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.