superbee_68
Well-Known Member
I want to share my 8 year long saga trying to solve a driveline vibration issue. I finally fixed it last night and want to share so others who are as frustrated as I was can learn from my mistakes.
1968 Dodge Coronet
440 w. A-833 Overdrive 4-speed
8-3/4 rear end, 742 case, 4.10 Suregrip
Stock but rebuilt suspension
Since the car was restored, I have always had driveline vibration issues. The car starts to shake around 65 mph and gets progressively worse as I speed up. It felt like it was coming from the driveshaft tunnel area in front of the back seat. It was a combination of a vibration you could feel and a loud noise. The problem was at it's worst about 8 years ago when I swapped in an over-drive 4-speed and had a new driveshaft made. Here is what I did to solve this in order over the years:
Get driveshaft re-balanced and change u-joints, still vibrated.
Swap 742 chunk for a new to me one, 3.90 gear, upgarde to sealed wheel bearings, slightly unrelated but still happend, still vibrated.
Many years later, measure driveline angle, rear end pinion compared to tranmission output. Found that it needed shims to get the pinion pointing more down. Bolted in 4 degree shims to point the pinion down. Marginally better but still vibrated both under load and coast.
Got a brand new driveshaft built at a different shop reusing the old transmission yoke, but new u-joints. Still vibrated.
Swapped from solid motor mounts to rubber motor mounts. Vibration got slightly better, but still there. Re-checked pinion angle, still correct with the 4 degree shims. Still vibrated.
Swapped to a new transmission case, new transmission gear set, and complete rebuild on transmission, along with all the upgraded parts you can put in an overdrive 4-speed. Still vibrated.
Bought new tires, still vibrated.
Swapped from factory steel wheels to Wheel Vintiques replica steel wheels, a bit wider than stock. Still vibrated.
Pulled off wheels and brake drums and spun car up to speed on jack stands to check for vibration in rear end and axles. Vibration seemed to be coming from driveshaft, not axles or rear end.
Swapped from a 3.90 gear to a 3.55 gear to slow down driveshaft speed. Now the car could get to 75 miles per hour before vibarting, but still did. I just shifted up the vibration speed 10 mph or so. (My new 3.55 gears whine too, even after putting it together and back apart at least 30 times to get pinion depth and preload perfect, fun)
Pulled new driveshaft out and sent it to a different driveline shop. This shop diagnosed a slightly bent ear on the transmission yoke, causing a flat spot in the u-joint bearings, the shaft to go out of round about .030", and put it out of balance. Less than 500 miles on this new-new shaft and it was trashed. You could see the bent transmission yoke ear when manipulating the yoke side to side and watching the rubber seal on the u-joint compress and open up as you went back and forth. They put on new u-joints, brand new tranmission yoke, straigtened the shaft, and did a high speed balance.
Put in the re-done driveshaft and ... hold your breath ... the vibration is gone!!!
To be fair to myself, a lot of the things I changed made the car better to drive, needed to be done, or looked good, rubber mounts, trans rebuild, wider wheels, etc. But I sure did a lot of throwing unecessary parts at it to finally get a fix to the driveline vibration. If the shop who originally ballanced the shaft almost a decade ago had checked/caught the bent tranmission yoke, I would have had many more years of enjoyable driving.
Lessons: Check the yokes, both transmission and rear end if you are chasing a vibration issue. Don't always trust your driveline shop to know what they are doing. Never give up!!!
1968 Dodge Coronet
440 w. A-833 Overdrive 4-speed
8-3/4 rear end, 742 case, 4.10 Suregrip
Stock but rebuilt suspension
Since the car was restored, I have always had driveline vibration issues. The car starts to shake around 65 mph and gets progressively worse as I speed up. It felt like it was coming from the driveshaft tunnel area in front of the back seat. It was a combination of a vibration you could feel and a loud noise. The problem was at it's worst about 8 years ago when I swapped in an over-drive 4-speed and had a new driveshaft made. Here is what I did to solve this in order over the years:
Get driveshaft re-balanced and change u-joints, still vibrated.
Swap 742 chunk for a new to me one, 3.90 gear, upgarde to sealed wheel bearings, slightly unrelated but still happend, still vibrated.
Many years later, measure driveline angle, rear end pinion compared to tranmission output. Found that it needed shims to get the pinion pointing more down. Bolted in 4 degree shims to point the pinion down. Marginally better but still vibrated both under load and coast.
Got a brand new driveshaft built at a different shop reusing the old transmission yoke, but new u-joints. Still vibrated.
Swapped from solid motor mounts to rubber motor mounts. Vibration got slightly better, but still there. Re-checked pinion angle, still correct with the 4 degree shims. Still vibrated.
Swapped to a new transmission case, new transmission gear set, and complete rebuild on transmission, along with all the upgraded parts you can put in an overdrive 4-speed. Still vibrated.
Bought new tires, still vibrated.
Swapped from factory steel wheels to Wheel Vintiques replica steel wheels, a bit wider than stock. Still vibrated.
Pulled off wheels and brake drums and spun car up to speed on jack stands to check for vibration in rear end and axles. Vibration seemed to be coming from driveshaft, not axles or rear end.
Swapped from a 3.90 gear to a 3.55 gear to slow down driveshaft speed. Now the car could get to 75 miles per hour before vibarting, but still did. I just shifted up the vibration speed 10 mph or so. (My new 3.55 gears whine too, even after putting it together and back apart at least 30 times to get pinion depth and preload perfect, fun)
Pulled new driveshaft out and sent it to a different driveline shop. This shop diagnosed a slightly bent ear on the transmission yoke, causing a flat spot in the u-joint bearings, the shaft to go out of round about .030", and put it out of balance. Less than 500 miles on this new-new shaft and it was trashed. You could see the bent transmission yoke ear when manipulating the yoke side to side and watching the rubber seal on the u-joint compress and open up as you went back and forth. They put on new u-joints, brand new tranmission yoke, straigtened the shaft, and did a high speed balance.
Put in the re-done driveshaft and ... hold your breath ... the vibration is gone!!!
To be fair to myself, a lot of the things I changed made the car better to drive, needed to be done, or looked good, rubber mounts, trans rebuild, wider wheels, etc. But I sure did a lot of throwing unecessary parts at it to finally get a fix to the driveline vibration. If the shop who originally ballanced the shaft almost a decade ago had checked/caught the bent tranmission yoke, I would have had many more years of enjoyable driving.
Lessons: Check the yokes, both transmission and rear end if you are chasing a vibration issue. Don't always trust your driveline shop to know what they are doing. Never give up!!!
