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Old 10-12-2004, 11:15 AM
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driveshaft angle c-v joint rear wheel drive

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.

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Old 10-13-2004, 09:24 PM
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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.
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Old 10-14-2004, 07:37 AM
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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.

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Old 01-13-2006, 07:37 AM
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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
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Old 01-13-2006, 08:41 AM
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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.

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:
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. short driveshaft high angle ujoints. 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
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Last edited by powerrodsmike; 01-13-2006 at 08:50 PM.
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