Brakes Slipping? or ABS Operating at 3mph?

[Paul Davis]

I am experiencing a problem almost indentical to that posted by Texassizeruckus on 4/25/05. I could not find a post that described an ultimate fix.



I have a '01 2wd ST and I recently replaced the front brake rotors with the SP Diamond Slotted rotors with the integral speed sensor pick-ups(the fan-looking arrangement)



Since replacing the rotors, I am also experiencing a "brake slip" when coming to a stop. It only does this when I use relatively little break pedal pressure. For most normal or even hard stops, there is no slip. The brake pedal does "slip" also, moving down maybe 1/4" (just like texassizeruckus experienced). I have learned that I can deliberatley cause 2 or 3 "slips" by being careful how I apply pressure to the brake pedal.



* The ABS warning light is not on.

* My Check Engine light is not on.

* When changing the rotors, I did clean the ABS sensors with 0000 steel wool, just to polish corrosion off the surface. I have worked with magnetic pick-ups for 20 years & have not had any problems.

* I did not bleed the brake lines, like I should have, but no air entered the brake system.

* I have not tried (yet) to remove electrical power from the ABS system to remove it from the hydraulic circuits.



My first thought on this was that is seems that the ABS system was kicking in as the wheels were coming to a stop. I think there is actually a minimum speed before the ABS system is even supposed to operate - something like 20 mph. I have also thought maybe one of the semi-metallic brake pads was slipping.



After driving about 1000 miles, I still haven't solved the problem. I have looked at the brake pads and rotors and they look just fine. There is no oil or grease on the rotors.



Have any others experienced this "slipping"?

 

[Todd Z]

Two things,

did you lube the caliper slides and the anti squeal/rattle clip[s also??? They can hang up and then release causing a slipping then a slight drop in the pedal..

Also IF your not feeling the ABS pulsate the pedal, then the issue is not ABS...



And even if no air/dirt entered, when you compress the caliper there could have been a bubble or slight rust chip in the line/abs or caliper that you moved into the system, causing the issue...



Todd Z

 

[EddieS'04]

You say you did not bleed the system. If you pushed the pistons in and didnot push the old fluid out, you might have trashy fluid in the ABS unit. I never push the caliper pistons in without opening the bleeders.

 

[ChrisP Riley]

I know exactly what it is!! I have an 01 S/T also and when i changed mine they did it too. What it is, is the fan looking thing on the back of the rotor. It is either to close or too far from the ABS sensor. i think mine was to far in. Try pulling it out carefully and evenly and that should take are of it. Please let me know if this helps. Later on, Chris

 

[Richard L]

Perhaps a damaged ABS Sensor, or perhaps the pulse ring is dirty, or not the correct type for the Sport Trac? However, I think either would make your brake slip?



I'm thinking that Todd may be on the right track. The pads can be sticking or installed incorrectly. The rotor may not have been cleaned properly and has some grease or a protective coating that was not removed.



It's also possible that your caliper bores have some corrosion that is causing the pads to stick and engage unevenly. This could explain why heavy braking does not cause a problem while the caliper sticks only during light braking.



The sticking caliper is caused when the piston bore gets rusted or corroded and the pitting causes the piston to stick. This is most noticable after new pads are installed because the pitting is caused by the fluid behind the pistons. When new brake pads are installed the oisons are pushed back in to allow for the thicker new pads. Now the spiston are riding over the pitted part of the bore that used to be behind the piston.



Also, If you just pushed the pistons back into the caliper bores without releasing the bleed screw, you pushed the dirty contaminated fluid back into the ABS unit and may have clogged up something or caused the ABS unit to malfunction? You should never push the pistons back into the bores without opening the bleed screw to avoid pushing the contaminated fluid back into the ABS and/or Master Cylinder.



...Rich

 

[Philip Stanfield]

i'm having the same problem on my 02 trac...and i also just changed the pads and the rotors...so should i just open up the bleeders and force out all the fluid and put new brake fluid in? i think i may have forced the pistons back in too fast or hard because at one point a little brake fluid shot out from the piston...any suggestions?

 

[Richard L]

Phillip,

If you pushed the pistons back and fluid shot out the piston, you may have clogged up brake line and now you have a leaking caliper. It's possible that your piston bore was corroded and pitted, and when you pushed the piston back you damaged the piston and/or seals.



That caliper needs to be rebuilt or replaced (if not rebuildable). I would recommend trading in both calipers for rebuilt units, because if one is damaged due to corrosion, the other one is probably not too far behind. Since most rebuilt calipers are fairly inexpensive, I will usually replace the old calipers with units every time I change front brake pads and avoid all potential problems.



I have been doing brake jobs for many years and I always recommend opening the bleed screw before pusing the pistons back. This servers a number of purposes:

1. It removes much of the contaminated fluid and does not force it back into the ABS unit or the Master cylinder.

2. If you capture the old fluid in a jar, you will get a good look at the condition of the fluid and any contaminates.

3. It makes the pistons easier to push back with just your fingers. By using your fingers to push the pistons back, you can feel any binding or or grating that would indicate a rusted, pitted, or otherwise damaged caliper bore. If you use a C-clamp, you have no way of knowing if your caliper is bad and you may be wasting your time and money doing a brake job that will soon fail.



...Rich

 

[J Fennell]

Identical Scenario!!!!! Same year, model, and same replacement rotors= exactly the same problem. Here's what I posted originally.





I just installed the SP Performance Diamond slotted rotors (I bought the ones for an '01 Explorer Sport, but I've seen posts here that say they are the same as the '01 ST's) on my '01 ST and I now have an ABS issue. When I am coming to a stop, just before the truck rolls to a stop the ABS kicks in and pulses my front brakes. I've checked the ABS sensors and the tone rings for any damage and cleaned everything numerous times with no change. The new rotors appear to be identical to the stock rotors in dimensions and the tone rings have the same diameter and number of teeth.



Update-

I found that one of the rotor's tone rings was a little off by using a ruler to measure the distance from the tone ring to the surface of the rotor using a straight edge. It was off on one side about 1/16th of an inch causing a change in the air gap at the sensor as the rotor rotated. I believe this may have been the majority of my problem.



So far, the problem has not reappeared. I'll drive it a few weeks to burnish the new rotors then put the new pads back on it. We'll see what happens then.



The tone ring had obvisouly been slightly warped or bent in transit. I fixed mine by creating an equal air gap between the rings and the pickup on both sides by using a large screwdriver to bend it back in place. I have not had a problem since (about 6 months).



Good luck!!

 

[Paul Davis]

Wow. Thanks for all the comments.



I did lube the caliper pins.

I did Not lube the anti-rattle clips. Would doing this get grease on the rotors?

I wished I had known there was a bleed screw. My repair manual scared me out of bleeding the systems due to a risk of getting any air into the system ans ultimately into the ABS unit.



I don't think I am getting any pulsing from the ABS. I think I will look next at a sticking caliper. One reason I replaced the rotors is I had an extreme uneven wear on the left front rotor. The inboard brake pad would wear much faster than the outboard pad. I thought this might have had something to do with a wreck a couple of years ago where a truck hit my Trac at the left front wheel.



I tried to paste a photo of the old brake pads, but I guess I don't know to do that on this site.



Thanks again.