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post #1 of (permalink) Old 12-02-2002, 07:38 PM
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OK, how short can my driveshaft be?

Well, after looking a my spreadsheet long and hard on what my CJ-5 project is going to cost and the time it is going to take, I think I am going to have to revise my plan.

THE PLAN was a 5.0 EFI/NP435/D300, axles to come later, probably outboarded D44s, but that is next year or so. Right now I am half down to the fram and I am finding all of the other stuff that needs doen on a '74 that I didn't look at when I came up with THE PLAN. I have the 435 and the 300, don't have the 5.0. Thinking I would like to drive this thing sometime soon.

So...., THE PLAN version 2.8: If I put the 435 and 300 in behind the 258 I save a bunch o' cash and time. But I just got back in from the garage, and my 435 with the adapter is going to come in at 15 inches, and whatever is in there now (T90, T14 I really don't know) is only 9 inches. That is 6 inches out of my rear drive shaft, and I am not too crazy with my driveline angle as it is. I have a CV joint somewhere out in the garage.

My question to anyone who has fought this driveline battle: If I put a CV joint at the 300 and roll my 44 up enought to get a driveline angle ~7 degrees, will that work OK? I have a 2.5 inch lift and run in the desert (rocks).

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post #2 of (permalink) Old 12-03-2002, 07:08 AM
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Re: OK, how short can my driveshaft be?

[img]images/graemlins/smirk.gif[/img] The minimum length of a driveline might be determined by how much angle has to be overcome, AND how much slip is needed. If both drive and driven yokes are perfectly in line and no slip is needed then the driveline, obviously can be all u-joint and no tube or slide yoke. Taking into consideration the amount of movement that a rear axle has to have, the driveline is going to have to have about 10" of straight tube at the least. [img]images/graemlins/tongue.gif[/img] [img]images/graemlins/smile.gif[/img] It's good that you are doing all this planning on paper and not by the cut-and-try method. [img]images/graemlins/tongue.gif[/img]
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post #3 of (permalink) Old 12-03-2002, 08:18 AM
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Re: OK, how short can my driveshaft be?

Yep, I did the old "let's try it and see what happens" methodology on the first CJ I redid. That didn't work really well. I think I am going to go back out and get some more measurements and break out an old geometry book, see what my actual drive line would look like. One of the thing I really liked about the original PLAN was that I could move the 5.0 way forward, it looked like I could have picked up at least 7 inches of rear driveline length. That woulda been nice.
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post #4 of (permalink) Old 12-03-2002, 10:07 AM
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Darn math

Well did some measuring. I hate it when the measurements don't tell me what I want to hear. [img]images/graemlins/mad.gif[/img]

Bottom line: right now I have a 19.75" driveline and 10" of vertical difference for a delightful 30 degree driveline angle. If I do the swap I will have a 14.9" driveline with a truely frightening 42 degree driveline angle. If I rotate the D44 up, I can take about 1.5 inches out of the vertical difference, getting a better angle at the rear end and reducing the angle at the T/C to about 32 degrees. CAn I get that much rotation with shims or am I going to need to move my spring perch? Can CV joints live at 30 degrees of driveline angle?

Man, every time I think I have an easy solution...........
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post #5 of (permalink) Old 12-03-2002, 12:34 PM
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Re: Darn math

Here's a little clip from tom wood's site on driveline geometry.
</font><blockquote><font class="small">In reply to:</font><hr />
Most drive shafts will, depending on components used, incur a binding interference at about 30 degrees. You DO NOT , I repeat DO NOT want to run a drive shaft at any where near this angle. you need to allow for axle droop, frame flexing and differential roll. All of which can momentarily alter the operating angle of the "U " joint to the point that it will cause what I refer to as an IMMEDIATE &amp; CATASTROPHIC FAILURE. Ultimately you need to be certain that your driveline will rotate freely under full axle droop

[/ QUOTE ]
I was just going over this with my tj. I ran with my pinion way too low for about 6 months before getting the control arms to correct my problem. Well, it ate the centering pin of the cv joint from binding. I replaced the center piece with the ball on it, and that has lasted me about a year. A couple weeks ago it got to vibrating REAL bad, so I pulled the shaft out and took it to inland truck parts, only to find it had wallered out the centering pin. $250 to fix or $269 for a new shaft, hmmm. So i bought the new shaft and an angle finder. Right now it's running with a 15-1/4" shaft at a 21 degree angle and is driving smoother than ever. But it looks to be about the max without the driveshaft starting to bind again. good luck.
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post #6 of (permalink) Old 12-04-2002, 03:37 AM
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Re: OK, how short can my driveshaft be?

My driveshaft is 10 5/16" long from u-joint to u-joint, i got it from TOM WOODS DRIVESHAFTS he make's them all the way down to 9 1/4". Of course it works great for me because i dropped everything down to compensate. i only have about 6 degrees driveshaft angle. And cost don't worry about cost you can always sell everything you own to get money for your project i stuck probably $15,000 in mine and it's still not done yet i don't even have a paint job yet. LOL
post #7 of (permalink) Old 12-04-2002, 01:42 PM
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Re: OK, how short can my driveshaft be?

10 5/16"?!? Wow. I just talked to them (Tom Woods), and it looks like this may work. If I rotate my rear axle up 25 degrees (pointing straight at the T/C), they can make a double carden drive shaft thatis 13 " long that should work just fine. Will have a 25 degree angle at the T/C but they say that should still work.

Cool, this project just got much easier and cheaper. [img]images/graemlins/cool.gif[/img]May even be able to drive it one day.

post #8 of (permalink) Old 12-06-2002, 02:15 AM
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Re: OK, how short can my driveshaft be?

The only downfall about the whole thing is that my driveshaft costed me $450 but my driveshaft is solid they said they took a solid piece of steel and machined it. No tube and it is heavy duty. all i have to worry about is braking u-joints.
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