The 1999 LS400 brake pedal assembly design has side to side end play that produces an audible clunking noise.

There are two plastic end bushings that go over a sleeved spacer which slips over a bolt with a grip which mount the brake pedal assembly to the body.

I replaced these along with springs, nut, brake light switch pad, brake booster pivot pin (scored) and clip.

There was a slight improvement, but still side to side clunk. Sound just like a bad front strut bushing.

This is unacceptable.

This occurs because Lexus elected to save a few pennies and use a regular bolt instead of a precision shoulder bolt which results in about .015" - .020" tolerance between the collar ID and bolt OD.

Initial brake pedal travel must overcome any mechanical tolerances before actual braking occurs.

To resolve this problem a proposed solution is a hardened metric shoulder bolt to be machined to eliminate tolerance in the collar.

Attached is Lexus parts diagram of the brake pedal assembly components, a photo of items replaced and a close up of the brake bolt inside the collar depicting the gap.







Lexus exploded parts diagram of brake pedal assembly.





Brake pedal assembly components replaced.





Gap between bolt and collar bearing.

 

Your right on, there are many things they could have improved on, especially since they were in the pursuit of perfection back then.

 

were you successful in your solution? i don't have this clunk in my pedal.

 

No side to side endplay on the brake pedal when you move it with your foot?

I visited a 1998 LS400 that exhibited the exact same problem.

Not sure what year LS400 you have.

 

The solution to side--to-side rocking/clunking is using a precision M10 diameter shoulder bolt offering improved precision fit over regular bolt with threads.

As you see from side by side image of bolt and collar, the length differential of the collar and grip (unthreaded) sectionof the bolt suggeststs the collar bearing is on threads on one side.

Holo-Krome offers M10 diameter shoulder boltsm

However, the threaded end of M10 shoulder bolts typically is one size smaller, here M8, so have inquired of manufacturer regarding availability of M10 shoulder with M10 thread.

Optionally, I acquire a longer M10 shoulder bolt and machine with M10 threads. Blueprinted solution, but am not enthusiastic about remachining over concerns of integrity of the threaded end unless performed by knowledgeable machine shop.

Will post adtional information as available.







M10 diameter shoulder bolt with M8-1.25 threads. Possible to use, but requires shoulder length to be exact for each particilar vehicle body through-hole bracket mount....not the best engineered solution..

 

Is the bolt undersized (47124)? I would feel that by adding in a spacer for the (47101B) would reduce the play. (?)

 

I was able to find a standard shoulder bolt at Home Depot that was perfect length and was glove fit tight through the body bracket holes and had much less slop than did the OEM bolt when inserted into the tubular sleeve.
Used 3 M10 flat washers from Home depot- one on the head side and 2 on the sleeve after it placed through the body bracket along with the OEM lockwasher to take up the remainder of protrusion before placing M8 lock washer and M8 self locking nut. (belt and suspenders)
Much better, however not perfect..
a shim as you suggest between the pedal assembly and body bracket would eliminate the remnant tolerance, but would have to hunt for very thin M10 washers.

The other offending component was the master cylinder clevis. Plenty of slop between it and the brake pedal arm.

I used two of the same Home Depot M10 zinc plated steel washers on both inside faces of the clevis. Problem solved.






Shoulder bolt selected. It is typical the have an undercut immediately beneath the head on the shank which i did not like so....





M10 washer..





Shoulder bolt is perfect fit(top of screen).two M10 flat washers and one M10 Lock washer used to fill the gap. One M8 lockwasher and one M8 Self-locking nut used on threaded portion to cap it off.<br/><br/>Look at the gap between the brake cylinder clevis(has yellow grease) and brake pedal arm<br/><br/>This confluence soalswad also causing noise...





Brake master cylinder clevis after shimming... worked wonders..<br/><br/>The new clevis pin also had some tolerance with brake pedal arm...I was considering having it bronze bushed .but overall, $10.worth of parts, and Toyota Body Grease has made a significant improvement.<br/><br/>Next project is gas pedal plastic bearing pivot assembly. Noticeable slop here too. Metal pin on plastic bearing...

 

Replacing the Lexus brake pedal pivot bolt with Holo-Krome precision shoulder bolt significantly decreased the side to side movement of the brake pedal and minimized the clunking noise...but .005" tolerance still remained and could still discern some noise in the pivot mechanism.

The new Lexus

OEM pivot bearing bolt replacement diameter is .390" and the new replacement OEM collar I.D. is .400"...so .010" tolerance....too much.

The custom-machined collar is same O.D. and length but has .394 I.D. and Holo-Krome bolt O.D. is .3937..so ultra-precision fit.

I obtained the hardened (12.9) Holo-Chrome shoulder bolts from Holo-Krome and the custom machined collar from HR Slater Co. on West 18th St., Chicago....very reasonable.
Have a few spares if anyone interested. P.M. me.
Holo-Krome shoulder bolt and new collar on left....OEM bolt and collar right

 

You can always machine your own bushing to custom fit it to the bolt

 

I ended up doing that...

First I ordered and attempted to use all OEM replacement parts...it helped slightly.

Next I swapped out the OEM brake pedal pivot bolt (at body) with a precision shoulder bolt....much tighter fit through body bracket and reduced side-to-side movement and more positive brake actuation. (removing mechanical tolerances provides improved brake actuation)

Then had machine shop fabricate a replacement collar/spacer that fits precisely over the shoulder bolt...another .005" tighter.

The remaining issue iis the split nylon shoulder bushings( that slip over the collar/spacer and between the brake pedal arm pivot hole) still allows slight side play...

In order to 100% solve this isue will require replacing them with a metallic component...or possibly fabricating something out of nylon without the darned split...

 

For years my buddy's would tell me that I could use a mill, lathe and welding gear. Once one is accustomed to a certain level of preciseness, parts made for the mass world are disappointing. I know people who buy machines to tear them apart and replace, re-machine as necessary. This same person took a Harbor Freight lathe and made it into something very accurate. He enjoys the challenge so we were I wouldn't mind a lathe and mill, I just don't have the garage space nor 3 phase for the big stuff. A water jet and heat treat oven would be nice too.

Glad you got these parts worked out. Good for the rest of us when it comes to fixing this and others you've mentioned.

 

I checked ours today and prior my awareness didn't catch it. Ours doesn't clunk though. If I'm piddling around I'll see about adding washers to take up some of the gap. Probably not till winter or fall when it cools down.

 

So I extracted and removed thr brake pedal assembly and delivered it to H.R. Slater Company in Chicago for fabrication of a solid Bronze bushing to replace the ineffective OEM slit -style plastic bushings...

The bronze bushing completely solved the problem.and eliminated all side play and remainder of clunking.

The pedal feels more solid when depressing pedal with more immediate braking...what I mean by that is through elimination of excessive tolerances in brake pedal to chassis pivot bearing and brake booster/master cylinder-clevis-clevis pin--brake pedal arm, there is less delay to actuation with tighter tolerances. This image of the OEM split plastic bearing assembly...while cost effective, however an imprecise method, especially in a mechanical linkage of braking system. Replaced with new plastic OEM style bushings and they faoled to meet expectations.


New bronze bushing fabricated by H.R. Slater Company in Chicago.
Notice the bushing (NOT press-fit) protrudes about .025" (on each end) This permits the chassis U bracket to clamp onto bushing, and NOT onto brake pedal pivot...you DO NOT want the chassis U bracket serving as a bearing surface....

 

Bumping this old thread to just comment I have this problem too. I'm going to give the replacement of the hardware a shot.