Knocking in rear suspension after changing to new struts

[Mr DOHC]

hey

i just change my MX83's rear struts to the supra ones, since i put them in i get a bad knocking when the RHR corner gets alot of extension of compression, i thought it might just be the spring re-seating itself, but its been over a week and its only marginally better.

Its not an awesome sound at all

[Viper]

I have exactly the same issue.
Both sides.

Ive removed and swapped out both sides (shocks and springs), swapped springs, same deal. Tightened everything up to buggery. Same deal.

I 'think' its the coils binding on the rubber tophats under compression.

I.e. as the springs compress the top the of spring tries to rotate about due to the extra length, and the sound/knocking is the result of when the slip occurs between the spring and the tophat.

Im going so compress the springs and jam some grease/lube and see what happens.

Otherwise I'm totally stumped too

BTW, using KYB Supra shocks and Kings Lowered MX83 Springs

[Mr DOHC]

yeh, same combo here, old springs tho, no issues with old std shocks, cept they were fucke

i will try to get up under it this weekend and do that, when do you plan to do it?

[Viper]

Weekend. Plan to also have another look too, as its been a good 2-3months installed, so I should be easily able to see wear points, etc.

Fkn pain in the ass though. Get bagged every time work mates are in the car with me...

[seamonsta]

I had the same problem, I think you will find it is the bump stops flapping about, sikaflex them up FTW

[Mr DOHC]

it happens mostly on big extension, and its a knock u can feel. definately not bump stops

[Viper]

I had the same problem, I think you will find it is the bump stops flapping about, sikaflex them up FTW

Nope, not that. First thing I tried.

Its definitely to do with the springs. You can hear the vibration when the 'clunk' occurs.

Sound gets worse (more frequent) when the car is loaded up with weight too, which again points to springs/compression.

[seamonsta]

I have the same KYB/Kings combo and have no problem at all, even towing a trailer. maybe there are other bushes in the suspension that are shot? Sway bar mounts (the plastic bits) have been known to break as well, check them.
Or, maybe the car is haunted!!! OMG call the ghost whisperer ASAP.

[PeteH]

Hi,

Vote +1 for checking your sway bar to lower control arm connection points.

When the nuts on the plastic link loosen it can make a hell of a clunking sound. And noticing it more when your suspension is loaded also makes sense as this will unload the sway bar and allow the link to flog around. It happened to me when I changed the rear struts over in my MX83. Initially I thought I had broken a diff mount, was pretty happy to find out it was just a loose nut.

Just something to check while you are under there

Cheers,

Pete

[Viper]

Good idea Pete.

Will check it out.
Maybe even tonight

[seamonsta]

I know you guys are certain it is from the rear, but if you have changed the fronts to the RAV4/Kings combo and not put a big enough spacer under the shock inside the tube you will also get a knock when the shock moves up and down, just a thought cause i had to remove one of mine and redo it with a bigger spacer.

[Viper]

Update.

Had a look over the weekend. Everything is tight, including swaybars and linkages.
I however, forgot to bring spring compressors so could not do what I had intended.
I still think its the likely culprit.

And the Sound if def. coming from the rears

Any luck DOHC?

[Mr DOHC]

nah, i was at the drags all weekend

glad its not swaybar links, $120 each genuine only

[Viper]

Serious.. Fuck that.
I'd make them myself from scrap steel.
Stronger and free ;p

[Viper]

Right, problem SOLVED.

It was what I expected. The coils bind with the rubber on the tophats and when the spring compresses quickly it moves on the rubber give the 'clung' sound.

So, just compress the springs down, jam in some grease, and voila, problem gone ;p
No idea how long the grease will last, but can always reapply

[PeteH]

Hi,

That's good news.

But can you explain how the spring is moving? It shouldn't be able to rotate as the bottom seat stops that, and there shouldn't be too much lateral movement as the top hat has a spigot to locate on the ID of the spring.

Thanks,

Pete

[Viper]

The 'spring' itself doesnt move, but as its compresses, the 'compressed' spring attempts to rotate around the shock in order to try and balalnce itself out.

As the bottom of the spring cannot rotate around, the top must do so.
Without the grease, the top binds with the rubber and makes a not so nice sound.
With the grease it acn be free to rotate around.

I think its in the order of like 1-2mm or something very small.

[Mr DOHC]

reppage for you

[PeteH]

Hi,

Ok so not being entirely convinced with the spring rotating during compression explanation, due to having owned/owning vehicles with coil rear setups and never having experienced this problem first hand, I spent some time yesterday afternoon with a tensile testing machine, some helical compression springs and a drop saw………the joys of being bored at work and not having to report to someone….

So what did I find??? Well in short I found that springs that sit neatly between the upper and lower seat, i.e. ends are ground and are parallel to the seats, do not display rotational or lateral movement when compressed. But springs that do not sit neatly, ie the top leg contacts the seat on an angle, tend to try and kick out or over when compressed.

Mr DOHC and Viper, I believe the cause of your problem is ill fitting springs, ie the top and/or bottom of the spring do not contact the spring seats properly and the result is the spring is trying to push out sideways when being compressed. The knocking sound is the spring moving relative to the upper seat until it is either stopped by the top hat spigot or it has found the "happy" point.

Grease may work for the short term but once lubrication is gone the noise will return. I'm sure the grease just allows the spring to slide instead of popping and grabbing. A possible solution would be to have the spring end ground so that it is closer to parallel were it contacts the spring seat…………….or maybe just get new springs with a better fit??

EDIT: I think I now know how the guy that reinvented the wheel feels

Cheers,

Pete

[Mr DOHC]

but mine are 5 year old springs that used to be ok?