LT1 POWR

I thought this was because my stock driveshaft was out of balance, but I just replaced it with a 3" chromemoly balanced driveshaft when I put in the built 4L60E and the 12 bolt and the vibration is still there.

I have a chassis mounted torque arm with QA1 rod ends so I know its not going to be quiet, but I feel that this vibration is not normal. I also have poly motor and tranny mounts. Should I rotate the driveshaft 180º and see if that helps? I really don't know what else could be causing it unless it's the pinion angle which I also need to adjust when I get some time.

It seems to start above 50mph and doesn't really diminish until I get on the gas over about 15-20% throttle. But definitely when coasting from 70mph or even maintaining speed around 60-70mph.

LT1 POWR

Well I rotated the driveshaft 180º and I also lowered the LCA's to the lower hole and I adjusted the pinion angle and the vibration for the most part is gone. I don't know if it was one of the things or a combination of all of them.

I still can't hook up on the street,not even at 40mph for that matter, but we'll see if I did anything to my 60' time at the track in a few weeks.

My question is, if it was the driveshaft, why? Shouldn't it be neutrally balanced and not matter which way it goes in?

Also if anyone ever wonders measure your pinion angle on the flat spot on the torque arm and not on the differential. Its more accurate. There was about a 3º difference between the two, enough to through off your pinion angle. At least that's how it was on my strange 12 bolt.

97FormulaWS-6

Pinion angle most likely is what I'm thinking... the DS should be fine; especially if adjusting the pinion angle made it go away.

Normally when trying to diagnose problems like this you need to change one thing at a time; not 4... makes it easier to say what was the cause and solution.

LT1 POWR

Well, I really didn't care what it was, just as long as it went away. I had to adjust a few things while I had the car up in the air so I just did it all together. Plus it was my only day off in who knows how long. So I might not have gotten a chance to adjust things for a while.

Now I have a new problem. I was driving today and on these sharp little drop offs or bumps, couldn't tell, there was a loud thump/pop coming from the rear. Like maybe the rear end was making contact with the body or something. Anyone ever hear of anything like this? I'll be able to jack it up Saturday and take a look, but I'm just looking for some suggestions as to what to look for.

97pontta

My 9 inch rear hits the under the car in two different spots, the torque arm mount on the housing and the upper torque arm bracket mount. I used a hammer to add a little clearance when I initially installed the rear and didn't have any problems. Recently I installed some Sportline lowering springs in the rear to make up for the lift I had gotten from the larger axle tubes. With the lowering springs it is now hitting the body again slightly. Not sure what type of torque arm you are running but if it’s a body/chassis mount type you will hear and feel more of the road, more so when the road gets rough.

corey0224

Check your rubber bumpers, my car was doing the same thing and I discovered that both of my bumpers were completely gone. I replaced them with some from energy suspension.

LT1 POWR

The bumper jouces are new. I found out that the torque arm is hitting the body. I can't really clearance it without dropping the rear end so I guess it'll have to stall like that for a while.

What holes are the torque arm bolt supposed to be mounted to the rear end with, the drivers or the passengers? I think if I moved the torque arm so that the bolts mount through the drivers side holes it'll have more clearance, but I don't think the casting on the rear end will allow it without modification of the torque arm/differential.