19 replies to this topic

[Keith Novak]

I've been experiencing an odd clunk in what seems to be the RF of my suspension although I do realize sounds often come from somewhere other than where you think. I notice it sometimes mid corner and often very pronounced during hard braking or when changing directions. I can feel it in the wheel and sometimes all the way through the seat. It's loud enough that I can hear it over the exhaust and when it happened backing out of my paddock this weekend, people nearby all looked, presumably to see what I backed into.

A few months ago I disassembled the entire suspension, cleaned and inspected everything and no sign of anything wrong with the control arms, ball joints or shocks. Everything was tight except a sway bar bracket had loosened up so I thought that was it. I've removed the shocks and moved the control arms their full range of motion and couldn't find anything binding or hitting things. The hubs are new and rebuilt (didn't fix it). The brakes are new from East Street (didn't fix it either). Everything is tight and seems as it should. There is a little bit of play in the depowered rack but I may just notice it because I'm looking for something.

Any clue what could be causing this?

[Alberto]

Have you replaced the alignment cams yet?

[Keith Novak]

Yes. Those are new too. I do did replace my bent 1.8 subframe prior to noticing this with one off a 1.6 if that changes anything to do with the other hardware.

[Ken Wilkinson]

Even if you haven't replaced the alignment cams, go back and tighten them again...that is your problem. Use a 1/2 in. breaker bar and socket on the nut and a long arm wrench on the bolt head and put your weight into them. I had the same problem and a quarter turn on the LCA bolts fixed the problem.

[Keith Novak]

Thanks, I'll give that a go. The rear one is a pain to get really tight due to clearance issues.

[Ron Alan]

Even if you haven't replaced the alignment cams, go back and tighten them again...that is your problem. Use a 1/2 in. breaker bar and socket on the nut and a long arm wrench on the bolt head and put your weight into them. I had the same problem and a quarter turn on the LCA bolts fixed the problem.

Ok...so I understand, your saying the LCA cam bolts...front or rear are sliding from one side of the slot to the other causing the noise? And to slide both cam washers have to rotate...or be loose enough to rotate? I guess I'm wondering why you wouldn't notice this immediately just based on toe or camber of the wheel...unless it moves back somehow every time to where it was set? We were trying to diagnose a similar situation this weekend(clunking noise) and this was one of the things we checked. But all the bolts seemed to be right on the marks they were set.
In case anyone else may have found a different cause of a "clunking" noise...please share!

[Glenn]

Sway bar bind? Or sway bar hitting the suspension........

[Jason J Ball]

Sway bar bind? Or sway bar hitting the suspension........

+1 Sway bar is sliding across and hitting mounts/rear sub-frame under load. Your allowed to add stops so that it won't move side to side for this reason.

[Ken Wilkinson]

Ok...so I understand, your saying the LCA cam bolts...front or rear are sliding from one side of the slot to the other causing the noise? And to slide both cam washers have to rotate...or be loose enough to rotate? I guess I'm wondering why you wouldn't notice this immediately just based on toe or camber of the wheel...unless it moves back somehow every time to where it was set? We were trying to diagnose a similar situation this weekend(clunking noise) and this was one of the things we checked. But all the bolts seemed to be right on the marks they were set.
In case anyone else may have found a different cause of a "clunking" noise...please share!

In my case I think the front lower control arm was sliding on the bushing just enough for contact to occur between the bushing and the mounting point. The position of the cams did not change.

[davew]

Based on your desription, it is the allignment cam bolts. They need to be much tighter than the factory spec.

With a hoist we use 2 wrenches and puls as hard as possible. On jack stands you need at least a 2 foot breaker bar.

Dave

[DrDomm]

+1 Sway bar is sliding across and hitting mounts/rear sub-frame under load. Your allowed to add stops so that it won't move side to side for this reason.

Stops? How, welded? How much room to slide?

[Johnny D]

This one?

http://scca.cdn.race...astrack-may.pdf

Spec Miata
1. #7405 (Jim Drago) Allow flat washers under the say bar shackles.
Clarify section 9.1.8.C.4.d, by adding the following language: "Metal shims of up to 1/8" total thickness may be added between each anti-roll bar mount shackle and its stock mounting point on the chassis."

[bigsmittyJAS]

Ok...so I understand, your saying the LCA cam bolts...front or rear are sliding from one side of the slot to the other causing the noise? And to slide both cam washers have to rotate...or be loose enough to rotate? I guess I'm wondering why you wouldn't notice this immediately just based on toe or camber of the wheel...unless it moves back somehow every time to where it was set? We were trying to diagnose a similar situation this weekend(clunking noise) and this was one of the things we checked. But all the bolts seemed to be right on the marks they were set.
In case anyone else may have found a different cause of a "clunking" noise...please share!

I am no suspension engineer, but I have always understood the "clunk" from undertightened cams as attributed to the bushing itself slipping, not the eccentrics. The steel bushing is bonded to a rubber outer core to give some compliance. As the control arms pivot, the bushing wants to twist, but the clamping force from the eccentric bolts (along with the spring rate of the rubber bushing) resists the rotation. When the bolts are not tightened sufficiently, this clamping force is not there and the bushing "slips" in the housing causing the "clunk". I have had this problem many times in both my autocross Miata and my SM. Without fail, torquing down on the eccentric bolts fixes the problem. It is probably a good idea to replace those bolts every once in a while if you make a lot of alignment adjustments.

[Ron Alan]

I am no suspension engineer, but I have always understood the "clunk" from undertightened cams as attributed to the bushing itself slipping, not the eccentrics. The steel bushing is bonded to a rubber outer core to give some compliance. As the control arms pivot, the bushing wants to twist, but the clamping force from the eccentric bolts (along with the spring rate of the rubber bushing) resists the rotation. When the bolts are not tightened sufficiently, this clamping force is not there and the bushing "slips" in the housing causing the "clunk". I have had this problem many times in both my autocross Miata and my SM. Without fail, torquing down on the eccentric bolts fixes the problem. It is probably a good idea to replace those bolts every once in a while if you make a lot of alignment adjustments.

Great description! Makes complete sense....and I imagine this will mess with your setup when this occurs mid race! And just to confirm, all suspension bolts that involve bushings need to be torqued under load correct?

[Bench Racer]

This one?
Spec Miata
1. #7405 (Jim Drago) Allow flat washers under the say bar shackles.
Clarify section 9.1.8.C.4.d, by adding the following language: "Metal shims of up to 1/8" total thickness may be added between each anti-roll bar mount shackle and its stock mounting point on the chassis."

No, this rule was added to eliminate the bind in the sway bar. Previous to this rule change adding shims/flat washers under the sway bar bushing bracket was not legal. Each bracket that holds the sway bar bushing has two bolts which mount the bracket to the rear sub-frame or front chassis bracket. Metal shims/flat washer of 1/8 inch total maximum thickness may be placed between the bracket & the surface the bracket is mounted to. With the sway bar assembled including shims/flat washers & not attached to the control arms the sway bar should rotated down from it's own weight or with a slight down ward touch of a finger. Without these shims/flat washers when the mounting bolts are tightened the sway bar bushing is squeezing tightly on the sway bar which causes bind to the sway bar when connected to the control arms during suspension function.

+1 Sway bar is sliding across and hitting mounts/rear sub-frame under load. Your allowed to add stops so that it won't move side to side for this reason.

The "two stops per sway bar" being referenced in this ^ post are added inside the bushing/brackets & around the sway bar so the sway bar can not slide left or right down it's length crossways to the car. just inside the rear sway bar mounting brackets lightly clamp a vise grip to the rear sway bar, it would be the same with a two stops added.

[LarryKing]

just inside the rear sway bar mounting brackets lightly clamp a vise grip to the rear sway bar

Hee heeee!

Or you could buy a couple 5/8" split collars at most full-service hardware stores. Actually cheaper than visegrips and not as likely to fall off on-track.

[Bench Racer]

Hee heeee!

Or you could buy a couple 5/8" split collars at most full-service hardware stores. Actually cheaper than visegrips and not as likely to fall off on-track.

Must be the Squirrel that posted this ^. Should I have used the words as an example to get the idea, lightly clamp a vise grip to the rear sway bar, it would be the same with a two stops added. Before I implemented my stops I tried a split collar on the rear sway bar & without modification the split collar would not fit.

[bigsmittyJAS]

And just to confirm, all suspension bolts that involve bushings need to be torqued under load correct?

Yes. Otherwise you risk preloading them. Learned that lesson the hard way.

[Glenn]

Must be the Squirrel that posted this ^. Should I have used the words as an example to get the idea, lightly clamp a vise grip to the rear sway bar, it would be the same with a two stops added. Before I implemented my stops I tried a split collar on the rear sway bar & without modification the split collar would not fit.

HOSE CLAMPS

[Bench Racer]

HOSE CLAMPS

YES, with a Nylon flat washer.