"feels like brakes slipping" 2000 tahoe z71 gmt400 4L60E

[hwhwhw]

Hello I have a 2000 tahoe z71 gmt400 4L60E with 5.7L engine.

Upon braking, at the last 10% of braking, it feels like the brakes are "slipping". To be more specific, it feels like the caliper lets go and then reclamps, sometimes multiple times, just at the very end when the truck is almost to a complete stop.

There is no problem stopping from speed or stopping hard, but if coasting to a stop at like 20mph it will do this shudder kinda thing at the very end. Or if in a parking lot going slowly into a parking spot, it will kinda let go for a second and then finish stopping.

It's easily reproducible when applying the perfect amount of brake pressure. Sometimes it makes me wonder if the ABS is activating unnecessarily. It's almost like abs chatter.

---- Here is the catch... ---

Over the weekend I had all the brakes replaced. While under there they found a rear axle had busted a seal and flung grease everywhere, so I got pretty much a complete rear rebuild. Diff flush, repacked. Brake flush, bled, high temp fluid (as was before). New calipers pistons pads on front. New drums on rear. New brake hoses to the front (they were partially collapsed/squished). New battery (unrelated, it was due).

Picked it up figuring this would fix it, drove around the mall, I can still reproduce the original symptom. It's not as bad as before, and not as noticeable as before, but it's still there. Drive up to a stop sign at about 20-25mph. Press lightly on the brake pedal. Vehicle comes to stop. Last tiny bit the brakes feel like they release then re-grab.

Now I am getting worried - if it's not the brakes then...?

If it is the brakes then how did replacing everything not fix it...

 

[hwhwhw]

Before anyone votes transmission, I took it out this morning and replicated the issue upon stopping while shifted in neutral, and in 2 and 3. So I don't think it is possibly related to trans or torque converter. It really feels like the front left brake caliper just releases then regrabs. Happens at low speed / coasting and at high speed / hard braking to stop. Adds a couple feet onto stopping distance unexpectedly at the last second (vehicle is 90% stopped and coming to a complete stop and just then in the last 10% there is a noticeable "shudder" I hate that word but it feels like something lets go). Can feel it in the pressure on the pedal and noticeable to passengers.

 

[SunlitComet]

Pull 60-amp Abs maxifuse from underhoid power box and pretest. There is no danger in doing so. Post detailed report.

 

[hwhwhw]

Found exact same symptom posted on another forum (https://answers.yahoo.com/question/index?qid=20111208124338AAboAGI)

Blames rust or corrosion on ABS sensors.

Found a GM Recall about the same issue http://www.consumeraffairs.com/recalls04/2005/gm_abs.html

"A GM spokesman says the problem occurs when salt and other road grime gets into the area covering the antilock braking system sensor near the wheel hub. The problem activates the ABS at speeds much lower than normal, requiring a longer stopping distance."

So I looked up the source of the recall...

http://www-odi.nhtsa.dot.gov/owners...Category=R&searchCriteria.nhtsa_ids=05V379000


GM RECALL NO. 05068.

NHTSA Campaign Number: 05V379000

---------- Post added at 02:17 PM ---------- Previous post was at 01:44 PM ----------

Found the original 05068 posted here:

http://www-odi.nhtsa.dot.gov/acms/cs/jaxrs/download/doc/ACM5671334/RCRIT-05V379-9258.PDF


This was redacted with 05068B, and then again for 05068C, with different VIN breakpoints:

http://ww2.justanswer.com/uploads/TedG/2011-02-24_183129_abssensrcl.pdf


"Condition

General Motors has decided that a defect, which relates to motor vehicle safety, exists in certain 1999-2002 Chevrolet Silverado, 2000-2002 Chevrolet Tahoe, Suburban, 2002 Chevrolet Avalanche, 1999-2002 GMC Sierra, 2000-2002 GMC Yukon, Yukon XL vehicles located in the areas listed below. These vehicles may have a condition permitting corrosion to occur between the front hub/bearing assembly and the wheel speed sensor. If the brakes are applied while the vehicle is traveling at a speed of greater than 6 km/h (3.7 mph) but less than 16 km/h (10 mph), the corrosion may cause an unwanted anti-lock brake system (ABS) activation. If this condition occurred where stopping distance is limited, a crash could occur."


This is exactly my symptom. However, after two dealerships told me my VIN is invalid, and the GM recall website says there are no recalls on my vehicle, and the PDF breakpoints indicate my VIN is not in the range, it looks like it's going to be an uphill battle to get them to acknowledge.

Maybe I should just replace the ABS sensors and move on... I am also afraid if I take it to a dealership they will just "clean" the sensors and put them back in.

 

[SunlitComet]

Still waiting for you to pull the fuse and test again.

 

[hwhwhw]

Waiting to get access to the vehicle again - won't be until 10 or 11pm tonight. Then i'll be hunting for that fuse with a flashlight. I'm also tracking down a scan tool that should show ABS activation.

---------- Post added at 02:57 PM ---------- Previous post was at 02:56 PM ----------

For anybody else searching GM Recall 05068C here is a direct link to the pdf

http://www-odi.nhtsa.dot.gov/acms/cs/jaxrs/download/doc/ACM9183234/RCRIT-05V379-8709.pdf

"These vehicles may have a condition permitting corrosion to occur between the front hub/bearing assembly and the wheel speed sensor. If the brakes are applied while the vehicle is traveling at a speed of greater than 6 km/h (3.7 mph) but less than 16 km/h (10 mph), the corrosion may cause an unwanted antilock brake system (ABS) activation. If this condition occurred where stopping distance is limited, a crash could occur. "

 

[hwhwhw]

Still waiting for you to pull the fuse and test again.

I pulled the 60A fuse for ABS and tested again - now the vehicle stops as expected and there is no "shudder" during low speed braking (10mph - 6mph).

Symptoms are exactly as described in recall 05068C

Going to have all the abs sensors cleaned but I've heard they will most likely break and be impossible to get back in, and they are allegedly part of the hub assembly ?!

 

[SunlitComet]

they mount on the the hub and have a hold down bolt. if anything the holes might just need any rough material cleaned out of them to get them in easy.

 

[hwhwhw]

Dealership traced the data from all the ABS sensors and front left was the only problem, the other three were perfect so decided not to mess with them. They were able to pull the front left, clean it, and replace it, without snapping any plastic, so I escaped without having to replace the entire hub assembly.

Diag, labor, tax, total = $111.

Actually stopping in the parking lot instead of activating ABS at 7mph and running into parking barrier = $Priceless.