[buckhorn]

I have a 49 ford w/351-w engine & a.o.d. trany. rear end is 77-8" maverick. Am getting vibration at speeds past45m.p.h. Myengine is 5degrees down ,axle is2-degrees up ,shaft is pointing toward trany shaft. should I have custom made shaft w/ double cardan c-v joint or does any ford product, like lincoln town car already have this?my existing shaft was built w/std. u-joint ,but while doing checks on this vib. problem yesterday, I used a dial indicator on shaft & found it was out by .090" ! Is this deflection caused by bad angle or by bent tube. I haven't abused or raced car . Strictly show& cruise.

 

[HotRodMan]

When I built my hot rod I installed the differential 3 degrees up and had the engine/transmission 3 degrees down. You might try this before doing anything expensive. Next you can try disconnecting the drive shaft at the differential rotate 180 degrees and re-install. Sometimes that will make a difference. If this fails and you are sure its the drive shaft causing the trouble, take the drive shaft to a professional to have it checked.

 

[Centerline]

I agree with the above answer. Also make sure the U-bolts holding the driveshaft to the pinion yoke are not overtightened. If they are it can cause vibration at speed. The correct torque is 17 foot pounds, no more.

Centerline

 

[[email protected]]

question about pinion angles responces

why would you point the axle up above center any amount of degrees..(just asking to learn a different way) i have always pointed my axles down from center 5 to 8 degrees so that when i took off and the springs wrapped up from torque the drive shaft would be strait in line.. am i reading or understanding wrong what everybody is saying (maybe so) i had a 4x4 ford truck that the rear axle was pointed up about 4 degrees and when i would pop the clutch racing off road it would bust the yoke and the housing but when i pointed it down about 6 degrees it stopped doing that .. i am asking this to better under stand what it is i am reading

 

[powerrodsmike]

I didn't realize this post was so old before I typed all this stuff, so I'll leave it. Is this car lowered alot? There is a maximum operating angle/ shaft RPM relationship that a u-joint cannot exceed without vibrating. You must first have the output shaft of the trans and the pinion shaft aligned. In other words, a line drawn through the crankshaft/trans centerline and a line drawn through the pinion should be parallel. (You will compensate for axle wrap by angling the pinion down 2* more in the front for leaf springs) This needs to be set with the suspension loaded. Now measure the u-joint operating angles. This is the actual angle of the 2 shafts connected by the u-joint you are measuring. The angles and speeds should fall within the specs in this chart. anything more and you will get vibration.
DRIVESHAFT RPM MAX. NORMAL OPERATING ANGLE

5000 3.25*

4500 3.67*

4000 4.25*

3500 5.00*

3000 5.83*

2500 7.00*

2000 8.67*

1500 11.5*
I found this chart here:http://www.drivetrain.com/driveline_angle_problem.html
Here is a link to a thread here that may help you determine whether or not you need to use a double cardan u-joint. http://www.hotrodders.com/forum/short-driveshaft-high-angle-ujoints-57557.html. There are some really good links in that thread that can help you. Disregard the little argument by 2 members in the beginning of that thread as it really doesn't apply to your problem. The vibration issue we had with that car was cured by using a double cardan u-joint on the front, because the operating angles were too great to work with a single u-joint type driveshaft.(thank you to triaged for helping us with that) Also, I don't think you can check the driveshaft for runout without pulling the driveshaft out of the car and having all of the u-joints and shafts in line. I believe,(I could be wrong on this), the operating angles create an oscillation of the shafts, which would show up as runout on a dial indicator.. Hope this helps, Mike