The Stovebolt Site Forums The Shop Area Driveline Vibration, rumble in driveline

Hello, New to the forum,

I've had the 55 3100 (later, second, style) for 4 yrs and have over 25k miles. Mostly original, it's great. My trouble and question comes after an upgrade to 3:38 ring/pinon, and a Muncie cast iron 4speed. That changed the drive shaft length. Now I had a vibration that would come on @ 52 mph (2300 rpm) and get worse as the speed/RPM increases. After new springs, it was worse. Took and checked angles on engine, drive shaft and pinion, it called for some spring wedges and it took most of the rumble vibration out, but not all. I found some play in the rotation of the pinion and and was concerned it might be coming out of fit. I pulled the assembly out, cleaned, and checked. All good. The play is in the spider gears, just like it was before the pinion and ring change. Outer axle bearings all good. I reassembled, and it was still there. So I put 140 wt gear oil in and it smoothed out some, enough to take a 2500 mile trip this month. Now I have the drive shaft to the shop to double check it's balance.

Under power, up a hill, or accelerating, smooth. Let off the gas on a steep hill, or up to a stop, smooth. Lower speeds, smooth. It just seems to be happening when running along at speed (2400+ RPM). Maybe I'm not supposed to go over 55?

Any one have any ideas or suggestions on where to got with this??

Many thanks, Bud Van Deusen

Open driveline - a friend had similar issue after he changed a U-joint on the driveshaft. He unbolted the U-joint and rotated it 180. He said it worked. But if the driveshaft is balanced, wouldn't it work no matter how it was installed? Anyway, Welcome!

Are your Motor Mounts at the Bellhousing in good condition? Sounds like you were on to something with the change in your pinon angle, does it match the transmission angle? Hopefully the Driveline Shop can sort it out with a rebalance.

Waiting on the report from the driveline shop, but I was going to say the u-joints out of phase.

What are the angles, tail shaft to driveline, and driveline to pinion? Both these should be in the area of 1/2 to 3 degrees, up to 4 or 5 is OK, but 3 is ideal. No other angle matters. Out of phase u-joints can't cancel out each other and will create vibrations. Same with different angles at each end, just not nearly as bad as out phasing. A carrier bearing on two-piece driveline can also make noise and vibration.

A bad pinion bearing can make a lot of noise.

With low gear ratio, the engine is now working much hard to pull the truck at a lower rpm and higher speeds. Check the tune up and spark plug condition, you might be feeling a rough running engine under a load.

With a 3.38 ratio, his RPM shouldn't be that high at speed.

Thanks Gents!
The problem of the vibration is seeming to be pointing to the drive shaft. The angles I had were the engine - 3.25 deg, and now the pinon is at -5 - 6 degrees.
The out of phase yokes is encouraging. I may try that if the shop has no luck w/ balancing.
I had installed new engine mounts just 2 yrs and 15 K miles ago.
I will keep Y'all informed as it progresses.

Cheers, Bud

The spread between your engine angle and the pinion angle are too far apart.
This will cause u-joints to bind and prematurely wear out and vibration eventually.

What Carl said. Your pinion and transmission flange centerlines when extended should be parallel. Or in other words, the angles from vertical should be identical.

Go to Harbor Freight or Amazon and get one of those cheap magnetic angle finders, round dial with red needle. Its the fastest way to find driveline angles.

All you need to measure is the transmission shaft output angle to the driveshaft angle. Then driveshaft to pinion angle. Both ends need to be in the 1/2 degree to 3 degrees range for ideal operation and close to equal. You can be up to 4 or 5 degrees, but it must be the same at each end. The rear angle is always changing due to bumps, humps, loads, and general driving around, but as it changes, the front is also changing, so equal them them out. Starting at the ideal 3 degrees insures that during most of your diving, the u-joints have roller bearing movement and are not at the extremes of there operating range.

Here is what a phased and out of phased driveling look likes, https://managedmobile.com/wp-content/uploads/2018/02/driveshaft01.jpg If the guy that shortened the driveshaft welded the cap back on wrong, it would explain your issues. Even a few degrees off would be wrong. A two piece driveshaft would have the second section 90 degrees from the first.

With a slower driveline rpm, balancing will not be as much of an issue. It's still important, just not as much as would be with higher gear ratio.

And with the lower gear ratio, the engine and driveline has a lot more torque on it trying to pull the same load at a much lower rpm.