1996 1 Ton Chevy 4x4 ABS problem... interesting one!

Chad Flaugher

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Both my business trucks are 1996 chevy trucks. I am very familiar with the early Vortec engines, so I tend to stick with what I know. Besides, the new trucks are PLASTIC! :laugh: Anyhow, the 1 ton developed an interesting problem this fall. On dry pavement, the ABS will kick in at low speeds while turning right. It only happens occasionally, but it's been scary in a parking lot a few times! I put new rotors, hubs, pads, and calipers on the front, and new wheel seals and shoes in back. Still have the problem. The only circumstance that couples the problem is turning hard right. All the new parts did nothing. ABS light comes on maybe once every two weeks, but shuts back off right away. Any Ideas? :help:
 

82rude

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faulty sensor on that side ?
disconnect the abs at the box under the hood and if the problem goes away its the abs sensor most likely.least with my f150 that's how it worked.maybe the hub is the problem?
 

GA_Boater

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The sensor on either side or the sensor wiring being pulled when turning right? Or a rub through on the wiring? Just guesses, Chad.
 

Chad Flaugher

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I appreciate the guess! If I remember correctly, when I replaced the hub, it had a new wire from the hub to the plug assembly @ fender penetration. That would be the only section of wire exposed that would move with the steering. I took the "replace everything" approach thinking that it would fix the problem. Thanks for the feedback!
 

Chad Flaugher

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82rude The problem existed before and after I replaced the hubs and everything else.
 

gm280

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I had problems with a '96 S10 anti-lock brake system on my dad's Chevy truck. And after having it checked a few times, nobody could pin point the problem and finally told me to change the anti-lock electronics. Well even a used "brain" would have doubled the cost of the truck. So I, in my weird wisdom, decided to take the "brain " off the truck and open it up to see what a "brain" actually looked like and did. Of course electronics is/was my career field so what could I actually do...break it? So I did open it up and looked over the ridiculously few actual parts soldered on the circuit board. And after testing every one of them I found a cold solder point on a modulation relay with my DVM meter. I resoldered all the solder connections and installed it back into the truck and WALA...it worked perfectly since then. So everything with anti-lock brakes is a suspect until proven otherwise... Even the individual front wheel sensors can cause issues even if they ohm out perfect. And some anti-lock brakes use only one sensor for the rear wheels. So check everything, but not by replacing parts. It gets too costly that way! JMHO!
 

82rude

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82rude The problem existed before and after I replaced the hubs and everything else.

sorry my reading comprehension was wayoff chad I didn't see that you had replaced the hub already.gm280 has the ticket im sure.
 

wrench 3

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Usually an ABS releasing the brakes at low speed is caused by a wheel speed sensor dropping out (stopping transmitting) at that speed. It's normally for such a short period of time that the only way to spot it is to graph all the sensors on one screen, freeze frame them and compare the patterns. Find someone with a scanner.
 

gm280

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Some times the wheel sensors are not the issue even with a scanned and report bad sensor. The sensors only read the teeth as they spin by the sensor. So if anything is caught in the teeth of the sensor, like grounded metal particles from bearings or anything the teeth could have hit or brushed against at some time, it will make that sensor appear bad when it is the teeth section needing cleaned. So as I stated before, don't buy parts to FIX your problem. Verify the part is bad first!
 

Chad Flaugher

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Well the teeth are (or were) brand new, so that would eliminate contamination, and the sensors would be brand new as well with the rotor swap... At least I'm pretty sure. My one ton is way different than the half ton, and I did 'em both at the same time. gm280, I envy your circuitry and electrical know how. I've done clutches, transmissions, u- joints, intake manifold gaskets, exhaust systems... Heck, back in the day I shoe-horned a '93 Chevy vortec engine into an '87 Toyota 4x4 with all my own fabrications. But electrical? Nope My brain just aint wired that way. Your story about ABS "brain surgery" on your dads truck is baffling to me! :eek: However, with all new teeth and sensors, and new wire coming off of the A-arm, I think you are on to something with the "Brain".

Let me get sort of off topic for a sec. What if I pulled the fuse to the entire ABS system? I grew up driving vehicles without ABS, and I kind of hate it anyhow. Would there be negative repercussions?
 

gm280

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Chad, how an anti-lock system works is those teeth pass by the pickup sensor. And that sensor provides a pulse to the "brain" for every tooth that passes the sensor. In other words, it counts the teeth going by. Now all the wheels are sending their rotational speed by how many pulses are sent to the brain. When you apply the brakes, if any of the wheel sensors stops sending pulses to the "brain", or if one wheel is sending a lot less pulses to the brain, then the"brain" modulates (pulses or turns on and off) the fluid going to that wheel to allow it to move again instead of dragging because it is locked up. And all wheels are balanced in their braking abilities instead of completely locked up. And that little slipping sound or chirping sounds you usually hear during hard braking will stop the vehicle quicker then a total brake lockup. So look at the brain as allowing brake fluid to stop and go at a very fast rate to a locked wheel when the pulses from the sensor counting the teeth passing it and it stops coming in in the proper amount...Not the hard to understand once you see how it all works together. The brain of the system has some relays to start and stop the brake fluid motion going to any totally stopped wheel or non slipping wheel during braking. Hope that helps a little...
 
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you say you replaced the hub. Is that in reference to one hub or both hubs? You also said it was "scary", now my Suzuki has been doing the same thing for a while and ive been to lazy about cleaning the sensor and I would say its annoying but not scary. So maybe its doing something that we don't expect as abs is meant to allow for you to steer a vehicle even during a emergency stop . For example the truck is not stopping fast enough or the truck is pulling to one side,etc. I guess what im asking is what is the problem.
 

Chad Flaugher

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gm280: I understand the physical principal of ABS, as well as what it's supposed to do. It's basically designed for people who panic in emergency situations and slam on the brakes. In most cases, it's a good thing, as it assists in steering because the tires don't lock up and skid. It's the ability to test the inner workings of the "brain" and narrow it down to a single "cold solder" that I lack. I can't seem to wrap my head around how inconsistent this problem is! It happens once every 7 - 12 days. It doesn't matter if it's cold outside or warm, slick or dry, engine temp, etc. If it was the brain, why would it only do it when turning right? So frustrating!:frusty:

glenn: I replaced everything on both front axles. On this truck, the hub contains the sensor, wheel bearings, cogs, etc. Completely different set up than the half ton truck, and probably your set up as well. I say scary because when your turning into a parking space between two cars in a big 'ol long bed 4x4 4 door truck and it don't wanna stop... SCARY! The ABS kicks in like your on a sheet of ice when I turn right on dry pavement. It happens under 10mph because you have to be going that slow to turn hard enough. I'm not scared in the way of injury, it's more fear of crunching a car in a parking lot. If I stand on the pedal, it'll slow down... slowly. It does not pull or anything. Just makes that growling ABS sound and won't stop for crap! Sometimes, it makes that noise without even touching the brakes!
 
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glenn: I replaced everything on both front axles. On this truck, the hub contains the sensor, wheel bearings, cogs, etc. Completely different set up than the half ton truck, and probably your set up as well. I say scary because when your turning into a parking space between two cars in a big 'ol long bed 4x4 4 door truck and it don't wanna stop... SCARY! The ABS kicks in like your on a sheet of ice when I turn right on dry pavement. It happens under 10mph because you have to be going that slow to turn hard enough. I'm not scared in the way of injury, it's more fear of crunching a car in a parking lot. If I stand on the pedal, it'll slow down... slowly. It does not pull or anything. Just makes that growling ABS sound and won't stop for crap! Sometimes, it makes that noise without even touching the brakes!

ok that's strange especially the last quote about the noise with out touching the brakes as one of the abs sensors is on the brake pedal. if it was my truck I would probably take it to a dealer or call around to find someone with a scanner that could read the abs data. The codes should be stored from when you have seen the light on the dash. Also they can pull live data from the sensors to see what each part of the system is sensing. It almost sounds like a pressure problem in the abs system
 

rbh

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This might sound weird, but are your hubs in?

When your doing your hard right turn the U-joints are binding? thats almost a ABS feeling.
 

gm280

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After reading your last replies, I would assume you have power brakes. Is there any possibility that your power brake system is going bad, or a vacuum hose with a crack in it and when you turn hard to one side that hose is more opened then normal straight driving. That could also account for it happening without touching the brake pedal as well. IDK without being there and testing things. Just a suggestion to check. I am sure you bleed the entire brake system as well when making changes to the system... IDK! :noidea:
 

dwco5051

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That truck I think has hydroboost power brakes. The power is hydraulic pressure from the power steering pump. Making a hard turn while at idle speed can cause the brakes to get goofy if the accumulator in the boost system is not working right. Shut the truck off while parked and then push on the brake pedel. You should get what seems like a normal pedal for one or two pumps before it goes soft. If not the accumulator is bad.

Just had to replace mine a few weeks ago.
 

Chad Flaugher

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rbh: Hubs are definitely disengaged. It's exactly the same sound and feeling as when breaking hard on ice.

gm280: I know, right? I've been turning wrenches for a hobby for 25 years, and this is just baffling to me. It's super hard to test a whole lot, because it only does it randomly every week or two. I do want to have the code scanned. Anybody that has the right diagnostic equipment, will want the job of fixing it! I think I'd rather disable it.

dwco5051: Here is what happened. Started truck, braked a couple times in park. normal Shut truck off, and brakes felt normal for 10+ pumps. That is very interesting to hear about the power brakes being tied into the power steering... hmmmm I'll be looking into that more for sure. This is the first 1 ton I've owned, and there is a tremendous difference between it, and all the other vehicles I've wrenched on. What exactly is the accumulators job, and where is it?
 

dwco5051

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dwco5051: Here is what happened. Started truck, braked a couple times in park. normal Shut truck off, and brakes felt normal for 10+ pumps. That is very interesting to hear about the power brakes being tied into the power steering... hmmmm I'll be looking into that more for sure. This is the first 1 ton I've owned, and there is a tremendous difference between it, and all the other vehicles I've wrenched on. What exactly is the accumulators job, and where is it?

The brake booster is between the firewall and master cylinder. The accumulator is part of the hydroboost and it stores pressurized fluid to operate the booster when the power steering pump doesn't supply enough. It is the can shaped device on the engine side of the booster. Make sure your powere steering fluid is topped off. You might be starving the booster in a hard turn.

A more detailed explanation.

http://www.freeasestudyguides.com/hy...ke-assist.html

 
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