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Front Driveshaft Length Issues V6

Discussion in 'Early CJ5 and CJ6 Tech' started by kenb, Oct 6, 2021.

  1. Oct 6, 2021
    kenb

    kenb Cleverly disguised as a responsible adult

    Detroit
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    I'm in the process of transplanting a 67ish V6 drivetrain into a M38A1 frame. The original frame of the Jeep was rotted beyond saving and I happened across a very clean A1 frame locally. I cut out the original motor mounts and welded in the V6 mounts. The old frame was a factory V6 model.
    I've checked several different ways and I'm confident the location of the mounts in the new frame match where they came out of the old one. I went with M38A1 style spring shackles since that seemed more straightforward than attempting to change spring hangers. The springs are the ones from the V6 frame.

    Yesterday I dropped the engine and transmission into the frame. Things seemed to line up well. However, I ran into an issue with the front driveshaft. It's nearly maxed out in length. If I raise the jeep up by lifting on the frame (full suspension travel), the driveshaft is maxed out in length and has no end play. Naturally compressing the springs is not an issue.
    Conversely the rear driveshaft is close to fully compressed when installed. I do need to check and see how much room that has before it's fully compressed.
    As the jeep sits the length of the front driveshaft is 23-3/4" and the rear is 18-3/4" between u joint centers.
    Here is a marginal quality photo showing what's in working with. IMG-20211006-WA0005.jpg
    Is this at all normal? Do I have a parts compatability issue? I should have taken a closer look at how this lined up before removing from the old frame.
     
  2. Oct 6, 2021
    jeepstar

    jeepstar Well-Known Member 2021 Sponsor 2020 Sponsor

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    ordering a new driveshaft is out of the question?
     
  3. Oct 6, 2021
    ITLKSEZ

    ITLKSEZ Hope for the best, prepare for the worst

    Post Falls, ID
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    Shackle reversal changes the natural swing of the front axle from rearward to forward as it drops, so when your driveshaft used to generally not move much under droop, because it was basically swinging around the transfer case, it is now swinging away from it. If you use a driveshaft with a standard amount of travel, you’ll have to make sure it’s comfortably in its travel zone throughout its travel.

    Climbing up a hill in 4wd will be the test. The front suspension will be unloaded, and as the front axle claws for traction, it will pull the axle even further away while pointing the pinion down toward the ground under power. I’ve been on countless trail rides where front driveshafts separate because of this.

    If you’re going to buy a new shaft, make sure you opt for a long enough spline to compensate for this, and for the plunge it will experience under heavy breaking and bumps.

    I have no personal experience with A1s; did their front driveshafts have longer splines than the 5s?
     
    FinoCJ and dnb5853 like this.
  4. Oct 7, 2021
    kenb

    kenb Cleverly disguised as a responsible adult

    Detroit
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    Thanks for the replies. I will probably need to source a longer driveshaft. Any suggestions on where to find one? This is something I've never shopped for. I had a spare CJ5 shaft from a 4F model lying around which is longer but the U joints are a different size.
     
  5. Oct 7, 2021
    Rick Whitson

    Rick Whitson Detroit Area 2021 Sponsor 2020 Sponsor

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    Ken, I have a set of 66 V 6 driveshafts from a donor Jeep if you want to try them, they are stock size, if that will help. The Donor jeep had only 27K on it.
     
  6. Oct 7, 2021
    kenb

    kenb Cleverly disguised as a responsible adult

    Detroit
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    Could you please extend the front shaft to max length and measure it? I've been checking center of u joint to center of u joint. That way I can see if it's longer than mine. Thanks!
     
  7. Oct 7, 2021
    jeepstar

    jeepstar Well-Known Member 2021 Sponsor 2020 Sponsor

    Sheboygan
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    tom woods driveshafts are great.
     
  8. Oct 7, 2021
    colojeepguy

    colojeepguy Colorado Springs

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    Just measure the length you need & take them to a drive line shop.
     
  9. Oct 7, 2021
    timgr

    timgr We stand on the shoulders of giants. 2021 Sponsor 2020 Sponsor

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    Just looking at this - I think you have two options (really three - you could abandon the project). Change the lengths of the driveshafts, or move the engine forward. If you had both chassis side-by-side, you could measure and see where the offset comes from. I suspect it's the combination of parts that just add up different; ie not attributable to one part.
     
  10. Oct 7, 2021
    jpflat2a

    jpflat2a what's that noise?

    Riverside CA
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    It's much more important to have the engine/trans positioned properly on the frame.
    Sounds like the engine mounts are already welded in place so move on from there.
    Driveshaft mods are normal for any type of conversion.
    Just get them lengthened or shortened as needed when everything else is positioned properly.
    Might be the last item to take care of.
     
    colojeepguy and Twin2 like this.
  11. Oct 7, 2021
    termin8ed

    termin8ed I didn't do it Staff Member

    Mason, MI
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    I've got a really nice V6 frame sitting in the woods:sneak:
     
  12. Oct 8, 2021
    Rick Whitson

    Rick Whitson Detroit Area 2021 Sponsor 2020 Sponsor

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    I will today Ken, Friday, and post it for you. Rick
     
  13. Oct 8, 2021
    colojeepguy

    colojeepguy Colorado Springs

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  14. Oct 8, 2021
    kenb

    kenb Cleverly disguised as a responsible adult

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    Thanks for all the replies. Yes, the motor mounts are welded in already. Side by side with the old frame they are in the same place as near as I can tell. I'm guessing it's the margin of error there plus the difference in spring hangar style that is causing the problem. I agree I probably should get the driveshaft work done last.

    You should have told me that 6 months ago!

    Thanks Rick
     
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  15. Oct 8, 2021
    jeepdaddy2000

    jeepdaddy2000 Member

    Eagle Point oregon
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    When I transplanted my drivetrain into an M38 frame, I wound up moving the engine forward. While this helped with the driveline issues (I also transplanted a T18) it also provided clearance for the upper bellhousing bolts. It did tighten up the fan clearance though.....

    Your options are to move the motor mounts or retube the drivelines. If you go with the latter, you can usually have the work done locally for a lot less than a specialty shop like Tom Woods.
     
    AKCJ likes this.
  16. Oct 8, 2021
    Rick Whitson

    Rick Whitson Detroit Area 2021 Sponsor 2020 Sponsor

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    My 1966 V 6 front drive shaft is 20 3/4" long closed up and 23" even opened up center to center. Hope this helps, Rick. Phone # 734 776 7659. You can have it if your need it.
     
    Last edited: Oct 8, 2021
  17. Oct 8, 2021
    duffer

    duffer Rodent Power

    Bozeman, MT
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    Depending on the style of axle spring perches, you could drill another set locating holes and move the axle back 1/2 to 3/4" that may solve the problem.
     
  18. Oct 8, 2021
    kenb

    kenb Cleverly disguised as a responsible adult

    Detroit
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    I appreciate the offer but it sounds like your driveshaft is shorter yet than mine.
     
  19. Oct 11, 2021
    Rick Whitson

    Rick Whitson Detroit Area 2021 Sponsor 2020 Sponsor

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    Ken, you do know that the V6 has a different grill and radiator that is shorter than an F134 don't you. The V6 is moved more forward more than the F134 and the transmission and transfer case sits back farther and the crossmember is moved back farther than the F134. That could be why you are having problems with your drive shafts. I gave my V 6 radiator to G I Joe, it is a complete V 6 grill with all the lights and radiator still in it. He will sell it to you I think if you want to go that way. Let me know, Joe lives in Rockwood.
     
  20. Oct 12, 2021
    Steve's 70-5

    Steve's 70-5 Active Member 2020 Sponsor

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    If you move the engine forward which will move the transfer case forward. What is that going to do to the rear drive shaft length?
     
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