Anyone have experience with the UMI Rotojoint Rear lower control arms versus poly bushing? I am running a set of ancient Edelbrock with poly bushing and was wondering how much harsher the ride would be, if at all.

 

While I'm not installing the same LCA's I am installing founders performance LCA's with a poly/rod ends today. I'll let you know what the difference is

 

It will probably ride better. Poly is a terrible choice for the rear arms, and for most things for that matter.
I had the rotojoints on my 92 for years and was very happy with them.

 

I got my new LCA's on and the ride is night and day better then the poly/poly units I had on. Should've got these years ago

 

Yup, poly binds up the suspension pretty bad, even lubed up.
i dumped poly yrs ago

 

Perfect, I'll be adding this to my to-do list for sure then.

 

I installed UMI roto-joint LCA's about 1000 miles ago. I didn't notice a difference in noise, though the car isn't exactly quiet.

 

I've used the Roto-Roto LCA in the past.
they perform better than Poly-Poly LCA by a mile.
However, they basically have the same harshness and noise as Rod-Rod LCA.
So kinda a pointless mod foy anyone not looking to harm ride quality.
Poly-Poly LCA are also no good as they bind, squeak, and hurt ride quality.
​​​​​

I recommend OEM 1LE rubber LCA in a nice daily driven car or cruiser.
or bite the bullet and use DSE LCA since those don't bind or have the harshness of rod-rod combos.

 

Hmmm, those DSE are almost a $200 premium over the UMI. It's not a DD by any stretch of the imagination, I got a '23 3LT 6MT for that. Might see 2000 miles a year so a bit of harshness is acceptable. The LCA I have in there are really the only thing I can think of that are making this nasty unloading clunk that's not exactly reproducible.

 

Poly LCA tend to have short lifespans as well.
I've seen multiple ppl have weird axle hop + shaking due to the poly wearing out.
I love rod-rod LCA, but obviously it takes away street mannors.
as far as DSE stuff, the quality tends to be worth the price premium.
​​​​​

 

Firebird Rear Suspension Flaws:

The Firebird rear suspension from 1982 through 2002 needs a little help with locating the differential under the chassis. The panhard rod does somewhat of a decent job laterally but what about fore and aft?

The bushings in the lower control arms are basically the problem. If you look at the lower control arm bushing you will notice air gaps on each side of the center bolt hole. The air gaps allow the differential to move fore and aft and also shift during cornering. The panhard rod has nothing to do with this movement. As a result, when you accelerate out of the corner, the rear end actually shifts and points out of the turn. This helps the car oversteer. Something we don’t really want.

Global West Advantage: Problem Solved with Rubber Bushings

The solution the Global West Suspension (Quiet Ride) rear lower control arm for the Firebird (model years---1982, 1983, 1984, 1985, 1986, 1987, 1988, 1989, 1990, 1991, 1992). The arm is designed with a spherical bearing on one end and a rubber bushing on the other end. There are no holes in the rubber bushing.

We deliberately designed the arm to use rubber because the bushing acts as a noise insulator for the street, yet we still have the control for high performance driving including racing because the bearing and the tubular arm don’t deflect. The differential does not move fore and aft nor does it shift creating oversteer during hard cornering. It is the perfect solution for the enthusiast on the street and occasional trip to race track.

For straight line acceleration the rubber bushings can generate an oscillation leading to reduced traction. Aftermarket polyurethane control arms solve some of the problem and create others. The polyurethane does not allow the differential to pitch as it needs to around corners and over bumps. The result is oversteer and a stiffer ride over bumps. Straight line acceleration is better because we have removed the air gaps in the rubber.

Replacement rubber bushings are available without the holes, and an improvement over the stock setup is achieved. However, there still is a problem. The rubber increases resistance as the suspension moves through its intended path, thus changing the spring rate, and we still have some deflection through the control arm and bushing. Some people box the lower trailing arm to gain handling; however, boxing the control arm increase the resistance during cornering and affects the rate the car sees. This leads to oversteer.

 

I ended up getting these and finally installed them this past weekend. Took a whopping 30m, probably the easiest thing I've done on this car. Set the length by turning down a pair of wood dowles to fit into the bolt holes of the old fixed length arms and screwed them down till they were the same. I only drove it about a mile but it seemed to feel more nimble. Really hard to A/B though because I got new tires too, and God knows going from 25 year old rubber to new, performance tires make a world of difference in their own right. They weren't cheap but I feel like it was a good choice and wouldn't hesitate to recommend.