LS400 intermittent brake problem

[Colin M]

I wonder if anyone can shed any light of an intermittent brake problem that is occurring on my LS400 Mk 3.

Occasionally, usually at low speed when braking and just before coming to a stop, there is a grinding/grating noise and some juddering. I have taken the car to my local garage for them to have a look. The fault did not appear on their first road test, so they gave the brakes a good look over and inspection, reporting that “All look to be in good condition. No signs of uneven wear, scoring or corrosion”.  The fault did occur on a second road test and the tester said “It feels like the abs system is kicking in”  but he was unable to run a diagnostic check as the garage did not have the correct adapter plug to access the OBD port.

Before taking the car to the garage, I had thought about a possible abs fault which might explain the juddering as the brakes are being applied on and off but would not have expected any accompanying grinding/grating noise. I had also thought about a small stone being trapped somewhere around one of the brake discs (we have a gravel drive), which I mentioned to the garage but there was no sign of any stone.

I may have to visit a main dealer to get a diagnostic check (is the LS400 diagnostic plug an unusual one so other garages are not likely to have an adapter to gain access?) but thought I would put up a post on here first before doing so to see if anyone else has experienced anything similar. Any comments or suggestions gratefully received and thanks for taking the time to read this.

 

[Malc]

I'm not at all sure that there's any appropriate OBD port etc with our ancient steeds ........... someone with greater knowledge might know of this tho'

......... there's a ( physical )  grinding noise with juddering .?    it's physical ... get someone else / somewhere else,  to get the car up on the ramps and really really check each wheel .......  hopefully you will discover that stuck stone somewhere

Good luck

Malc

[Razor61]

i think the garage may be right with the ABS kicking in.
Have a watch of the YouTube video in the link below, you can hear the noise the car makes when the ABS kicks in.

https://youtu.be/TTQvz18oeoI

[Tinonline]

2 hours ago, Razor61 said:

i think the garage may be right with the ABS kicking in.
Have a watch of the YouTube video in the link below, you can hear the noise the car makes when the ABS kicks in.

https://youtu.be/TTQvz18oeoI

Agreed … if there’s no stone or dust guard or suspension related issue it might a simple job of removing front wheels and abs sensors: cleaning and cleaning the gear rings in situ. A sensor might be faulty so replacing both would be one method but OE is a bit steep on the wallet. Plenty of good alternates. I believe the abs would tend to grab though and it’s usually on one side…

Do you have OE brakes? Plenty of non OE pads will make a noise…

[Colin M]

Thanks, guys, for your helpful comments. Giving the abs sensors a clean up might be a good first step to see whether this solves the problem.

 I am not sure whether the abs sensors are OE or not. They have been on the car since I have had it and there is no record in the service history (which is pretty comprehensive) of them having been replaced. They just might be the original ones!

 I do have OE brakes as regards pads and discs - new front discs and pads were fitted about three years ago.

[Tinonline]

It’s a good start…do clean the gear wheels of the abs with ear buds you’ll need quite a few and on removing the sensor which may take gentle wiggling and persuasion…you’ll see the teeth through the hole…

You mentioned your brakes were inspected…were they cleaned too? 
With the wheels off the ground might be worth checking there’s no play in the wheel bearings.

[Colin M]

Thanks, Simon. Is the first step to remove the sensor (and is it threaded so removal is by unscrewing or is it a push fit so it needs wiggling out) in order to access the gear wheels? Also, are the gear wheels on the end of the sensor that goes into the hole so as to mesh with the teeth that can be seen through the hole? I have done a fair bit on work on brakes over the years but never anything on abs (as you can probably tell by the above questions …).

Re the brakes, yes, they were given a good clean as well as an inspection.

[BigBoomer]

This may help.
https://www.clublexus.com/forums/ls-1st-and-2nd-gen-1990-2000/742151-help-with-abs-wheel-speed-sensor.html

The following is probably not for an LS400, but the design of the system and the principle is the same.

 

[steve2006]

I had this fault on a series IV LS400 and it turned out to be a build up of grit and metallic particles on one of the ABS wheel sensors.

This decreases the gap between the sensor and toothed reluctor ring and gives false readings to the computer.

The problems in sorting the issue are removing the sensors which after extracting the single retaining bolt tend to still be stuck in the hub and gaining enough access to the reluctor rings to give them a good clean.

It is also a known problem that the reluctor rings can crack so check also for this.

IIRC it was the rear nearside on mine probably due to the rears  accumulating more road crud and more gutter crap on the nearside.

Symptoms are as you describe and also the brake pedal lifting slightly under your foot with the  grunching ( new word?)  sound.

[Howplum]

All very useful information. Another job to go on my "to do" list, which never seems to get any shorter!

[Tinonline]

Well there’s the perfect advice above!

Its a pull out. You’ll see a rust build up around the area so block hole and as carefully as poss sandpaper or file away but gently does it. Then get to the rings.

My issue was new wheel bearing and clean ring one side and on untouched side a lot of grease on the toothed ring. So removed the grease, cleaned up and this process equalised the condition of both rings.

End of issue that was locking one wheel on coming to a halt from low speed.👍🧐😁

 

[Tinonline]

Oh and you have OEM parts. Good. If not cleaned by garage take out pads clean discs and pads with brake cleaner, rid callipers of soot,  re grease, put back. See that no stones, grit, stuff rubbing. 👍

If it’s abs one side will grab and kind of skid on slow stop or kick in at end of your braking as vehicle comes to a halt.

Sensors are a tight fit so if they won’t wiggle out, very gentle all around especially at bolt locations with a thin blade/screwdriver prise mm by mm. Then they should start to let go.

[Colin M]

Thanks for all your helpful comments. I will have a go at removing the sensors and see if I can clean up the reluctor rings.