To poly the leaf springs...

[Rishi]

I searched and couldn't find this topic.

What's the recommendation on using polyurethane bushings at the rear leaf springs? In the front, I'm planning only to place poly on the UCA and (anti) swaw bar bushings.

I'm learning these bushings are not ideal to use everywhere. I'm doing some rear leaf spring work, and got mine cleaned up and I'm preparing to reinstall. But I'm wondering if there is benefit to replacing the bushings with poly. The factory-looking bushings in there now still look pretty good. But I don't intend to revisit the rear leaf springs for years, maybe even the rest of my life, ha ha. So if I'm gonna do it, now is the time. The hangers and such, are all OEM.

 

[Dave6T4]

A buddy of mine did that on his '67 Belvedere, but changed it back to new Moog pieces, because the ride was too harsh.

 

[coloradodave]

In my opinion it is all about the intended use of your car. Going to autocross it or want it to stick to mountain roads as a priority? By all means poly everywhere. Want a comfortable, quiet ride and the ability to drive long distances and keep your hearing? New, OEM bushings. I set my car up to take on a more Pro-Street / drag race look. It's all poly. At some point soon I'm going to go back to stock bushings so I can enjoy the longer drives more. In my case I spent a lot of money that would have been utilized better in other areas of the car.

 

[Rishi]

okay, good feedback so far. thank you.

This is for a mostly street driver, and I want passengers to enjoy the ride. I don't have great delusions it will ever handle like a European sports car. Yes, I want to drive it safely on mountain roads, but autocross is unlikely.

I once went all poly on an e-body and I too, found it fatiguing to drive and was a little sorry I was so aggressive with poly bushings. Sure, I want the best handling these big block monsters can offer, but not at the expense of a back injury.

I'm hearing poly on the rear springs may be too harsh. very good to know.

 

[j-c-c-62]

You might do a compromise on the leaf's, OEM front, urethane rear, or even only half urethane in the rear (tops or Bottom) being the rears might be an easier to change out later if desired. The other's comments above have merit IMO, me, I just turn the stereo up and drive faster, it shortens the trip and softens the ride.

 

[PurpleBeeper]

You might do a compromise on the leaf's, OEM front, urethane rear, or even only half urethane in the rear (tops or Bottom) being the rears might be an easier to change out later if desired. The other's comments above have merit IMO, me, I just turn the stereo up and drive faster, it shortens the trip and softens the ride.

That’s clever! As you say, it’s easy to swap out the rear leaf spring bushings later

 

[Runner 68]

I go with poly whenever I can for the durability. Changing out bushings is a PITA.
A little more harsh ride? Absolutely. Big horsepower in an old Mopar muscle car a little harsh? Absolutely.
Driving the combination of the two is harsh. That's the fun of it for me. Get a helmet.

Drive the Beemer if you want a smooth ride.

 

[Rennkafer]

You might do a compromise on the leaf's, OEM front, urethane rear, or even only half urethane in the rear (tops or Bottom) being the rears might be an easier to change out later if desired. The other's comments above have merit IMO, me, I just turn the stereo up and drive faster, it shortens the trip and softens the ride.

That's basically how my Hotchkis springs came, poly on one end, rubber on the other.

 

[Rishi]

Googling around just to get an idea of the OEM replacements, poly alternates, cost, sources, etc, I am surprised how different websites give conflicting parts for this application.

For the rear shackle bushings, both the Moog K-7308 and the K-7309 are recommended. I see some reports the bushings are occasionally "loose" and sure enough, those two bushings vary a little in their dimensions by 0.10-inch.

The same thing occurs with the front pivot bushing, again, two are mentioned numerous times, the RB-90 and RB-91. One being 1.50-inch diameter, and the other 2.00-inch. I see forum posts where places like Rock Auto sometimes recommend and ship the wrong part.

So far, I think the OEM parts from Moog might be the K-7308 and RB-91. I'm gonna need more confirmation before I can order some parts.

My thoughts are like "these sources have had 50-years to figure out the right part, and they still get it wrong."

 

[j-c-c-62]

Drive the Beemer if you want a smooth ride.

I have owned 3 BMW's, 320, 635, 735, and you are correct, each of those offered a smooth ride, and also handled great, meaning IMO, a rather high bar.