This might be workable to handle thrust. Basically keep the design I originally described with the stepped inner shaft and sand off the flanges on the urethane by 1/16” and insert these on the end.

McMaster-Carr

Perfect.

Hi Sean,

I am a newbie on the forum with no privileges to PM you until I get a higher post count. Nevertheless, I am interested in your "kit" for 3-4 miatas. THANKS!

I will follow up with some math on why ¾” is too small.

12mm fine thread grade 10.9 bolt like the stock camber bolts tightened to 90% of proof load will generate 15,463 lbs force worth of clamp load. Typical torque spec is 75% of proof load but we tend to over torque these to keep them from slipping on cars with super grippy tires that see track and autocross duty so I assume 90%.

Area of contact between sleeve and bracket with slotted 12mm hole.

¾” sleeve = 72.6 mm^2 = 0.1125 in^2
7/8” sleeve = 134.8mm^2 = 0.2089 in^2

Contact pressure from tightening
¾” = 137,448 psi
7/8” = 74,020 psi

Yield and ultimate strengths of various materials.

1018 Mild steel, Yield = 53,700 Ultimate = 63,800
316 Stainless, Yield = 60,200 Ultimate = 89,900
6061-T6 aluminum, Yield = 40,000 Ultimate = 63,000
7075-T6 Aluminum, Yield= 73,000 Ultimate = 83,000
Guess on the subframe flanges material Is it is a High strength low alloy steel. It seems remarkably durable anyway. Typical yield for such a steel is around 80,000 psi or better.

Conclusions:
¾” sleeve is too small.
7/8” just barely big enough.
If you’re going to make sleeves out of aluminum better use 7075-T6.

17-4 PH Stainless, Yield = 145,000 Ultimate = 160,000

--Ferdi

I had looked at that. bet it is a bitch to machine. and if the tube dosn't yield the chassis side still will anyway.

I also looked at washers a 3/8" washer has a 7/8" OD. could bore ot the center to 12mm maybe and have them work for what I need. they make them in 17-4 stainless. I think my experiance is that a standard drill bit won't do it.

McMaster-Carr

I have no Idea how much its going to cost to get 16 4mm thick 7/8" od, 12mm ID washers machined from 7/8" bar stock the way I have it currently designed.

True that the chassis side will probably yield before 17-4 would. But, I mainly mentioned it because it's actually easier to machine than 316 and costs about the same.

--Ferdi

17-4 is a common material used in aerospace when aluminum and Ti just won't cut it, but I think a better option is 440 stainless for this sleeve.

Yield - 186,000 psi
Ultimate - 254,000 psi

Its not ductile at all, but you don't need ductility for a compression loaded clamped material.

Its half the price of 17-4, and even cheaper than 316 stainless.

With this strength, using 3/4" would probably be fine with a safety factor of 1.35. Using 7/8" would have a safety factor of 2.5. I would probably just go with 7/8" though, for that warm and fuzzy feeling.

The 440 is probably harder to machine than 17-4.

It would be fine for the sleeve but the slots on the chassis would still be smashed and become un-usable after just a few times of adjustment.

it doesn't need to be that strong if you can't upgrade the chassis as well. Im pretty sure the steel used at that location on the subframes is stronger than 1018 mild steel but not that much stronger. Its not unlike a BMX bike dropout. if you road your bike to school once and a while the rear dropout design on a bmx bike works fine. If you were a hardcore BMX racer changing gearing doing crap loads of starts and jumping you had issues with dropouts becoming mangled from trying to keep them tight enough that the wheel wouldnt slip.

https://www.miataturbo.net/attachmen...ine=1420581474

But you could also put hardened washers between the steel tubes and the chassis, which would also give you a better surface for the bronze to ride on. Now I realize we're really starting to up the part count here.

17-4 is easyer to machine than 316? I did not know that.

The thing that makes 3xx stainless a complete dick to machine is that it work hardens. So like after your tool makes the first cut on the metal the surface is now harder than the billet was before you started. Mega amounts of suckage.

This is what I have designed for the Camber bolt locations. all the locations without camber bolts are fine with 3/4" sleeves and no washers. current descision is rather to machine the washers out of round bar or just buy 17-4 3/8" washers that have a 7/8" OD and bore the centers out to 12mm. I designed the washers at 4mm thick off the shelf washers are 2.66 to 3.33mm thick.

https://www.miataturbo.net/attachmen...ine=1420583472

Yes, plus a bunch of tolerance stack-up. At some point, I would just install sphericals in the same manner as in the rear upper.

Yup, you gotta get at it and not fiddle-fart around taking off a thou at a time.

--Ferdi

I understand, just thought it would be worth mentioning since it is cheaper and stronger than 316 and 17-4.

If its cheaper, weighs the same, and is strong enough to perform the intended function, I see 440 as a better material for this application unless the machining costs are higher than 316. I'm not saying that you can now torque to 200 ft-lb instead of 100 because the spacer would be twice as strong.

I'm sure the 316 you bought will be a noticable improvement over the ES sleeves. I'm also sure that 17-4, 440, and a number of other materials would work just as well. I just threw another option out there.

As for the chassis side of things, 7/8" would be better for the chassis as well, more clamped area means less bearing stress. I wouldn't do 3/4" on the front lower for this reason.

Does anyone know how 440 compares to 17-4 when machining?

Bob, what happens in the washer to steel interface that wouldnt just happen in the steel to chassis interface, besides gaining a little extra surface area since its not slotted.

Ferdi I wouldnt really worry too too much about the tolerance stack up. The steel sleeves are already cut for a loose fit into the chassis and if bob was going to add the thrust bushing option then he's literally belt sandy polyurethane as one of the operations that would effect the tolerance stack.

The slots are key to the issue, for the 7/8" they reduce contact area of the bolt clamp surfaces by 51" and for the 3/4" they reduce it by 58% over not having a slot. Without the slot 3/4" would have plenty of contact surface to not yield things.

The nice thing about the polyurathane is it flexes just enough to absorb some missalignment and tolerance stack up. I was just talking to Emillio and he was describing delrin bushed front suspension that was totally bound up because the pivot axis of all the bushings werent lined up. they run a mix of delrin and some urathane ones at specific locations to keep from binding. also there is no room for much tolerance on sleeve lenght or flatness of chassis flanges etc with delrin.

personally I think most of the static friction of the urathane ones comes from the shaft and not as much from the thrust surfaces. you can grease the crap out of them put them in by hand and 5 minuts later there is no way you can spin them by hand and you need a press to push them back out.

I think thats all fair. And really the thrust component is probably minor and it is going to be noticeably more work for you to put the bushing in it.

I'm not sure about the mixed poly and delrin. The bushings that needs to be stiffened up the most are the rear lower outers. In every miata I've tested this on, that covers 18 year old stock rubber, 1 auto-x season old poly, brand new poly, and 1 auto-x season delrin they are all able to have the rear tire flexed in the toe direction just by man handling the tire with it in the air. And if you look at it while someone else is doing it you can see clear as day that its the outer rlca bushing deflecting. Now that we have a spherical in the outer upper this is going to be slightly worse, but the spherical does allow us to go with fully metal bushings in the outer rears. BUT in braking or accelerating with poly inners in the rear and all metals in the others it could bind due to the inner uppers flexing. So you'd have to make the inner uppers the same way as the outer lowers and then it couldnt possibly bind unless the car, arms, upright, or long bolt are in some way tweaked from how they were brand new. Which is probably asking a lot. At worse, a sleeve kit like the one already in this thread in those two bushings + bobs poly setup is probably the best setup this side of going to all sphericals.

i find it highly unlikely that any of us are going to have anything heat treated, we should stick with the as machined numbers.

440 in the annealed state is around 60k. 185k is going to be a hardened variety



i didnt work your math backwards to see the values you use. but i assume this is aggravated even more by the fact that the slots are larger that 12mm by a good bit to allow for a little of the vertical displacement from the camber bolt as it travels through its arc. which results in even less surface area and more contact pressure, closer to the edges to boot.


i did exactly this per emilios advice on the front lower, and plan to do the rear the same way. i used a 1" sleeve. the flange on the delrin takes all the force under braking, and the rubber bushing in the rear position locates the arm longitudinally under all other conditions.

https://www.miataturbo.net/attachmen...ine=1420592303


440A- 45%
17-4PH(A)- 48%
just slightly better
https://www.carbidedepot.com/formulas-machinability.htm

cam bolts are 12mm not 14. the long bolts on the front upper and rear outboard lower are 14. rear upper are 10. yes proper sizing for a 12mm bolt is 24mm washer diameter. closer to 1" than 7/8" actually.