wicked vibes man!!!

#1 05-30-2003, 03:50 AM

I need a little help - first off its not a truly FSJ but the webmaster said I could post about it (yea I actually got permission)
this is the deal = it a 71 commando but almost all parts are FSJ and it has 327 vig ,nailhead 400, "J" shift D20 27 front 44 rear w/ 64 cj 5.38 r&p. I was getting a wicked vib. at road speeds and thought it was the driveshaft /u-joints -got it balenced -didnt go away next I thought pinion vs. out put angle adjusted drivetrain to -4% and pinion to +4%(this should equilise stress on joints. Still vibrated then I thought T-case Bearings so I replaced them (they were bad )and new thrust washers to set preload. no change so I pulled the 400 only to find that both output bushings were toast (end play was almost 1/4 in. each way) started to get parts only to find that it was a 64 model and the valve body is diff. so I found another one (73)and am in the process of building it . my question is do any of you think that I might finally solve my prob. or might it be a bent axle or something . BTY when I put it togeather I raised the drivetrain 4.5 in.so nothing hangs below the frame rails.
Any advice would be VERY apriciated!
thanks in advance
Matt

**River Beast** · #2 05-30-2003, 03:58 AM

what is your driveline angle? there is a point the too much angle will cause vibes reguardless of relationships of pinion to output shaft angle.

I ran mine with 19 degrees with a small vibe... a CV shaft took care of it...

#3 05-30-2003, 04:12 AM

I will measure it - not really sure 19 deg. to much you say?

#4 05-30-2003, 04:19 AM

If I go with C.V. I have herd that you dont want to equlize the stress points because the joints wont get turned and no turning = no lube . So would I put my driveline back to level and C.V. at the output or leave it at -/+ 4 at the output and pinion?
thanks todd

**River Beast** · #5 05-30-2003, 04:37 AM

MAtt,

with a CV setup... it is optimal to have 1 degree delfection off the pinion... in other words the pinion should be directly point to the output of the T-case and the CV would be at the T-case...

like this....

the way you have it set up now for singel joint application is like this....

There is a method to the madness when it comes to angles vs length.... here is a chart to explain the horizontal measurements....

#6 05-30-2003, 05:03 AM

Thanks for the pics Todd
but -stupid question?
if the pinion is angled directly at th T.C. how dose the rear joint get lubed?
Dont the caps have to turn in order to spread the greese on the pins?
Or will the natrual up & down of the axle cause the angle to change enough to rotate the caps?
thanks again

**River Beast** · #7 05-30-2003, 05:13 AM

the suspension motion and natural spherical movement of the the ujoint will keep everything lubed... you would think a ujoint rotates evenly across the 360 degree rotation... not so... that is why we develop vibes... here is an illustion of accelleration and decelleration thru the elliptical path of a ujoint...

Drawing illiterates elliptical path of universal joint from end view while operating through drive shaft angle...this is why you should leave 1 degree pinion deflection in the pinion joint.. it also allows for slight axle wrap when you have the 1 degree negative in the pinion.

#8 05-30-2003, 05:25 AM

You Rock Todd !!
I talked to 2 diff. driveshaft shops and they coulbnt explain it to me like you did . Thanks SOOO much . I think I will probably go C.V. as soon as I get the gundam's tranny back in because I am planning on 4 in. springs also and I know that my angle will be just wicked!(28 1/2 in. ground to frame with 32's or 30 with 35's)
Thanks again!!

**River Beast** · #9 05-30-2003, 05:28 AM

No problem..... you will have to change the yoke at the T-case to add the CV shaft... FYI

#10 05-30-2003, 05:30 AM

Why will I have to change yokes?

**River Beast** · #11 05-30-2003, 05:58 AM

the single u-joint style yoke uses U-bolts and the CV style head bolts directly to the yoke....

#12 05-30-2003, 06:19 AM

Do you mean the yoke with the flat round plate with the 4 bolt holes that was on my parts case? or something else?

**River Beast** · #13 05-30-2003, 07:37 AM

You can use that flange yoke and have them make the CV head to match the flange yoke.... that's easy... if you still have it..

#14 05-30-2003, 07:55 AM

I sure do but its slightly bent inward on one side (more like a dent than a bend)the rest of the plate is totally flat and squaired perpendicular to the splines, should I replace it or do you think it will work?

**River Beast** · #15 05-30-2003, 08:41 AM

I would not use a bent flange.. you are asking for vibes... buy a not flanged CV yoke to go with your CV shaft when you have it built.

#16 05-30-2003, 08:48 AM

cool, thanks
Once again --You Rock Man!

jjk · #17 05-30-2003, 09:57 AM

RIVER BEAST!! D@MN!! Dude I'm impressed... I know that I'm new here, but wow!! It's nice to have guys like you around...

**River Beast** · #18 05-30-2003, 10:01 AM

Thanks jjk..... just trying to help out and spread the knowledge that I have learned from so many here on the forum....plus research...

jeepguzzi · #19 05-30-2003, 11:30 AM

GEEZE, Todd, is your next career going to be a math teacher?? I can see you in a white short sleeved button down shirt, big black glasses, pocket protector with the chalk holder in it, hair parted down the middle,brown shoes, white socks, bow tie and suspenders and calling your students Mr. and Miss.

**LRRH** · #20 06-01-2003, 04:29 AM

Quote:

bow tie and suspenders and calling your students Mr. and Miss.

WOW!!! It's a little rough to see Todd wearing a Bow Tie!!!

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