Pulsating ABS With Normal Braking On Dry Surface

[Pete_L]

My '93 2wd Explorer, equipped with a limited slip differential, has developed a problem wherein upon applying brakes on a DRY surface, the ABS starts to pulse at slow speed, & gives that familiar "machine-gunning" sound, as if it was slipping on ice ( or any wet pavement ). Is this likely caused by the rear speed sensor or a RABS sensor or even some electronic module? I plan to have it scanned for ABS error codes at the dealership ASAP, as it drives you crazy! Anyone have any ideas RE: cost for parts or repairs? Can used parts be used? ThanX!

 

[v1rotv2]

I have seen this problem. The cause was warped rotors. The ABS thinks it is going in and out of a skid. Have your rotors checked.

 

[Hokie]

Could also be a sticky caliper or caliper slider pin bolts, at low speed the computer could be sensing the speed difference between the wheels and kicking on the ABS. Mine was doing the same with a sticky caliper slide pin.

 

[Pete_L]

Pulsating ABS @Slow Braking Speed (under 15-20mph till stopped)

Had a garage mechanic check the rotors ... not warped...the calipers seemed okay...no sticking pins or parts. The Ford dealership mechanic tried to read the codes with their scanner, but apparently it couldn't communicate with the older pre-1997 Explorers...therefore, no error codes...& besides, the ABS dash lite didn't come on when this premature ABS braking problem had occurred so....I was advised that both front wheel sensors as well as the rear wheels sensor should be monitored by connecting voltmeters to all 3 of them while actually test-driving the vehicle (not just spinning each tire individually while the SUV is raised up on a hoist with a voltmeter hooked up one sensor at a time); then perform an ohmeter check of the sensor wiring harness(s) & connections; next, swapping the electronic module with a known good one. As this would probably be labor intensive & (>$100/Hour) expensive @ the dealership, I disconnected the ABS at the module under the hood & have taped over the ABS dash lite for now. Incidently, the dealership would have to order the 2 ABS sensors (as they recommend replacing them in pairs) @ ~$180/pr., as 2wd 93 Explorer wheel sensors are not a common stock item here...So I'm open to any further comments guys...though, "You really don't need ABS anyways, just as long as the brakes work!" ain't one I want to settle forever! ThanX again....

 

[BeetleBailey]

Did unplugging the module make any difference? I'm also curious on how the mechanic checked your rotors? And I also wonder why the dealership could not pull diagnostics on it? Just curious, Bailey.

 

[Pete_L]

Pulsating ABS @ Slow Braking Speed ONLY (ie. <20mph)

After disconnecting the ABS contoller module, the braking problem @ slower speeds completely disappeared, but of course, the ABS dash lite came on & remains lit under the black tape used to cover it. The rotors (& both tone rings also) were visually inspected only ... but no apparent serious warps were detected when each was spun with each tire off. The mechanic did mention that the driver's side lower ball joint seemed somewhat loose, which might account for a poorer sensing by the wheel sensor, but I kind of disregarded that as pulling straws a bit...The dealership service stated that it didn't have the ability to draw error codes from my 93 model because their electronic scanner unit couldn't communicate with the ECU in my older Explorer ( ie. supposedly they code only pull codes from 1997 & newer versions)...& besides the ABS dash lite wouldn't come on during the slower braking speed ABS problem...therefore no codes. He still felt that it was likely a wheel or rear ABS sensor problem, but it would have to be checked out the old fashioned way by-hand testing using VTMs for each front wheel & one for the back ones...So for now.....No ABS!

 

[ma96782]

I wonder.....what IF you bleed the brakes? Bleed a lot of the old fluid out.

I mean that there may be some dirt in the line? Hey.....it's a cheap try/check.

Aloha, Mark

 

[BeetleBailey]

Checking rotors by "eye", is crazy. And your dealership should be able to diagnose your ABS problem. ABS is still controlled by your comp. Sounds to me like they're to lazy to actually do it.JM.02 I could actually agree to a rear sensor being faulty but I doubt it. I would, in my unprofesional wisdom, do a complete brake job and see what happens. Bailey.

 

[xjames]

I agree with the brake job. My 91 had the same problem and the dealer told me that my rotors were fine and the sensors were "probably bad", and if that didn't fix it that I would need to replace the comp. There were no lights to indicate an error. So the first thing I did was bought 2 new rotors, a set of pads, and big bottle of brake fluid. I also replaced the wheel bearings while I had the rotors off. I completely flushed the entire system out with the new fluid. Much to the dealers amazement this fixed the problem without the need for a new sensor or comp. and especially without the dealers outlandish labor rates. Kinda makes you wonder just wich cracker jack box you have to buy to get an SAE certification these days.

 

[lilbeefy]

I wonder.....what IF you bleed the brakes? Bleed a lot of the old fluid out.

I mean that there may be some dirt in the line? Hey.....it's a cheap try/check.

Aloha, Mark

changing the fluid worked for me in my 96.

 

[RJDriver]

I thought I'd add my 2-cents.... I just solved the exact problem being discussed here. To recap the issue....while applying normal, steady brake pressure on dry pavement, the ABS appears to "kick-in" and scare the daylights out of ya....possibly missing a stop sign or intersection stop light!!! YIKES!!! The interim fix was to pull a fuse or two to disable the ABS.

My problem also tended to turn the wheel a bit which lead me to believe it was just one side....but I'm more of a replace both sides kind-of-guy...because if one side has gone bad, then the other may be shortly behind it.

I searched through the threads and here is what I did: my rotors were less than a year old, so I put the thought of warped rotors on the back burner. I leaned towards bad front sensors. Upon inspection, the left front sensor had snapped off clean, leaving the probe lodged in the mounting hole; so that one was a no-brainer. I decided to go ahead and replace both front hub assemblies; there is a great how-to thread complete with pictures. The hubs I bought came complete with the sensors already installed. Since, everything was torn apart, I cleaned and lubed the moving parts on the brakes as a way to hedge my bets. Once it was all back together, I repowered the fuse box and test-drove it around the neighborhood. So-far-so-good; knock on wood!

We have a 300-mile road trip over Thanksgiving that should provide an ample sampling of driving conditions....if it's not fixed, I'll be back here looking for my next answer!