Project FD RX7 Restomod: Part 3 – SuperPro Front Swaybar and Steering Rack Bushings

We fix a bad clunk and steering issue with a stiffer SuperPro front swaybar and steering rack bushings.

When Project FD RX7 Restomod was purchased, it had a pretty bad clunk coming from the front suspension when turning and braking.  When buying 30-year-old cars with the plans to actually DRIVE them, it should be expected that a lot of work will need to be done, especially when it comes to ball joints and bushings.  This clunk was an annoyance, but not bad enough to address immediately.

However, after installing far grippier Continental Extremecontact Force tires in Part 2, this clunk not only got worse, but the car’s alignment and steering was thrown off from heavy cornering.  Spirited driving on canyon roads would cause the steering to be off to the right after heavy cornering to the left, and then shift to be off to the left after an aggressive right-hand corner.  This could only mean one thing; the steering rack was moving.

SuperPro polyurethane FD Mazda RX7 FD3S Steering Rack BushingTo solve this issue, we decided to use SuperPro’s polyurethane steering rack bushings.  SuperPro has a great reputation for not only the performance of their suspension bushings, but more importantly, the lack of NVH and squeaking that is common with many polyurethane bushings.

Through extensive testing, Superpro has created a unique polyurethane elastomer with special resins and curing agents that give their bushings the performance and attributes that has made them well-respected in the bushing industry.

Their bushing designs are not just copies of original OEM bushings, but rather are specially developed from scratch to take full advantage of the unique material properties of their polyurethane that is extremely durable and has the best features of rubber and plastic.

MotoIQ Project FD3S FD Mazda RX7 RestomodWith the car up on the rack at FSE Irvine, a body repair shop and race team based in Orange County, California that puts on track days and driving schools with their Formula 4 cars; we were ready to find our clunk and steering issue.

FD3S FD Mazda RX7 stock steering rack bushing movementWe quickly found the source of the steering problem.  As we suspected, the steering rack was moving and these witness marks on the steering rack bushing is proof that the rack is moving back and forth, every time we corner hard, thanks to the super sticky and far wider Continental Extremecontact Force tires and wide Titan 7 wheels we recently installed.  We never experienced this problem previously because the stock wheel and tire combination couldn’t create anywhere near as much cornering grip.

FD3S Mazda FD RX7 dead swaybar end linkAs we started to remove the stock front swaybar, we found the source of our clunk.  The end links were completely worn out and had a ton of slop.

3 comments

  1. Looking forward to reading more articles as this project continues!

    You are developing a responsive and engaging setup, whilst maintaining characteristics to make the car safe and pleasant to drive everyday. As much as I love factory backed GTE/GT3 cars, and wild race/hill climb builds, it is equally enjoyable to see a balanced, practical build like this. As always, fantastic content from everyone at MotoIQ.

  2. I am always really surprised by this kind of steering rack designed used on so many cars. It’s basically asking for eventual play because it’s ability to move side to side is not properly constrained. I have only seen a handful of cars that actually properly locate and constrain the rack with bolts directly into the subframe. I know that early 911’s do this while later ones have a similar setup to the RX-7. I am assuming that it’s an NVH issue.

    It’s such a huge increase in steering precision and feel to have PU bushings in a steering rack. I think it’s probably one of the cheapest upgrades, and if you have the chance to do it to your vehicle, it’s an absolute must.

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