road surfaces you mostly encounter, so I'm wondering if you're always on pavement or use the truck off-highway frequently. I've never heard of cleaning Wheel Speed Sensors in all my years of dealing with ABS, but maybe this is common in rural areas.

Since this started after you replaced the brake linings, I'd be looking closer at the new front and rear brake linings that you installed. It sounds like you might be like me and avoid dealerships, if at all possible. So, if you didn't install GM brake linings (I don't), the new linings don't have the same properties as the old linings and this might be confusing the ABS system. Aftermarket linings are never exact replacements for OEM linings. You mentioned a spongy brake pedal too, and this can be adjustment of the rear drums or the new linings can be "softer" than the original linings. Different lining materials have different hardnesses that can actually be felt in the brake pedal, so it is conceivable that this is the cause of the spongy pedal.

If the Front to Rear brake balance is not the same as before, you may have a greater tendency to go into wheel lockup on one end of the truck, causing the ABS to activate more frequently than before. Usually, the rear wheels are more likely to lockup than the fronts in a lightly-loaded pickup, but there are no guarantees with the new linings. If you bought the cheapest linings available, you may have exaggerated the problem because cheaper linings are even farther from the properties of the original linings. I tend to buy linings above the cheapest available at the parts store and have settled on a particular brand that has been more consistent than other brands for me.

For what it's worth, that darned noise and pedal pulsing is normal for GM's Truck ABS (Made by Kelsey-Hayes), and it scared the daylights out of me the first time I had it happen to me. I think they call that feature "Driver Feedback" so you know the ABS is working!

I'm also wondering if the valves/pistons that were stuck in the other owner's truck are within the Kelsey-Hayes ABS controller instead of the Calipers. I would think that if you have a front caliper stuck, you'd know it on the first stop when the truck yanks to one side. On the other hand, the fluid displaced by the Caliper pistons being compressed needs to flow back through the ABS Controller, but the ABS valves are normally open and allow the brake fluid to bypass back to the Master Cylinder. I suppose it's possible that there is a special technique for compressing the calipers on these trucks, but I've never changed the linings on one of these to know and really doubt it.

Hope all of that helps.

You failed to mention the type of road surfaces you mostly encounter, so I'm wondering if you're always on pavement or use the truck off-highway frequently. I've never heard of cleaning Wheel Speed Sensors in all my years of dealing with ABS, but maybe this is common in rural areas.

The truck is almost always on pavement. I don't have much of a reason to be on gravel or dirt. It does happen, but not very often.

I do try to avoid the dealership if I can. They are extrememly over priced. They want about $550 to change out the wheel speed sensor. A small local shop will do it for around $250. That's a HuGE difference and the main reason I don't like to take it to a dealership. I'll take it there so they can tell me what's wrong, but I won't pay them to fix it.

I did adjust the rear brakes a little the other day and things have gotten better. It's not near as bad as it was. It only seems to happen when I've slowed down to under 10 mph. Just before it comes to a complete stop, the pedel will sometimes (not always) drop a little further (spongey feeling), sometimes stutter a bit, and make kind of a groaning noise.

hey dude i work in a shop the problem with your along with a thouson others is ther is rust build up under speed sensor just hane to remove sensor clean rust under and re instal sensor i own a 97 z71 and did the same thing

hey dude i work in a shop the problem with your along with a thouson others is ther is rust build up under speed sensor just hane to remove sensor clean rust under and re instal sensor i own a 97 z71 and did the same thing

Thanks for the input. Where were you last month? LOL
I had a local shop take a look at it and they told me the same thing. Of course, they charged me to take it all apart and clean it up, but it works the way it's supposed to now.

It's funny that the dealership wanted to sock me $550 to replace a part that didn't even need to be replaced, but a local 'small guy' shop knows this little trick and charged me a fraction of that. I think the dealership would have probably just cleaned the sensor and charged me to replace the entire assembly! No more dealership for me!!!

As I posted in another thread someplace, the dealer boys work flat rate.Your not gonna get it cleaned.Replace it or see ya.The little shop dude has a little more room for that.Any shop worth the wieght in gold should have knowen that problem.As a tech you MUST know your tools and MUST know how to use them.You would crap your pan't if you really knew how many shops have the tools and the tech hardly know how to use them.