rear driveshaft angle - vibration problem

[miked]

how does one measure driveline (tcase output & pinion shaft input) angles??

trying to chase down a vibration in the rear driveshaft. I have done the following after installing my 3" lift:

1) converted rear driveshaft to double cardan, with double joint coming off D20 side.

2) balanced shaft, twice

3) new spicer bearings, twice

4) rebuild rear end, once (thankfully $$)

if i pull the rear drive shaft and run it in 4wd it drives like silk, very quiet. but with the rear shaft in, it gets a strange vibration starting at about 60mph.

the vibration is difficult to explain, but here goes: it starts very light and then grows for about 2 seconds and then fades out for about a second. if i drive faster than 60 then the cycle seems to go faster proportionaly to the speed. 70 is as fast as i dare take it, sounds like its ready to come apart.

since the vibration goes away with the rear driveshaft removed I figure its got to be the angles out of whack as the driveshaft comes out of the D20 and goes into the rear end. But I can't seem to get a handle on how to measure the angles, or even what to look for.

any and all help appreciated, rather not take it into the shop to try to chase this down.

I saw RB's explaination in another thread (http://www.ifsja.org/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic&f=2&t=005249) for front shafts about std and max driveline angles but have no clue how to measure these for either front or rear.

[Iron Horse]

I am by no means an expert in this area. With the dbl. carden in your rear shaft, you will need to make sure that the shaft is in direct line (parallel) with the pinion- otherwise vibration will occur. Check out Tom Woods Custom Drive Shafts (http://www.4xshaft.com/) Go to the TECH section at the top of the page~ some really good stuff. Hope this helps.

[miked]

Thanks for the reply, digging thru the info now. Hoping this will help

[Veepster]

why did you put the double Cardon in the rear when you only have 3" of lift?

[miked]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Veepster:
why did you put the double Cardon in the rear when you only have 3" of lift?<HR></BLOCKQUOTE>

strength, extra u-joint life, smoother driveline action -- and relief of driveline issues like this.... supposedly.

i think i may have a handle on whats going on, it might be that the pinion flips up under speed due to spring wrap which in turn mucks up the angle at the pinion. it should look like this for vibration free action:

http://www.4xshaft.com/images/cv_angle.gif

but it doesn't. so i'm going to work on moving the pinion down abit. lets see how it goes

[ August 30, 2001: Message edited by: miked ]