I've got a crazy idea about trying to replace my Torque Arm with a 3-link style upper control arm.
I'd like to be able to use a "regular" rear end and free up my driveshaft tunnel space for two exhaust pipes all the way back. I also want to eliminate the "bang" that I feel in the supsension whenever I hit bumps at certain speeds. I'm blaming the poor ride on the straight-line connection of the torque arm to the rear end. To me it seems that if you have some angularity in both upper and lower control arms, it would put more of the shock of hitting bumps into moving the arms and using the springs to absorb it.

I've got a donor car to cut the entire floor area out of in the probable mounting area. I could use this to mock up the area where the front mounting brackets and bracing would need to be and fabricate the parts before installing on my car. I would want the new front mount to have a lot of different mounting hole locations for experimentation of forward mounting locations, in both vertcal and horizontal planes for the new upper link.

So, does anybody know what length I would need for the upper link? Would it be about 2/3's of th length of the lower arms? Or an equal length? I'm thinking about using the diagrams and notes from some of the other posts here, and other sources, about LCA locations and angles and Instant Center calculations.

Many years ago I played around with an early Chevelle's stock 4-link style control arms. As I remember, the mounting points may have been farther away from the rear end housing center line (vertically), And I wonder if this would give a better leverage advantage strength-wise for the mounting points on the housing itself? What I mean by leverage advantage is the does the distance between the housing top mounting hole and the bottom mounting hole have to have enough length along the vertical plane to resist the two opposing twisting forces being transferred to the rear end? It looks like the 3rd gen's lower ca mounting holes are closer to the housing centerline and I'm wondering if that could be a problem?

If the lower control arm locations work out OK, it seems like installing an upper link would not be all that hard to do. All you would really need to do would be to remove the torque arm, have brackets on whatever rear end you end up using, and install your forward bracket and bracing to the floor board. All of the shock, brake and panhard bar hardware would be unaffected.
In my case, I don't even care if I would have to cut up into the rear seat area for the forward mount and bracing. You might even be able to make a cool mini console out of it between the two rear seats or something.

So what does anyone think about this? I know that modifying suspension geometry can really be opening a can of worms, but I would be attempting to follow the original lines and dimensions where possible. And if it doesn't work out all that well, I can just cut it out and start over, or go back to the torque arm.

 

this has been discussed before, and there really in so easy way to do this without re-building the entire rear layout of the car. The floor is not strong enough to support a 3rd link other than the torque arm.

the bang sound you are hearing is probably a failing/failed torque arm mount/bushing.

What "normal" rear would you use? how may factory 3 link cars with that setup are out there? the only one i know of is the new mustang. the rest of the "normal" rears are for a triangulated 4 link, which again will not really be practical in this car.

the torque arm style setup actually works very well, it just gets a little cluttered in the driveshaft tunnel when you start trying to do dual exhaust, or use an aftermarket torque arm setup

Buuut, if you have a plan and want to give it a go, do it, and post pics, you will the the first i know of.

As for exhaust clearance, it would probably be easier to re-design the driveshaft tunnel that mess with the rear, and even that would be a huge undertaking

 

It's not so much that there is an existing factory car out thre using a three link setup. It's just so much easier and cheaper to fabricate a simple bracket to the top of any one of several different rear end housings than it is to make up the required brackets to make other rear ends "look" like a stock 3rd gen rear end with it's mounting bolt holes cast into the front of the housing.

And I agree that the floor boards aren't strong enough to stand up to the forces of the upper link. That is why I mentioned the mount with bracing. Several things come to mind, heavy plate contoured along the floor pan in this area with the bracket sides built up on another plate. The plate could then be supplemented with square or round tubing spanning across, maybe at an angle, to the next heavy floor or frame member. If that member is not strong enough, it too could be braced. It seems doable to me. After all, that is all that is done to the floor where the transmission crossmember attaches, and it is taking on the forces of both the transmission mount and the torque arm.

I'd love to read the other posts where this has been discussed before. I'm pretty new to this board, but other boards that I participate in have ways to search the board archives, can this be done here too?

 

Ditto on the TA's chassis-side bushing, but you should also check the tightness of the attachment of the TA to the axle. There should be no relative movement whatsoever between the TA and the pumpkin, otherwise there will be noise and questions concerning structural integrity at a minimum.

As for 3-link design features, you need vertical distance between the LCA and UCA axle pivots in order to minimize things like SVIC migrations and pinion angle changes as the suspension moves. As you note, greater vertical separation at the axle between the lowers and upper(s) does reduce the loads that the links will experience, which is a good thing wherever repeated loading and fatigue is involved. Of course, with a "regular" rear end, plan on revising the LCA brackets as well, since all of the triangulated 4-link arrangements use converging lowers rather than the purely (or nearly so) fore/aft alignment of the 3rd/4th gen F-body LCAs.

The arrangement and amount of structural reinforcement involved for introducing an upper link where none exists as OE is probably going to depend on things like individual use, engine output, transmission and axle gearing, and existing OE chassis condition. This is not a trivial matter, and I happen to know of a case where both floorpan cracking and axle side UCA bracket deterioration occurred (the hole "wallowed out", probably due to insufficient clamping force for the application).

Generically, a 3-link is more easily tuned for increased anti-squat without affecting the axle steer, though a TA can easily provide enough A/S for street/auto-X/road course activities.


Norm

 

I actually had one custom made for a 4th gen car.

It used custom subframe connectors with an integral crossmember/DS loop which was the mounting point for the 3rd link. It also used a bracket to mount it to the factory rear end torque arm mounting points.

Unfortunately the car was destroyed in a fire before I could thoroughly test it out. It was holding up under some near bumper dragging wheelstand launches though. It all fit under the stock floor.

 

Thanks for the replies, guys. Good tips!