So, I've read the writeups on installing CV drive shafts and I'm about to install my Tatton shafts front and rear but want to have a better understanding of driveline angles before I begin. Maybe someone can help me out.

My question:
The front and rear driveshafts use the same U joint assembly. Now, I know you are supposed to angle your pinion in the rear to make a 0 degree angle where it meets the pinion for proper setup. But in the front angling your pinion changes your castor angle. If I have my castor set around 6 degrees, the pinion angle will not be zero when aligned with the shaft, right? Why do you have to angle the rear but not the front when the drive shafts use the same U joint assembly? And why is this ok?

To get my rear at a zero angle will require me to do a bit of trimming and moving things around (trimming shock mounts, moving sway bar back, trimming bump stop).

any help in understanding the why would be awesome.

Thanks,
Jeff

 

You answered your own question. Because of Caster considerations, the front angles are a trade-off between vibes and flighty handling. No need to worry about caster in the rear, so that shaft gets angled correctly.

 

So with a 4-5" lift with my front pinion angled up will it fall in the suggested 6-8 degree zone? If that's the case then I guess it all makes sense now.

 

Or 6-8 degrees puts me close to in line with shaft but at a small compromise of driveline angle?

 

That 6-8 degrees you are referring to is from the DIY Alignment write-up? That is based on a stock driveshaft, and using an angle finder, not an alignment rack. (angle finders measure straight lines, alignment racks measure some type of an arc - just a heads up that the numbers will not be the same).

With the cardan shaft, you need to deal with the trade-off. Enough caster to make the flightyness liveable, enough pinion to not have vibes. Don't use someone elses numbers as your guide, and don't expect to be in that 6-8 range. I would guess that you will be in the 4-5 deg range, but you need to check it for yourself.

Flighty handling is better than vibes...

 

Thank you. This conversation is super helpful. Is there an angle (using the angle finder) that I can reference for an acceptable angle for both no vibes and decent steering with a 4-5" lift?

 

Any angle you use will be a compromise and there really isn't a good angle. If you make the DS angle decent, steering will be very flightly. Our company 2dr JK has our older std caster PR and handling is barely adequate with a 4" lift. The DS angle is a real priority. Too much angle can and will lead to early DS failure and worse. The t-case front output shaft bearing DOES NOT like the added angle that you have if you retain the stock 4* of caster after a lift. This is one of the reasons that our ProRock Unlimited housing has been so popular. The added caster in our housing is the ONLY way to correct the caster issue without cutting and turning the end forgings (the 'C's) on the stock housing.

 

Do a search on Transfer Case Grenade and you will see why front DS vibes are a bad thing ...

 

X2 !!

There are quite a few threads with pics of exploded transfer cases to back that up. Opt for flighty handling instead of living with vibes. And I'll toss out a vote for the PR44 Unlimited. Expensive, but I love mine!

You could also look into Spyntecs, and some even pull the front shaft and just re-install when they get to their wheeling spots. Neither are a substitute for proper angles, just tossing it out there.

 

Wow, I had no idea this was such an issue. I've been driving with my stock driveshafts with 4" lift for quite a while and I'm sure the angles aren't ideal. This thread is super helpful. I'll try to get the front driveshaft angled as much as possible and go from there. I didn't realize I'd have to sacrifice the steering geometry.