False ABS Activation LS400

[Tinonline]

(long post warning: please ensure you have you’re preferred beverage ready and are comfortable) 😁

Typical, after the hassle of working through a front wheel bearing replacement: finding a garage that would split the hub, extract and install and fretting about OE or non OE…there were unintended consequences.

I’d driven over 40 miles and it was my return journey. As usual, the Lexus sat nav only knew the Roman and medieval cart tracks, so I ended up more cross country than intended. Some of my sojourn was spirited. Halfway point saw me detoured through Farnham in Surrey and on braking to a stop from 5 mph downward the ABS on the wheel with new bearing kicked in without need. It did it on every firm stop. There was no ABS light activation.

Oh great, so I wondered what in the wheel bearing was wrong…incorrectly mounted? Wrong way around…? Except there’s no magnetic reader…dirt…as the bearing had worn in from grease?

I tried again from cold this morning…same from a modest speed: it grabbed and squawked with the brake pedal flutter. Just on the one wheel.

OK, so Google revealed this was a common potential problem with all wheel bearing repairs and sometimes brake replacement; but it wasn’t that easy to pinpoint a fix.

My Drivers’ side front had a new SKF bearing with new nut and oil seal. I had spray cleaned the disc and pads on that side. Everything had assembled easily and I’d torqued up all bolts to spec. Nothing untoward occurred in the first miles post new bearing fitting.

So I removed the drivers’ side wheel/removed the abs sensor with a 1/4 drive 10mm socket. A small bit of dirt sat indirectly - a little on the sensor head, the speed ring looked relatively clean.

Using cotton buds I cleaned the ridged ring via the sensor mounting hole. It was lightly grubby. Then packing said hole, I took to my metal file and filed away the rust buil-up around it and the surrounding areas. I wiped it with a WD dampened area of cloth after blowing away debris. 

The sensor was cleaned with a cloth and tiny bit of WD on the cloth before wiping clean. I’m not a fan of copperslip, but I smeared this around the collar/seal of the sensor. I refitted the sensor using the handled file and soft mallet to work around the shoulder of the unit and pushing by hand I observed it was firmly home with a little of the copperslip squeezing out from the body of the sensor. 

Then to the untouched side. Wheel off/spray cleaned the discs and through the back of the caliper, wiped off the dirt. This time on removing the sensor I was greeted with a different sight. The speed ring was well greased and the sensor was covered by a decent layer too. Again using cotton buds I cleaned off as much grease from the speed ring as possible. Removed it too from the sensor. I repeated the process of filing away rust build up to a clean flat surface, used the copperslip and put everything back together.

The sensors’ 10mm bolts were torqued to 7.8 Nm.  by the way.

I disconnected the Battery and went away for a coffee. With the later LS400 after reconnecting the Battery it’s a turn of ignition key to position ON so ignition and dash etc are on and wait for 6 minutes then switch off. Then you are good to go.

All fired up so off for my test drive. 

I know the experts talk about different tolerances, too much signal variation between the two wheels on the axle, air gap from sensor to ring…and I’m sure that’s exactly what it is. 

I’ve equalised the sensors working environment I suppose. If they were both grease covered maybe that would have been fine. 

All is well and back to normal. Hopefully this will continue. 🧐

I reckon if you can’t balance it all up it makes sense to replace both bearings. But there again, given mine was shot for example, and it didn’t once trip the ABS, it does seem to be about balanced operating conditions for the sensors.

Probably, I could have just worked on the non repaired side to achieve the fix.

Hope this is useful.

(apologies the photos are a bit rough)

 

 

 

 

 

[BigBoomer]

This is amongst the many reasons why you always replace brake pads and disks in pairs. Unbalanced braking is not safe.

On my GTR1400 you can mount the front wheel the wrong way around.
This means that the reluctor ring is on the wrong side for the sensor, and hence ABS error.
It's amazing how often it comes up on the forum. 🤣

[Tinonline]

Pads and discs no option but in pairs.

Shock absorbers same. Springs you should too. 

Coil on plugs on some cars like Jags : all of them … wheel bearing I believe is a unit by unit replacement if the mileage is moderate.

[The-Acre]

15 hours ago, Tinonline said:

Pads and discs no option but in pairs.

Shock absorbers same. Springs you should too. 

Coil on plugs on some cars like Jags : all of them … wheel bearing I believe is a unit by unit replacement if the mileage is moderate.

A good bit of info which should be very helpful to someone, and an impressive picture of your thumb! 

[Tinonline]

1 hour ago, The-Acre said:

A good bit of info which should be very helpful to someone, and an impressive picture of your thumb! 

To explain😂left of thumb is the sensor covered in grease … it’s not obvious if you don’t know the part! T’other one was clean: not grease covered.