Technical TORQUE ARM QUESTION chassis help

Ok guys need a bit of help here. On my 41 buick that I built a few years back is down. I converted it to open drive years back when I did my build. I thought the stock trailing arms that was once on the torque tube that I made hook to the frame would be enough to hold the rear end. (stupid me ) Well it did work for years but broke this year due to the rear end force wanting to rotate. I have it fixed but wanted to add a torque arm to help take the load of what the old tube did at one time. So my question is how terrible would it be if my torque arm is 10" or so SHORTER than my trailing arms. I can have two solid bars that come off a bracket I made for my rear end. Or is it best one arm but maybe not as strong due to only one and space I have up to the center of the X frame where my trailing arms meet up to the frame.?

 

Is it parallel leaf spring car? I'd check into drag race leafspring floating mounts, they let the rear rotate a little. The leafsprings travel straight up and down, the trailing arms will travel in an arc so they'll be binding. If you think of the chevy pickup with trailing arms you'll recall they used coil springs, not leaf, for this reason. The floating mounts that dragracers use cage the rear and lets the rear rotate a little on that pin sticking up in the spring to locate it on the spring pad.
The rear won't rotate independant of the trailing arms so your 'torque arm' is doable, they'll all travel together in 'bump' or 'rebound'.
Check Competition Engineering C2030 for the floater kit and you'll see how it works.

 

The car has coil springs.

 

Having the arms swing in a different arc due to the length variation is not a particularly good thing. Depending on the method of pivoting the arms (heim, rubber bush etc) you are taking the chance of putting the rear end in a bind at the extreme ends of the wheel travel. Plot it out or make a popsicle stick scale model and cycle it to see you how much variation there is in the arcs. Using your drawing as an example you have roughly a 25% variation in arm length so there is going to be some conflict there.
OK, I just did a quick plot myself and if the mounting points at each end are at the same height the torque arm will try to pull the rear end forward about 1/4" more than the original trailing arms (using 6" of vertical travel as an example) if the arms are horizontal at ride height.
A single torque arm is more than sufficient and also reduces the chances of getting things bound up as the chassis rolls on its longitudinal axis. There are bushes available that have plenty of compliance in one plane and little at a 90 degree axis and something like that would solve the fore and aft issue. Look at the aftermarket torque arms for live axle Camaros for examples of what works.

Roo

 

I looked into this problem when I had my '38 Buick some time ago. A torque arm would work, but it must be triangulated, that is to say, work in the same plains as all the other members.

By and large, the most popular and practical way of converting these Buicks to open drive is to get the trailing arms out of a '60s Chevrolet C10 or C20 Pickup (they used open drive and Coil Springs) and, with a few brackets, bolt them up to your axle and frame just as they were used in the trucks.

 

This is an aftermarket C10 trailing-arm setup that I found just by googling "Chevrolet C10 Trailing Arms":

 

ok. so better to go with a single arm and get it dam close to the trailing arm pivot. not my pic below but similar, bringing that torque arm up to the current arc as close as I can.

 

Thanks guys! this helps a lot. I will try to match the arc and try the set up. Going to make it all bolt on. Once on, I can have my kids bounce on the rear bumper while I look to see if all moves nice or if I see binding. Worse case is if it binds I add ladder bars in then remove my old trailing stock channel arms. I want to do that just not now with the body on. I plan to remove the body in two years for body work and paint. Would rather do the ladder bars then so I can get good weld angles and make it look nice and safe.

 

Why not make your ladder bars fit the stock location on the front? Bolt them there and weld to the rear.

 

If you can make your trailing arms pivot at the rear axle the upper link will work fine. If not your best bet is to connect the front of the upper link to the front edge of your trailing arms front pivot point. I found out first hand that early ford wishbones don't hold up well with open drives! I made a single link arm from the center section to the front of the top of the wishbone where it pivots at the frame.

 

pat-the trailing arms cant pivot on the rear axle. they are spot welded / bolted in place from the Buick factory in 41. I too plan to build a torque arm in my roadster build. like you said, early ford bones are not that strong alone.