First the car info: 70 challenger T/A 340 4spd. Engine and transmission are not original to car both 1971. The car drives perfect 1st through 3rd gear any speed any rpm but when you depress the clutch and shift into 4th gear there is a noticeable vibration at 60 mph and higher. Fourth is good driving less than 60 on back roads. Universal joint are new rear bushing in trans is new,rims and tires new and balanced. There are no noises like a bad a bearing. Has anyone had a similar problem? Any guesses welcome.

Can we assume you've driven the car in 3rd gear exceeding 60 mph with no vibrations?

Yes up to 70 mph

[quote=340swing]First the car info: 70 challenger T/A 340 4spd. Engine and transmission are not original to car both 1971. The car drives perfect 1st through 3rd gear any speed any rpm but when you depress the clutch and shift into 4th gear there is a noticeable vibration at 60 mph and higher. Fourth is good driving less than 60 on back roads. Universal joint are new rear bushing in trans is new,rims and tires new and balanced. There are no noises like a bad a bearing. Has anyone had a similar problem? Any guesses welcome. [quote/]





transmission mount
driveshaft balance
driveline angle
pinion angle

is the vibration on Acceleration or De-acceleration or both?

The trans mount is new. We are trying to figure out pinion angle is that the same as driveline angle? And if not where do I go to figure that out. I think acceleration or driving steady speed. Not there as car decelerates you feel it in shifter and pedals as soon as you push clutch in to shift to 4th and stays there until you get under 60 mp

Need to find a place to balance Drive shaft. Anyone know of a place in Connecticut

I've had the same problem for years. It's so bad, I just stay off the freeway. Not sure where to start looking. I'll just change one thing at a time till I find it.

Fastmark do you have a 4spd? Have you tried anything yet.

Your driveline angle is the relationship of the transmission angle, driveshaft angle, and pinion angle, and how they are phased to each other, you need to have an inclination meter to accurately measure the angles of each component as they sit at ride height in the vehicle, keep in mind the pinion angle changes (rotates upward)under acceleration by several degrees

Hopefully you've eliminated any wheel/tire imbalance problem by trying another set of rims/tires? even a slipped/ruptured belt/cord in a tire can cause what appears to be a driveline vibration

here's a few diagrams on driveline angle, keep in mind this is under acceleration conditions regarding some of the pics/measurements

if the driveshaft speed is the same when it acts up in 4th as it is in 3rd when it is OK that inclines me to think that the shaft/ujoints/angles are OK & that it is clutch or tranny or mount related & more the trans cuz of the shifter vibration.

Thanks dayclona I'll check it out the diagram helps

I've chased the issue with my 4 speed Challenger. Bell housing runout, pinion angle 1.5 both ends, different center section, different axle shafts, new mounts. I'm going to recheck the drive shaft again. That leaves only the trans which I rebuilt. It's quiet and shifts perfect. Though this car has kicked out a few u joints in its day from abuse. I'm wondering I'd it's possible the output shaft is bent. I had a friend bust a front u joint on the freeway. 727 that bent the output at about a 30 degree angle.
Doug

Yes. Its an AAR. It was an auto car. I put in a four speed many years ago. I've had it for 40 years. I've changed motors, mounts, balanced the flywheel, changed driveshafts and even a transmission. I can't imagine that it would be my rear end. I've got another car that I am restoring right now and then I'll start over from scratch. It's better than when I started trying to find it. I just don't drive over 65. Not much help but good luck to you.

Surprised no one mentioned the pilot bushing, had a 383 Satellite act almost identical as described but seemed it was more on decal clutch and the pilot bushing was wollered out.

All the 4 gear stuff is moving in 3rd same as in 4th only moving at a higher RPM related to speed. The only variance in 4th is the 1-3 gears are spinning at a different speed than the output shaft but that also happens to 2-3 when in 1st, 1&3 when in 2nd and 1-2 when in 3rd. The input as well as everything in front of the trans spin actually work harder in the lower gears but are under a load constantly. The output shaft, rear bearing, rear bushing and everything behind the trans work the same related to speed. So that leaves the cluster and the roller bearings in the back of the input, the cluster is under a load 1-3 and idle in 4th, worn roller bearings might create a vibration when not under a load. When in 4th, the input is locked to the output and the bearings in the rear have to keep it centered to a degree but it seems worn bearings here would cause more of an issue when spinning than when stable not to mention the synchro will do some centering as well. So if I was going into the tranny looking for this vibration I would be looking for worn roller bearings in the cluster gear or a worn cluster shaft. This is also an area where I have seen either ignored for fear of them falling apart or allowed to fall apart when being installed and then ignored. A heater hose is your friend.

Check the rear yoke. At one time it might have kicked out a u-joint and spread the yoke. Had that happen, not real noticeable except the joint fits loose side to side causing missalignement and vibaration higher speed.

Is the bellhousing original to the engine?

Howdy, been chasing a similar vibe. for a long time also. 72 Cuda 340 4 spd. Went through all above and tried internal balance harmonic balancer in case I had a forged crank. checked flywheel to make sure it was the right one. (with balance drill outs) Also rebuilt trans with new stop rings, new pilot bushing, input shaft. Still vibrates above 70 mph and what ever the corrisponding engine speed is in any gear. (you may want to see if that is the case with yours) At this point I am going to pull the motor and have it freshened up with a stroker kit, full balance, and new clutch. Still open to all ideas. (spend too much time verifying that it has the correct cast crank, balancer and flywheel)

Get it on a chassiss dyno. It's a great place to verify axle runout, bent rims and out of round tires.

Here's an interesting video that demonstrates driveshaft angle issues.

Wow! Seems there are a number of people here that have this or similar problem. This is not my car but I will be updating this post as we go. I'm determined to fix it. I'm leaning towards input shaft/pilot bushing at the moment. Thanks for the input I will update this but be patient it's snowing here driving it will be tricky