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View Full Version : What's the deal w/ 80 front driveshafts?


60wag
02-11-2008, 12:54 PM
Why does the 80 front driveshaft defy the standard setup for orienting the two universal joints? I understand the cyclic speed variation of a ujoint as is bend angle increases and the need to operate them in oriented pairs to reduce vibration. So is it the lateral offset of the tcase and front pumpkin that comes into play on an 80?

Nay
02-11-2008, 09:28 PM
Why does the 80 front driveshaft defy the standard setup for orienting the two universal joints? I understand the cyclic speed variation of a ujoint as is bend angle increases and the need to operate them in oriented pairs to reduce vibration. So is it the lateral offset of the tcase and front pumpkin that comes into play on an 80?

The joints aren't "in-phase". Lateral offset where the two mounts were not on the same fore/aft plane would create a compound angle that would be impossible to solve. "Out of phase" is the only answer I can come up with, but I don't understand it. My setup should vibrate like crazy and it doesn't. I'm about to make it worse with Slee blue caster bushings (have OME now).

The "broken back" configuration may add more tolerance as well, but I have no idea why.

nakman
02-11-2008, 09:40 PM
Maybe it's a ploy to get you to open the FSM more often.. I don't get it either. But I just read the "driveshaft woes" thread again, just for fun and a trip down memory lane. Some good stuff in there, like this:

Bikeman
02-11-2008, 09:59 PM
The joints aren't "in-phase". Lateral offset where the two mounts were not on the same fore/aft plane would create a compound angle that would be impossible to solve. "Out of phase" is the only answer I can come up with, but I don't understand it. My setup should vibrate like crazy and it doesn't. I'm about to make it worse with Slee blue caster bushings (have OME now).

The "broken back" configuration may add more tolerance as well, but I have no idea why.

I have the "blues" with exactly 3.5" lift over stock and no driveline issues. Hijack off.

Hants
02-11-2008, 11:01 PM
I just upgraded from OME to blues on my Heavy lift, and went from "slight" vibes from 65-75 to "more-than-slight" vibes from 62-80. :(

Now I'm going to have to install a 12K winch to see if I can fix my vibes. :)

nakman
02-11-2008, 11:33 PM
Continue the hijack.. I've got J's in front with Mr. Gasket spacers, and have a little vibration between 60 & 75. Running the OME castor correction bushings. I'm thinking of upgrading to Slee's DC shaft to correct, then stock bushings, plates, and 4" springs.