lower control arm bushings

[dusterbd]

OK, buddy of mine and i are in a discussion about lower control arm bushings in all poly suspension setups. all other parts stock. figure id stick it out for all to read.

When using the poly lower control arm bushings, they never seem to sit correctly. the control arm does not locate completely tight to the K-frame, leaving a gap that varies from car to car. we agree that this cannot be good for maintaining alignment, bumpsteer, and ackerman throughout the suspension travel.
he says that this can cause the torsion bar and lower control arm to move during braking and cornering. id have to agree with that.

the controversy comes in here. i say that its that the strut rod bushings are actually thicker than the rubber that was replaced, causingthe strut rod to be at a different location, pulling the bushing in the lower control arm out of whack. its fixed by an adjustable strut rod.
he says that the problem is not in the strut rod, it lies in the bushing design itself, and to replace it with a stock shelled rubber bushing.

so now weve been standing in his driveway looking at his duster and his neighbors demon for a week, and were at a stalemate.
help us out, we have a case of girl scout cookies riding on this.
thanks
michael

[dwc43]

Both of you are wrong. Go to www.firmfeel.com and you will see the extra ;iece that is needed when installing polly bushings in the lower control arm. You just installed them and left out a piece that you did not buy.

[dwc43]

Matter of fact, here's the exact link you need. It shows the adjustable strut rod and greasable pin.

http://www.firmfeel.com/adjstrut_b.htm

[bbeckwith]

DWC43,

That's pretty cool setup that FirmFeel has there. When I did my front end using Poly stuff, I questioned the manufacturer about this very problem and they suggested I grind the strut rod bushings down, (which I did with a belt grinder) to get the lca in the proper position on the pivot, so I would tend to agree with DusterBD that the strut rod bushings are the culprit here. While my method works for cheap, those adjustable strut rods are a cool item, but I'm not sold on it being necessary when you can just trim the strut rod bushings you have already. However, when money is not a problem, I would think these the way to go.

[dusterbd]

DWC: on the link you gave me, it said that the bushings were thicker, necessitating the adjustable strut rod. so what benefit, other than greasability, do the lower contol arm shafts have? thanks for the link. i didnt realise that they had that info on there.
michael.

[swingin72]

I ran into this same problem when doing my 72 Dart. The LCA doesn't want to go far enough forward. I actually assembled it that way and have driven it for 2 years with no problems. One of these days I should tear it apart and trim the strut rod bushing. It is, in fact, too long of a strut rod with the new bushings installed. My LCA sat about 1/2" too far back. I can definitely feel some "wander" from time to time, just don't feel like taking it back to the alignment shop after doing it over...

[Clair]

Originally Posted by dusterbd

When using the poly lower control arm bushings, they never seem to sit correctly. the control arm does not locate completely tight to the K-frame, leaving a gap that varies from car to car... i say that its that the strut rod bushings are actually thicker than the rubber that was replaced, causingthe strut rod to be at a different location, pulling the bushing in the lower control arm out of whack. its fixed by an adjustable strut rod.
he says that the problem is not in the strut rod, it lies in the bushing design itself, and to replace it with a stock shelled rubber bushing.
michael

You're right, the strut rod bushing (in every case I've seen) is basically a piece of poly that was, at best, molded from an original rubber piece. Since the poly doesn't compress like the rubber did, you end up with strut rods that are longer than they need to be when properly torqued. This was killing me on my Valiant... couldn't keep it aligned (I do my own), and the car was twitchy most of the time. Nail the brakes hard, and it firmed up a little, but not for long.

When I installed my Viper calipers, I tore the LCA's off and replaced the rear strut rod bushing with a cut-down version of the same piece. I first measured the distance from the LCA to the strut rod mount in the K with the LCA fully seated against the K. Fortunately, it came out to be exactly the same side to side, so no other problems there. Then I knew how long the strut rod and rear bushing had to be, accounting for a little crush. I fabbed it all up, trimmed the bushing down as necessary, plugged it all back together, and whaddyaknow, I've got 3.7* of +caster, 0.75* of -camber, just a hair of toe in, and IT STAYS THAT WAY. The car is a joy to drive now.

All that said, the Mopar LCA bushing rubber is so thin, I don't really think there is much benefit to going to poly in that spot. I mean, unless you just want to, that is. My car's got poly all over, front and rear, but on a more regular car, I'd go with rubber in the LCA. And your buddy is partially right... putting rubber in the LCA will hide a lot of the strangeness of the poly SRB's. I know, I had the same SRB's (as in, re-used them) in my previous suspension with all rubber bushings except the SRB's. No problems there, only when I went to the poly LCA bushings.

Another perk of the rubber bushings is that they add spring rate to the suspension. Since the rubber is bonded to the steel shell, and the shell is pressed on to the shaft, the rubber has to twist, not slide, when it moves. THe bushing acts like a spring. Ehrenberg popped off with a number like 20#/inch, and that's a bunch on a limp stock suspension. If you don't bump up your t-bars when you go poly, you may notice the suspension is softer. That's about twice the difference as going from 0.890" (383/440) bars to 0.920" bars.

Clair

[fastback340]

Yup the strut bushings are to thick. I was unaware of this problem till a few months ago. Now my lower control arm bushings are toast. Im gonna swap in Rubber LCA bushing this time and I have a set of Adj. strut rods to go on aswell.

[dusterbd]

hmm.... rubber bushings effectively add spring rate?
thats a ton cheaper than going up another few steps in torsion bars in my car.....
thanks for all the info. ill let him see the pics.
also, on a related topic, will the lower control arms, whes still using all poly bushings and having the lower control arms located properly via the strut rods, still move back and forth under hard maneuvering?
thanks for all the help guys. looks like im not getting my girl scout cookies though....
michael

[dusterbd]

clair: could you by any chance give me the dimensions for those strut rod bushing modifications?
thanks