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Rear Suspension Knock


Need4Speed

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Certain types of progressively wound springs suffer a peculiar problem in that the more closely wound coils which become coil bound at certain loads, and thus progressively increase the spring rate as ride height reduces, clatter together to make a knocking noise. i made some specials for my Skyline that i wanted to have a bearable ride on the road but have a very rapidly rising rate in roll and front / rear weight transfer. because the topmost coils were almost touching at normal ride height any bumps had them immediately start to close up, and they rattled crazily. knew waht it was and was happy to live with it. If this is your problem my custome springs for the MKIV will fix it, or you can try putting some sort of damping material around the coils, but this ofeten rubs away in time. Just another idea...

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Chris

 

The top coils are touching under load, but I'm surprised it's only rattling on one side. The o/s never makes this noise. The car is hard at the rear which makes for good track days but wheelspin over bumps on the road is a problem. Whether or not the rattle is caused by the spring, the rear set up needs a little investigation. My feeling is that the rebound damping is a little soft for the spring rate, causing the car to leap a little.

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Originally posted by John Packham

Chris

 

The top coils are touching under load, but I'm surprised it's only rattling on one side. The o/s never makes this noise. The car is hard at the rear which makes for good track days but wheelspin over bumps on the road is a problem. Whether or not the rattle is caused by the spring, the rear set up needs a little investigation. My feeling is that the rebound damping is a little soft for the spring rate, causing the car to leap a little.

 

Don't forget the piston inside the shock can come loose and knock, as can the valve stack inside. Nothing you can do save change the shocks if that's the case...

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Originally posted by John Packham

Chris

 

The top coils are touching under load, but I'm surprised it's only rattling on one side. The o/s never makes this noise. The car is hard at the rear which makes for good track days but wheelspin over bumps on the road is a problem. Whether or not the rattle is caused by the spring, the rear set up needs a little investigation. My feeling is that the rebound damping is a little soft for the spring rate, causing the car to leap a little.

 

As I said before to you in this thread JOhn.....

 

This is exactly what I was on about, as I had this problem .....the springs were bottoming on the top coils and making noises exactly what you described......

Does not sound like springs, thats why I told you to check that.

My money is 100% on that still, whatout even seeing the car!

Oh wellllll........!

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Yeah I hear you, but I've had this car apart and it logically the springs aren't making this noise. For example, why is it only on one side. The springs are the same type. The n/s has this knock under slight bump, but the o/s never does it at all. The progressive coil winding is designed to bind so why no noise from one spring. Maybe I should try swapping the struts to see if the knock moves.

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Originally posted by John Packham

Yeah I hear you, but I've had this car apart and it logically the springs aren't making this noise. For example, why is it only on one side. The springs are the same type. The n/s has this knock under slight bump, but the o/s never does it at all. The progressive coil winding is designed to bind so why no noise from one spring. Maybe I should try swapping the struts to see if the knock moves.

 

I am unsure if these springs you have are factory Toyota, or aftermarket. Many aftermarket springs are appalingly badly made, with varying rates, varting free lengths, and most commonly, very varying length at fitted load. Maybe one spring is wound poorly? My Skyline ones knocked because i had them made to do a rather special task, normally a properly made progressive spring will have the coils slowly and progressively come together along their length, at no point do 2 separate coils smack together. A poorly made coil spring can have the coils meet over a virtual full winding, with a bang. maybe this is what is happening in your case. Also, road cars VERY rarely have close tolerances on corner weights, they may be perfectly linear in response between the rear pair, but one rear corner of the car is much heavier than the other. This could even be because of a fault in a FRONT spring. Can you borrow a pair of standard rear springs, just to test?

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Chris, would it be likely that the TRD Bilstein stuts would have such marginal springs? As far as corner weights are concerned, I haven't measured them as the car is too heavy for my corner weight guage (single seater scale). I know what you mean about spring quality. I'm going to swap the struts to see if the knock moves to the other side.

 

Supra Pilot, would you know this knock if you heard it? I might drive over your way and get an opinion.

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Probably would John,

 

I had it on the right rear alone(mainly), I got new 'Bilstein' to compare heights and pre tensions etc. All seem correct with em!

 

I refitted and put a thin rubberized material between the top 2 coils and it has gone away, I also noticed when I reseated and fitted the strut back into position (with load) the coils now had a bit more clearance.

 

Another thing, have you removed the shock itself from the spring assy. If the shock is dead, as this will affect the spring loading also!

 

Cheers.

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I suppose you have to ASSUME the springs are TRD ones and correct for the shocks, although you did mention a lack of rebound damping? Possibly the fastest test for coil rattle is put LOAD of weight in the back and get the springs top coils to lock together. You'll perhaps find about 4 hundredweight of bags of something heavy and 2 big rear passengers will pull the car down enough.

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I think I've found it. Somebody in the past history of this car has bodged the rear suspension. The o/s strut (the quiet one) has three washers in the top mount to form a spacer and the n/s one doesn't. Pic 1 shows the n/s strut and the spacer at the top of the damper rod. Unfortunately this spacer is not long enough to seat into the top mount so pulls the damper rod through the top mount. Quite what should be in there I don't yet know. This tells me the TRD Bilsteins were not a facotory fit and whoever fitted them last was a moron.

 

Are the boots shown in pic 2 the same as the standard Toyota ones or are they particular to the Bilsteins?

 

Next question. There appear to be no markings on the springs except the two red marks shown in pic 3. Do these look familiar to anybody?

 

Finally when compressed and released, the dampers both return to extended length. Is this normal on this type of strut?

 

Thanks for all the ideas on this guys, even if it only made me look to try and prove you wrong!

spring_knock.jpg

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Steve

 

That's the spacer I need. I'm going to make some up. Have you got the spacer on upside down? Could you do me a favour and tell the length overall of that spacer?

 

Where did that smilie upside come from?

 

And have you got a boot rubber to go with that strut, a photo would be appreciated if you do.

 

Cheers

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John on a NEW shock, it is extremely hard to compress(push down), especially a sports type,, very very hard.

If you are able to compress the shock easily, then it's on it's way out!

If it compresses and stays in that position, then the shock is dead!

It should return very slowly after compression.......

 

Picture 2 is basically just a dust cap for the strut, as shite can get on the shaft and with the up and down movement(in and out), can eventually erode or damage the seal(shock leaking).

Can't remember exactly how the whole boot (picture 2 is made up), but it looks like it also has a built in or should I say attached 'damper' or buffer at the top.

Some buffers are seperate units to the boot.

 

Hope this make sense to you, and anyone feel free to correct me if I am wrong on this.......

Cheers

Dom

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