lowered pinion angle help....

[merlin65]

hey everybody, my truck (shortbed 3 speed sagi, 3:73 12bolt posi) is lowered 6inch springs, 2" blocks in rear and cut springs in front. For a grand total of 8" in rear and 7 in front. well she rides great and have always been satisfied. But the truck always had driveline vibration at around 70 under some throttle (short bursts of hell yea on interstate). Never bothered me too much since I dont travel over about 62 mph. But tried to fix it with some 4 degree shims from Carls Speedshop. Put them in with fat side toward front to kick my pinion yoke up to match my transmission. Drove it and now the vibration is at 35mph. I can feel it when I run out second gear before hittin third. It is also there at the bottom of third. So it seems it is not engine fan or anything like that. Brand new tires, new balance, but did it with old tires before I changed them and u joints are good. Blah Blah. It seems like pinion to me.
I was rappin to some guys and they said to try to reverse the pinion angle to be pinion yoke down. I agreed what the heck, gotta take them out anyways might as well spin them around to be fat side toward rear of truck. Do you guys think this might work? Before adding any shims the pinion was level pretty much with ground, kinda a 0 degree condition. did great except for high speed runs. Any help is appreciated. Someone has to have messed with this problem. thanks guys

[kieth]

If you have coil rear springs, try relocating the front I beam arms, (drill the yokes out on the crossmember and turn them upside down) this will get you a better angle on the driveline.......I think that is why some folks replace the crossmember......Kieth ?

[merlin65]

I have been thinking about the crossmember. Very interesting, anyways my driveshaft is dang close to the upper hoop of my stock crossmember. not close to touching, but close. Thanks for the reply

[fleetsidelarry]

there are actually 2 factors involved. one is the relationship of the pinion angle to the engine/tranny center line. on a one piece drive shaft you are right, the angles are supposed to be the same or nearly so (but not in a direct line, that is, not in the same plane)

the other factor is the amount of angle on the u-joints. this may be the problem in your case with such a large drop. u-joint angles need to be around 1°.

if you have an angle finder check all three (engine/tranny CL, drive shaft, and pinion) angles to see what you have. You may also have to raise the tranny mount, if possible.

someone put this link in a sticky recently but here it is again:

http://www2.dana.com/pdf/J3311-1-HVTSS.PDF

[kieth]

Originally Posted by merlin65

I have been thinking about the crossmember. Very interesting, anyways my driveshaft is dang close to the upper hoop of my stock crossmember. not close to touching, but close. Thanks for the reply

By reversings the mounts on the crossmember you also change the pinion angle. When you reverse the mounts it moves the holes for the beams higher on the crossmember and that changes the pinion angle. Kieth

[kieth]

I am cheap so that is why I thought of drilling the mounts out and reversing them....instead of a new crossmember. I also cleaned out the flanges of the crossmember to allow the exhaust to go thru there ....not that my truck is lowered but to make the whole installation neater and if I so desired I can lower the truck in the future without more mods. Here is a picture of the crossmember and the brackets for the I beam arms, see how easy it would be to reverse them, just drill and bolt back in. You have a better pinion angle.

http://kieth.smugmug.com/Trucks/66-G...874_6EYgj-A-LB