Sportcross Front Suspension Knocking

[tonyT]

My 2002 IS300 sc front suspension 'knocks' badly on uneven road surfaces. Even a small ripple across the road makes it knock.

I've done a search here and although this seems to be a common problem, there doesn't appear to be a definitive cause- rather it could be anything or a mixture of faults!

My mechanic has given it a quick look over but can't find anything obviously wrong.

The steering feels fine, very accurate with no play. Also the ride feels good, well damped with no play. The front pads and discs were replaced when I bought the car, just a month (1000 miles) ago. I have read that if the pad retaining springs are missing then the pads can rattle, but the springs are in place.

I read that the caliper slider pins can wear causing the caliper to knock when the car is driven over bumps. To test this I drove the car over a road that always causes the knock, but rested my left foot on the brake pedal to slightly apply the brakes.- Instantly the knocking stopped! I've since noticed that under braking there is no knocking noise,

So, does this mean that the slider pins and caliper bushes need replacing (I have seen an overhaul kit with all the parts needed) or has pre-loading the suspension by lightly applying the brakes stopping whatever is causing the noise to stop ?

What a dilemma- I don't want to start diagnosing the fault by systemically replacing components until the cure is found!

Sorry for the long rambling post- but can anyone help?

[BarneyTT]

Tony, as you have found out, this is a difficult problem to solve/cure. I have replaced virtually all of the caliper parts and the knocking remains. Having had everything checked twice by an independent garage and Lexus Bristol I'm convinced, as are Lexus Bristol now, that my problem lies with either the suspension top mount or the shock absorber (these are known for having a noisy inner valve on some cars) I'm going to get both the front top mounts and shock absorbers replaced this year.

Sadly, no hard and fast fix as each car seems slightly different with this problem.

I even wrote to Lexus head office to see if they could offer any advice, they replied but sadly could not offer any further help or suggestions beyond what I have already tried and proposed for the future.

I bought all my caliper parts from Lexus and it wasn't cheap (approx £300). On the plus side all my calipers have had a complete overhaul, on the downside it didn't cure the knocking noise! It's a really annoying problem and can spoil an otherwise fantastic car.

Once I get the mounts and struts replaced I'll post an update.

[tonyT]

Thanks Barney. I have to admit that I am leaning towards shocks and mounts as there is no play in any of the ball joints/calipers.

What make of shocks do you intend to get?

[BarneyTT]

Probably KYB, the same as fitted by Lexus originally. I looked into other makes but it's a big step up in cost and as I love the standard ride they seem the obvious choice for me.

[tonyT]

The one thing that would worry me is that I have heard of people replacing their shocks with OE KYB's and getting the knocking return!

I would prefer a different make, Sachs or suchlike.

[BarneyTT]

Agreed, but as I intend to only replace the front shocks and mounts it's something I'll have to take a chance on, money no object the best bet would be to fit new after-market shocks all round.

The other option is to have different make shocks on the front but I'd rather have the same all round to be honest.

[tonyT]

As long as you have the same either side I doubt if it matters to much if they are different back to front.

I've been trying to source Sachs shockers, loads of places list them but have no stock!

When do you think you'll do yours?

[BarneyTT]

My mechanic friend said the same Tony but I'm just being a bit fussy I suppose.

Not sure when I'll be getting it done, hopefully later in the year as we have a fair bit going on right now.

[tonyT]

found this place that has Sachs front shocks in stock at a reasonable price-

http://www.bestpartstore.co.uk/1225250

[BarneyTT]

Not a bad price, any ideas what they are like in terms of performance and ride compared to originals?

[tonyT]

I haven't tried them so can't compare. Years ago I used to work on BMW's and we always specified Sachs or Bilsteins as they were the best.

[tonyT]

Further news in the Saga-

My car went to be serviced and MOT'd at my (good) local garage. The MOT tester tends to be a bit overzealous, so I thought if anything was wrong with the suspension he would find it.

The result- clean bill of health even though he had been briefed to be extra vigilant.

Beginning to look like Shocks. I've found a place where I can get Sachs at a reasonable price. Don't want to use KYB as I'll probably be back in the same place in a couple of weeks!

Anyone used Sachs? Where they quiet?

I'll have a good think before I spend money.

[BarneyTT]

Good news Tony, much the same result as mine when it had it's recent MOT.

It would be interesting to hear of anyone's experience of Sachs shocks.

Going to pick my refurbed wheels up next week and once funds allow I'm going back to the knocking issue to try and resolve it, still not a 100% sure which shocks to buy though.

[rincewind]

Barney/Tony - any update on this as I have the same issue, like yourselves I believe it to be the OEM shocks.

[tonyT]

OK-

this is purely my findings with my own car- so don't blame me if it doesn't work the same on your car.

With hindsight I had 2 knocking noises- one was an almost constant 'chattering' medium frequency. The other was a hard bang but only over certain road surfaces.

The 'chattering' was cured with new Sach shock aborbers- hard to find but not expensive imo.

The hard knock I found was a simple thing- the caliper pins on the front brakes wear so the calipers 'jump' over bumps, completely different in the sound the pads can make going backwards and forwards while parking for instance.

I bought an overhaul kit off e-bay (loads available- make sure you also get the pin bushes and the correct silicon grease) cost very little. Took a short time to do and Yippee- noise gone!

Also check your drop links- these can wear as well.

If I was starting from scratch- calipers 1st- as soon as you undo the pin bolts you'll know if there's wear, you can feel and see it so a no-brainer. If ok, check drop links ( these are all cheap and simple to replace)

Failing those, shock absorbers- mind you if the car has done a few miles always good practice to replace them as a matter of course.

Good luck- it can be cured!

[BarneyTT]

Sorry, thought I had updated this thread:

I have now had the Sachs shocks fitted along with genuine Lexus top mounts and I'm almost noise free, I still get an occasional creak on bumpy surfaces but it's 90% better than it was an certainly acceptable to live with. My problem wasn't caliper related but certainly shock absorber/mount related.

[tonyT]

Good news Barney- just goes to show how diverse this problem can be, Really pleased with mine now, silence is Golden as they say!

[BarneyTT]

Thanks Tony and really pleased to hear yours is now sorted as well.