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Stumped! LS400 Mk4 knock from front suspension/steering

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Hello folks,

I have a Mk4 LS which has a problem that I (and 2 mechanics and an Mot tester) can not source.

When driving the suspension feels fine, however when braking and when going over small dints in the road at various low speeds, you get this horrible knocking sound and sensation front what appears to mainly be from the n/s/f but also sometimes on the o/s/f.  It is like a bone-on-bone knock as if the shocks were gone.  

After having two non-Lexus mechanics (who are very good) look at the car and drive the car - they literally can not see what the problem is.

My question is, what could it be?!

I even took it to another garage for an Mot (kwik fit) and they passed it with only advisories on some corrosion and a bulb (did not even know I had one out).  Afterwards I spoke to the Mot tester and he said he felt/heard the noise but could not advise on a fault because everything seemed in order!!!!  

Any thoughts greatly appreciated.

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Check the upper control arms especially the ball joint ,way to check is jack car weight off the front wheel and place a tyre lever or bar at the bottom outside edge and push upwards at the same time clasp the ball joint ,if it is suspect you will feel it moving about.

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Thank you Phil for the reply.  I will ask the garage to check this and hopefully that will be the cure!

Many thanks

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Sounds like drop links for the anti roll bar in my experiences that were the same

Sent from my SM-G920F using Tapatalk

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99% sure it is your lower control arms.

To test this you drive on a flat ground and drive 5mph and slam the brakes every few seconds. You should hear a knocking noise. That is where the problem lies. 

You cannot see rubber damaged on the control arms, only when there are small cracks which looks alright but is not.

When you have done this let us know.

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Thank you both.  I will have this added to the list to be checked and will report back once it has been in the garage.  Hopefully, the fix is in sight!

Many thanks again.

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Hi there 

Did you ever get to the bottom of this?

i have just bought an LS400 and it has the exact same issue 

thanks

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amongst all sorts of other stuff I also replaced the front Drop Links, that sorted those ' clunks '

what Ls400 is yours J4cK ?

I ask because the Mk3 one's are now only seemingly available one-sided, your mechanic will have to buy a pair the same and cut and weld ..........  simple job if he's competent

Malc

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On 9/22/2019 at 10:32 AM, Malc said:

amongst all sorts of other stuff I also replaced the front Drop Links, that sorted those ' clunks '

what Ls400 is yours J4cK ?

I ask because the Mk3 one's are now only seemingly available one-sided, your mechanic will have to buy a pair the same and cut and weld ..........  simple job if he's competent

Malc

Sorry for long reply - mine is a 99 so mk4 I believe

I've replaced the upper control arms and no luck yet!

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In my older Car, I used to get a knocking noise because the Brake disc back plate was heavily corroded and starting to break up and would flap at times.  No longer available to purchase I have had to wire it to the Caliper onto a non moving part.  Difficult job to sort, and so I'll put some glassfibre on to the back at some time to strengthen - as a long term temp measure!

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On 6/8/2018 at 11:27 PM, ls400lpg said:

99% sure it is your lower control arms.

To test this you drive on a flat ground and drive 5mph and slam the brakes every few seconds. You should hear a knocking noise. That is where the problem lies. 

You cannot see rubber damaged on the control arms, only when there are small cracks which looks alright but is not.

When you have done this let us know.

I can tell you about a similar issue I had on my 1996 MK3 LS400 which may help. Symptoms: when stabbing/slamming the brakes there was a clunk at the front end. With the car on the ramp you could also see where the anti roll bar had been moving in the bushes. The cause was the lower front suspension arm bushes or 'BAR ASSY, STRUT' bushes. They looked fine on the car but once taken off the car you could see where they were cracked all the way round in the middle which meant the arm wasn't solidly attached to the centre tube/bushing anymore. I replaced them both along with the drop links and anti roll bar bushes and it cured the problem. I guess when braking sharply the 'BAR ASSY, STRUT' was moving laterally and this moved the ant roll bar as well. It's not an easy job to replace them though and the bushes themselves are not available separately anymore, only the complete arms are available. £330 for both sides from Lexus Parts Direct, one side is cheaper than the other for some reason.

I went down a different route, see my post link below.

 

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Hi Razor61

 

I was doing some digging and came across what i believe might be the bushes that you were referring to? Does this look correct to you?

https://www.ebay.co.uk/itm/2-x-Lexus-LS400-Front-Lower-Arm-New-Poly-Polyurethane-PSB-Bushing-Kit-1990-2000/183479746676?hash=item2ab83ec074:g:bcMAAOSwvYZbvgNd

 

Thanks,

Jack

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Hi Jack, the poly bushes in the link don't look right and look like the front lower arm bushes not the front  'BAR ASSY, STRUT' rod bushes. The failed bushes on my car were the front  'BAR ASSY, STRUT' rod bushes.

The poly bushes I bought for the 'BAR ASSY, STRUT' rod are PSB531 but I didn't use them in the end. I was going to fit these poly bushes as the original OEM bushes are no longer available and see whether they affected the ride etc too much. I figured I'd give it a go and if the ride was too hard, fit new OEM arms. But I found some rubber bushes that would do the job. The rubber ones I bought and actually used are part number 48674-40051 (cushion, strut bar) and they are originally made for a Toyota Century. The diameter is the same as the originals but the width is greater meaning about 10mm more rubber. I'm glad I didn't fit the poly bushes because of the work involved replacing them again with rubber bushes or replacing the arms.

After doing my car, my advice for anyone thinking of replacing these bushes would be:

The vast majority of the work is removing the arms themselves. If you are good with spanners, have all the needed equipment and tools, somewhere to do the work off road, access to a good press and plenty of patience then replace just the bushes as I did if you want to save money. If you have the cash then buy new arms and no need for a press. Because of all the stuff you need to remove its a good idea (in my opinion) to replace the drop links, anti-roll bar bushes and clean/de rust/ rust treat anything you can see and get to including the inner wing arches etc.

 

 

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Thanks, Razor!

Did those century bushes need adapting or they fit just with a bit of pressure applied?

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2 hours ago, J4ck100 said:

Did those century bushes need adapting or they fit just with a bit of pressure applied?

No need to do anything with them, they will press in with a decent press but make sure they are central with equal over hangs as they are wider than the originals (this will become apparent when you do it) Getting them pressed out is the harder bit, I couldn't shift them with a 10 ton diy type press. An engineering company pressed them out or 'got them out' for me.

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You can get the original OEM bushings from LEXUS suppliers in the US or Japan.  I have replaced them on two LS400 .  Paid ca 35$ each + taxes and shipping. 

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1 hour ago, Mikaelse said:

You can get the original OEM bushings from LEXUS suppliers in the US or Japan.  I have replaced them on two LS400 .  Paid ca 35$ each + taxes and shipping. 

I’d like to know, and others I’m sure, which US or Japan supplier/s if possible, the suppliers I tried in Japan and in the US could not supply them. One US supplier listed them and I ordered them online only to be told they were not available anymore.

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Lexuspartsnow website

image.thumb.png.ab454b942ff266a4eceadaf2af3167aa.png

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I hope this helps as alternative.  I bought from AMAYAMA.COM last time. One year ago. They still stock them.
Before that ca 2016 I bought from a US Lexus dealer . They may be out now...
 Bought stuff from AMAYAMA several times. Seems only OEM stuff. Arrives promptly perfectly packed. 

CUSHION, STRUT BAR Genuine Toyota (4867440051)  . 
Right now below 20 Euro each. Buy the bolt also .
I needed new ones.  The washers and the nut I also bought . Nice with new shiny things.

 

 

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On 2/21/2020 at 7:34 PM, Mikaelse said:

I hope this helps as alternative.  I bought from AMAYAMA.COM last time. One year ago. They still stock them.
Before that ca 2016 I bought from a US Lexus dealer . They may be out now...
 Bought stuff from AMAYAMA several times. Seems only OEM stuff. Arrives promptly perfectly packed. 

CUSHION, STRUT BAR Genuine Toyota (4867440051)  . 
Right now below 20 Euro each. Buy the bolt also .
I needed new ones.  The washers and the nut I also bought . Nice with new shiny things.

 

 

Thanks

 

Have you got part number for the bolt and washer/nut?

 

Assume the 48674440051 cushion can be used for both LHS and RHS

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