Q: why do all the aftermarket kits move it to the cross member or off the trans?

I thought the purpose of the torque arm was to translate the twisting motion of the engine and trans into downward force on the right rear? It’s why it’s mounted on the tail shaft.

Sure you could break a tail shaft, you could break anything with enough engine but GM designers deemed that not a critical factory and per its intended design, its trans mounted to take advantage of the engine/trans twist.


The next level in performance should be a torque tube design or a beefy tailshaft. Where the shaft is enclosed in a solid tube that connects the whole drive train to gain the benefits of motor torque or twist and be able to handle lots of power. Early cars had them.

It seems like your going backwards with a cross member mounted one, no ehy?


What real benefit over not breaking a tail shaft housing does it have mounted to the cross member?

It’s basically just now a 4th link isn't it???
[3rd gen stock is 3, 2 LCAs, 1 panhard, 3 links of connection, not including shock or springs.]

I guess maybe it now still does "transfer" torque, but it takes torque/twist from the rear end and translates into the body. Instead of taking torque/twist from the engine/trans and translating it into the rear.


I could be all goffy'ed up and wrong thinking so plz use dumb hilly billy terms.

A drawing wont hurt either of where these magical forces are going.

 

Wow. The torque arm has nothing to do with engine twisting to plant the rear wheels. if you grab a stock arm you can twist it with your hand. So it should have little to no efect from the twisting motion of the engine.

The best way I can describe it is it's a modified 3rd link of a 3 link suspension the 2 lower contol arms and the torque arm. you don't count the panhard bar as that is only keeping the rear from moving side to side and dosen't efect the pinion angle. It's not a true 3 link because it is bolted to the rear and not mounted with a pivot.

Moving the mounting point to the cross member not only takes stress off of the tailshaft it also reduses stress on the trans mount, witch is a nother week point in high horse power applications. So if you wanted to make a tailshaft that could handle the power you would also need to run solid mounts among other issues. I hope I didn't come off rude and I am no expert but I hope this help.

 

In high HP situations, it's probably better to move it off the transmission. When you launch, the front of the torque arm is pushed upward. The stress on the side of the tailshaft could distort the housing and break the tailshaft housing.

Since the torque arm is being forced upward and it's attached to the rear of the transmission, all that upward force is being applied to the tranny mount. That soft and squishy rubber mount can only take so much abuse. A poly mount is much better. I would never recommend a solid mount, even for my car.

Moving the front mount to the tranny crossmember eliminates all the stresses on the transmission or the mount and moves the lift point directly to the crossmember. It also changes the position of the IC by moving it back and downward slightly.

 

I never would have thought the Torque Arm would twist the rear axle, but I couldn't tell you that for sure. But a 4-link definately has 4 bars and doesn't count the panhard/track bar.
And the stock third gen rear suspension is a form of three link in my mind, although it is correct that it is ridgid and doesn't pivot, and it is called a Torque Arm and not an Upper Link. Definately not what you see labeled as a third link setup.

 

You gave a very professional answer

 

The difference between a torque arm suspension and a 3 link is that the torque arm is bolted to the diff and when the diff rotates on acceleration, the front of the torque arm lifts. A 3 link is similar to a 4 link in that the arms themselves don't lift. They push and pull creating an imaginary IC point where the top and bottom arms would eventually meet providing they're on angles where they could eventually meet.

A torque arm IC is very similar to a ladder bar system where the front lifting point is at a fixed location. A ladder bar can be adjusted up or down to fine tune the IC height but the torque arm is fixed. Neither can reposition the IC forward of backward. The torque arm system is better than ladder bars for street use because it doesn't bind while going over bumps.

 

Thank's vetruck.

stephen, I was trying to keep my explanation as simple as posable as to not add any more confusion. As always you're knowledge on suspension angles and operation amazes me. And no I was not recommending using a solid mount I just said that to show him there were other issues with his idea.

I think you're last post kind of gives us an idea why it's called a torque arm, as it uses the "torque from the rear differential to push the axle down"? I seem to think this must be diminised with the arm being so long but still must be present to some extent. I always asumed gm used this to save room in these cars because this was the best suspension without taking some more space from above the rear for a 3 or 4 link.

 

My guess is that GM chose that OE arrangement to meet handling targets as well as NVH requirements. Locating the chassis side pickup of the TA off the tailshaft allows the resilient mounting of the powertrain to absorb a lot of the road noise and gear whine. Back around 1980 or whenever the basic design was set, there weren't any engines strong enough to cause durability issues. Not according to whatever GM durability testing was able to uncover.

But if you've got enough grunt to break the tailshaft, before that happens you're probably distorting the tranny case, which isn't a good thing anyway.

The TA only requires a slightly larger tunnel, and doesn't cause any ground clearance issues if the basic design of the car has it in mind. An upper 3rd link does have potential effect to rear seating, and there are some rear crash considerations. The current Mustang does have a short upper 3rd link, but keep in mind that the S197 has a 107" wheelbase, vs 101".

Specifying a TA/PHB rather than a version of the G-body converging 4-link allows the rear roll center to be placed significantly lower (about axle center height, vs top of pumpkin), and also allows for a lower amount of axle roll steer. Both of these effects make for a more nimble-driving car whose handling is more consistent as you go from turn-in to steady-state mid-corner. Certainly an appropriate direction to tune for in the F-body, relative to the sedan-ish G-body.

The TA does geometrically add load transfer under acceleration. This behavior is the same as that in a 3-link, 4-link, or ladder bar suspension, where axle torque is converted into a vertical force. The only difference is in the geometric construction and the actual numbers used in the math. BTW, any "torque arm" that uses a little rod-ended link on the chassis side really IS a 3-link suspension (it only looks like a TA; the geometry is pure 3-link with the 3rd link just tipped on its side).


Norm

 

And not to mention moving the TQ arm mount to the crossmember widens your options for transmissions that do not have the boss for the mount on the tailshaft.

 

Something else to consider is that with our torque arm relocation crossmembers we have added additional holes to the mounting flange that will allow you to move the front of the torque arm up or down. This will effect the way the suspension hits the tires on at the dragstrip. Raising the torque arm up hits the tires harder but for a shorter amount of time and lowering it will result in a softer hit but for a longer time. If you have any questions about our products please let me know.