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I measured up the rear lower control arm as per the specs on miataturbo.net and all is exact. But when I put the long bolt through it binds up in the opposite bush. This is the passenger side RLCA outer.
I "think" the rear bore is actually twisted very slightly, possibly from the factory? I put a straight edge across the 2 bores and there is a mm or 2 off straight:
<--Front Rear-->


The issue is when I put the long bolt in it binds about 2cm from being all the way in. If I put the bolt in from the rear its very clearly out of alignment as you can see here:


Top:


Bottom:



BUT: the passenger side LCA seems out about the same amount but the opposite way (the front bore is off alignment). The bolt itself isn't bent. On the drivers side both bolts slide all the way in with zero effort. Both bolts bind up on the passenger side.
When I put the knuckle in, I've got to tap the bolt to get it all the way in.

The reason I started hunting this is I had an issue with the RLCA-O passenger poly bush being pushed out of the control arm. The bushes were replaced under warranty, I installed as per instructions, all went smoothly and easy but when I test drove I still had a clunk under weight transfer (starting to move and stopping). Jacked it up and the RLCA-O has moved rearwards 2mm on the new bushes already.
Pushed the bush back into place and I can see scoring on the new metal sleeve already.

Would this small amount of misalignment cause the bush to bind and slip in the control arm or is something else at play here?
Not sure if this binding was there when the original rubber bushes were replaced with Poly as that was done by a local race suspension specialist.

Thoughts?

The previous RLCA-O poly bush after 2 track days:

I think that misalignment would be from the factory.

To me the real concern is the photo in your second post. That looks like the bush has moved inwards 5 or 6mm!
There is no gap between the hub knuckle & the arm bushes on my NB8A, so the bushes can't move like that (unless both bushes moved the same amount the same way).

Are they single "cotton reel" bushes or 2 piece bushes put in from either side of the housing?
If 2 piece get rid of them & put in 1 piece Superpro.

Roadrunner wrote:I measured up the rear lower control arm as per the specs on miataturbo.net and all is exact. But when I put the long bolt through it binds up in the opposite bush. This is the passenger side RLCA outer.
I "think" the rear bore is actually twisted very slightly, possibly from the factory? I put a straight edge across the 2 bores and there is a mm or 2 off straight:

The issue is when I put the long bolt in it binds about 2cm from being all the way in. If I put the bolt in from the rear its very clearly out of alignment as you can see here:

BUT: the passenger side LCA seems out about the same amount but the opposite way (the front bore is off alignment). The bolt itself isn't bent. On the drivers side both bolts slide all the way in with zero effort. Both bolts bind up on the passenger side.
When I put the knuckle in, I've got to tap the bolt to get it all the way in.

Thoughts?

I can't remember if mine went straight in 4 years ago. I remember having a hammer to tap things though.
Keep in mind the arms are several pieces of pressed steel welded together. Plenty of potential for things to be a little out during manufacturing.

I don't think that part of the arm could possibly bend under any condition other than a hard impact.

I.L Motorsport rubber is your friend.
The rubber should tolerate the misalignment better.
You will still need a hammer to tap the bolt in.

Or source another rear arm.

RS2000 wrote:Are they single "cotton reel" bushes or 2 piece bushes put in from either side of the housing?
If 2 piece get rid of them & put in 1 piece Superpro.

Those look like Superpro to me.

BTW the Energy Suspension 2 piece ones in that rear lower outer location also come with washers.
Once installed there is no gap at all, so no chance anything can slip.

I bet ya the Superpro ones have compressed into the bore, or the lips have been sliced clean off, as they are soft and compliant. That's what looks like has happened in the picture.

I went down the pure Poly path and never will on a NA/NB for track use again.
I had problems like what was posted(but on the front lower control arms) with Energy Suspension. I changed to Superpro and had the same problem but even quicker. In the end I went to I.L. Motorsport rubber with a thrust washer and solved, not to mention it drove better and critically faster on track as well.
BYW roadrunner had this problem up front as well which I'm not sure he has resolved yet.

All my rear ES poly were binding after 2 years on a car that was not daily dríven so had bugger all use in the rain and only did about 5000km's. Basically was a track car with plates. Was fun regreasing all the bores with no grease fittings fitted.

Yes I've sourced another control arm and yes they are one piece SuperPros.
Looking and measuring I can't see any signs of bent metal or kinks so I can only assume this arm was like this from the factory and with the rubber bushes it was never a problem. Now I have the stiffer poly bushes in there's less give to correct the off-angle and its binding up.
Also found measurements for the rear subframe so I'll measure that up this week too just to double check all that. But I'd like to think if that was bent it would show up in the many wheel alignments I've had over the last couple of years.

FFS poly bushes! And you wonder about them binding

Poly binds, full stop. It binds to the sleeve, about which it is supposed to rotate - the poly bush is supposed to be held by the housing in the suspension arm, but in my experience it will rotate in the housing as often, if not more often, than it rotates around the sleeve. I have a theory that if it is not rotating in the housing, it is actually acting exactly like the rubber bushes, held at both the inner and outer surfaces and as the arm moves the poly twists between the two fixed faces. Good for geometry, bad for spring rate (to the extent that the additional rate is not factored into the selection of the spring rate).

I would be surprised if that small misalignment had any effect on whether or not the poly is rotating around the sleeve, or within the housing. It is a flexible bushing after all. Remember that the bolt will straighten everything metal out when it is tightened so the axis of rotation for the sleeves will be around the bolt. Therefore the inner bore of the poly has the same axis of rotation, at least until it binds to the sleeve ...

Final word on poly: it is the ricer's choice. Racers will find something better.

Before you consider other poly options chasing this issue, it may be worth noting that when I was getting MCAs for my car I was basically told:
a) we (i.e. MCA) only recommend you use either rubber bushings or rose joints; and
b) we strongly recommend you don't touch poly bushings because of the binding issue.

That was leaving aside the well documented issues with bushes breaking up/moving around.

My dad's race car (not an MX5) also had poly bushes which eventually disintegrated completely, leaving the rear suspension completely free in its housing. Good fun under brakes and just getting it to the mechanics under its own power was a worry.

That's interesting!

They probably haven't heard of poly/bronze, or Madjak's similar but even more esoteric solution. I am surprised that they didn't mention delrin though, perhaps they thought the problems in castor locations ruled it out.

Roadrunner wrote:Yes I've sourced another control arm and yes they are one piece SuperPros.
Looking and measuring I can't see any signs of bent metal or kinks so I can only assume this arm was like this from the factory and with the rubber bushes it was never a problem. Now I have the stiffer poly bushes in there's less give to correct the off-angle and its binding up.

The Superpro technical section says that the 'bullet' grooves in the outside of the bush are to cater for misalignment of control arms etc.
I still think axial movement of the bush is more of a concern than rotational binding. It looks like you need washers/spacers each side of the knuckle?
Have you checked the length of the superpro crush tube with the length of the OE rubber bush.

RS2000 wrote:
The Superpro technical section says that the 'bullet' grooves in the outside of the bush are to cater for misalignment of control arms etc.
I still think axial movement of the bush is more of a concern than rotational binding. It looks like you need washers/spacers each side of the knuckle?
Have you checked the length of the superpro crush tube with the length of the OE rubber bush.

Measured up and all exact. The original bushes in the last photo had cut it's flange clean off the rear face of both bushes and allowed the arm to move rearwards off the bushes. Like what happens to the front lower inners with thrust force under braking. That's what I assumed was happening here too till I took more notice of the bolt tightness and found the misalignment.

Time will tell when I get the replacement arms this week, straight edge the bores, put the bushes in and go for a drive. At least I have the tools to do this myself so isn't costing me labour.

StuwieP wrote:Before you consider other poly options chasing this issue, it may be worth noting that when I was getting MCAs for my car I was basically told:
a) we (i.e. MCA) only recommend you use either rubber bushings or rose joints; and
b) we strongly recommend you don't touch poly bushings because of the binding issue.

Yeah I won't be putting different brand polys in. Either Sadfab Delrin or rubber if the free replacement superpros fail again.

greenMachine wrote:FFS poly bushes! And you wonder about them binding

Interestingly all the other poly bushes are super free moving with no binding at all. When I disconnected the outer bolt the lower and upper control arms moved freely under their own weight like when they were first installed, same with the front arms. Not saying it won't happen, because it will and I anticipated having to re-lube eventually but the only rotational binding I've had so far is this bent arm. I'm now on the waiting list for Sadfab delrin
If I had my time again I would have skipped the poly all together.

Roadrunner wrote:If I had my time again I would have skipped the poly all together.

WHERE'S THE LIKE BUTTON!!!

I have rubber in my current SE in good condition and will also change over to the Sadfab Delrin kit if and when my rubber ones start losing their effectiveness.
I had Delrin in my previous SE front upper control arms, after many years of track abuse the bushings were like new. The metal sleeves even had corrosion yet barely any wear on the Delrin.


What I'm more amazed at is that Superpro gave you replacements!
Both Energy Suspension and Super Pro were quite happy to tell me that they have not heard of these problems before.

All these manufactures need a good kick, but will play the get out of jail free card of that they were used for racing if you challenge them, so all warranty is void!!!
Here are some quotes from both ES and Superpro from a few years ago when I had issues.

sharp, poorly welded edges are cutting the flanges off the bushing edges. This doesn’t fall under manufacture defect, he will need to buy a new set of bushings. We would also recommend that the arms be replaced or at least cleaned up so that they do not destroy the bushings again

the bushes have been designed for street use not racing but in saying that we do have some customers using the bushes in their race cars

BTW Superpro were also investigating a redesign when I had the problem on the front in 2017, and then it all went quiet.

It's just funny that when I put I.L. rubber in the problem went away. Oh and faster lap times.

Luke wrote:BTW Superpro were also investigating a redesign when I had the problem on the front in 2017, and then it all went quiet.

It's just funny that when I put I.L. rubber in the problem went away. Oh and faster lap times.

Talk I heard is that redesign happened 6 or 7 years ago in the front by going to 90durometer inners.
Superpro were really good about it. Sent upgraded 90duro when the original front 80duro failed. When the 90duro failed they sent new ones and the rear outers as well. I also asked for non offset pins for the front lowers and they sent out non offset too free of charge after they had already sent the bushes.
Apparently they have just been taken over by Fulcrum.

I actually had a thought last night. When the replacement arms arrive (I got a left and right side lower because they were cheap enough) if the rubber bushes are fine in them, I won't swap the poly into them given the only drama I had in the rear I had before poly was the rear upper inner slipping. Poly in the uppers, rubber in the lowers. Thoughts?

Depends on the condition. But there can't be too many low-mileage NB suspensions around ...

A better combo would be delrin/rubber, and then you avoid the poly problems, while retaining some compliance for road driving. For racecar, delrin with rubber in the four necessary compliance positions, if you don't want those in poly/bronze.

I've got my name down for the sadfab delrin kit so will be doing the whole shebang when they come through, but they likely won't be ready till the end of the year when I was speaking with sadfab recently, so need something for the interim.
Bugger it, if the rubber bushes look ok, I'll just put the arms in as is, string align it myself and see how it goes. If the rubber is shot after a drive I'll swap the polys in and be done till the sadfab set arrive. Obviously the issue I'm having in this rear outer spot is from the bent arm, so not really the polys fault,it's just the stiffness of the poly is exasperating the situation. I imagine with delrin in this spot right now I wouldn't even be able to force the bolt into position with delrin being less flexible than poly.
At least this is something I can do myself so isn't costing me anything.

I just can't believe the arm is bent on the rear bore and nowhere else. that's the strongest part of the arm!