The front suspension bushings fall under four (4) areas, to consider:
- Upper and lower control arm bushings.
- Sway bar bushings (frame and at torsion bar).
- Torsion bar bushings (pivot (K-frame) and end (control arm)).
- Shock bushings.
My opinion as to bushings. Urethane (or polyurethane, which might be the same thing?) are wonderful for suspension systems – but they do have a cost (ie: ride quality). Thirty years ago, I installed all poly bushings into my ’68 Charger and my ’69 Road Runner. I didn’t get my Road Runner completed to know much about it (had to sell car to pay for a divorce, in an incomplete state). The Charger was extremely rough riding afterwards, using 15” tires (this was thirty years ago…). I ended up switching out the control arms (all 4) after replacing bushings with rubber, first. I then sold existing (poly) arms to a friend. I was so much happier afterwards, without much difference in handling. With urethane bushings in upper and lower control arms – I could feel every leaf, bug and grain of sand I drove over – or more importantly, so did my kidneys. That would be a bigger issue, now I'm thirty years older (sigh).
I’m a firm believer of having/using rubber for the control arm bushings (upper and lower).
That said, I will use only urethane for sway bar bushings. Rubber has “too much” give. Ride quality is not affected one iota for either bushing type, but sway bar does come into action much quicker (almost as if you have a faster steering gear).
A person can disconnect the sway bar (something many drag racers do, because of weight and it allows faster weight transfer from front to rear on takeoff), but you will find on a hard turn, the car rotates excessively, almost to the point if feels like door handles are about to grind against the pavement on hard turns.
Torsion part bushings are different. The factory had either regular rubber bushings for control arm ends and middle (pivots) and for police use, firmer bushings for both. The firmer police bushings evaporated just after ’89 (M body production stopped). The regular rubber bushings have recently evaporated (last couple of years) – so the only available torsion bar bushings now are urethane (unless someone has a hoard of new rubber bushings, somewhere). I hadn’t had the pleasure of working with urethane torsion bar bushings, yet – so can’t offer much comment there.
In my opinion and experience, urethane pivot bushings should work excellent. I would think rubber would work better for the end bushings (to control arm), sense you wants a little give there – but hadn’t heard anything negative, so far.
Shock bushings wear out, just like shocks wear out (look at upper right corner of fifth picture down). I have friends who will replace the (new) rubber shock bushings with urethane. Personally, I don’t know that it makes a hill of beans worth of difference on shock bushings, sense shocks are there to dampen bumps and to keep car from bouncing after a bump. Most new shocks come with rather hard bushings to begin with. My opinion is to use what comes with your new shocks and you should be fine.
Now what will make an even bigger difference is with replacing the rubber K-frame mounts with Cast Iron (Mopar Performance), with aluminum (FFI, for example) or with urethane. I think a metal would work better than urethane – but any of the above will make a huge difference over the rubber (even new rubber, if you could find any.
These rubber bushings shown are in better condition than most I've seen.
FFI versions. Nice, but pricy.
Rear suspension is a different matter.
I’m not aware of anyone making urethane rear suspension front oval-shaped bushings. The oval bushings are an issue in of itself. The same oval bushing was used for ’83-07 minivans – so a supply of bushings will not be a problem for the foreseeable future.
If rear leaf spring is removed for any reason, for my own cars (or friends), i recommend inserting two bolts/studs/rods (ie: something solid) marked by red arrows - into the two holes, and re-install (per side). That will firm those bushings up, a lot.
If you are going to have new leaf springs made, I recommend using the round (rubber) front bushings (‘60’s B-body) and you should be good.
If you see any cracking or rubber issues, in any of the rear bushings, go ahead and replace with new bushings.
Again, I recommend with rubber, for I don’t see, except for in a full-time race car possibly, that urethane bushings will improve anything but increased noise.
Now the ISO-clamp, is a different issue. That system did nothing for performance, did nothing for ride quality, and did nothing for improved part longevity. IMO, it makes cars with a tad (or more) performance hop more, makes any handling piss-poor, makes ride quality worse (when new, even worse with a few decades are on the clock), and the lower “U” shaped bracket is a known part failure (at blue circles).
Replacing any FMJ rear suspension ISO-Clamp system with an older style shock plate (or FFI ISO eliminator, or similar) will improve getting power to the ground (with those capable of traction issues), improves handling, improves ride quality, it gets rid of the troublesome lower ISO clamp (“U” shaped bracket) and it raises the rear suspension about ½”/13 mm (because of removal of upper rubber biscuit mount). The rubber biscuits have not been made for a couple of decades.
Now many members have replaced the rubber biscuits with urethane ones and have had good luck with them, but you still have the troublesome “U” bracket to worry about.
I firmly believe that even on an /6 car (like Ole Yellow, for example), removing the ISO-clamp with older shock plate, ISO eliminator or using urethane biscuits, will help the ride . . . a lot.
BudW
