Sign in to follow this  
Phettu

A Wee Knocking On My Lovely Ls400

Recommended Posts

:blink:

Good morrow,

i wonder if anyone has had this wee problem, on my lovely 94' Ls400

i have a knocking from the front , sounds like i have a stone in the front offside tyre, which i have checked and i do not, i'm no mechanic, and i don't know if it's likely to be bearings or drive shaft or something else. could anyone shed any experience on it at all

thanx muchly, Phettu

Share this post


Link to post
Share on other sites

is it there at low speed but disappears above 20 or so? if so, how about a warped disc and the brake pad catches and clunks the calliper in it's housing? once speed picks up, pads move further away, so it stops.

Share this post


Link to post
Share on other sites
once speed picks up, pads move further away, so it stops.

Why would the pads move further away at speed?

Share this post


Link to post
Share on other sites

the long answers is.... at slow speed the calliper floats in and out as the warped disc goes around and the pads follow it, but as the speed picks up, the mass of the calliper can't float in and out so easily, thus allowing the pads to push the pistons further into the calliper. this continues until the pads are barely kissing the high spots of the disc as it whizzes past. thats why when discs are warped, the brake pedal travels further to bring the brakes on.

short answer...... cos it does!

Share this post


Link to post
Share on other sites

B)

Thanx alot greybeard, for the long and short answere. i will check that out, as there is also a squeek on the same side i think at slow spead when i brake. thanks mucho.

Phettu

Share this post


Link to post
Share on other sites

the long answers is.... at slow speed the calliper floats in and out as the warped disc goes around  and the pads follow it, but as the speed picks up, the mass of the calliper can't float in and out so easily, thus allowing the pads to push the pistons further into the calliper. this continues until the pads are barely kissing the high spots of the disc as it whizzes past.  thats why when discs are warped, the brake pedal travels further to bring the brakes on.

Find it hard to believe that calipers do any floating about. I would have thought they're fixed hard and fast to the suspension.

Doubt even more that the pads follow it around. I take it you mean float in and out too.

As the speed picks up, I doubt the calipers will be affected as they're stationary relative to the car, the only thing that changes in the brakes will be the speed of the disc going round.

Sorry none of this makes sense still.

Share this post


Link to post
Share on other sites
This link explains what floating calipers are all about.

http://www.off-roadweb.com/tech/0401or_brake/

thanks for this - i obviously should have looked it up rather than rely on my memory!

unless of course, someone has replaced their pads themselves and can confirm whether our callipers are indeed firmly fixed or floating. i know we have four pots per calliper, two on each side, but i would have thought there was a calliper float facility, simply because of the way mine respond (my front discs are warped).

even if our callipers are firmly fixed, the pads will still move further apart if the disc is warped, cos at speed, the high spots will push back the pistons. but before this happens, the action of the high spot hitting the pad each time it comes round, could still cause a 'knock' sound as the pad backplate shifts slightly.

Share this post


Link to post
Share on other sites

If you have pots each side then I doubt it would have a floating caliper.

Share this post


Link to post
Share on other sites

Greybeard is right - Has anybody driven a car before that has been left standing for a while? If the brakes are slightly out of true, as the "high" spot catches the pad surface, it will scuff the disc. If the brakes are slightly sticking, you can get noise which is relative to speed and should gradually disappear as the car builds up speed. Although the opposite side of the disc will be a "low" spot, and hence not catch the disc without applying any braking force, the force of the high spot pushing the pad against the caliper piston could generate a cliking type sound, especially if somebody has left shims etc out in the past!

I should think it comes down to the fact that with the amount of force applied to the calipers with the brakes depressed, the brake pads will be able to clamp the disc satisfactorily. However, if the brakes are warped and/or sticking slightly then the pads will not return away from the disc quickly enough, and potentially could cause noise.

I believe that the LS400 calipers (on my model anyway) have only two pistons per caliper. Both pistons are on the inside of the brake disc, and hence the caliper has lateral movement to compensate for brake wear. Without this movement, the caliper would be unable to apply brake force to the side without any pistons.

Please correct me if I am wrong?

Cheers,

Will

Share this post


Link to post
Share on other sites

i've not personally taken mine apart, but when i had the calliper pistons re-sealed a month or so ago, the garage said they had four pots per calliper (but bearing in mind a load of other things they said, which then turned out to be untrue, maybe they made-up the 4 pots thing just to charge more!) i've got to crawl around the car to check the disk/rotor size in order to get some new ones, so that should determine the issue. apparently 1990 LSs had their discs changed to a deeper offsett and thicker disc, so i'm not sure which one i've got. i'll also be able to establish whether the calliper is firmly attached.

Share this post


Link to post
Share on other sites

Unless Lexus have gone back on themselves in technology, my 1994/M series II has two pistons per caliper (well it did a week ago when I fitted new front pads!).

The rear calipers are of only a single piston per caliper.

Hope this helps,

William

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this