Mk4 LS400 front brakes pulsating/juddering

[mrdoofa]

I have a 1999 LS400 and think it's brilliant however, I have noticed whenever you apply the brakes there is a pulsating sensation coming from the front of the car and through the brake pedal. The best way I can describe the feeling is a combination of ABS pulsating and the feeling you get when you drive over horizontal raised lines in the road such as you get when approaching some roundabouts etc. The car actually brakes and comes to a stop just fine without pulling to one side or needing extra effort. It does seem speed related, the faster you go the more pronounced it is, it does feel linked to wheel rotation, ie: the pulsating is faster or slower depending on road speed. The car has just passed an MOT about a month ago and the only advisory was slight play in front lower suspension ball joints both. It has had new tyres all round fairly recently although they seem to be budget tyres. As I said the car brakes fine and the problem only shows when braking. Any ideas what it could be or where to start investigations? Cheers!!!

[ambermarine]

Martin

This could be a faulty abs sensor in the hub of one of the front wheels , it will pulsate on one side but the car will not lose its line of trajectory in the same way this does not happen when the car skids on one wheel due to ice or aquaplaning which is what abs is designed to do.

The best way to find out is to disconnect the sensors by degree on both sides and then run the car on the road and apply normal brake testing.

If the pulsating is not present you have a fault in the abs system.

Alternatively you could disable the abs system by putting the car in snow mode which may work towards confirming it is the abs that is faulty

 

[Tinonline]

Sounds like warped brake discs. Well known issue and these match the symptoms. You might be able to see this by spinning the wheel or inspecting the disc with the wheel off.

[messi]

I second that, it sounds like warped discs

[keybasher2]

Sounds exactly like mine did.New discs and pads,jobs a good en.

[MLW]

I agree. When a car starts shimmying under braking it is usually because the discs are 1/2-3 mm out of true centre. Solution is to replace the front discs and pads and see what happens. If that does not fix it go to the back brakes, but 70+% of braking is on the fronts, so start there.

[mrdoofa]

Thanks everybody for your replies, I was thinking along the lines of warped discs, it certainly makes sense from the symptoms I'm having. I'll hopefully get it in the garage this week, are new discs and pads expensive for the LS400?

[alien1974]

mines doing this too, discs and pads were changed 20k ago though

[Redsteve]

Hello Martin,

after 8 years of ownership of my MK IV LS I have finally fixed this exact problem on my car.

When I bought the car the brake vibration was there and I thought is was damaged discs so I changed them. The problem went away for about a month and then came back just as bad as it was before.

Over the years I have cleaned the discs, cleaned the hubs, tried multiple brands of pads, all to no avail.

Towards the end of last year I had to change the front pads as they had got ridiculously low and when I tried to push the caliper pistons back in I noticed one of them was seized solid. I knew one of the pistons had been a bit sticky in the past but I had always managed to get it working again but this time I couldn't get it to move so I bought a pair of second hand calipers from eBay to replace the originals.

I fitted the replacement calipers and the brake vibration was reduced by about half. Brilliant, I thought, all I have to do now is change the discs again and it might be fixed.

I ordered a pair of brembo discs and brembo pads from Eurocar Parts with a 25% discount (£119.60 delivered) and set about changing them.

I got the side that had the seized caliper done with no problems but when it came to the other side I just couldn't get the caliper mounting bolts undone. I tried all day but eventually had to give up. I know it was not ideal but I drove the car with one new disc and new pads on one side and the old stuff on the other side for a week before I managed to finally get the caliper bolts undone and the new disc and pads fitted to the other side.

The point of this ramble is, as soon as I had changed the first disc the vibration problem disappeared completely. When I got the second disc done it was still perfectly smooth braking.

I have done several thousand miles on the new discs and the problem hasn't returned. I think what has been happening is that the damaged caliper has been damaging the disc and so until the caliper problem was resolved the braking vibration was never going to get fixed.

Moral of the story is;

Carefully check your calipers are working properly, even a slightly sticky piston can cause problems.

 

Steve.

 

[steve2006]

All very good advice as per usual from fellow club members, I would suggest seeing as you need to dismantle the front braking system you replace those advisory LBJs at the same time, not a lot extra in time and around £120.00 the pair for OEM Lexus replacements.

[mrdoofa]

Thanks again for your help guys!!! I'm gonna get my mechanic to check the calipers and discs. It's great being a member of this club, great advice and input as always. I'll report back as soon as I've had it checked over. Cheers again!!!