GM Mechanics please step inside

[eddyyy302]

I have 2 quick questions on a 2001 Chevy 2500HD.

1. Recently the front driver side brake started dragging. I took the pads out, cleaned the metal slides, lubed them and the pad with synthetic brake lube and put it all back together. With both shims/slides in, the pads fit VERY tight, the passenger side only has one shim/slide as i'm guessing when the pads were replaced they were too tight and it was removed. What I don't understand is; this is a dual piston caliper, when pushing one piston independently of the other, it moves freely and the other piston pushes out, however compressing them both at the same time is extremely difficult like a frozen piston. Is my problem likely a bad brake hose not allowing the pressure to release or is that activity normal for a dual piston caliper and are the pads too tight in the holders?

2. The ABS and brake lights light frequently, I have read hours worth of info on the issues. Initially I was told the code was for the passenger front abs sensor, I removed it and cleaned it and the mounting surface, which did not help. I want to probe the sensor and verify that it is physically bad before replacing it. What/how do I go about verifying it's condition? I know where the connection is for the harness, just need to know how to test it and what I am looking for.

Thanks in advance for any help!

Dan

 

[HotRodKush]

1. The reason that one piston moves easily when the other one is pushed, is because you're displacing the fluid from one side of the caliper to the other. When you push both at the same time, you're pushing the fluid against the resistance of more than just one piston - the fluid has to push back into the master cylinder so it'll be much tougher. That's why they sell tools to aid in this process - doing it by hand can be a chore. The reason that the pads are too tight (assuming you mean that they don't fit over the rotors) is likely because you didn't push the pistons back far enough for the new, thicker pads to clear the rotor.

2. Usually you can check the resistance of the ABS sensors to check their functionality. They're all different though, so without a shop manual I can't tell you what the correct readings would be.

 

[fxstdavew]

It's very possible you have a bad hose. They are ten years old there is no harm in replacing them now.
As for the resistance reading on the sensor compare the reading to the opposite side.

 

[4BT]

+1 on the brake hose, they usually swell shut around the bracket that mounts to the control arm. My old 96 suburban had a swollen hose that caused the affected caliper to lock up.

 

[eddyyy302]

1. The reason that one piston moves easily when the other one is pushed, is because you're displacing the fluid from one side of the caliper to the other. When you push both at the same time, you're pushing the fluid against the resistance of more than just one piston - the fluid has to push back into the master cylinder so it'll be much tougher. That's why they sell tools to aid in this process - doing it by hand can be a chore. The reason that the pads are too tight (assuming you mean that they don't fit over the rotors) is likely because you didn't push the pistons back far enough for the new, thicker pads to clear the rotor.

I understand the concept of the pistons moving in relation to each other, what I am saying is if they both move independently, it shows that they aren't seized. I am using a tool to depress the pistons, but it is much harder than normal or even the passenger side, which is why I am asking about a failed brake hose.

As far as the pads go, the issue is that they fit tight in the holder/slides, I am able to depress the pistons plenty to get the caliper back over the pads, but the pads fit tightly in the holder itself with the caliper off.

Thanks for the ideas so far.

Dan

 

[eddyyy302]

+1 on the brake hose, they usually swell shut around the bracket that mounts to the control arm. My old 96 suburban had a swollen hose that caused the affected caliper to lock up.

Was this an intermittent problem? The brake would lock up, you use the brakes and it would unlock enough that the vehicle wouldn't pull and so on?

Dan

 

[Sureshot]

I have an 05 2500hd. I have had trouble since swapping out wheelbearings. At 30mph or so the ABS sensor loses the signal (light comes on) and thinks the PS wheel has stopped and then pulls to the drivers side when applying the brakes. I have swapped out the ABS sensor twice to no avail.

 

[eddyyy302]

I have an 05 2500hd. I have had trouble since swapping out wheelbearings. At 30mph or so the ABS sensor loses the signal (light comes on) and thinks the PS wheel has stopped and then pulls to the drivers side when applying the brakes. I have swapped out the ABS sensor twice to no avail.

Yup, this is one of the common problems, they also say that when your hubs are going out you will experience the same abs issues prior to the bearings making noise. My issue seems to be a bad sensor and I hope that fixes it. Most people that have issues similar to yours have an interesting way of remedying the problem.

Dan

 

[fxstdavew]

fwiw .not all pads are created equal. You are saying the metal foundation of the pads is tight in the caliper bracket? If so take a file and dress the pads so they can slide. They need to have some drag or they will squeal when braking. also again replaced the hoses.

 

[eddyyy302]

fwiw .not all pads are created equal. You are saying the metal foundation of the pads is tight in the caliper bracket? If so take a file and dress the pads so they can slide. They need to have some drag or they will squeal when braking. also again replaced the hoses.

Right, these pads are NOT new, they are at about 60% and have caused no issues to date. I did use the prep tool and clean them down to bare metal as well as the area under the slides on the caliper mounting bracket as they tend to rust and squeeze the pads. The passenger side has only 1 thin slide/shim and makes no noise.
Keep the ideas coming!
Dan

 

[Ohio Auto]

1. The reason it moves freely while only pushing one piston is because the fluid displaces the space occupied by the other piston..thus pushing it out. When compressing both pistons at the same time..the fluid has no place to go. Which..could indicate a collapsed/partially collapsed brake hose.

2. If the RF wheel is dragging due to a faulty brake hose..it will trip the ABS light for that wheel. The computer senses a different RPM on that wheel (slower due to drag) and trips a fault that you have a problem. Probably not a sensor at all...fix the dragging brake first.

 

[fxstdavew]

you want the shims in there if not over time the pads wear a knotch/ groove into the caliper bracket.

 

[eddyyy302]

2. If the RF wheel is dragging due to a faulty brake hose..it will trip the ABS light for that wheel. The computer senses a different RPM on that wheel (slower due to drag) and trips a fault that you have a problem. Probably not a sensor at all...fix the dragging brake first.

Thank you for #1 being a definitive answer. On #2 you are mixing the sides and issues up. The ABS issue has been ever since I purchased the truck and is the PASSENGER SIDE, the dragging brake started 2 days ago and is the DRIVER'S SIDE. I took the brake apart the same day that it started dragging and it was ok for a day or so. When the truck was inspected the codes were read and the code was for the passenger side abs sensor, I am asking how to test it.

Dan

 

[eddyyy302]

you want the shims in there if not over time the pads wear a knotch/ groove into the caliper bracket.

Agreed, that is why I didn't remove it from the drivers side, instead I greased it and tried to remedy the problem. I was not the person who removed the slide from the passenger side.

Dan

 

[Ohio Auto]

Thank you for #1 being a definitive answer. On #2 you are mixing the sides and issues up. The ABS issue has been ever since I purchased the truck and is the PASSENGER SIDE, the dragging brake started 2 days ago and is the DRIVER'S SIDE. I took the brake apart the same day that it started dragging and it was ok for a day or so. When the truck was inspected the codes were read and the code was for the passenger side abs sensor, I am asking how to test it.

Dan

Still the same principle...the computer is seeing two different rates of RPM on the front wheels....it could set a code for either wheel.

Fix the known mechanical issue first....then contend with the electronic/computer related issue next.

Not saying it will fix the problem..but it is the logical progression of repair.

 

[eddyyy302]

Still the same principle...the computer is seeing two different rates of RPM on the front wheels....it could set a code for either wheel.

Fix the known mechanical issue first....then contend with the electronic/computer related issue next.

Not saying it will fix the problem..but it is the logical progression of repair.

Absolutely agree, and I AM most concerned about the sticking brake issue, I just do want to throw parts at it. I know there is a method of testing the sensor itself for resistance or open fault, I just do not know what it is. I am likely going to replace the brake hose this weekend a lightly file the pads to fit a little better, then go from there.

Still open to suggestions.

Dan

 

[Ohio Auto]

Absolutely agree, and I AM most concerned about the sticking brake issue, I just do want to throw parts at it. I know there is a method of testing the sensor itself for resistance or open fault, I just do not know what it is. I am likely going to replace the brake hose this weekend a lightly file the pads to fit a little better, then go from there.

Still open to suggestions.

Dan

You can back probe it...it is an off/on switch that you should see cycle by selecting the A/C setting on your multimeter and spinning the wheel. It produces an A/C current..not D/C.

I have the spec around here somewhere for ohm resistance..if I can find it I'll post it.

Also if it is an intermittent code/fault be sure to wiggle the wiring harness around as you're reading your numbers.

 

[robertearl]

Here is a link on how to check the speed sensor with a digital VOM.

http://www.gmforum.com/showthread.php?t=296517


Reb

 

[tcsalvage]

if you think the hose is collapsed pump up the brakes and open the bleeder on the caliper, if fluid squirts out the hose is collapsed if no fluid and wheel still doesn't turn its the caliper. as for your abs sensor it could be the wiring but this is usually seen on the drivers side were it bends on top of the frame and goes up to the abs module.

 

[tcianci]

Still the same principle...the computer is seeing two different rates of RPM on the front wheels....it could set a code for either wheel.


The computer sees 2 different rates of rpm on the front wheels every time you're doing anything but going straight ahead. IIRC, the ABS system trigger when the wheel speed sensor signal goes away, indicating a locked wheel.

The pads don't fit into the caliper bracket because you need to take the stainless steel sliders out and scrape and meticulously clean the caliper bracket surface then the stainless sliders will fit correctly and so will the pad. I have experienced this on my 2000 GMC and my 2001 GMC.

Good luck with the ABS system... I love these trucks but that ABS system is not too robust at all.

 

[eddyyy302]

The pads don't fit into the caliper bracket because you need to take the stainless steel sliders out and scrape and meticulously clean the caliper bracket surface then the stainless sliders will fit correctly and so will the pad. I have experienced this on my 2000 GMC and my 2001 GMC.

Good luck with the ABS system... I love these trucks but that ABS system is not too robust at all.

The bracket was cleaned with a prep tool down to clean metal, the pads still fit very tight.

I am the type of person that likes to have everything working properly, I literally spent 4 hours reading the chevy truck forums only to realize that most parts of the ABS systems have faults and they aren't the easiest to remedy.

Dan

 

[35chevypu]

for abs walk fix (50% chance itl fix it) remove rotor then remove abs sensor you will see rust buildup on face of hub where sensor bolts.put piece of paper towel in sensor hole then use angle grinder and small disc or dremel to remove rust from mating surface.(dont remove metal only rust buildup)reinstall sensor and roadtest.if doesnt fix sensor is most likely bad replace sensor or bearingassembly. as a note be very carful removing sensor so u dont break it.twisting it carefully back and forth to get it to spin in bore first usually works best.

 

[eddyyy302]

for abs walk fix (50% chance itl fix it) remove rotor then remove abs sensor you will see rust buildup on face of hub where sensor bolts.put piece of paper towel in sensor hole then use angle grinder and small disc or dremel to remove rust from mating surface.(dont remove metal only rust buildup)reinstall sensor and roadtest.if doesnt fix sensor is most likely bad replace sensor or bearingassembly. as a note be very carful removing sensor so u dont break it.twisting it carefully back and forth to get it to spin in bore first usually works best.

Yup, did this and cleaned to bare metal with scotch brite pad on prep tool. No change and I am guessing the sensor is bad, but I want to (and will with the methods previously mentioned) test the sensor before just replacing it.

Dan

 

[jgm27]

connect your dvom to the harness and set the dvom to AC volts and spin the wheel. You should have over 350mV @ 1 second per revolution of the wheel.

 

[oilslick]

I would just replace the bearing on the side that indicated the abs problem, next replace both calipers and hoses,neither of which is that pricey from napa,if you are from the rust belt it prob needs rotors anyhow and the pads are worn uneven. I have been down this road before I am just giving you a shortcut to sucess and safety! Check the brake line running to the rear of your truck for corrosion as well.

 

[35chevypu]

acv test will show good or bad sensor. gm sensors are pricey and can usually buy good quality aftermarket brg assy for not much more.use scanner and watch abs data for wheel speeds to drop off and as a failsafe watch dump valve activation in data screen as a foolproof way of knowing which wheel abs is being activated on and replace sensor or brg assy on that wheel

 

[Sureshot]

dmax.com has lifetime warranty Timken bearings and replacement bolts etc. I have had great service from them.

 

[WRX/Z28]

1. The reason it moves freely while only pushing one piston is because the fluid displaces the space occupied by the other piston..thus pushing it out. When compressing both pistons at the same time..the fluid has no place to go. Which..could indicate a collapsed/partially collapsed brake hose.

2. If the RF wheel is dragging due to a faulty brake hose..it will trip the ABS light for that wheel. The computer senses a different RPM on that wheel (slower due to drag) and trips a fault that you have a problem. Probably not a sensor at all...fix the dragging brake first.

Still the same principle...the computer is seeing two different rates of RPM on the front wheels....it could set a code for either wheel.

Fix the known mechanical issue first....then contend with the electronic/computer related issue next.

Not saying it will fix the problem..but it is the logical progression of repair.

If you have one wheel turning faster than the other in a straight line, one tire is skidding.

 

[bgott]

If you have one wheel turning faster than the other in a straight line, one tire is skidding.

Or mis-matched tires.

 

[WRX/Z28]

Or mis-matched tires.

True. Being that this was in explanation of a brake problem, I'm guessing that's not the case though.

I'd bet money on a wasted brake line though. +1 for that.

 

[mrbreezeet1]

I understand the concept of the pistons moving in relation to each other, what I am saying is if they both move independently, it shows that they aren't seized. I am using a tool to depress the pistons, but it is much harder than normal or even the passenger side, which is why I am asking about a failed brake hose.

As far as the pads go, the issue is that they fit tight in the holder/slides, I am able to depress the pistons plenty to get the caliper back over the pads, but the pads fit tightly in the holder itself with the caliper off.

Thanks for the ideas so far.

Dan

You can file the tops and sides (Ears) of the pads so they fit looser. (Not too loose though)
Open your bleeder valve and see how they go in now.
It is usually a good Idea anyhow.