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Unread 11-30-2012, 01:01 AM   #1
82JeepCJ7
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DIY Double Cardan rear drive line for CJ

Ever since I got my CJ7 back on the road, I have been dealing with driveline vibrations. I clocked my T-case flat and raised the transmission and transfer case up so I could run a flat belly pan. This put the rear driveline at a even steeper angle.



The solution is to use a rear drive-line with a double cardan joint at the upper end. Some people label them a CV joint, but that is incorrect.

I began my search for a suitable drive-line to cut down. The first driveline I tried was from a 1989 Chevy 3/4 ton truck. The 3R Double Cardan joint uses 1350 U-joints which are strong, but the design did not offer much angular use for wheeling. So, I scrapped that idea.
Next I found a front driveline from a Jeep Cherokee. In stock form, they have a double cardan joint. A serious plus is the front output yoke on the NP231 also has the same 26 splines as the Dana 300. I was able to pick up a good used driveline and yoke for $40.



The first thing I needed to do was replace the rear output yoke. The nut was spun off the output shaft with a 1-1/8" socket on an impact gun. The nut came right off. The yoke actually slipped right off with no tools. The NP231 yoke slipped right into place. I had to seat the yoke with a chunk of 2x4 and a hammer tapping it. Once it was seated. I placed the washer and nut back on the shaft and torqued it down to 120 ft lbs.





Once the yoke was in place, I took a measurement from the rear end yoke to the center of the transfercase yoke. I came up with a running length of 23¾".

Next I measured the slip yoke on the Cherokee driveline and it was 3" total. I centered up the slip yoke, and took a measurement from center to center on the U-joints for a running length. That came out to 32¼". I subtracted the 23¾ running length from that to get 8½" I needed to shorten the shaft. The yokes were marked with a couple of punches on each end so they could be phased correctly later.

I measured back from the weld on the slip yoke 8½" and made my cut mark.


I then put the driveline in the cut off saw.


After the driveline was cut, the inside was cleaned up with a flapper wheel on a die grinder.

The cut off piece of tube with the slip yoke was clamped in a vice. The weld was ground down flush.


A die grinder with a cut off wheel was used to cut the weld down to the yoke.

The two pieces were separated.


The end was dressed up with a flapper drum in a die grinder.

The slip yoke end was pressed into the main tube making sure the phase the yokes correctly using the marks made before. I place a level on each of the yokes to ensure they are correctly phased.


I also check to make sure the ends are parallel. I measured this 4 different ways to make sure the shaft is strait. The correct way would be to chuck the driveline up in a lathe and check the run out with a dial indicator. Since I do not have a lathe, I did the next best thing and measured to ensure it was strait. Tack welds were made in 4 equal spaced places. The shaft was checked again to make sure it is strait.
Welds were made in 4 passes, 1/4 at a time.



At this point, the shaft was done. It was hung up and prepped for paint.


And painted.


After the paint dried, the driveline was bolted into place.




A test drive was conducted to see how the new driveline compared to the old driveline. The results are incredible. No more vibrations starting in 3rd gear and getting even worse in 4th gear to the point I was unable to go over 40mph. Now the Jeep drives smoother than most trucks I have driven.

The driveline will be removed and taken to a drive shaft shop to ensure it is strait and balanced. New U-joints will also be installed at that time.

Overall, the result was better than expected. I have about $45 invested. Being able to weld helps out a lot, but this is a project that is worth the effort.


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Unread 11-30-2012, 06:56 AM   #2
gojeepin
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Quote:
Originally Posted by 82JeepCJ7 View Post
[B]... The solution is to use a rear drive-line with a double cardan joint at the upper end. Some people label them a CV joint, but that is incorrect...
A double cardan joint IS a CV joint but unlike the "captured ball" CV joint the center module of the double cardan phase shifts twice per revolution. The result however, is still constant velocity in and out. I cover that in greater detail in the article in my signature block.

Quote:
Originally Posted by 82JeepCJ7 View Post
... I also check to make sure the ends are parallel. I measured this 4 different ways to make sure the shaft is strait. The correct way would be to chuck the driveline up in a lathe and check the run out with a dial indicator. Since I do not have a lathe, I did the next best thing and measured to ensure it was strait. Tack welds were made in 4 equal spaced places. The shaft was checked again to make sure it is strait.
...
All in all, the way you did it method gets you in the ballpark and will work just fine offroad.

Quote:
Originally Posted by 82JeepCJ7 View Post
... The driveline will be removed and taken to a drive shaft shop to ensure it is strait and balanced. New U-joints will also be installed at that time.

Overall, the result was better than expected. I have about $45 invested. Being able to weld helps out a lot, but this is a project that is worth the effort.
I think you're wise to have a driveshaft shop take care of any other issues it may have (e.g. balance) before driving it on the road much.
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Vibration? Bump steer? Wandering? Read: Steering, suspension, and driveline basics. An article on how it works and where to look for problems.

83 CJ7, 4.1L 6cyl (4.0L bored .030" over), 35" tires, T-5 transmission, Dana 300 TC, Trussed AMC 20.
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Unread 11-30-2012, 06:59 AM   #3
82JeepCJ7
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Measurement of the slip yoke alignment was accomplished mainly with the use a parallel blocks (1-2-3) and a strait edge and dial calipers. Talk about tough holding 3 things at once. There was no way I could hold the camera and do this as well. Not enough hands. LOL
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Unread 12-03-2012, 09:40 AM   #4
lsukevinc
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what year cherokee did the drive shaft come from?
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Unread 12-03-2012, 12:48 PM   #5
Noplainsdrifter
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I built 2 drivelines very simalar to the way you described but I used a magnetic mount dial indicator and trued it up that way with great results.
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Unread 12-03-2012, 01:47 PM   #6
82JeepCJ7
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The driveline was from a 1996 automatic. I am going to take it off and to a driveline shop to check it for strait and balance it.
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Unread 12-03-2012, 03:05 PM   #7
CSP
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Any '91-01 Ford Explorer front driveshaft is another good donor. I worked at a hot rod shop in college that also was the local driveshaft shop. We built shafts from tiny cars to mining dumptrucks/loaders. We never balanced driveshafts. We did get the runout to be less than 0.005" though, which took care of any balancing issues.

'82 I thought you had converted your D300 to a flange type output. I remember that from another thread.
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Unread 12-03-2012, 06:02 PM   #8
cj7ole
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One thing I note from the Tom Woods website is that with a setup like yours, you may need need to add wedges to tip the rear axle so the pinion points straight up the driveshaft (minimal joint deflection at differential).

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Unread 12-03-2012, 08:32 PM   #9
82JeepCJ7
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I went away from the flange and use a NP231 yoke. My rear spring perches were welded on with the rear yoke pointing at the t-case output.
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Unread 12-09-2012, 10:19 PM   #10
Alex77cj7
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Anyone know if I would be able to just take one of my old h-yokes and mount it on my driveshaft to use as a FCC driveshaft?? I have an h-yoke from my old bronco I would use the whole shaft but its locked up.. Only good part is the h-yoke. I believe it's the right size for the stock u-joints..
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Unread 12-11-2012, 07:56 AM   #11
CSP
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I'm not familiar with any yoke that's referred to as an H-yoke. I'm guessing that any yoke from a Bronco probably doesn't have the same diameter and spline count as a CJ transfer case.

What's an FCC driveshaft?
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Unread 12-11-2012, 08:01 AM   #12
Alex77cj7
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Quote:
Originally Posted by CSP
I'm not familiar with any yoke that's referred to as an H-yoke. I'm guessing that any yoke from a Bronco probably doesn't have the same diameter and spline count as a CJ transfer case.

What's an FCC driveshaft?
Meant dc.. I posted a pic of one
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Unread 12-11-2012, 10:14 AM   #13
Noplainsdrifter
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I used the front yoke and CV drivseshaft from a early Bronco to make mine. Bronco's have a D20 and 10 spine output shaft.
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Unread 12-11-2012, 07:54 PM   #14
82JeepCJ7
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Yup, they are 10 spline.
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Unread 12-12-2012, 07:37 AM   #15
CSP
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Not every CJ is 10 spline though. The early Dana 20s were and that's it. Later D20s and D300s are 26 spline.
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