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Rear pinion angle

Discussion in '80-Series Tech' started by -Spike-, Aug 13, 2006.

  1. -Spike-

    -Spike-

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    Just returned from a great wheeling run. Unfortunately, I took some damage. Both rear lower control arms are slightly bent, and my rear driveshaft is dented and bent, causing some vibration. Fixing the control arms has been covered extensively and I've got a handle on that. My question for the board, and hopefully Christo, is rear pinion angle options- specifically, is it possible and adviseable to rotate the rear pinion up?

    I have the Slee 6" lift, with adjustable rear upper control arms. When I installed the arms, I positioned the rear pinion to be parallel to the output shaft of the t-case (essentially horizontal), therefore achieving equal angles at both u-joints. I thought at the time I might be better off pointing the pinion upwards, maintaining equal but opposite angles on the u-joints. This would push the driveshaft up several inches at the rear axle, for more clearance. Without enough information about it, I chose to go the traditional route and worry about it later- that time has come.

    My concern is that the pinion may not get oiled properly, and that there may be some other issue that I'm overlooking. Christo, is this a regular practice at your shop? If not, on your truck?

    I did search, there's a wealth of information but weeding through all the front pinion problems to find a post on the rear is impossible, and the search didn't find the specific phrase 'rear pinion angle' so if this has been covered please forgive me and point me there.

    -Spike
     
  2. LandCruiserPhil

    LandCruiserPhil Peter Pan Syndrome Supporting Vendor

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    I run a DC rear shaft pointing at the transfercase. Also you may need to shorten the lower control arm to get the tires to stuff after rotating the pinion up.
     
  3. Grench

    Grench SILVER Star

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    How about a picture of what bent it?
     
  4. -Spike-

    -Spike-

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    You want a picture... of a rock?

    -Spike
     
  5. Grench

    Grench SILVER Star

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    With an 80 slammed into it? Sure. It would give me an idea of what kind of line to avoid so I don't do this to my truck. Was it a shelf or a boulder field that resulted in the bends? To get all 3 at once, I'm guessing a shelf. Were you going up or down?

    More my curiosity than anything.
     
  6. Nay

    Nay

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    You want to do a DC shaft and rotate the pinion up. Rule of thumb that I am aware of is 11-12 degrees of pinion angle will be fine as far as oiling goes. Given the length of the rear driveshaft, I think you'd be within tolerance. I don't know if the rear diff has any special oiling ports/mechanisms that would alleviate any concerns independent of angles.

    I'm actually suprised you are still running the stock driveshaft.

    Nay
     
  7. -Spike-

    -Spike-

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    http://datsun510.arizonagt.org/k5/pyeattaug06/P5150437.jpg

    http://datsun510.arizonagt.org/k5/pyeattaug06/P5150436.jpg


    The shelf, as you correctly guessed, had a particularly high point in the middle that grabbed my DS. The bent arms might or might not have happened at that shelf, but there were many other opportunities on that run to hit them.

    http://datsun510.arizonagt.org/k5/pyeattaug06/ has pics of the run.

    I hadn't heard of too many problems running Slee's 6" lift with the stock driveshaft, so I didn't bother changing it. No vibrations or other issues for me, until now. I figure if rotating the pinion up using a stock driveshaft with equal angles will work, it will take the driveshaft higher than a DC shaft would.

    -Spike
     
  8. sleeoffroad

    sleeoffroad Supporting Vendor

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    Bottom line is we typically run it with a stock shaft and make the angles parrallel. Depending on amount of lift etc etc, sometimes this does not work, and we go the other route and install a CV and point the pinion at the transfercase.
     
  9. Tools R Us

    Tools R Us

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    Rotating to the CV pinion angle is well proven. I would be concerned about the front pinion bearing oiling if it was rotated for broken back configuration with the stock type shaft. Maybe the oil storage ring and oil slinger from the front could be added to the rear pinion increasing the oiling?

    Nice pix, looks like more mud than when we were there, did you do the last step?:cheers:
     
  10. -Spike-

    -Spike-

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    Thanks for the help guys. Hmmm, oil slinger...

    Did not do the last step as I was late for my date to meet my wife in Payson. Brought her back to the camp site to spend Saturday night in the pines. I did run about half of Upper, which is where the damage occured. There is an, um, 'bypass' to get out of the creekbed before you hit the last obstacle.

    DBax did attempt it in his yellow 'X'. I have even more respect for him now, or is it fear? He beats that poor vehicle to a degree I have never before witnessed. Do not ever challenge him to a game of follow the leader, no matter what you might be driving- he will NOT quit just because it doesn't look possible, he has to prove it. Often, he makes it possible through sheer will or something.

    -Spike
     
  11. Nay

    Nay

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    Nice pics :cheers:

    I think those pics speak for themselves - everything you can do to increase clearance has value, and if you need a new driveshaft then consider it a trail mod and go double cardan (CV). The stock shaft will make a nice trail spare.

    Nay
     
  12. Tapage

    Tapage Club 4X4 Panamá SILVER Star

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    I'm always worried about my pinion bearing .. so at this point I try to overoil it ( teh entire axle ) in a hill or something like that to try put more oil inside to compensate the pinion angle ..
     
  13. Grench

    Grench SILVER Star

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    Thank you for the pictures! The arms & shaft wind up being abused on a shelf like that. I wonder what it would take to design something to take some of the abuse from them without hurting the breakover angle.

    Any old school skate boarders out there? I'm thinking something akin to a 'bird'. I.e. a set of static ramps runing about parallel to the arms. I can't think of anything to connect them to though since they'd be between the frame and the DS. Maybe I'll lay under the truck for a bit and think.

    There is something about that suspension triangle on the rear end where the arms & shaft sit just down & out of the protection of the frame & sliders. It makes me want to bolt something in there.
     
  14. Tools R Us

    Tools R Us

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    The arm and driveshaft angles are dynamic, change with flex. So the only way to effectively protect them is to make them their own skids. Make the arms out of stronger tube and retube the driveshaft with thicker tube so that they can support the truck's weight without damage.
     
  15. -Spike-

    -Spike-

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    No problem with the arms. No problem with the tube. I envision problems when the truck weight is supported on the driveshaft, in the u-joints , yoke, and pinion/t-case bearings. Having the yoke or u-joints spinning against immoveable rocks concerns me. I may do a combo, making new arms from .250 wall DOM, re-tubing my bent driveshaft with .125 or .250 tube, and rotating my pinion. I have a spare front 3rd member, so I might try to fit the parts you mentioned above to better oil the pinion bearings. I've never seen them, so I will have to investigate further to better understand what I'll need to do.

    The rear arms and driveshaft have always been my biggest worry when crawling over rocks (well, my cat too, but a local muffler shop is confident they can remedy that, so I'm waiting for an excuse) so I'm kind of excited to get this taken care of. What's that saying, 'NO FEAR'? :D

    -Spike
     
  16. Grench

    Grench SILVER Star

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    Right. However, when are they most likely to be damaged? When the droop, there is less weight on that corner, so I'm less worried then. It is when they're getting compressed (taking weight) that I'm concerned.

    Picture a steel triangle with the same dimensions as the triangle made between the arms and the frame when the vehicle is at rest. Mount it just inside the frame right next to the arm. In this vision it ends just before the axle so there is nothing it can interfere with.

    When the arm is compressed by an obstacle, the odds are pretty good the obstacle is going to hit our steel ramp as well. It will likely mean that the tire on that end will loose some traction, but if the arm is sitting on a ledge, the tire isn't going to have much traction anyway.

    It would save the arms & shaft in many cases not by preventing the arms from contacting, but offloading the weight from them when they do.

    So, where is the hole in this idea? If there wasn't a big flaw, someone would have done it by now.
     
  17. -Spike-

    -Spike-

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    The flaw I see is that the arms themselves can be made to take the weight of the truck. Why add more stuff? Then the only soft spot is the driveshaft. A DC driveshaft or broken back setup will tuck the driveshaft up higher. The only time the driveshaft can get hit is when you roll over (or shift sideways and drop onto, as I did) a rock that fits between your lower arms. You'd have to have a skid under the driveshaft to prevent that, and I don't see that happening easily.

    -Spike
     
  18. sleeoffroad

    sleeoffroad Supporting Vendor

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    Moving a 6k lb tuck with one part stuck on a metal triangle is not going to work. Re-inforce the arms or buy upgraded ones. I have never lost a 120 wall rear driveshaft. I have bent some arms.
     
  19. Nay

    Nay

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    Another point, and maybe this is obvious, is that what it really being exposed here is not the arms or the driveshaft but the tire size.

    While you went to the taller lift, ultimately the 35's are the limiting factor. A DC shaft will help for sure, but what you see is that tire size is more important than pure extra lift. You already have the Slee 6" lift, it may be time for those 37's.

    Only bigger tires are going to make those arms and driveshaft feel shorter in the big rocks and big ledges.

    Nay
     
  20. -Spike-

    -Spike-

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    Yes, 37's are in my future, but any little bit helps. The tires are a $1000+ upgrade for one inch of clearance, the DC shaft is $450ish, the beefy lower arms are steel cost plus bushings, the pinion adjust is free with the stock shaft if it works and may gain me 3-4" of driveshaft clearance. It's also been my experience that bigger tires just means bigger obstacles, not less breakage. I feel the need to optimize everything, and hopefully spend less time/money fixing stuff I already visited.

    Thank goodness the truck is limited to 37's, or I'd be in trouble. It is limited, right? Never mind, I don't want to hear the answer to that.

    -Spike
     
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