TPI-Formula350-

I just got a UMI adjustable cross member mounted torque arm PN#2217. I have heard that it should be set to a reading of -2* on an angle finder. Where exactly do I attach the angle finder? Do I place it on the drive shaft or on the torque arm somewhere? Also is that -2* setting I keep hearing about the best setting for drag racing or auto X, both?? Thanks

SlickTrackGod

1st off- just get the 2* reading out of your head completely. THat does not apply to anything. SOmeone told you wrong info with stating that #.

Pinion angle under thrust load (forward acceleration) should match the crank shaft angle exactly.

Since the pinion will rotate upward under acceleration (tire grip forward causes the pinion to rotate backwards in the opposite direction of the tire direction, thus the pinion wants to thrust upward) you want to set the static pinion angle pointing 1* downward from the angle of the crankshaft/tailshaft angle. The driveshaft angle is "somewhat irrelivant" in MOST cases.(Ill explain more on this later)

Your angles from 1) crankshaft/tailshaft-to-driveshaft, and 2) driveshaft-to-pinion should match UNDER LOAD so as to cancel out harmonic vibrations.

When you lower a car, the stock torque arm is fixed to the pinion without adjustment. As the car lowers and the pinion comes closer to the underneath of the car, the angle of the pinion snout starts to turn downward towards the ground the more the car is lowered. An adjustable Tqarm will allow you to raise the snout of the pinion back up to maintain the proper geometry so as the angles match (again, match under load of applied throttle)

Now to the angle of the driveshaft/ The tailshaft -to-driveshaft angle AND/OR the driveshaft to pinion angle CAN NOT BE 0* If the uniersal joints operate at 0" the needle bearings will NOT properly rotate and the u-joint will prematurely wearout. You need at least 1* minmum angle betweeen each side of the joint in order for the needle bearings to rotate and lubricate properly. If you need example pictures I will draw a few.

Dean

SlickTrackGod

On the rare cases where a driveshaft angle coming off the crankshaft/tailshaft angle is too close to a 0* reading, you can shim the rear trans mount to raise the tailshaft angle to gain angle here. My car was extremely low and I had to do this so as to help the u-joints rotate, I then reset the pinion angle to 1* downward angle fromt he crankshaft angle so it rotated up about 1* under hard accelerations..

It is important to note that in extreme cases of a fulltime drag car running lets say 1000hp and lifting the front wheels off the ground, the raw HP yeilds a higher thrust angle as well as chassis bending under load will alter the crankshaft angle more off line with the pinion- in these rare extreme cases the pinion angle can be started with a static angle of more like 2-3*.

A car that sees normal hwy use should never use more than 1* compensation angle for thrust, otherwise you will wear out your u-joints from bad harmonics over time since the angles do not match and will cause noise vibration through the bearings (sometimes you will not even feel this for a few thousand miles but it IS happening if not set correctly.)

TPI-Formula350-

thanks for the info. I got that -2 angle number from UMI Performance who made the adjustable torque arm I'm installing.