72' Bronco Rear Driveshaft Angle (30 degrees)

[freedomof76]

I'm building my first early Bronco with the help of my brother in law, and we have hit another roadblock. A couple of factors have thrown off the rear geometry quite a bit and the rear driveshaft is sitting at 30 degrees. Here are the specs for the restoration.

360 HP Boss 302 from Ford Performance Racing
Ford C6 transmission (2.5 inches longer than C4)
Dana 20 transfer case
Ford 9" rear axle
3.5" Wild Horses lift
Will run 35" tires @456 gear ratio

We used 8 degree shims and the rear axle is now at 70 degrees - we are concerned that any more could affect the oil in the rear axle. Even with the 8 degree shims the driveshaft is still at 30 degrees.

What options do we have to fix the issue? If we leave it at the current angle, will we have a vibration (I'm assuming yes and we could also snap the driveshaft?).

I'm a noob, my brother in law has a ton of experience with cars but not Broncos or lifts.

 

[ransil]

are you doing the math correctly?/

http://classicbroncos.com/tech/measure-pinion-angle

 

[Broncobowsher]

The angle of the shaft to the ground doesn't matter. Itis the operating angle of the U-joint that matters. If the shaft is 30° to the ground and the joint is 25° to the ground, the operating angle is only 5°. That is the number that matters.

The pinion can be pointed up quite a bit and still be lubed just fine. Even the front pinion bearing. The oil pump in the rear diff (oil slung off the ring gear) will make it to the front bearing just fine.

 

[DirtDonk]

At this point though the other limiting factor due to the need for the shorter driveshaft, would be the overall angle of the upper dual-cardan style joint. You can match the rear with a pinion angle change, but at some point you run into the limits of travel for the upper joint. Seen it time and time again on short shaft setups.

Luckily you're only sporting a 3.5" lift, but the C6 will definitely complicate things.
What is the operating angle between the rear output yoke of the transfer case and the driveshaft? Is this the 30° you mention, or is that just in relation to the ground so far?

Can you even drop the driveshaft far enough to bolt to the rear axle pinion? If so you're ahead of the game. I've seen some where they could not attach the shaft because it was too steep at the CV head. Usually with taller lifts, but need to know how yours is.
Even if it still bolts up but you have little to no droop available for the rear suspension, something is going to break.

Got pics of what all you're working on?
Oh, and welcome to classicbroncos too by the way! Hope we can help you out.

Paul

 

[freedomof76]

 

[freedomof76]

I will get some more info on how the measurements are taken, in the meantime - here's a photo.

https://ibb.co/jhpu0w

 

[DirtDonk]

The good news is that you can't do, or decide a single thing yet.
Why? Because the body and other stuff is not even on the frame yet. So unless you get the suspension down to ride height, you won't know anything useful.

If you're a ways off from that point, you can compress the suspension using ratchet straps to approximately 9.5" between the top of the axle tube and the bottom of the frame rail in the rear (10.5" in the front) so you can test, fit and adjust things.

Good luck.

Paul

 

[DirtDonk]

Great looking setup by the way!
But definitely get that frame down. Common issue with new builds. You cannot set up driveline angles, driveshaft lengths, steering angles or anything related to them until the chassis is sitting at the proper expected ride height.

For reference we use 7" in front and 6" in the rear for a stock Bronco as a general starting point. This is not precise because Broncos were not precise from the factory. Nor were they all the same anyway, given different GVWR packages and vehicle options.
But it gets you darn close and has proven to be a very good starting point.
Thanks to Chuck at BC for posting that info up years ago after seeing us always throwing things out there before we had things sitting where they should be.

Hope that all helps.

Paul

 

[Crush]

Also your tcase looks very high in the frame. Did you make your own crossmember? If so you may have got it a little too high

 

[Skiddy]

are you doing the math correctly?/

http://classicbroncos.com/tech/measure-pinion-angle

doh, that's where I messed up a couple weeks ago welding on my new perches:-[ cut them off and fixed them today%)

 

[bronconut73]

I will get some more info on how the measurements are taken, in the meantime - here's a photo.

https://ibb.co/jhpu0w

Is it just the photo or is the transfer case too far over to the drivers side?
Almost looks like the drive shaft is at an angle.

 

[freedomof76]

Thanks you for the advice everyone, I have Bill from Frontrange Driveline coming over to look at the build this week for suggestions. I know we are taking the measurements all wrong. I will post his advice for future builds.