Driveshaft shimmy?

[Dattebayo]

Hey all. I've noticed my hardbody has a shimmy to it only when I take off in first gear hard sometimes and above 50mph. It's pretty obvious shaking from side to side and it makes handling it a little scary sometimes.

Is this possibly a driveshaft issue or would it be something esle? I just need a direction here before I start taking things apart. Thanks in advance.

[Rev_D21]

I would start by climbing under the truck and checking the driveshaft for obvious signs of damage. Next I would turn the driveshaft back and forth looking for play in the u-joints. If those check out I would then check the carrier bearing as the rubber rots and disappears over time and this causes driveshaft deflection. That's where I would start if I suspected the driveshaft of having issues.

[Dattebayo]

Carrier bearing was replaced, no damage visible to shaft, no serious play in the U-joints. Car is lowered 3", has 3* tapered lowering blocks in the rear, and has the carrier bearing raised 1". Still shimmying.

[Sharp]

Are you sure its your drive shaft and not just a cord broke in one of your tires?

[Dattebayo]

Tires are brand new and have been recently inspected..

[whomadewho]

Check rear springs ( center bolt not in place or broke.loose U bolts) When you lower a vehicle you need to check the splines in the drive shaft ( the splines need to be able to move back and forward ) raising the carrier bearing 1 inch may not be enough.

[Dattebayo]

All of that is fine, the U-bolts are brand new, the center bolt is fine, the drive shaft is straight on with a 1" raise. I swear, it's gotta be the shaft! Its all rusty, so maybe that’s where the weight went to unbalance it.

[whomadewho]

If the drive shaft were out of balance one would think you wouldn't notice anything taking off. Are we talking 2 wheel or 4x4. Have you had the drive shaft out? Sometimes it is hard to tell if a U joint is bad when the driveshaft is in the vehicle. How is the transmission mount?

[Dattebayo]

Actually, the wobble when taking off was confirmed by a google search to be a symptom of having straight drop blocks installed. I replaced them with tapered blocks to line up the driveshaft with the differential better and the shimmy at take-off should now be gone. I haven't test driven it yet as they were just installed yesterday...

It is a 2-wheel drive truck and the driveshaft had to come out when I replaced the carrier bearing, obviously. The trans mount looks solid to me, but I'm no expert.

[Dattebayo]

Test drive confirmed that shimmy at take-off was because of the straight blocks in the rear. Tapered blocks solved that part of the issue at least! Also, I noted an improvement on how the general ride feels in reverse gear as well.

It still has the shimmy at higher speeds, however. Since I have confirmed everything else to be okay, I'm going to have to assume it's the shaft unless anyone else can come up with some genius idea...

[D21hardking]

I would make sure that your shaft is in "phase". When you split the shaft to change the bearing, you may have put it back together "out of phase", meaning that it's not lined up to the holes it was originally mated to. Usually I mark a shaft before removal so everything goes back identically. May have to try unbolting the back half of shaft and turning it to the next bolt hole or even 180 deg.

[Dattebayo]

It was shimmying even before I took it out, but yes, I did match them up with marks before I took it out...

[Desert Rat]

If there's any angle in the 2 piece shaft at the carrier bearing, it's something you're going to have to live with unless you can move the carrier bearing mount up or down. I had a lowered Chevy with this issue...the carrier bearing ended up being too low and there was a "V" profile of the driveshaft when looking at it from the side with the carrier bearing at the low point of the V (obviously exaggerated, but you get the idea). The best fix would be to nix the carrier bearing all together and go have a one piece driveshaft made. Then ensure the pinion angle on the rear axle matches the angle of the transmission output as closely as possible.

[mouse53]

Anyone know how to rebalance the driveshaft if you forgot to mark the center flange when replacing the carrier bearing? I marked everything but the flange before I separated the 2 drive lines and now have a bad shimmy/vibration. I have removed the shaft, changed flange position on the front shaft 3 times now and still have vibration. Tires are about 3 months old, blocks and pinion position are good and raised the carrier about 3/4 ", and u-joints are good, But the front joint on the rear shaft is stiff in one position, easy on the other. Like move easy side to side, but up and down tight. I didn't think it would make that big a difference. Sorry wasn't trying to highjack this thread, but couldn't find info anywhere else.

[whomadewho]

Balancing the driveshaft is something that needs to be taken in to a shop. Might be cheaper to purchase a used driveshaft? There's also the possibility a weight fell off the driveshaft? Another possibility..... check the pinion bearing?

[whomadewho]

You might try removing the front driveshaft? If the hardbody is full time 4 wheel drive the vibration could be related to something in the front drive line?

[mouse53]

OK mine is a 91 2wd 4cyl 5spd and when I said front shaft , I mean front half that the carrier is pressed onto. i did get another driveline and it had zert fittings in the caps, but now it shimmys at 30+ and when I checked it, the ujoints are moving in the holes , like the cups are too small for the holes in the yoke, or the c clips are too thin. I checked and greased all the fittings before I installed it but now I have another setback. I did order a u joint from Rockford and am just waiting for it to get here so i can install it drive shaft #1. .

[whomadewho]

Just my opinion...... IF you install the U joint in the first driveshaft & the same vibration occurs, you're back to square one. If the driveshaft you purchased is original & hasn't been molested I would focus on using that one? The one you removed could be out of balance...... and there a good chance the shaft was heated to remove the Yoke? Went through a similar experience with my 1996 Nissan pickup. Noticed a vibration, when I checked the driveshaft, the driveshaft was flopping like a crappie out of water at the center bearing. Found another shaft for $35.00, works great so I didn't get the shaft. Mines a 4x4 & the front differential is bad. Went to manual hubs.

[mouse53]

OK update here. The new ujoint solved the problem and I have a spare driveline now. I made sure I lined up all the yokes when I reinstalled for the 7th time. I will make damn sure and mark every single thing if the driveline is to be removed ever again.. By the way Rockford is the greatest for u-joints, theirs installed easily and works nice. And my original drive shaft had not been removed as far as I could tell and no way any heat was applied as its too easy to warp the flange or other parts.

[mouse53]

Wanted to come back and thank Rev_D21 for sending me to Rockauto with the right part numbers. Thanks a lot , It is appreciated.