Dana 18, Is This Bad Or Normal?

I hate to harp on the driveshaft, but it looks from here that both the t-case and the pinion are both pointing down a little. If that’s the case, even at all, (especially in combination with the side-offset) a chatter will develop, and it will amplify in any slop in the t-case. Maybe it’s just a photographic illusion? The pinion should point up at the same angle that the t-case is pointing down to offset any ellipses in the u-joints.

 

James
I have a 20 or a 18 wide mouth if you want to build a tera low. WFO might getter done quick.

 

You have a keen eye. My pinion does slope down slightly. That might be the first place to start.

 

That would be nice but my sump for my gas tank is where the rear output on a D20 would go so I'm sorta married to the D18 unless I want to move my sump.

 

Thanks Jim. My week is booked and I've thrown about $2k or more at the Jeep this month (carb, winch, spare tire, gears, bearings and on and on) I can't justify any more spending or time for now. I'll take all this advice and figure it out at some point. Sure appreciate all the input from everybody, I'll get it figured out

 

Take a leap of faith and just send it

 

Understand James. I'm at the point of having to buy R&P's, bearings, and ? Where did you get your parts from?

 

I get a lot of stuff at Napa, as a city employee I get a large discount there. Stuff that Napa can’t get I just find places online to get it from. I got my gears through quadratec, they had a good price on them.

 

Thanks for the reply.

 

Long term either the diff needs offset or the transfercase output needs centered.

Until then if it were me...

^ What he said, it will be a good story.

 

Interested to hear your thoughts on this, is a horizontal offset worse than a vertical offset for some reason? I'm well within the operating range of my U-joints and I have less angle now with my high pinion centered than I did with my low pinion offset.

 

They are both equally bad despite what some may have you believe.

 

Here is something I find interesting to read:
BillaVista.com-Driveshaft Bible Tech Article by BillaVista

"Most of the equipment that uses driven shafts in a broken-back configuration though, are fairly low RPM (but not all). The reason is, due to the nature (geometry) of the configuration"

This is interesting the whole accelerating decelerating mumbo jumbo as the u-joint goes round. I wonder, where does the acceleration deceleration get dampened. Do tires soak it up while the ring and pinion are always accelerating or a 5lb sliding gear?

 

I still say run it on the Rubicon. Your flat towing there...... other than the drive to loon lake I doubt you will be in 3rd or 4th gear..... Put a little extra oil in it and lets go!

 

You've got a lot going on here.
Driveshaft vibrations will cancel themselves out for the most part as long as the u-joint angles are equal, or equally opposite.

An example of a standard configuration (bottom image) would be where the output is at 0°, the driveshaft is at 5°, and the input is at 0°. Both u-joint angles are the same at 5°. The angles of the joints remain relatively equal as the vehicle's suspension cycles. This configuration is how our jeeps should be (unless we're running a double cardan shaft).

An example of a "broken back" configuration (top image) would be where the output is at 0°, the driveshaft is at 5°, so the input should be set at 10°. Both angles are the same (relative to the driveshaft) at 5°. Broken back configurations are not typically found in autos because the u-joint angles would vary greatly as the suspension cycles.



As long as the output angle matches the input angle, either equally or equally opposite, the ellipses in the u-joint angles will cancel each other out. The driveshaft itself will still be speeding up/slowing down twice per revolution, but it won't be transferred beyond the confines of the u-joints.

If there are any discrepancies in the u-joint angles, the twice-per-revolution speed-up/slow-down will be felt in your seat, and it will usually only be felt as a hard vibration under acceleration. It will be heard as a chatter as it slaps any gear backlash on deceleration. It usually will be heard in the t-case on deceleration, just like what was heard in OP's video.

 

If you don't do it already since you are flat towing I strongly suggest removing the rear driveline.

 

If possible you could try raising the transmission mount or cross member by an inch or so? That would give the U joints a little angle and also give a little more ground clearance in the middle. I’ve heard you actually want the U joints to have some angle in order to keep them lubricating and not seizing up.

 

He’s already got an offset t-case and centered rear. There’s more than enough offset for cap rotation.

 

I have a full float setup with hubs so no worries there