need some clarification on tweaking in the rear end. i plan to make some adjustable lca's, and torque arm but i'm trying to figure out how far i am off now. i replaced my rear with a bigger 10bolt and it sits about 1-1.5 inches farther back than it should. i figure its the control arms so i'll make some new ones.

so my questions
how exactly do you measure pinion angle? won't adjusting the length of lcas change your pinion angle? i'm all confused about what exactly is your pinion angle and how to set it up.

since my rearend swap everything seems pretty good, car hooks well, but tires don't make much noise when i light them up, checked air pressure and that's good, i'm running yoko's.

just wondering what's going to happen when i replace the lca's and center the rearend back with the wheel well. i'm looking at fitting some slicks in soon and need to get this ironed out. my buddy has some 28x10.5's and 28x11.5's, i want to see what will fit.

please help i'm confused

 

i dont know, but if you order an adjustable torque arm controller, most of them come with a tool used to measure the angle and they tell you which is best. but i would think the lca's have little to do with that, check the TAC.

 

sorry but i don't really plan on spending 400-500 on an adjustable torque arm if i can fab one for $60. just alittle short on the knowledge of the angles, how to measure and so forth, i see the parts and how to make adjustable ones, no biggy. i guess the big problem i'm having is how the angle will affect hookup at all.

if you rearend is solid, regardless of angle then when the wheels turn it should go, that's how i think, i just know its not that simple but can't comprehend why therefor leading to my confusion.

 

The purpose of setting the pinion angle is to insure the pinion shaft stays roughly parallel to the tranny output shaft, and that the angles the u-joints work through are not too severe. The torque arm is the only thing that controls the pinion angle, since it is rigidly attached to the pinion shaft housing, and fairly rigidly attached to the tranny at the front. There is no way to adjust the pinion angle if you don't have an adjustment on the torque arm. Moving the axle forward or backward has minimum affect on the pinion angle, since the front of the torque arm is free to slide forward and backward.

The axle naturally moves forward and backward as the control arms pivot in an arc around the bolts on the body end. The TA must be free to move forward or backward, or the suspension will "bind". The stock TA and some aftermarket designs simply use the "slider" capabilites of the stock bushing arrangement. The aftermarket arms that attach to the body rather than the tranny need to allow for the front-to-back movement, and this is accomplished with a slider or simply by adding a pivoting "link" at the front of the TA.

Since you have apparently altered the geometry of the LCA's and TA with your "bigger 10bolt", you are going to have to fabricate your new TA very accurately to hold the pinion at the correct angle, or you will need to incorporate an adjustment screw like the aftermarket arms do. If you don't get it right, you are going to have problems with the u-joints, and possible damaging loads on the tranny output shaft and pinion shaft as a result of uneven u-joint angles.

To set the pinion angle, measure the angle of the DS, then the angle of the pinion shaft with a magnetic "angle finder", then subtract the two angle so that you get a negative value. Negative, in effect, means that the DS and the pinion form a "V" with the point aimed down to the ground. How big that angle should be depends on the compliance in the suspension and the torque that you are trying to transmit, since you want the pinion to "lift" only to the extent that it makes the front and rear u-joint angles equal.

 

this isnt my thread, but i have to say that you are the man. just curious, how long did it take to accumulate all the info you know about the f-body cars.

anywho, do you think ill need a new TAC when i replace my stock rear with a moser 12 bolt?

 

Thanks. Too many years... . My first F-Body was a 1968 Firebird 350 that I bought new.....

If you are making enough power to need the 12-bolt, you probably need an aftermarket torque arm. On the other hand, there are people who have managed to get into the 10's with the stock TA... so its sort of a toss up. The Moser TA mount might be a little stressful on the stock stamped TA, because I think the Moser uses 4 short bolts rather than two long ones that go all the way from the top to the bottom. Not sure though... I have a Strange and it uses the stock style long bolts.

I like the ability to set the pinion angle. I like getting the lifting load off the tailshaft of the tranny. But I don't like the extra weight and complications that seem to come with aftermarket TA's.

 

yeah injuneer is the man and knows his f-bodies for sure