So I just installed an adjustable full length UMI torque arm with their crossmember kit. I have verified my pinion angle (got -1 on the rear end, and 1 degree on the driveshaft, so I have a 2 degree split). I also have the front bushing in the 2nd set of holes from the bottom (read an old post from UMI that this was as close to factory as possible).

My issue is that the car jerks like crazy now. Accelerating or cruising there is a semi-constant jerking motion, and I can physically feel the car slowing down. Feels like something is binding almost. Taking off from a stop feels the same.

Did I screw up somewhere on this install? I followed the instructions and read probably a half dozen threads on getting my pinion angle right. I triple checked that everything is torqued and holding solid. Gonna call UMI tomorrow and see what they say, but I figured I'd post up on here too.

Thanks guys

Edit: Was discussing this with a friend of mine, and he mentioned that he always puts blue loctite on the jam nuts because he's seen them back off and cause noise/vibration issues (from play in the threads apparently). Just wondering if this sounds plausible to the more experienced.

 

So after discussing with some other folks, one mentioned that my driveline angle, not my pinion angle was what really mattered. So doing some reading and measuring I found that my motor/trans is tilted back 4.5 degrees (towards the rear of the car). If I'm reading all of this correctly... I need to match the angle of my trans with the rear end (so the rear would then be pointing up towards the front of the car 4.5 degrees). Wouldn't this throw my pinion angle way out of whack? At that point should I try to shim the trans mount to lessen my driveline angle to the point where the rear is parallel with the motor, and I have a 2 degree "V" at the rear/pinion? or should I set the rear end 2 degrees down from the drive angle, so that when it's under load I have both a parallel rear end and the correct pinion angle?

 

Unless you are pushing big horses and launching hard Id just put my stock back in. Tell people all the time aftermarket torque arms can open all kinds of cans of worms. I have seen it many times

 

I'm making around 470 at the wheels. I bought the torque arm more for the crossmember, as I wanted to get the mount off the tailshaft, and since UMI had a package (and I had some extra cash laying around) I figured why not both?

I may throw the stocker back in, but after doing some more research (and finding an awesome video describing what happens when your pinion and driveline angles are out of whack) I think I've got it fairly dialed in.

Here's the video, just in case anyone wants to see it:

 

I had a vibration issue once that was hell. I had to check pinion angles, bought new steel driveshaft, adjusted rear lcas and couldn't figure it out. Problem ended up being a busted poly trans mount lol But yeah, aftermarket torque arms seem to always throw a monkey wrench in to plans. Hope you get it figured out

 

Good morning. The UMI torque arm should allow you to achieve factory geometry.

We recommend using Tremec Toolbox or the Spicer App on your smartphone to determine driveline angle.

We are always available on support@umiperformance.com to answer questions.

 

I had it on my car and even after having it professionally installed and aligned I couldn't live with the clunks and banging against the body. Hated it! Went back to stock a short time later and sold the overpriced aftermarket ...at a loss of course. I think if you are going to track the car it's a necessary mod.

 

Yeah I'll be giving you guys a call in the morning. Even after adjusting the torque arm a half dozen times (trying angles that varied from 2 to equal with the driveline) I'm still getting a shudder. It's a bit less, but still nearly undriveable.