Brake Pulse, At Low Speeds And Light Pedal Pressure

nhproxr · October 7, 2010

I have a '03 Tahoe and it recently started doing something funny. When you brake at low speeds and with light pedal pressure, just before the truck comes to a stop the brake pedal pulses kinda like the abs is coming on. It increases braking distance cause with each pulse the brakes are disengaging. This is not to be confused with warped rotors...I know what that feels like and that is not what is happening. Like I said it feels just like the abs would during a panic situation or if skidding on ice or snow....only at very low speeds. Under higher speed braking or more pedal pressure the problem does not happen.

My wife primarily drives the vehicle and I am worried it may lead to a bigger problem if she needs to panic stop.

Thanks!

NV5600 · October 7, 2010

This problem is much more common than people know. I had the exact same thing happen to my 2005 Z71 recently. The ABS even kicked on once while pulling away from a railroad crossing well after I hit the brake. From what I've read, rust forms around and inside the ABS wheel speed sensor bore in the front bearing hubs. The sensors themselves also go bad. The kicker is that NAPA was the only place that would sell me a sensor without the entire hub assembly. There is a test using a mutimeter that is supposed to tell you which sensor is bad but I had a good idea which one had failed on my truck. There was so much rust around the edge of the sensor bore that it trapped the old sensor inside and I had to literally pull it apart to get it out of there.

I used a foam earplug and inserted it down inside the bore and went to work cleaning the rust out of and around the bore. You don't want to let any debris go down inside that hole and into your bearing. I removed the earplug and used a cotton swab with a little grease on it to swab out any debris. There was still a ring of rust at the very end of the hole so I had to go through the cleaning process again but eventually the sensor fit back into the hole like it was supposed to. The truck immmediately was back to normal and after a test ride, it seems to be fixed. It was doing the slow speed ABS chatter almost every time so I am confident this was the problem.

Also, NAPA includes a tube of some type of special grease that's supposed to be applied to the o-ring and around the hole where the sensor contacts the hub. It's thick, smelly goo but it should keep it from rusting up again.

mxdirtrider56 · October 7, 2010

When my brakes started pulsing on my 05 I had to resurface the rotors.

Vortec-Z71 · October 7, 2010

This problem is much more common than people know. I had the exact same thing happen to my 2005 Z71 recently. The ABS even kicked on once while pulling away from a railroad crossing well after I hit the brake. From what I've read, rust forms around and inside the ABS wheel speed sensor bore in the front bearing hubs. The sensors themselves also go bad. The kicker is that NAPA was the only place that would sell me a sensor without the entire hub assembly. There is a test using a mutimeter that is supposed to tell you which sensor is bad but I had a good idea which one had failed on my truck. There was so much rust around the edge of the sensor bore that it trapped the old sensor inside and I had to literally pull it apart to get it out of there.

I used a foam earplug and inserted it down inside the bore and went to work cleaning the rust out of and around the bore. You don't want to let any debris go down inside that hole and into your bearing. I removed the earplug and used a cotton swab with a little grease on it to swab out any debris. There was still a ring of rust at the very end of the hole so I had to go through the cleaning process again but eventually the sensor fit back into the hole like it was supposed to. The truck immmediately was back to normal and after a test ride, it seems to be fixed. It was doing the slow speed ABS chatter almost every time so I am confident this was the problem.

Also, NAPA includes a tube of some type of special grease that's supposed to be applied to the o-ring and around the hole where the sensor contacts the hub. It's thick, smelly goo but it should keep it from rusting up again.

Is there how-to thread on replacing the wheel speed sensors as I have this same problem with my brakes?

youcantkeepup! · October 7, 2010

odds are you will have to replace the hub, you can buy just the sensor but 99.8% of the time they are impossible to get out of your hub, they just break off

Vortec-Z71 · October 8, 2010

I was reading the thread below and some were saying that this problem led to a recall?

http://z71tahoe-suburban.com/iboard/index....showtopic=18187

NV5600 · October 8, 2010

Is there how-to thread on replacing the wheel speed sensors as I have this same problem with my brakes?

If you can change the rotors, you can do the repair. Once you remove the rotor, you will see a cable coming thru the dust shield that terminates into the hub. There is a little allen head bolt that retains the sensor. When you go to pull out the old sensor, it will probably break. Rust forms a ridge around the hole and the o-ring can't get past it. The outer plastic shell of the sensor stayed inside the hole and the guts of the sensor came out. Using a foam earplug, I plugged the hole and used a small screwdriver to pry the remaining plastic "tube" out away from the hole far enough to grab with needle nosed pliers. It'll pull out and then you have to ream out the rusty ridge that caused the problem in the first place. Remove whatever you used to plug the hole and look down inside to make sure you didn't drop anything down the hole. I coated the bore and sides of the sensor with grease from the kit as well as on the hub where the new sensor bolts down. The new sensor went right in. Seriously, the hardest part is taking off the calipers and bracket. If you have never had a rotor off before though, it could really be stuck on there. They seem to almost get welded by rust to the hub and turn a one hour job into a 3 hour cussing session.

If you have any reason to suspect a hub bearing, now would be the time to replace it. Mine were smooth, tight and quiet so I chose not to. If you knock a lot of crap down inside that hole, you'll probably be back in a couple thousand miles to change the bearing anyway. I know that I read somewhere that some vehicles in certain states were recalled for this but I thought that only covered up to 2002 or 2003 vehicles. You might be covered but my 2005 wasn't.

Vortec-Z71 · October 8, 2010

Is there how-to thread on replacing the wheel speed sensors as I have this same problem with my brakes?

If you can change the rotors, you can do the repair. Once you remove the rotor, you will see a cable coming thru the dust shield that terminates into the hub. There is a little allen head bolt that retains the sensor. When you go to pull out the old sensor, it will probably break. Rust forms a ridge around the hole and the o-ring can't get past it. The outer plastic shell of the sensor stayed inside the hole and the guts of the sensor came out. Using a foam earplug, I plugged the hole and used a small screwdriver to pry the remaining plastic "tube" out away from the hole far enough to grab with needle nosed pliers. It'll pull out and then you have to ream out the rusty ridge that caused the problem in the first place. Remove whatever you used to plug the hole and look down inside to make sure you didn't drop anything down the hole. I coated the bore and sides of the sensor with grease from the kit as well as on the hub where the new sensor bolts down. The new sensor went right in. Seriously, the hardest part is taking off the calipers and bracket. If you have never had a rotor off before though, it could really be stuck on there. They seem to almost get welded by rust to the hub and turn a one hour job into a 3 hour cussing session.

If you have any reason to suspect a hub bearing, now would be the time to replace it. Mine were smooth, tight and quiet so I chose not to. If you knock a lot of crap down inside that hole, you'll probably be back in a couple thousand miles to change the bearing anyway. I know that I read somewhere that some vehicles in certain states were recalled for this but I thought that only covered up to 2002 or 2003 vehicles. You might be covered but my 2005 wasn't.

I have an 03 and live in MA but I think coverage only went up until 2002. I just had my front pads/rotors replaced 8,000 miles ago so rust shouldn't be too bad. How can you tell when the bearings are toast? I have a vibration on my front passenger's side on the highway and I'm pretty sure that my tires are balanced. Would a bad hub cause this?

jsklenar · October 8, 2010

You should replace the hub assembly because the sensor is set in the hub to a certain depth. if it is to far in or to far out it will not read the air gap properly and your abs could kick on while brakeing or not work at all or just turn the light on. When getting a new assembly they are set up from the factory. But it dosnt sound like you have an abs problem, if you check the inner side of your rear rotors i think you will find them very rusted and possably flakeing apart. you probably just need rear rotrs and pads.

nhproxr · October 12, 2010

You should replace the hub assembly because the sensor is set in the hub to a certain depth. if it is to far in or to far out it will not read the air gap properly and your abs could kick on while brakeing or not work at all or just turn the light on. When getting a new assembly they are set up from the factory. But it dosnt sound like you have an abs problem, if you check the inner side of your rear rotors i think you will find them very rusted and possably flakeing apart. you probably just need rear rotrs and pads.

It feels like an abs problem. How would rusting rear rotors cause it have this brakes on and off feeling only at low speeds? I will certainly have a look at rear rotors.

Silverado_Monkey · October 13, 2010

I'm having this same issue on my 06. It just started a couple of weeks ago, and really is starting to get annoying. I'm still running the factor pads and rotors but they're on their last legs. I was planning to address the front rotors/pads and rear drums/shoes before it gets to cold to work on the truck. I guess I'll need to look into this ABS sensor thing too.

NV5600 - How much was that sensor at Napa? Are they only on the front? And is on one side or both? If it's not too expensive I'll just get'em and change'em out to see if it clears the issue up.

Also - Does anybody know where I can find the TSBs for my truck?

Thanks in advance

Bruno

NV5600 · October 13, 2010

I'm having this same issue on my 06. It just started a couple of weeks ago, and really is starting to get annoying. I'm still running the factor pads and rotors but they're on their last legs. I was planning to address the front rotors/pads and rear drums/shoes before it gets to cold to work on the truck. I guess I'll need to look into this ABS sensor thing too.

NV5600 - How much was that sensor at Napa? Are they only on the front? And is on one side or both? If it's not too expensive I'll just get'em and change'em out to see if it clears the issue up.

Also - Does anybody know where I can find the TSBs for my truck?

Thanks in advance

Bruno

Bruno, the sensor with tax and freight from the warehouse in Hebron was $54.XX. They'll probably have to order you one but they had over 160 of them in stock. They are for the front.