@2001LC I've tried a few more things. Retightened both front wheel bearings, replaced rear ABS sensors (all have been changed now) and checked (unplugged and replugged) all abs ecu plugs
If no DTC indicating a bad wheel speed sensors. Your old ones are likely good. So was not the issue.
I did the "Pump brake pedal rapidly. See how many pumps, until ABS alarms sound off and dash warning lights come on. 17 pumps or more is good indicator, 7 or less pumps, not so good" and the alarm and ABS light activated after 19 pumps so seems to be OK?
Yes. Sounds like good accumulator and seal in master.
I tried disconnecting the front sensors which as expected brought up the ABS light. I assume this would mean the ABS system is then disabled? The fault still randomly occurred so now I'm not sure whether it is a function of the ABS activating or not.
If ABS CPU detects most any DTC (code), not just brake related. It shuts ABS system down. DTC may correct and clear on it's own, in just seconds if no longer detecting trouble code. Meaning not all must be cleared. Which you may see dash lights. But these will not activate ABS braking.
So again I'll ask. Is this just dash lights, with actual ABS braking?
I'm very tempted to remove the aftermarket discs, pads and brake lines and replace back the factory ones to see if this eradicates the problem even though that's a fair bit of work just to try and rule all of those components out
Not likely a new parts issue.
Hey all,
My 98 HDJ101K has recently developed a very unwanted ABS issue. When moderately braking from anywhere around 30 mph to a stop as in approaching an intersection, the
Low speeds, are also low RPM. Alternator turns slower generates less power, especially if old weak. Voltage issues, can result in ABS lights, but would not activation of ABS braking. At least I've never heard of activation due to low voltage. Nor, can I think of reason it would.
"ABS will activate when there has been no lock up of any wheels."
Backing up a bit here:
ABS activation, happens when any wheel is turning (exception is wheel speeds, during normal turning) is at different speed than others. The ABS CPU see this, form input from wheel speed sensors. ABS then brakes, faster spinning wheels.
So to saying:"no lock up". Are you saying no wheel is being braked. It's just dash light coming on?
Or
Are you saying; ABS is braking (slowing vehicle). You hear the crunching sound of activation, and vehicle perhaps pull to one side or the other. Even though all wheels, were turning the same speed.?
It's intermittent and I'm struggling to find a distinct reason for it occurring. I generally lift off the brakes and the ABS action will continue for a little after before ceasing.
Are you saying: ABS system, is braking (slowing vehicle) even after foot is off brake pedal? Not just ABS light on dash?
I have tried emergency braking on dirt roads and the ABS activates as it should. Many times on sealed roads even with hard braking it will not occur.
This has started after having changed all discs and pads (to an aftermarket one DBA) and installing flexible braided lines to each calliper.
DBA rotors (disk) are very good disk and pads. I've never seen one with runout, out of spec. But, wheel hubs, transfer its runout to rotors disk. If wheel hub runout out of spec. Runout multiples, the further from center of axle. I've not seen runout so bad, it activates ABS (I've seen some very bad run out). But, If bad enough, at say just one wheel. Like FR. I suppose it could result in that pad and disk, running hotter than others. You'd likely see more brake dust at that wheel.
Tone ring needs to be in good condition. Wheel bearing tight, so that wheel speed sensors is not trying to read a tone ring that's wobbling. Oil seal, in correct, with flat side out.
Oil seal in backward, results false wheel bearing preload. Then as metal of seal rubs on inner area of knuckle spindle, it wears. Bearing loosen very fast.
Callipers were cleaned and slides lubricated so they all function well. Brakes were bled old fashioned way, simply opening rear bleeders and allowing pump to push old fluid out. Fronts were bled with the pump, hold, open bleeder method. I have bled them twice again since this problem started occurring. I have bled the accumulator 3 times with the 30+ pump method which seemed to lessen the amount of times this problem occurred but obviously hasn't stopped it.
The timing on how long booster motor/pump runs. Over 40 seconds with battery voltage about 12.4V. Is clue, air in system. Can also indicate a seal weep/leak or weak accumulator. I've also found, not using Toyota brake fluid, I get longer run times.
At no stage during pad/disc/hose change or the bleeding the process was the reservoir emptied to a point where it would have drawn air.
While flushing from rear, it's okay to let level drop below minimum, in reservoir. We then bleed, and must keep level above minimum during bleed.
There is a much larger accumulation of brake dust appearing at the right hand side front wheel.
As stated, could be a runout out issue. Can also be pad assemble issue.
Did you properly install the OEM outer shims in front calipers and the fitting clips? Many do not when using aftermarket pads.
The outer shims, grabs onto caliper pistons and clip o pads nearest wheel hub side of pad. The fitting kit, lock outer shim (outer edge, furthest from hub) to pads. Without them, pads will where faster. Pads ride on disk more so, than with proper shim install. They, connect pad to piston. Piston, pulls pads away from disk, as piston seal retacts piston (returns to relaxed state). If they're not installed properly, pads may wear faster. This could explain, more brake dust on one side.
I suppose it is possible, for a caliper piston to stick. But I've never seen this happen. Let's say front right caliper pads, rubbing disk most all the time. That disk and pads, would heat up more than others. Then as you brake, you get uneven braking from uneve heat. This "may" (i've never seen this), result in ABS (braking) activation, as that one wheel slow faster than others.
We have two different size shim kits. 98-02, fit the smaller pistons. 03-07 for the large pistons. Or so is case in the USA 100 series. Toyota increased front braking in 2003, with the addition of larger pistons in caliper. Mismatching calipers, from one side to the other. Say FR caliper is the updated (larger piston), and FL is the original (smaller piston). This would result, in one side braking more than other.
I have changed both front ABS sensors for new ones but am now at a bit of a loss to find the cause of this issue. No ABS lights / buzzers appear when it happens.
Has anybody experienced anything like this or have some sort of idea where I should go from here?
Cheers
If I understand correctly. This whole issue only began after you serviced wheel bearings and brakes (new DBA's). You then R&R some wheel speed sensors, due to ABS issue.
So it is more than likely, a procedural error during R&R. Not one of the part installed bad.
It is also possible you've a failing master. I've seen where ABS unit (black box on master) failing to deliver proper power to booster motor. These are usually form long term resistance issue in wiring, from battery to fuse box and on to master. This is almost always, due to acid corrosion. Sometimes, this can affect the ABS relays in fuse box, and on downstream to ABS, even booster motor. Other times, it just increased resistance at brake control wire. This is due to corrosion on it's leads, inside brake control wire boots (bottom of ABS unit and on booster motor). This can result in premature wear of booster motors commutator. We then sometime get, intermittent booster motor starts.
I just had one with brake alarms (ABS was not activating), I found many issues. I worked one by one, until ultimately replacing the master. Each I corrected had a positive effect.
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