Can I drive truck up to 70mph safely with just the front driveshaft installed?

[crazy4offroad]

14 bolt full-floater has a shorter pinion, semi-float should be about the same as your stock 1/2 ton one. It is possible the slip yoke is further out of the t-case now, perhaps as much as 2" (IF it's a full-floater).

 

[HotRodPC]

Remove both shafts, get it up to 70, and see if it persists.

Better find a very long down grade somewhere.

 

[Mattchu60]

I could take the rear shaft out like Jim suggested - would that hurt anything to have it freewheeling?

I tried the brakes thing on the way home, I couldnt really tell much difference.

 

[philjafo]

I had a vibration like that but it was between 40 and 45. The transmission mount was bad and it would move sideways a little putting the driveshaft out of phase. It was on a 2x4 truck so that might be why the lower speed vibration, or yours might be motor mounts instead of the trans mount.

Use a big pry bar on it to see if the trans or motor moves, it'll move some but if its broken it should be obvious.

 

[smurph20]

What about the front hubs being locked in and having a bad ujoint at the wheels. I have that problem now so I have to leave them unlocked.

 

[chengny]

I read that you recently installed a new rear axle. But to clear things up:

Not really discussed yet - did the vibration (or any vibration to a lesser degree) exist before the installation of the 14-bolt axle?

After the new axle was installed, was there a period of time were the vibration did not exist or has it been vibrating since day one of the install?

Do you know any history of the rear end that was installed.

 

[HotRodPC]

I could take the rear shaft out like Jim suggested - would that hurt anything to have it freewheeling?

I tried the brakes thing on the way home, I couldnt really tell much difference.

So that likely just means the problem isn't at the wheels. Which leaves something in the shafts, U joints, Pinions or Yokes. Obviously something that rotates.

While we're at it... What rear axle did you install? The 14b Full Float or Semi Float?

 

[Jims86]

I could take the rear shaft out like Jim suggested - would that hurt anything to have it freewheeling?

I tried the brakes thing on the way home, I couldnt really tell much difference.

When you are done, just shut the ignition off before you put it in park, let it freewheel till it stops.

 

[Mattchu60]

I ran it up to 70 with no shafts last night. It was smooth, no vibration.

Some people asked about the slip yoke in the trans, it goes it about the same as it did with the 10 bolt, I can see the old line where the seal was is now about 1/2" out of the tail. Still a lot of the slip in the transfer case, so dont think thats the problem.

The new axle is a semi floating 14 bolt. Everything feels tight and I checked the oil level in the axle last night, still full. nothing squeaks either when moving.

I think its something with the driveshaft. I may try to replace one of the new u=joints to see if it helps.

 

[Jims86]

I ran it up to 70 with no shafts last night. It was smooth, no vibration.

Some people asked about the slip yoke in the trans, it goes it about the same as it did with the 10 bolt, I can see the old line where the seal was is now about 1/2" out of the tail. Still a lot of the slip in the transfer case, so dont think thats the problem.

The new axle is a semi floating 14 bolt. Everything feels tight and I checked the oil level in the axle last night, still full. nothing squeaks either when moving.

I think its something with the driveshaft. I may try to replace one of the new u=joints to see if it helps.

May have thrown a weight. wont hurt to take it and have the balance checked.

 

[Mattchu60]

Im following a tread over on the 67-72 trucks site (they have a good 73-87 section) where a guy has the same problem. A lot of people there think its a shaft out of balance or a pinion angle issue. I'm in a smaller town in rural IA, not a lot of places do specialty driveline work around here - so not sure I can find a shop to balance the driveshaft or not.

Also, someone asked about about the truck vibrating prior to the 14 bolt swap, I couldnt tell you as I had oversized tires on the truck when it had the 10 bolt installed, I drove 59-60 in order to go 70 mph, and it didnt perform well so I avoided interstate if I could. Never got the drivetrain spinning over 62mph I would guess.

 

[chengny]

Assume the axle was bought as a used (as is) part - correct?

Have you checked the outer bearings for excess play?

Gm service manual lists "rough bearings" as the first thing to check when diagnosing a vibration problem in the rear axle area.

 

[Mattchu60]

My testing of the rear bearings was spinning the axle shafts, felt smooth, and pulling, pushing, etc on them, they seemed to be really tight with no movement and rolled smoothly. I assumed they were fine because of that. I assume you would hear them if they were bad as well? Squeaking?

I'm going to have my father take it for a drive today, he is very mechanical and hoping he can diagonse something from it.

Otherwise I may look into a new u-joint in the front or a driveline balance.

 

[HotRodPC]

My testing of the rear bearings was spinning the axle shafts, felt smooth, and pulling, pushing, etc on them, they seemed to be really tight with no movement and rolled smoothly. I assumed they were fine because of that. I assume you would hear them if they were bad as well? Squeaking?

I'm going to have my father take it for a drive today, he is very mechanical and hoping he can diagonse something from it.

Otherwise I may look into a new u-joint in the front or a driveline balance.

And normally applying the brakes while rolling at vibration speed, the brake shoes would center the drum and axle and vibration at least change a little. He did that test and said no difference at all. So that leads me to believe the problem is down the center of the truck somewhere, not out at the wheels. Could be anything from rear carrier bearings to front carrier bearings and anything in between like driveshafts, u-joints, Tcase, pinion bearings etc.

 

[HotRodPC]

And might add, with no shafts in the truck, The truck was put in gear taken to 70 mph and no vibration which would normally mean, the problem is behind the Tcase, carrier bearings to driveshaft yokes. Still doesn't mean the Tcase is completely ruled out though. It could still be a Tcase issue just not noticed without being under a load, but it wasn't an obvious issue.