Mar 6, 2007 update to the Mazda STS2 Miata project car

Delrin Downsides and Cocked Cams!

Back when we first converted our Miata from CSP to STS2 trim, we discussed the use of Delrin bushings. We also talked about the maintenance requirements in our “recipe” installment a couple of months ago. Well, its that time of year again and here’s the saga of our latest bushing rebuild.

Delrin is a wonderful substance that is self-lubricating and requires little maintenance. Unfortunately, the sleeves that are typically used inside of a Delrin bushing will rust when exposed to the elements. This can be minimized by using a lubricant as a sealer, but this maintenance must be done at least once a year if your car sees significant wet weather. Since we are about to embark on a six week trip to national events in California, we’ve just taken the time to go through and rebuild all of our bushings. Its a straightforward process of removing the mounting bolts for each to slide the sleeve out, cleaning & lubing it, then reinserting and tightening the whole thing back up.

That said, some sleeves are more straightforward than others. In our case, several showed significant rust. Left unchecked, the rust builds up, removing the proper bearing clearance, and the sleeve begins to drag and then bind up. In one case (see pic), the sleeve was completely bound and the bushing was rotating inside the control arm instead. Yikes! Some fine grit sandpaper makes quick work of the rust and a liberal coating of white lithium grease provides a good seal against further problems.

One hint on removing the huge bolt on the front upper control arms: You can get this out quite easily by first backing out the rearmost of the two sway bar frame mount bolts (12mm heads) until the backside is flush with the bracket. Now, the big a-arm bolt will slide right out underneath the bracket.

Before removing the lower bushings, we marked all of our alignment cams so we could reinstall them in the original positions and keep our aligment close. Still, we will visit our man Bill Kim at Soulspeed to get it perfect for the start of the season.

Lately, we’ve been having some issues with clunking under turn loads and each time it has proven to be a loose front lower camber adjustment bolt/nut. This is a very common problem in Miatas as the adjusters wear over the years. It shows up a lot on cars that have had frequent alignments, and ours certainly has been down that road. You can see in the pictures several problems which can occur, all of which were exhibited by one of ours. The original design has an eccentric cam with a D-shaped hole. The D gets rounded with use and it no longer stays indexed to the front cam. The front cam is held onto the bolt with a thin set of splines, which can be stripped. With both of these problems combined, our cams were 90 degrees out of phase! This puts tremendous twisting stress on the mounting bolt which explains why it kept coming loose.

Mazda has a redesigned part which has thicker cams for more spline engagement, finer threads for better nut retention, a double-V index in the cam for more working surface and tighter indexing, and an eccentric locknut to keep it from backing off. We recommend these parts be fitted at least in the forward positions of the front lower control arms, since that position takes the most stress in a corner. Best of all, they are relatively inexpensive.

Now our Miata should hold its alignment much better and our suspension will work as designed. You can add all the go-fast parts to your car that you want, but without proper maintenance on the basics, its a waste of time and money.

On to San Diego, El Toro and Atwater!

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