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Moderate shuddering normal?

I have an 88 B2 with a stock 2.9 and mitsu 5-speed. When I bought it (essentially stock except for an obnoxious glass-pack), I drove it home via backroads, parked it, and began a ~1yr + axle swap. Did a d44/9” swap, and am running 37” MTR’s. 5.43’s or 5.38’s out back, can’t remember.

Since I finished the swap there has always been a shudder in the drivetrain at about 2200 – 2800 rpm, notice it mostly in 3rd or taller gears. I am now 100% positive it’s not driveshaft related (running a well-balanced double cardan, angles are great, I’ve swapped in and out a new Tom Woods spare with no difference), don’t think it’s the wheels/tires anymore (as a recent experiment I've been running several ounces of BB’s in them now with no noticeable difference).

The shuddering is mostly just annoying, forcing me to cruise at 3300 rpm at about 60 or so on the hwy in 4th gear. If I upshift to 5th, brings the rpms down to the trouble zone, and the shuddering starts. Isn’t so bad because I don’t drive the pig far usually and the tired 170K 2.9 seems to need a few extra rpms, and I don’t care that much if the 2.9 eventually gives out (I’ll swap in a 4.0), but it seems a little obnoxious to cruise at that high of an rpm. I’ve even swapped out the glass-pack in favor of a slightly quieter, real spark arresting muffler so that the rev’s wouldn’t annoy me so much. I am suspecting it’s powertrain/tranny related, as the vibration/shuddering seems rpm-dependent albeit more noticeable in taller gears.

Again, I didn’t ever really drive it much before the swap, so I can’t rule out a pre-existing condition. Hasn’t got any better or worse. The fm146 and clutch were replaced about a month before I bought it, but the then stock B2 looked like it had seen some hard service.

Any ideas? Although a mnor annoyance for a trail rig, it would please me to no end to figure it out.

so it does it in all gears at 2200-2800?

if it were your tires out of balance it would only do it at a certain speed not at certain RPM's.

I would also think that the same would be true for driveshaft out of balance or a u-joint being bad also.

can you feel where it is coming from? rear, front, under the truck like the motor/tranny? have you checked your motor mounts? tranny mounts?

I think the same would apply that the vibration would be only in one speed for the rest of this but it doesn't hurt to throw it out there......what did your pattern on the gear look like when you set it up? did you do it your self, or did a shop do it for you? do you have a roaring noise comming from anywhere that gets noiser as the speed increase?

Push in the clutch and rev the motor to 2200-2800. Still have a vibration?
How about with the tranny in nuetral?

Then...go find a big hill that you can coast down at 60mph or so and push in the clutch. That should take the engine out of the equation. Still have a vibration?

Since your clutch was recently replaced before your purchase, there's a good chance the problem is with your clutch. The pressure plate may not be aligned correctly throwing the engine out of balance.

Take a good look at the motor mounts. It might be hard to tell there's a problem with them without pulling them out.

But to answer the question, no a vibration like that isn't common.

Sticjk the trans in 4th gear, at a stop, hold your foot on the brake and let the clutch out if the engine doesn't instantly die, it would be a clutch probelm. The clutch plate isn't that big and probably doesn't like you big tires. Also 2,9's have the leaking valve cover issue that could be leaking the oil down onto the clutch. I have seen that happen before.