Over active ABS ?

[drallan]

Over active ABS, speed sensor?

99 3.4ltd 4x4 165,00k

The past few days my ABS has been kicking in a lot more than I expect. At least I am assuming it is the ABS, I hear a loud grinding noise up in front of me coming from the engine compartment and I feel the pedal pulse and get stiff. Brake fluid level looks good, no lights and brakes were bled about 2 months ago when I had rear axle seals replaced. Otherwise braking is good and I have a decently stiff pedal.

I'm talking about a few times a day when I come to a stop at stop signs or pull in to my driveway. I think in the 1st 18 months I owned the vehicle it never kicked in, now it's frequent. The first time I felt it was about a month ago during one of the snow storms we got here in the mid Atlantic. It occasionally kicked in for the past month, but I always attributed it to the snowy/icy conditions. But for the past 3-4 days the roads have been clear, wet, but not icy and not a ton of standing water. I did have 1 instance where the pedal was rock solid and brakes barely worked. I pumped the pedal a few times and eventually the worked as expected. I chalked it up to the single digit temps and perhaps sticky vacuum check valve. Hasn't happened since.

I have used 4wd quite a bit over the past month and have driven through some pretty thick mud. I've taken advantage of the conditions and cycled down through 4lo and rear lock back up to 2wd. Suspension is stock but I'm running 265/75/16 Revo IIs. The rear 2 are at about 50% the front passenger about 25% and the front driver is down to the bars. I've got a set of AT/3s on the way (thanks to discount tire ebay deal) and they should be here by the end of the week, hopefully I can get them installed along w ITE/OTEs early next week. Only other things I have done recently are a few tranny drain and fills w/ valve line max life (level is good) and replaced front sway bar bushings and brackets.

Do You think it's just the bald front tire that is slipping? Or maybe the uneven wear is causing the computer to sense to great of a difference in rotation and triggering ABS? Sticky caliper? Anything other than the ABS I should be concerned about?

I guess I will find out once I get the new tires on, but am looking for things to checkout this weekend while the weather is nice before I get them on. Thanks.

 

[BlackCat914]

99 3.4ltd 4x4 165,00k

The past few days my ABS has been kicking in a lot more than I expect. At least I am assuming it is the ABS, I hear a grinding noise up in front of me coming from the engine compartment and I feel the pedal pulse and get stiff. Brake fluid level looks good, no lights and brakes were bled about 2 months ago when I had rear axle seals replaced. Otherwise braking is good and I have a decently stiff pedal.

I'm talking about a few times a day when I come to a stop at stop signs or pull in to my driveway. I think in the 1st 18 months I owned the vehicle it never kicked in, now it's frequent. The first time I felt it was about a month ago during one of the snow storms we got here in the mid Atlantic. It occasionally kicked in for the past month, but I always attributed it to the snowy/icy conditions. But for the past 3-4 days the roads have been clear, wet, but not icy and not a ton of standing water. I did have 1 instance where the pedal was rock solid and brakes barely worked. I pumped the pedal a few times and eventually the worked as expected. I chalked it up to the single digit temps and perhaps sticky vacuum check valve. Hasn't happened since.

I have used 4wd quite a bit over the past month and have driven through some pretty thick mud. Suspension is stock but I'm running 265/75/16 Revo IIs. The rear 2 are at about 50% the front passenger about 25% and the front driver is down to the bars. I've got a set of AT/3s on the way (thanks to discount tire ebay deal) and they should be here by the end of the week, hopefully I can get them installed along w ITE/OTEs early next week. Only other things I have done recently are a few tranny drain and fills w/ valve line max life (level is good) and replaced front sway bar bushings and brackets.

Do You think it's just the bald front tire that is slipping? Or maybe the uneven wear is causing the computer to sense to great of a difference in rotation and triggering ABS? Sticky caliper? Anything other than the ABS I should be concerned about?

I guess I will find out once I get the new tires on, but am looking for things to checkout this weekend while the weather is nice before I get them on. Thanks.

Sounds like you have a wheel speed sensor on its way out.

 

[drallan]

Thanks for the suggestion. Is there a diagnosis or test for that? I searched and found a few threads but none with a real diagnosis, some had you put an ohm meter on it and check for resistance, but if mine is failing but hasn't failed I'm not sure how reliable the test will be. And everyone else had and ABS or CEL light, should I just wait for it to go and throw a code?

Is it possible that it just gets dirty or cruded up? Potentially mud or gear lube from when my rear axle seals went out? At rough $100 a piece, I'd rather not throw parts at the problem, especially if I'm not sure which one. Is it something I can pull out and clean?

Any chance changing the tranny fluid did this? I just did a plug drain & fill early feb, then one again this past weekend.

Is this an immediate repair required or is it safe to drive for a few days until I can get to it this weekend? Obviously proper brakes are essential, but is this something that will just fail or will it just be an annoyance until I get it taken care of?

Some more info,
It only happens at low speed, almost before I come to a stop. Almost the slower I go the worse it is, hard braking doesn't trip it until I almost stop. No pulling during braking.

Thanks

 

[squabeggz]

Check to make sure your abs sensors are fully seated. I had this exact same issue after I redid my front end. I thought I got them seated all the way in, but they were just a mm or so from being totally seated. This caused my abs to trigger almost every time right before I came to a complete stop at slow speeds. I almost rear ended a few people due to this.

To fix it, I removed the sensors and wire brushed the mounting surface of the axle housing (rust can also build up and push the sensors up just enough to cause this problem....or so I have read). Mine were pulled out due to other work and not seated when re installed...I read the rust theory on other vehicle forums. Anyway, when re-installing, I put them in as far as I could by hand, lined them up to the bolt hole and then took a short piece of wood and a rubber mallet to gently but firmly tap the sensor into the fully seated position (do this at your own risk...probably not recommended but it worked for me. These things are plastic and expensive. I used the wood to give me a surface to hit since my mallet was too big to get a clean shot to the sensor in that tight space).

Also, careful with the rubber o-ring on the sensors. I almost lost one.

After this they set flush, even though they looked like it before as well. I could definitely tell the difference though. I checked all four just because it was easy. After this my problem was solved. Haven't had it happen since.

 

[Chuckles89]

You could always disable the ABS :hiding:

 

[1985taylor1925]

Theres a thread somewhere on the forum about the fritzy abs systems on our 3rd gens. It turned into a huge debate about whether or not we should disable it by pulling the fuse. I don't remember what year it was, but somewhere in the 3rd gen range they made some improvements on the abs. It might be 99, but again I cant remember. I do know that the 96 to 98s have a terrible abs system. The first year I had my truck my abs sent me about 10 ft into an intersection when one tire hit a patch of gravel on a dry paved road in the middle of the summer. The abs kicked in and I lost all stopping control . . . on a dry paved road on a summer day! After that happened a second time I determined (like many other have) that my abs made my vehicle more dangerous, rather than more safe as it is intended to do, and I pulled the fuse. But yours just sounds like the abs is not functionally properly. I am NOT suggesting you disable your abs. Not yet anyways . . .

 

[drallan]

I will definitely pull them this weekend clean and check them out. I haven't personally removed them, but I'm assuming they were removed when I had the rear axle seals done, so I'll check those first, maybe they didn't get seated properly.

It appears to be getting worse, in just the past few days it has gone from intermittent to almost every time I stop. Funny thing is, the slower I brake the more it occurs. If I come to a hard stop it doesn't happen, but if I slowly coast they pulse for a quick second right before the vehicle comes to a stop.

I may pull the fuse just for the next few days to stop they annoyance factor. But I'm not really keen on the idea of making it a permanent thing. It hasn't been an issue for the first year 1/2 of ownership and I'd like to really solve the problem. I transport my 2 y/o and soon to be infant in this car and want all the safety features possible. On top of that, not really sure what the insurance implications would be if there were to be an accident if I intentionally disable the ABS.

 

[jeremyc74]

My money is on the bald tire.

 

[drallan]

My money is on the bald tire.

At first I was thinking/hoping that would be the case, but do you think it is because it is slipping or that the tire size difference is tripping the system?

I could see it slipping if it occurred when braking hard, but the fact that the system kicks in when I am creeping to a stop at less than 5mph has me thinking that's not the case.

 

[jeremyc74]

At first I was thinking/hoping that would be the case, but do you think it is because it is slipping or that the tire size difference is tripping the system?

I could see it slipping if it occurred when braking hard, but the fact that the system kicks in when I am creeping to a stop at less than 5mph has me thinking that's not the case.

Hmmm...could go either way. It might be worth while to swap the rear tires to the front and take it for a test drive. Then you'd know.

 

[squabeggz]

This still sounds exactly like my issue. After I redid my front end, everything worked perfectly. It took a 500 mile road trip and a week or two of daily driving before it started happening. My ABS light never came on. It got worse and only seemed to happen right before I came to a stop at slow speed...around 5mph. They are a bit subborn to get out, so it was no suprise that they didn't get seated all the way back in. My money is still on the unseated sensors.

 

[squabeggz]

Hmmm...could go either way. It might be worth while to swap the rear tires to the front and take it for a test drive. Then you'd know.

There are wheel speed sensors on all 4, so I'm not sure moving the bald tire around would tell you anything. The abs would still activate and it would still sound like the front because that is where the abs module (grinder) is.

Before I redid my front end, my passenger front tire was basicly a racing slick due to completely worn out components. The other 3 tires were decent. During that time, I never had the ABS trigger like described.

 

[drallan]

There are wheel speed sensors on all 4, so I'm not sure moving the bald tire around would tell you anything. The abs would still activate and it would still sound like the front because that is where the abs module (grinder) is.

Before I redid my front end, my passenger front tire was basicly a racing slick due to completely worn out components. The other 3 tires were decent. During that time, I never had the ABS trigger like described.

So I was able to get under her for a bit this afternoon and pulled the rear two sensors. I can't say for sure, but it looks like the shop never removed them when doing rear axles seals. Both came out easy enough (I was overly causes not to break bolt tab as they are 16 yo plastic) but looked like they have never been touched. The drivers side was covered in grime and gear lube, the passenger side was slimy but not as bad. I cleaned em both up and reinstalled. Took maybe 20 min all together. Afterwards I took her for a test drive and low and behold I couldn't for the life of me trip the ABS. So looks like problem solved, I'll see how she holds over the next few days.

Now the bad news, I'm assuming they aren't supposed to be covered in gear lube. I'm hoping that the slime was just left over from the blown seals I had fixed, and because the shop didn't remove the sensors they were still wet from the old stuff. What had me concerned a bit is the fact that when I stuck my finger in both the sensor holes and felt the ABS ring it too was covered in gear oil. My understanding is that the seals are toward the inside of the axle in comparison to the ABS ring, so there is no reason it should be slimy. Again unless it is left over lube from the swap. Otherwise it means the seals aren't holding. There are no obvious signs of leakage from the outside, wheels are dry and the back of the drums looked good (didn't pull them off). Gear lube didn't come pouting out of the ABS sensor holes, but they are about level w the diff fill plug, so that isn't really a good indicator. This weekend I'll pump some more gear lube into the diff. If it doesn't take any then I'll assume the seals are holding,.

I'm having the same shop that did the seals install the tires, so I'll have them check everything out better when they have it up on the rack w wheels off. Hopefully problem is solved. Thanks for all the help. Fingers crossed.

 

[squabeggz]

Hope that fixes your problem. They don't have to be off by much to trigger the abs. Sucks about the gear oil. The shop should have cleaned out the old oil, so it should be dry in there. Doesn't sound promising.