DIY offset delrin bushings for the rear LCAs for camber correction
 

It says "use descriptive titles" :)

I was suffering from an excessive rear camber issue for a while.

Coupled with a lower than stock suspension, a worn rear upright bushing was making my right rear lean way in, with a 5.6 degree negative camber on that side.
The left rear was sitting at -3.6 degrees.

After much tweaking, and not being able to bring the camber angle to any sort of a reasonable level, I decided to take aggressive action.

The solution would be making offset bushings for the lower control arms (the outer ones) that would bring the camber angle to a level where the inboard adjusters would be able to, well, adjust the camber.

So, I ordered some delrin. That stuff is pretty inexpensive. Like, about $20 for a 55 mm diameter, 1 meter long bar. So, I got two one meter lengths, just to be sure. In hindsight, I could just get the 40 mm variety, that's even cheaper.

Anyway.. I removed the rear suspension, and then the a arms, and then I used the threaded rod method to remove all the outer bushings.

Next step was getting to the machine shop to make the delrin bushings.
I packed the a arms, hubs, the bushings I pulled out, and the drawings I made for the new bushings on my scooter and got to the machine shop.

The owner of the Machine Shop, Sinan, is a very cool, smart guy.
We ordered tea, and went to work.

https://www.miataturbo.net/attachmen...ine=1378081971

https://www.miataturbo.net/attachmen...ine=1378081971

The idea was to make two piece bushings, to be pressed in from both sides.

https://www.miataturbo.net/attachmen...ine=1378082110

And, they would have proper lips that would help us seat them correctly.

https://www.miataturbo.net/attachmen...ine=1378082110

I wanted the lower outside bushings to be offset. I figured drilling the cores 5.5 mm off center would suffice.

That was easy with the lathe. Chucking the bushing blanks with a 6.5 mm spacer on one side gave us the offset we needed. We used a 18 mm drill.

https://www.miataturbo.net/attachmen...ine=1378082388

https://www.miataturbo.net/attachmen...ine=1378082388

Sinan had some pretty high quality steel stock laying around. We used that to make the sleeves.
Lower bushing bolts are 14 mm, uppers use 10 mm bolts.
We drilled into the steel first, then reduced the diameter to 18 mm, and then really polished them at high speed. That removed another 0.5 mm or so, and gave us just the right clearance for smooth articulation inside the delrin.

I also used the existing holes in the lower arms to thread and install grease fittings. I just drilled the uppers in the appropriate spots for the same purpose.

As for installing the offset bushings, once positioned the first piece, I used the long bolt to line up all the remaining pieces. It was easier than I had anticipated.

Here are the bushings, installed:

You can see the grease fittings, too.

https://www.miataturbo.net/attachmen...ine=1378082875

https://www.miataturbo.net/attachmen...ine=1378083221

https://www.miataturbo.net/attachmen...ine=1378083221

https://www.miataturbo.net/attachmen...ine=1378083221

https://www.miataturbo.net/attachmen...ine=1378083221

https://www.miataturbo.net/attachmen...ine=1378083221

https://www.miataturbo.net/attachmen...ine=1378083221

I pumped grease in them till it flowed out from both ends. I am pretty sure I will not have any problems if I just grease them once a year.

There is about a 7 mm gap between the bushing halves inside the housing.The grease fitting points right in that void. I figured having a grease reserve in the center would not hurt anything.

I took the car in for an alignment, and the rears have -1.25 degrees of camber now.

Feels much smoother, makes no noise at all, corners better, and has less wheelspin when taking off now.

If you have access to a lathe, go for it.

I will do the fronts next, when I have time.

how do you ensure they don't rotate under load after being pressed in?

would have been easier to modify the ruca for an eccentric bolt.

nice work btw! you could also pin them or use some grub screws to hold the bushings in place if they dont already have a few thou of press interference.

Faith.


Kidding. The fact that the outer lips are D shaped makes damn sure they will not rotate.
There is also some ungodly friction between the bushings and the housings - cut them that way on purpose.

Maybe.

But then, I would still have old bushings in the lowers.
Also, the rear wheels would be pushed out at the top. I am pulling the bottom half in. Clearance!

Doesn't that mean you've now effectively increased your springrate due to the stiction between bush and wishbone?

Not at all.

The delrin is fixed, as in no movement, in relation to the housing at the end of the control arm.
What moves is the sleeve inside the delrin bushing.
And, that movement is very smooth.

So the zerk fitting.... I imagine there is a small space between the bushings where they don't sit flush, but what is this greasing exactly? Delrin is self lubricating isn't it? Doesn't some lubricants cause delrin to swell?

Just a couple questions, very cool idea. I'd love to make a set for myself, have any dimensions you want to share? ^_^

Gotcha, sorry I'd missed that you'd sleeved them too.

you shouldn't have to grease the delrin, they have a naturally self-lubricating.

I used grease primarily to keep moisture and other debris out.

I'm curious to see how this holds up over time. You could probably start yourself a neat little side business doing this, I know I've thought about it several times.

God I hated working with Delrin, same with Nylon and Teflon barstock. That shit refuses to break a chip and turns into a giant spaghetti mess.

MOAR depth of cut, and feed like a man.