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front brakes (both) draging. ABS?
07-20-2017, 02:26 PM
Post: #1
front brakes (both) draging. ABS?
Hello all, here's the background. 2005 chevy silverado 2 WD 4.3L 170K miles regular cab. ABS dashboard light would come on intermittently when i hit potholes or bumps in the road. The light would go out on it's own. The truck brakes would not pulse like ABS does on slippery surfaces. This has been happening for several years. Replaced front Rotors, calipers and pads on front D&P sides and front drivers side wheel bearing. All has been good for 3 weeks and 1k miles. ABS light continues to come on when I hit bumps. Recently ABS light would come on and brake pedal would pulse on dry roads no tire slippage. This only happend say 2-3 times while light comes on more often. I now am getting front brake drag both sides. Jacked up front end and both wheels spin but do hear slight drag. I pushed caliper piston in and wheel spun freely. When I changed calipers no brake fluid was leaking fro lines. I say this because in the past I would have to stick an ear plug in line to keep fluid from draining out during a brake job. I also tested the brake booster and seems to be ok if I tested it correctly. Master cylinder? Brake line hoses? ABS system? Again it is effecting both sides. Any thoughts. Sorry about the length. Thanks for your replies.
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07-20-2017, 10:31 PM
Post: #2
RE: front brakes (both) draging. ABS?
A problem with the ABS will usually NOT cause any brake drag so if you have enough drag to cause heat build up then head for the typical suspects of sticky calipers or the flex lines, both of which are common items at that age.

Hint: if you have drag and cracking a bleeder or line frees it up then it's the flex hose.... other wise it's the caliper.

As for the other issues, you can shoot from the hip or get someone with a proper scan tool to go over the ABS system, which will give you the exact codes for the malfunctioning components in just a few minutes. From my experience, when the ABS light comes on along with the brake light there's a problem with the ABS module, which is called an ECBM. (electronic controlled brake module) The micro relays go bad or the solder joints on the PC board crack, and it's best to replace the whole thing... although not cheap and it's a royal pain depending on where it's mounted. (along the frame rail on many trucks) Other codes may indicate the need for the pump / valve part of the system. The pulsing pedal on dry roads may be a bad sensor, bad harness, or another bad wheel bearing in the works. The scan tool should at least tell you which wheel is reading low so you can trouble shoot things.

BTW, both the ECBM and the pump / valve system for the ABS are typically available from Amazon.com or Rock auto for about half the dealer cost.

Hint from a professional stand point: If you see the screws holding the ABS module to the pump are rusty (they usually are) what I do is drill the heads off then after the module has been pulled free you can take the threaded part out with pliers, as they do not generally rust in that section, just the heads. At the dealer those metric screws are about $8 each (need 4) so I usually buy them at the hardware store in stainless or brass then coat with never-seize. If you can't get small enough heads to clear the module you can carefully grind the diameter down a bit to fit. The replacement screws will probably be 5 mm longer than the OEM screws, but there's enough room for that in the casting.
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07-21-2017, 06:46 AM
Post: #3
RE: front brakes (both) draging. ABS?
Thank you for your time. I have not yet begun to check out the ABS system. I am not getting a brake light with my ABS light. I plan on getting a scan at autozone to see what code it throws. Last night I removed the brake fluid and master cylinder. The fluid is dark ( can't see through it in a 3" dia bottle). There are also lots of small floating pieces of sludge in the fluid. When I opened up the master cylinder it had sludge in it and the fluid reservoir has a coating of sludge in it. Cleaned reservoir and cylinder with gunk and a few other chemicals. I then bench bled and reinstalled. Tonight I will bleed lines to clear out air and old fluid. More to come thanks again for the help.
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07-21-2017, 08:12 AM
Post: #4
RE: front brakes (both) draging. ABS?
Be careful about what kind of chemicals you use on a brake system. The Gunk brand brake parts cleaner is fine and made for the job but if you used Gunk "engine brite" cleaner you might have to throw away that MC because that has a petroleum base which will attack the rubber parts over time. Also, never use bleach on automotive parts as it is also harsh on rubber and plastic parts, never mind the toxic fumes when mixed with certain things.
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07-21-2017, 06:15 PM
Post: #5
RE: front brakes (both) draging. ABS?
Although I find all of this very interesting, I am quite confused. If I understood the problem correctly it is the ABS light coming on and the ABS not working. You were also concerned about slight brake drag.

So, "Slight" drag is normal as disc brakes do not have return springs. If they aren't getting hot or locking on, that is likely not an issue.

As to the ABS light. When the light is ON, that means that the ABS is "Disabled." That is why the brakes don't pulse on a slippery surface. The cause is likely a loose wire connection to a Wheel Speed Sensor (WSS), or a wheel bearing is failing. GM had a problem with corrosion getting under the WSS on their pickups. This usually caused the ABS to activate on dry surfaces and you would have almost no brakes. You didn't mention that situation so I am thinking that is not your issue. This usually happens to vehicles in areas where salt is used to melt snow and ice in the winter.

So I would get that scan done. Not sure if AutoZone's scanner does ABS? But if it does I think you will find codes relating to a WSS. If you post the code "Numbers" here we can review them and give you more advice.

Please keep us in the loop. It may help someone else.

Thanks for using the forum,
Garner

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07-22-2017, 10:28 AM (This post was last modified: 07-22-2017 10:29 AM by Rupe.)
Post: #6
RE: front brakes (both) draging. ABS?
Yes, as Garner mentioned there was a time a few years ago on certain vehicles where the speed sensor behind the wheel got "pushed back" due to rust build up and the increased distance (maybe 0.020") was enough to give a low reading at that wheel so the computer thought the wheel was starting to lock up, causing the ABS to activate. This is where the scan too can shine. It will tell you which wheel has the low reading. Sometimes you can chip off the rust and properly reseat the sensor and other times the sensor itself is the issue.

BTW, a decent scanner will also tell you if the code is current or in history. IOW, even if the light went off and there's no problem at the moment the code is still in storage.
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07-24-2017, 06:24 AM
Post: #7
RE: front brakes (both) draging. ABS?
I really don't think the corrosion under the WSS is the issue here since his ABS light is coming on. The issue here seems to be a loss of signal from the WSS. I have seen where it was as simple as unplugging the WSS, applying some dielectric grease to the connection, and plugging it back in. I have seen partially rubbed through wires giving an intermittent signal. And I have seen a bad wheel bearing causing metal cuttings on the WSS and fouling the signal.

I would suspect one of those last three. Here again, a good scanner can save a lot of work. It will tell you which wheel to look at and sometimes even narrow down the cause. If we get those code NUMBERS, we may be able to save you a lot of time and effort? Need those numbers though!

Thanks for using the forum,
Garner

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08-13-2017, 11:20 AM
Post: #8
RE: front brakes (both) draging. ABS?
Hey, it's been almost a month now. Any new information on this vehicle? Curious to know what you found.

Thanks for using the forum,
Garner

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