Question for those who run a double cardan rear

[rickcdewitt]

try not to get aluminum they can break,also just cut and turn your axle pads before you go with much shim.

 

[Will]

Yep, it's easy to move them.

 

[Evan]

Yep, it's easy to move them.

Could I just drill out the plug welds and rotate the pumpkin up, then re-weld? This might allow me to change the angle without even dropping down the rear end.

 

[Evan]

Ok. I bought an angle finder after work today and took some measurements. My driveshaft is operating at an 18 degree angle, and the pinion input is at a 4 degree angle. This means I would need an 11 degree shim in order to being the pinion angle to within 3 degrees of the driveshaft angle. That seems like a bit of an excessive angle for a shim to me. Thoughts?

Hard hard is it to remove the plug welds on the diff and rotate the pumpkin? At the moment I'm leaning towards getting a 2-joint shaft shortened and balanced.

 

[dumprat]

Grind the welds off the spring perches it is way easier! The tube should be shrunk into the housing and will not move if you just drill out the plug welds.

 

[MAKG]

Because the rear U-joint is not in line with the spring perches, it will be less than 11 deg. You can play games with paper strips to make a simple schematic model, or do the math (lots of law of cosines -- PITA). Or cut and weld the spring perches, with some test-fits and markings to get it right.

 

[Evan]

Because the rear U-joint is not in line with the spring perches, it will be less than 11 deg. You can play games with paper strips to make a simple schematic model, or do the math (lots of law of cosines -- PITA). Or cut and weld the spring perches, with some test-fits and markings to get it right.

I have been playing with paper strips and doing some crude thinking, and it seems to me that pinion the angle gained with a shim will be equal to the angle of the shim. Could you maybe give me an anology to help me understand how a 3* shim could change the pinion angle by say 6*?

I wish I had paid more attention when my professor covered the law of cosines in Analytical Trig my freshman year. I was probably checking out girls or recovering from a hangover.

The good news is that the tranny output and my pinion angle are both at exactly 4*. This is a perfect setup for a shortened 2-joint shaft in the back, if shims turn out to be impossible.

 

[blackbronc]

I agree with dumprat. I can see in your pic that the pinion is to low for a dub-cardan. Don't set it at zero though under load it will go negative possibly enough to actually break the rear cross. Recomendations I've seen suggest 2 degrees low so it will be more or less straight under heavy load and it needs to have some angularity to move the needles and lube around or they will burn up.

 

[Will]

I used a magnetic angle finder on mine. Stick it to the driveshaft, then stick it to something on the axle housing--I don't remember what. It wasn't hard. I ground off the old ones, put it together with the new ones just clamped in there, set it up, tacked them, took the axle back out, and welded them fully.

 

[blackbronc]

X degre shims will yield the same degree change at the pinion flange. but the rotation of the rear axle will raise the pinion higher up reducing the driveshaft angle. If you have an 11 degree differenceyou want to end up with about 2=9 degrees. I can't recommend that. Rotating the spring pads as others have suggested is the only good option. Shortened single cardan shaft is the easiest but running them at 11 degrees will make service life less than optimal, The needles have to move too far and fast and will run hot. Vibration will be higher than need be as well because of u joint oscillation.

 

[Evan]

I had a machine shop make me a set of custom balanced shafts. Went back to a single cardan rear, left the front double cardan. Cost was a reasonable $120 per shaft. That included the DOM.

There is a little rumble when I get above 55 MPH, due to the angle that the rear joints are operating at I'm assuming. Nothing bad though, as I keep the truck off the freeway and don't go much over 60. My dad's stock truck makes just as much noise.

I still have all the stuff to run a double cardan rear, so someday if I have the axle out I'll cut and reweld the perches. For now I'm quite satisfied with the on-road performance of the truck.