Sliding joint for torque arm front
 

I need to decide how best to allow the front of a torque arm to move in and out in very tight space constraints. A double rod end link would work but it needs more vertical space than a telescoping link with a large rod end at the end. A single rod end (or urethane end) will be in bending but at the end of the torque arm the loads are very low.

My main issue is deciding how to do a telescoping link. I've seen some versions on the market, but I want to fab my own. I can use teflon or other bearing materials. Has anyone done there own and used this type of design?

The car is a 70 mach I with a dry sump motor, my own front end (stock car type LCA, new frame channels, Pro coilovers, splined sway bar, etc.) and fullfloater in the rear. I am going to switch to a cambered rear once the torque arm is in. The torque arm is partially fabbed already and will mount on the pass side of the tunnel down low (it's tight).

Thanks for any input.

i don't know how well they handle side loads but could you modify a set of slide-a-links? or build something off the design? it would give you your up and down movement, roll movement and your in and out movement.

http://www.jegs.com/images/photos/2472100.jpg

You don't really need a sliding torque arm. Yes, it would save a little space, but you are inviting wear and bind issues under acceleration and braking (and yes, I know they are built and sold that way). I've engineered and built a number of street torque arm setups, and along the way I've found a little piece that solves most space constraint problems.
http://rwoe.150m.com/tmp/20080201/013.jpg

This is a toe control link from a early 90s BMW 750 sedan. It's basically 2 spherical bearings built into a forged "dog bone" housing. To give you an idea of the size, those are 14mm (9/16) bolts going through it. The whole thing is about 2 1/2" long, far shorter than you could get with a M/F rod end setup. They are still available as replacement parts.

If I'm on a project where there is a real space issue, I build the front end of the torque arm with an upward jog so the bottom hole of the dog bone is level with the bottom of the arm. Since the dog bone has freedom to move in all planes, it will try to fold over under braking, so you'd need a small lateral locating link between the arm and the chassis.

If you are committed to the sliding end idea, QA1 makes a 3/4 X 7/8 shank rod end (p/n RMX1214) that is about 50% stronger in bending strength than the standard 3/4 end. I would get a 6" long piece of 1 1/4" machinable bronze round stock, drill and tap it for the 7/8" rod end, and slide it all the way into a piece of 1 1/2X.120 wall DOM or 4130 tubing, which would be the forward end of your torque arm. Use a jam nut and thread the rod end in completely.

Hope this helps.

Thanks for the ideas. I have a 91 M5 with a similiar part and understand what you are getting at. I have also seen dogbones with two spherical bearings which is similiar in concept as well. I was not entirely clear on what you meant by needing another lateral locating link though. Do you mean that the torque arm could move sideways and down instead of purely front to rear (a twisting motion)?

Thanks again

Exactly. There is nothing preventing it from "folding" over to the limit of the spehricals when you hit the brakes.

An M5 eh? Nice! I have a '93 M5 in Calypso Red.

I'm confused here... why would braking exert a force on the arm other than a downward motion? Obviously there will be twisting of the arm depending on the individual height of the rear wheels, but for the arm to flop over, wouldn't the axle need to be radically off kilter?

Shiny Side Up!
Bill

You're right, braking force is directly the opposite of acceleration, but it's a LOT of force, and with spherical bearings, there is nothing holding them in alignment with the "dog bone". Take 2 big ball bearings, set them one on top of the other, and press down really hard. They will shoot out to the side. Same sort of deal.

Ah! Got it! Thanks!!

Shiny Side Up!
Bill

I like the idea of allowing some movement of the front of the torque arm to prevent binding/bending (from the roll axis location). Can you show an example of the second link? I do like the small dogbone from the BMW, but I don't want to over-constrain the torque arm front if it isn't needed either. Another approach would be to use some type of limiters or stops I guess.

http://i.ytimg.com/vi/dF4oVOzaSCQ/hqdefault.jpg

Here's an example of the side link. It doesn't restrain the arm in roll at all. Don't mind the coilover...this one is on a dirt late model.