Lower control arm quandary

[Cudamike56]

Long time member, first time posting. I'm in the process of replacing the worn out rubber front end bushings in my numbers matching 68 Cuda 340 Formula S with a polygraphite kit from PST. To reinstall the lower control arm/strut assembly, the factory service manual states that the assembly is mounted in the K frame and front crossmember with the new (aftermarket) strut bushings in place and the retaining nuts at the strut and control arm pivot pin are to be installed "finger tight". As the nuts are "locking" type, finger tight is only few threads in and the pivot pin is far from seated in its the K frame bore. The manual goes on to say that from there you install the torsion bar, steering knuckle, etc. including the wheel, lower the car to the floor and set the ride height followed by tightening/torqueing the two finger tight nuts. If I wind the strut nut in and compress the bushings a bunch, the pivot pin will be pulled in, although still nearly a 1/4 inch from being seated. I'm assuming that this situation will prevent full reinstallation the torsion bar and its rear retainer clip. I can push the arm in to seat the pin but it will spring back when I let go due to the strut bushings and I anticipate the same thing would happen if I attempt to install the torsion bar. Can anyone tell me what am I missing here or am I over thinking this?

 

[72bluNblu]

The pivot nuts can be a lot more than “finger tight”. The reason for not torquing them while the suspension is unloaded is to keep from tearing the rubber LCA bushings. The rubber in the original bushings is friction fit with the pins and shells, it doesn’t rotate in the shell. The pins don’t move, the lca travels up and down, and the rubber bushing just flexes back and forth. So they need to be loose until they are at ride height. That way the rubber has enough range to flex as the suspension travels, it’s starting in the middle vs at one end (ie, suspension fully unloaded). If the pivot pins are torqued while the suspension is unloaded the rubber doesn’t have enough flex to accommodate the full range of travel in one direction and it tears.

As long as the pivot nuts are loose enough that the pins can still rotate when the suspension is loaded everything is fine. The car settles to ride height, the rubber bushing is centered up in its range of travel, and you torque the pivot nuts which stops the pins from rotating.

Here’s the other thing- that’s for rubber bushings. With the poly bushings that reuse the factory LCA shells it doesn’t matter. The bushing spins inside the shell, so you can torque the pivot nuts whenever you want.

I haven’t used PST’s kit, so I don’t know what they recommend or specifically how those bushings are made. Typically though the bushing material will spin in the shell or on the the pin, because the poly is so tough it doesn’t flex like the rubber does. But regardless, you should be able to tighten the pivot nuts 99% of the way home, just don’t completely tighten them or torque them to spec until the car is at ride height and you’ll be fine either way.

 

[Cudamike56]

The pivot nuts can be a lot more than “finger tight”. The reason for not torquing them while the suspension is unloaded is to keep from tearing the rubber LCA bushings. The rubber in the original bushings is friction fit with the pins and shells, it doesn’t rotate in the shell. The pins don’t move, the lca travels up and down, and the rubber bushing just flexes back and forth. So they need to be loose until they are at ride height. That way the rubber has enough range to flex as the suspension travels, it’s starting in the middle vs at one end (ie, suspension fully unloaded). If the pivot pins are torqued while the suspension is unloaded the rubber doesn’t have enough flex to accommodate the full range of travel in one direction and it tears.

As long as the pivot nuts are loose enough that the pins can still rotate when the suspension is loaded everything is fine. The car settles to ride height, the rubber bushing is centered up in its range of travel, and you torque the pivot nuts which stops the pins from rotating.

Here’s the other thing- that’s for rubber bushings. With the poly bushings that reuse the factory LCA shells it doesn’t matter. The bushing spins inside the shell, so you can torque the pivot nuts whenever you want.

I haven’t used PST’s kit, so I don’t know what they recommend or specifically how those bushings are made. Typically though the bushing material will spin in the shell or on the the pin, because the poly is so tough it doesn’t flex like the rubber does. But regardless, you should be able to tighten the pivot nuts 99% of the way home, just don’t completely tighten them or torque them to spec until the car is at ride height and you’ll be fine either way.

Thanks for the detailed input. Sadly, PST did not include any directions with the kit to give guidance for installation, but they do use the old LCA shells to carry the lubed up poly bushing as you surmised. Now I know that the pivot shaft spinning in the poly bushing is "normal". I think I'll use a conventional nut to draw the pivot shaft to its seat, as trying to tighten the locking type nut causes the shaft to spin in the bushing before the pin gets anywhere near seated. Once the torsion bar is in and I know the arm won't slide back, I'll swap the nuts and complete the set up. Thanks again.

 

[TrailBeast]

The pivot nuts can be a lot more than “finger tight”. The reason for not torquing them while the suspension is unloaded is to keep from tearing the rubber LCA bushings. The rubber in the original bushings is friction fit with the pins and shells, it doesn’t rotate in the shell. The pins don’t move, the lca travels up and down, and the rubber bushing just flexes back and forth. So they need to be loose until they are at ride height. That way the rubber has enough range to flex as the suspension travels, it’s starting in the middle vs at one end (ie, suspension fully unloaded). If the pivot pins are torqued while the suspension is unloaded the rubber doesn’t have enough flex to accommodate the full range of travel in one direction and it tears.

As long as the pivot nuts are loose enough that the pins can still rotate when the suspension is loaded everything is fine. The car settles to ride height, the rubber bushing is centered up in its range of travel, and you torque the pivot nuts which stops the pins from rotating.

Here’s the other thing- that’s for rubber bushings. With the poly bushings that reuse the factory LCA shells it doesn’t matter. The bushing spins inside the shell, so you can torque the pivot nuts whenever you want.

I haven’t used PST’s kit, so I don’t know what they recommend or specifically how those bushings are made. Typically though the bushing material will spin in the shell or on the the pin, because the poly is so tough it doesn’t flex like the rubber does. But regardless, you should be able to tighten the pivot nuts 99% of the way home, just don’t completely tighten them or torque them to spec until the car is at ride height and you’ll be fine either way.

You got it, even though you haven't used the PST stuff before.
I put the poly bushings in with the pins still tight and the lower arm had full travel with no resistance.

Thanks for the detailed input. Sadly, PST did not include any directions with the kit to give guidance for installation, but they do use the old LCA shells to carry the lubed up poly bushing as you surmised. Now I know that the pivot shaft spinning in the poly bushing is "normal". I think I'll use a conventional nut to draw the pivot shaft to its seat, as trying to tighten the locking type nut causes the shaft to spin in the bushing before the pin gets anywhere near seated. Once the torsion bar is in and I know the arm won't slide back, I'll swap the nuts and complete the set up. Thanks again.

Just put your pins in and tighten them up with their OE nuts.
As mentioned the poly bushings don't need to be at ride height when tightened because the move in the bores anyway.
OR, do it however you want.

 

[Cudamike56]

All good info guys. Thanks. Think I'll also use a large C clamp to hold the LCA in position against the pin/K frame until the T bar is set, as otherwise the strut and new bushings want to push it back off the pin and away from the frame with the poly bushing in place. Although if anyone has a better method, I'm definitely open to suggestions.

 

[Jim Lusk]

It shouldn't push the LCA off the bushing when everything is tightened. The T-bar really doesn't hold the LCA in place.

 

[Cudamike56]

I wouldn't think so either, Jim, and it probably wouldn't in the factory setup as they used a one piece strut bushing that "folded" into the cross member opening and appears to have been not as thick as the 2 piece aftermarket replacements. Unfortunately I haven't been able to track down OEM bushings for it. I suspect the thicker strut bushings acting on a floating (for lack of a better term) LCA lubricated poly bushing is causing the actual arm to held away from the K frame/pivot pin seat. As I mentioned, I therefore am hoping to crank down the strut nut and compress the bushings enough to eliminate as much of the "push back" as I can, then clamp the arm to close up any remaining gap. I'm hoping once the T bar is driven back place and secured, everything stays put. But again, I'm open to ideas. I've attached a photo of the tired OEM bushing vs. the PST supplied poly bushings that have very little give.

 

[Bodyperson]

It's been a while since I worked on one of these so it is hard for me to understand BUT... that bushing is going to adversely effect things. Its just wrong.

 

[S'cuder]

I've heard that because they're thicker, the urethane strut rod bushings can cause the rod to push against the LCA, possibly causing a tendency for it to bind. Possible solutions include using OEM style bushings, or adjustable strut rods.
Firm Feel touches on the subject on the page where they sell their strut rods: Firmfeel Mopar Suspension and Steering

 

[72bluNblu]

The poly strut rod bushings aren’t a good duplicate of the originals. The issue is the poly doesn’t compress enough. Which means the effective length of the strut rod changes. And that means you can’t reuse the stock strut rods without modification if you expect them not to bind up the LCA’s.

The original strut rod set up was a “one size fits most” scenario anyway. They worked well enough because the rubber is soft and there was a lot of give and play between the rubber LCA bushings and rubber strut rod bushings. If you start eliminating that play, then you have to be a lot more accurate with the length of the strut rod to keep the LCA from binding. Poly bushings reduce a lot of play, so, you have to get the strut rod length right.

I use adjustable strut rods for exactly that reason. Eliminating flex and play in the suspension makes the handling more accurate and predictable, which is great. But it also means your suspension components have to be more accurate too, otherwise they will not work as intended.

 

[S'cuder]

Here's some nice images illustrating the issue by FABO member @Mattax. He offers a solution of modifying the bushing.
Making A-Body Strut rod Bushings Work

 

[Mattax]

Here's some nice images illustrating the issue by FABO member @Mattax. He offers a solution of modifying the bushing.
Making A-Body Strut rod Bushings Work

Thanks. Yes. Just as Firmfeel shows, it's a problem that mostly showed up quickly when using polyurethane (and later nylon) LCA bushings. But even with rubber LCA bushings (which really are fine for most) I think its worth trial fitting and doing a slice and stack as needed. I wouldn't just go by my measurements especially if its a car with later strut rod version. Another approach is like 72bluNblu mentioned, use an adjustable strut rod.
An easy way to slice the bushings was by turning a small wood fixture on a lathe. Use the fixture to hold the bushing and slice it on the wood lathe.

 

[TrailBeast]

All good info guys. Thanks. Think I'll also use a large C clamp to hold the LCA in position against the pin/K frame until the T bar is set, as otherwise the strut and new bushings want to push it back off the pin and away from the frame with the poly bushing in place. Although if anyone has a better method, I'm definitely open to suggestions.

It shouldn't push the LCA off the bushing when everything is tightened. The T-bar really doesn't hold the LCA in place.

Once greased and in place mine pushed back also, because the bushing is just tight enough when the pin goes in to make it want to slip back off.
I used a tie down for the dirt bikes, but a clamp would work just as good.

 

[AJ/FormS]

My LCA pushed back too.
Keep in mind that as the strut gets longer and permanently relocates the LCA further back, it steals caster and that is bad news, cuz A-bodies don't have enough caster to start with. So, IMO, slicing those poly bushings is a good alternative, as long as you maintain a working range with them, and don't crush them solid after tightening.
That is what I did, plus the problem solver Moogs up top, and was able to get close to 5* caster at zero camber. After readjusting the camber to .5Neg, I was left with ~3.5* caster which seems pretty good in my streeter. That was 1999, and the car still drives nice with over 125,000 miles on her since then.

 

[Cudamike56]

My LCA pushed back too.
Keep in mind that as the strut gets longer and permanently relocates the LCA further back, it steals caster and that is bad news, cuz A-bodies don't have enough caster to start with. So, IMO, slicing those poly bushings is a good alternative, as long as you maintain a working range with them, and don't crush them solid after tightening.
That is what I did, plus the problem solver Moogs up top, and was able to get close to 5* caster at zero camber. After readjusting the camber to .5Neg, I was left with ~3.5* caster which seems pretty good in my streeter. That was 1999, and the car still drives nice with over 125,000 miles on her since then.

Good day all. I'm finally getting back to update the results of all your good input on my "quandary" and am happy to report that using member @Mattax's suggestion and sketches I was able to modify the strut bushings and sleeve by "shaving" them the right amount to allow the LCA pivot pin to correctly seat. As the pin still wanted to spin in the poly bushing when attempting to tighten the factory locking nut, I installed an standard 8 grade nut and washer with thread locker in its place torqued to spec. Once I get the front disc brake conversion completed, I'll get it aligned and should be good to go. Thanks to @Mattax and everyone who put out suggestions.