Odd brake pedal "springing" feel at near stop.

[Robbabob]

'03 LS TB with 206.5K I6
currently have different brand tires F to R, but same size

Nearing a complete stop, the final a few feet have a springing (as my wife calls it). I call it an ABS feeling. If I drive it with a mission: not babying the stop, but coming in a little aggressive then level it out without too much babying, it won't do it. I realize my description could mean different things to each person reading this, but maybe a few questions by you could help with a better explanation.

No idiot lights or anything to signal an issue or problem, just the odd feedback when nearing the stop.

She'll be getting 2 new tires to have a matching set all around on Tuesday, but she wanted me to post this and see if there is anything we could be looking into if y'all don't think it is a tire issue.

Thanks in advance!

 

[jeffro312]

I'm probably way off but wouldnt a slightly warped rotor cause something like that... no warped enuff to feel at higher speeds but as you slow more pronounced

 

[Old Coot]

I'm probably way off but wouldnt a slightly warped rotor cause something like that... no warped enuff to feel at higher speeds but as you slow more pronounced

Yes! It could. Vibrating brake pedal feedback not associated with ABS could be a warped rotor. Be sure the wheel lug nuts are all torqued the same @103 ft. lbs.

Just a couple of others things to check.

Disc brake rotor run-out should be no more than 0.002"

Disc brake rotor thicknes variation should be no more than 0.001"


The frequency of the vibration should slow as the wheel rotation slows.

A rough wheel bearing or improperly adjusted wheel bearings can also induce vibration in a brake pedal.

 

[The_Roadie]

Marginal and aging (salt-abused) rotor speed sensors at the front hubs have also been reported to fire off the ABS when slowing to a stop. You can test this by pulling the ABS fuse to disable the system for an experiment.

 

[Robbabob]

I appreciate the input and idea, and hope to get more after you read this additional info:

I've had plenty of warped rotors and this is not the case here. Runs great and no wiggling of the steering or giggling of the tummy, LOL. This is pedal related only, and only at the nearly stopped period when babying the stop.

Thanks!

 

[Robbabob]

Marginal and aging (salt-abused) rotor speed sensors at the front hubs have also been reported to fire off the ABS when slowing to a stop. You can test this by pulling the ABS fuse to disable the system for an experiment.

Ah yes. Will test this tomorrow at lunch.

Thanks!

 

[Robbabob]

Marginal and aging (salt-abused) rotor speed sensors at the front hubs have also been reported to fire off the ABS when slowing to a stop. You can test this by pulling the ABS fuse to disable the system for an experiment.

Much time has past... update now:

Pulled the ABS fuse and sure enough the issue went away. Found a great reference thread on the axact issue last July; solution there was they replaced entire hub since the sensor cost and entire hub were close enough in price.

Now for the $$$$ question... what is the level of difficulty to pull the sensor out and clean it? Sounds fairly easy, but accessible? I've changed rotors, but never a hub... ~thinking I need to take the elevator to go browse the video department; "basement- viedeos and tech DIY documents"~

Thanks in advance!

 

[Indybp57]

Much time has past... update now:

Now for the $$$$ question... what is the level of difficulty to pull the sensor out and clean it?
Thanks in advance!

Not difficult at all. There is one allen head screw and a push-in metal pin that holds the sensor to the hub. The allen comes out easy enough, but sometimes the pin head will shear off trying to pry it out, which is what happened to me. You can drill it out or just leave it, the screw by itself seems to be adequate. The issue with the sensors is rust builds up under the sensor mounting plate and increases the gap from the sensor end to the hub teeth. After removing the sensor make sure the mounting surfaces are completely clean of rust and debris. You can use a jewelers file and some emery cloth to clean those surfaces. Once you have the sensor removed it will be quite obvious what to do. There is a complete tutorial either here, or on that other un-mentionable site that goes into quite a bit of detail about this, and it even tells you how to measure the voltage output of the sensor when you are turning the wheel by hand. I was having similar funky brake pedal issues and this took care of it.

 

[Robbabob]

Thinking on cleaning the sensor this weekend as the wife is getting quite tired of this. Someone please confirm or correct me: the dealership can determine which sensor is activating the ABS. I thought I read this somewhere.

Else, we'll just have to check them all.

Thanks y'all!

 

[Robbabob]

Not difficult at all.

I found the written tutorial on the Voldmort site. I assume you also removed the disk and hub to access the sensor..... was hoping to not have to do that much effort. I'll do the time, though, whatever it takes.

Thanks again!

 

[mrphoenix80]

the dealership can determine which sensor is activating the ABS.

Any scan tool with abs data display can tell you which one. As you slow down the sensor that needs cleaned will skip some numbers(9,8,7,6,5,0), and good sensor will show all(9,8,7,6,5,4,3,2,1,0). It has been a while since I looked at the data stream some trucks will not show under 3mph.

However if one is rusted enough to change the air gap and give false activation the other is not far behind. Also I don't think I have ever done a rear speed sensor cleaning. So I would do both fronts.

 

[Indybp57]

I found the written tutorial on the Voldmort site. I assume you also removed the disk and hub to access the sensor..... was hoping to not have to do that much effort. I'll do the time, though, whatever it takes.

Thanks again!

Remove the brake rotor, caliper, and caliper mounting bracket. You do not have to remove the hub itself. Turning the steering wheel one way or the other will give you pretty easy access. Remove the sensor, clean away all the rust, and make sure the sensor mounting plate is nice and flat before reinstalling it. If you shear off the metal push rivet I wouldn't fret over it, you can drill it out or just forget it. Mine has been fine without it. Good luck.

 

[c good]

Marginal and aging (salt-abused) rotor speed sensors at the front hubs have also been reported to fire off the ABS when slowing to a stop. You can test this by pulling the ABS fuse to disable the system for an experiment.

The Roadie nails it again! I always enjoy learning new quirks of our rides! c good

 

[Robbabob]

Close the books on this one. Cleaned the ABS sensor on both sides in front and the issue is gone.

Found another, though... time to start a new thread and learn something new.

Thanks y'all!