I need some advise

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C.Rector

C.Rector

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Hello Gentlemen
I have just completed a swap in my 72 D100 longbed. I replaced the original 3 speed manual trans with an A833 overdrive. Durring this I had to replace the bellhousing and fiywheel along with a new clutch kit and replaced the 2 piece driveshaft with a one piece unit.
After the installation The truck has picked up a serious vibration that starts around 40 miles an hour and goes thru 65 or so. It seems to get a little less after 60. It doesn't change depending on the gear you are in or if you are at a steady speed or if its still in a pull .It does matter if you are in neutral or if the clutch is in or out.
I took the drive shaft to a local drive line specialist and had it balanced and new joints installed. Still remains the same.
I have noticed that if you keep the truck in a constant pull thru the gears it seems to not vibrate until you let the suspension settle down and maintain a cruising speed.
The only thing I can think to replace now is the transmission mount and I plan to change it this weekend.
Can you guys think of anything else that could cause this? The front bearing was also changed in the trans before installation just to be safe also.

Any help will be appreciated. Thanks in advance
 
No idea. If the truck was long (bed?) enough that it used a 2 piece shaft, why did you change that?
 
I'm betting it's the removal of the 2-pc shaft. Center supports are in there for reasons. My impression is the pinion angle is all over the place when you're driving with the longer single shaft.
Does it vibrate with the truck not moving, just revving up while sitting still?
In what shape are the leaf springs?
Did you check pinion angle?
 
I agree on the pinion angle. Also, how long is the new driveshaft? I am guessing abnormally long, and a long shaft will have more of a tendancy to "whip", especially if there are any loose u joints, worn slip yoke bushing in the transmission (any play in the slip yoke?) Or incorrect u joint straps at the differential yoke (large and small straps look very similar and can be mixed up).
 
There used to be a weight that would bolt to the tail shaft of the trans to dampen vibration also. I've seen them on a couple of transmissions.


I'm not saying that this is your problem, but if you can find one and try it, it may help.
 
How much play in the front yoke in the trans tailshaft. Bushing might be bad.
 
Personally I don't think it's because he went from a two piece drive shaft to a one piece because a lot of long beds came with a one piece from the factory . What shape is the slip yoke in and is it in the transmission far enough . Or maybe to far in ?
 
my 73 D100 had something along the same lines. mine was a 360 np435 8.75 setup. did a new clutch, flywheel, and trans mount. had a HORRIBLE vibration towing under heavy loads. (5000#+) replaced the carrier, helped, wasn't completely right. did leaf spring bushings. solved. my 66 dart, just did a full suspension/disc swap. pinion angle was 3 degrees with the 7.25. swapped in an 8.25, balanced driveshaft, and stronger shackles that weren't almost rusted in half. 1 degree angle. I had a vibration. 30-50 mph. bought shims to increase the pinion angle to 2.5 degrees. fixed. good luck!
 
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