Weezzer

Like the title says, I recently installed a MWC 9" with 3.9 gearing using the short torque arm and tunnel mount. Also installed a Strange CM drive shaft at the same time.
Now if I shift to 6th I get a vibration like the DS is out of balance. This only happens below 63 MPH. Once I get past that and go faster it goes away.
It doesn't happen in any gear but 6th. I've got very little whine, and that's only on deceleration. I tried to hold my pinion angle between -1 & -1.5 degrees.
I'm gonna try rotating the DS 180 degrees and see if that helps, if that doesn't work the only thing I know to do at this point is send the DS out for rebalancing.

Anybody got any good tips towards solving this problem?
Thanks.

Low N Slow

iTrader: (4)

I fought the same kind of vibes on mine, I don't think yours is a drive shaft balance problem if it goes away at speed. What I thought was drive line vibration ended up being some exhaust vibrations.

Intercooler2

iTrader: (24)

Yea look for anything hitting. On mine we had to heat the pipe that goes up over the axle and dent it with a hammer slightly so it wasn't contacting. Look for shiny spots.

Weezzer

I don't believe its hitting, if so the problem wouldn't disappear as I speed up.
Its got to be something else causing this senario.

INMY01TA

iTrader: (1)

Did you add the body mounted torque arm just before this problem appeared?

Weezzer

I've got the short tunnel mount arm with the polyurathane bushing.
But if that was the problem wouldn't it do it on other gears besides 6th?
And it only does it in 6th below 60 or 62 MPH.

And if it was from luggin the engine it looks like it would have done it worse before with the 3.42 gears, the 9" has 3.89 gearing.

I'm gonna try turning the DS over and recheck the pinion angle. I tried to set it between -1 & -1.5 degrees. It sounds good as I can only hear a slight whine on decel and I have to listen close to even hear that.

I've only got 30 miles on the rear so far. Eric told me over the phone its possibly caused by a change in harmonics from the new hardware. But if that was the case it looks like lots of other people w/manuals would have this same problem and so far I've not really seen any others (did a couple of searches) except for one or two that cured it by having the DS rebalanced, however; their problems seemed to do it in more than one gear - IIRC.
That is one avenue of consideration, especially if it acts differently when I rotate the DS 180 degrees.

Cliff

iTrader: (19)

From what you're saying, you have the answer. Try that first.

Weezzer

Update: I turned the DS 180 degrees; approx. 70% of the problem is now gone.

At this point I'd say it was a crap shoot to re-balance the DS because of the outcome I got above. I mean, it seems like some of this problem is in the yoke or yoke assembly. So balancing the DS more accurately could cause the problem to get worse instead of better.

I think I can live with the small vibe I'm getting now, at least till I can ponder this some more...