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Do I really need a CV shaft?

73k5blazer

73k5blazer

End the H1B Program!
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I've got 3' 8" length, 21degrees total , running NP205 and 14bff with 1350 yokes.
Need to have some D-shafts built, was thinking a cv shaft, but then I have to rotate the 14b up. Is it really necessary? I'm not into super twisty rock crawling, I only have 2.5" of spring lift. So will a 2 joint shaft spin OK without vibration on the highway and be ok at full droop?
I read a 1350 will go up to 20 degrees max, so mine would be running 10.5 degrees normally. Too much stress?
 
It's not the type of wheeling you do, but the speeds that shaft turns on the road/highway. Less working angle = less chance for vibration.

If you have 10* down angle at the t-case you should have 10* up angle at the pinion. These angles will cancel each other out while the shaft spins, in theory. With only 2" lift I bet you can get away with it if your angles are correct. I've heard of people doing 4" lift without vibration. All comes down the the angles.
 
Unless you're talking about a $$ special C/V joint, a 2-joint shaft will take more angle without binding. But the C/V will take more angle without vibration. With your low lift and the angles set correctly, I bet you can get decent results with the standard-style shaft.

I drove for years with about 13 degrees in the joints. There vibration was definitely noticeable, but no so bad that I had to do anything right away. The lighter the driveshaft, the less it will vibrate.
 
Thanks for that.

Well, I just re-took the measurements. It's sitting 21 degrees total right now, i'd say +/-2degree error. I still have to add, spare 35" tire (on alum rim, on the back of the already installed Kert swing away tire carrier bumper), receiver mount warn 9500 winch in a holder on the cage behind the rear seat , the rear seat. And 45 gallons of gas, ok 20 to be average. So it'll squat just a little more, I'll probably be 19 or 20 when it ends up? Hard to tell.
I think I'm gonna try a 2 joint shaft. I hate vibrations though, drive's me insane.
 
73k5blazer said:
It's sitting 21 degrees total right now, i'd say +/-2degree error.
Click to expand...
What do you mean? 10.5 in each joint? The angles are the same, right? Are you having any vibration problems?
 
Yeah, um, boy do I feel stupid. Your right, 22 degrees. I just built a deck with wrap around stairs and got used to, measure total angle, divide by 2, cut boards.
I was splitting, but that's not the case here. It'll be 22 degrees each joint. Ouch.
Well, I guess time to revised the plan.
HOw much can you rotate with shims? Probably best to cut the pads and re-weld them on and get a CV shaft, eh?
 
Yeah, 22 degrees in each joint is probably too much. I didn't think a 465/205 combo was that long. I wonder if the glass body is turning your 2.5" springs into much larger lift. A little bit of trig should tell you how much angle the C/V would have after the pinion was rotated up - maybe 15-18 degrees? The 205 does have a fixed yoke, right? I know there is a less common slip yoke version, which would shorten the driveline and increase the angle.
 
Yeah, the 205 has a fixed yoke.

I'm not sure the glass body is all that much weight savings, with all the steel in the cage and cage supports, the heavy DIY4X bumpers...mabey 500-750lbs savings, it'll be interesting when I get it back on the scale to compare with before numbers.

Well, seems some rotation of the 14b is nessesary. Grrr....I hate grinding.
 
73k5blazer said:
Yeah, the 205 has a fixed yoke.

I'm not sure the glass body is all that much weight savings, with all the steel in the cage and cage supports, the heavy DIY4X bumpers...mabey 500-750lbs savings, it'll be interesting when I get it back on the scale to compare with before numbers.

Well, seems some rotation of the 14b is nessesary. Grrr....I hate grinding.
Click to expand...

I think there is something wrong with the math here.
I can't see how you have that much acngle with only 2.5" lift?
Did you twist your engine tranny combo up to compensate for the front?
I was running 2.5" lift on my K5 with a 465/205 fixed yoke and it was closer to 12 degrees, and I didn't drop my tcase or anything, it was all stock location. :dunno:
 
Ok, well, how to measure?
I measured, straight off the t-case, then cut small piece of wood 1/2 dowel I had to and jambed it in between the axle yoke and the t-case yoke. I have a magentic angle pointer if I stick that on the t-case toke, the center dowel pointing down to the axle is 22 degrees.
So, is that divided by 2 because 2 joints will take it, or is really 22degrees?
 
Stick the angle finder on the T-case output and find the angle the output shaft is sitting at. Then stick the angle finder on the driveshaft. The difference between the two numbers is the angle in the joint.

EDIT: Oh wait...You don't have a driveshaft. Now I understand why there are so many unknowns. You can still do the same process. It sounds like you're using the angle finder like a protractor. That will only work if the T-case is sitting at 0 degrees.
 
I have a hard time believing that each joint would be at 22 degrees. Pulled up one of the side shots of your Blazer and held an angle finder up to the estimated location of the t-case output....22 degrees would have the driveshaft hitting the ground before reaching the rear axle.
 
I'll have to take some more detailed measurements when I get back in town.
I agree, no way I should be running that high.
 
Ok, finally took some final measurements with a proper angle finder.

I have the tcase pointed down at 4, shaft is 15degrees and 14b is point up at 3 (all relative to level ground).
So I have 11 degree operating angle on the tcase to shaft and 12 degree operating angle on the shaft to axle joint.

That seems a bit high to me, but I'd need 12 degree shims if I want to run a cv shaft, most I can find is 10. Is 12 too much to rotate the 14bolt up?
CV shaft or 2 joint shaft?
 
From what I understand, or what the driveshaft shop told me, 12* is about the maximum safe working u-joint angle. Not that they can't operate beyond that but they will break easier and wear out faster.

I'd try running the shaft with those angles, if you measured correctly they look good.

It's not bad to have the pinion 1* down either. Spring wrap under power will even that out.
 
I ran a typical 2 joint driveshaft on a blazer I had u joints operating at about 15 degrees, they wore out a touch faster but no vibes
 
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