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J10 Suspension Questions

Discussion in 'Jeep Truck and FC Tech' started by FinoCJ, Oct 23, 2021.

  1. Oct 23, 2021
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member 2021 Sponsor 2020 Sponsor

    Denver, CO
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    Helping a friend with a 1977 J10 (honcho), and doing some suspension work with installing a 3" lift springs. Got two basic questions:

    1) the rear leaf springs are SOA, and the centering pin is not in the center. It appears from some of the springs we've seen, that one end is about 5" longer than the other end when measured from the centering pin. It seems pretty evident from our test fitting that the long end of the spring goes to the rear, and the short end forward. This seems to place the axle in a good spot.....BUT, the aftermarket spring manufacturer has been very clear that the long end goes forward. I think the manufacturer is mistaken. Can any of you confirm? Maybe grab a measurement, or maybe someone has a FSM with diagram?

    2) Axle shims. The aftermarket springs came with axle shims for the rear pre-installed on the stack of leaves....As the manufacturer suggests installing the springs opposite of what we think is correct, that means the shims are backwards. The thick end of the shim would then be pointed forwards, and on a SOA, that would rotate the pinon down. So we can just spin the shim 180, and that is what my friend is doing, but those shims are 7 degree shims, and I think its actually going to rotate the pinon up too much (some of this comes from having just gone through a bunch of drivetrain positioning and planning on my 58 willys, with regard to parallel but offset, and 3 degree of engine tilt to the rear.) Additionally, my measurements indicate there is about a 7 degree difference built it between the spring pads and the pinon...in other words, if the spring pads were flat (which they are not when mounted), then the pinon would be up by 7 degrees. This built in difference allows for the spring pad to be down to the front a 4-5 degrees due to how the the spring is mounted higher in the rear at the shackle than at the front spring eye, but keep the pinon up at 3 degrees or so. Any j-truck owners out there with lift kits mind getting a picture or some measurement or any thoughts on rear axle shims?

    thanks....its a cool J10 honcho with a 401 for what its worth....
    [​IMG]
     
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  2. Oct 23, 2021
    ITLKSEZ

    ITLKSEZ Hope for the best, prepare for the worst

    Post Falls, ID
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    Does it specify that the instructions are for the rear suspension? Is it possible the instructions are for a front kit? From pics I can find online, both F/R springs are asymmetrical, and both longer sections are toward the ends of the vehicle. The 7° shims would fit the front better to keep the caster angle in check.

    Did it come with 4 springs? Most kits just have front springs and lift blocks for the rear.
     
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  3. Oct 23, 2021
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member 2021 Sponsor 2020 Sponsor

    Denver, CO
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    yes - all four springs getting replaced. The fronts are, of course, much shorter OAL - not sure if they are asymmetrical or not...they were installed when I got there and he didn't seem to be concerned about them. My quick look seemed like everything was good - and we did discuss at some point if he had checked the caster (he had not), but I didn't do anything with the front - it is a D44 open knuckle....

    I was initially wondering the same thing we he called me, but when I got there, he showed the shims came pre-installed on the springs and shipped from the manufacturer (rough country), and they are definitely on the rear springs (which are much longer overall than the fronts). But I guess its possible they should have come pre-installed on the front springs and not the rear? I'd have to investigate the instruction sheet a bit more which is not in front of me....I'll see if he can shoot me a pic of the instruction sheet/diagram - its well worth verifying which springs (front/rear) they show the shims going on. It was already late when I stopped by on my way home yesterday at 9pm, so I wasn't able to spend much time getting into the details.

    I didn't look at the front all that much, but from everything logical, the long end goes toward the bumper on the rear for sure....heck, even the old springs that came out had the long end toward the rear (We confirmed with some old pics he had). But with this arrangement, the shims turn the pinon downward, and there is just no situation where you would want to turn the pinon downward in this case (axle lower than the transmission output). I think that is what is causing him the most consternation - he was initially hesitant to change something that came assembled...

    Of course he called the manufacturer (twice) and according to him (I was not present for the conversations) both times they have confirmed the springs go long end forward on the rear which places the fat end of the shim rearwards and tips the pinon up - so it hasn't been very helpful. He has been checking reviews and I think was trying to get on the IFSJA forum as well....I showed him how to c-clamp the spring pack, loosen the center pin a bit and spin the shim around or potentially remove it entirely. So he was going to try mounting them with the shim spun around...but I am still not convinced he really needs the shim on the rear at all, and maybe they really should go on the front to help with caster....
     
  4. Oct 23, 2021
    dnb5853

    dnb5853 Member 2021 Sponsor

    Grand Mesa, CO
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  5. Oct 23, 2021
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member 2021 Sponsor 2020 Sponsor

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    We all know things don't always work out exactly how they are advertised, but yes, according to RC, the 3" kit should require no modification to any other parts. If you go to the 4" or more kit, you have to start messing with some additional issues. They call it a 3" lift, but its not that much from what I can tell...its more about replacing worn out and damaged springs with new and getting a bit more clearance....The original post in the thread you post is kind of the same issue we are dealing with...sounds like they had issue with the shims as well, but its hard to know exactly what they are referring to as the pics don't come through.
     
  6. Oct 23, 2021
    iharding

    iharding Quitter

    Tacoma, WA
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    It might be right? If the axle attached on the "uphill" part of the spring (it is closer to the front than the bottom of the "U") maybe it needs downward pinion angle adjustment? Might want to put it together and see.
     
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  7. Oct 23, 2021
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member 2021 Sponsor 2020 Sponsor

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    I'd should have taken some pics - the geometry of the spring is hard to describe - a picture would show this easier. But no matter which way the spring is mounted, the spring pad is behind the bottom of the arch...with it in the forward position (short end forward), the spring pad is closer to the bottom of the arch and will only be tipped down to the front a few degrees....with it mounted in the rearward position, the spring pad is tipped down to the front even more - about 7 degrees or so. In either case, using the shim as the instructions describe, it just pushes the spring pad even further down to the front.
     
  8. Oct 23, 2021
    Fireball

    Fireball Well-Known Member 2021 Sponsor 2020 Sponsor

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    At some level, none of this "bolt-on" stuff fits right. You need to mount the springs so the wheel is centered in the wheelwell and then figure out what degree and what direction of shims you need if any. The ones included may work or they may not.
     
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  9. Oct 23, 2021
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member 2021 Sponsor 2020 Sponsor

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    I agree...the owner isn't, or maybe wasn't, as comfortable with that idea as I was initially...and honestly, if you were in his inexperienced shoes, would you believe me or rough country, heck even with experience he wouldn't believe RC nor me :D
    Anyway, from what I gather, I think he's moving in the same direction. He spun the shims around and this morning and is mounting the springs the way we think they should go (long end towards the bumper) with the shims to oriented to tip the pinon up. I suggested before its all tightened up, we should investigate the pinon angle and make sure its not too high - I may have just volunteered myself to go over and help out. But I also think he should look into the front axle caster just to make sure it isn't a problem. He's a lot like me in that he has limited tools and space (single car garage) and works solo, learning the hard way. Those damn leaf spring packs are like 75lbs apiece, and moving around that big D44 on an small tippy floor jack is sketchy enough...he can really use an extra set of hands. I am on house winterizing duties between trying to get the brake system on the 58 back up and working - but maybe late today I can get over there. FWIW - he's 25 and kind of taken to this old jeep so that is cool, and the 401 J10 is definitely cool.
     
  10. Oct 23, 2021
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member 2021 Sponsor 2020 Sponsor

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    I think we are getting there....With the leafs long end toward the bumper, and the shims to the rear (tipping the pinon up)...here is the position of the rear axle. The axle is perfectly placed in the wheel well and the stance is great - so there is no changing which end of the spring goes to rear. But I think the pinon is too high...From this pic, it actually looks like its pointed upward more than the driveshaft is. If we remove the shims, the pinon will drop down 7 degrees, which I think is going to be about right. If the shims are spun 180 degrees, the pinon will rotate down about 14 from pictured, and it actually begins to point downward, below horizontal.
    [​IMG]
     
  11. Oct 23, 2021
    dnb5853

    dnb5853 Member 2021 Sponsor

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    The differential pinion shaft should be parallel to the transfer case output shaft (assuming a standard U-joint on both ends; no CV joint). This arrangement keeps the U-joints rotating at the same speed (angular velocity).
    The overall driveshaft angle should be moot if both pinion and output shafts are parallel.
     
    Last edited: Oct 23, 2021
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  12. Oct 23, 2021
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member 2021 Sponsor 2020 Sponsor

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    Agreed - parallel but offset as mentioned above...Since we can't see the transmission output in the above picture, but we can infer that with an axle that is lower than the transmission, that the angle of the driveshaft with respect to horizontal has to be greater than the the pinon angle....thus the pinon needs to go down...
     
  13. Oct 23, 2021
    dnb5853

    dnb5853 Member 2021 Sponsor

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    Sorry, I thought you were there assisting with the install and could see the transmission/transfer case output.
    Since the J trucks are low slung, I thought the output shaft may be on the low side especially if it's Quadratrac.
     
  14. Oct 23, 2021
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member 2021 Sponsor 2020 Sponsor

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    No, not in person there today - maybe tonight. But I also have seen the basics of the truck geometry in person, so that helps. FWIW, the output is a quadratrac, and the angle is probably only 2-3 degrees (stock configuration), so the pinon would need to be about that as well...its higher than that in the picture in my opinion. I probably should have said it this way:
    I think we can infer that with an axle that is significantly lower than the transmission (it has been lifted a bit as well), that the angle of the driveshaft with respect to horizontal is probably greater than the the pinon angle....thus the pinon probably needs to go down...
     
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  15. Oct 23, 2021
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member 2021 Sponsor 2020 Sponsor

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    He couldn't get a decent picture that allows comparison of the pinon to the trans output, but he said the pinon is up for sure. Additionally, he ran into an issue where the shim has rotated the axle to the point that the body of the shock hits the axle housing (or something) and it won't go on the shock mount, or the shock has to flip upside down...lots of fun as always....he's pulling it apart and will go sans shims....With the shims one way, the pinon was just slightly down, with the shims the other way, it is too high...so hopefully this hits the sweet spot and maybe allows for the shocks to work as well....
    I still think there is some chance the shims are for the front axle to help with caster...so I asked about the directions just to investigate further and see what I thought of them....they are no longer around apparently. Ha...
     
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  16. Oct 23, 2021
    Fireball

    Fireball Well-Known Member 2021 Sponsor 2020 Sponsor

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    Also note a lot of street cars have the pinion gear a degree or so down from the ideal angle so the joint angles are ideal when the axle wraps a little under load.

    Not saying you need to target that, just saying if you are a degree or two too low, it's fine. A degree or two high is less ideal.
     
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  17. Oct 24, 2021
    timgr

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

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    With a conventional driveshaft, the driveshaft angle should split the difference between the transfer case and the axle.

    upload_2021-10-24_13-5-4.png

    This is copied from the Tom Woods tech article about driveshaft geometry. Driveline Geometry 101

    JMO - get your magnetic protractor on there and measure the angles. The magnetic angle finder they sell for saw blades works well. Very handy. https://www.amazon.com/Digital-Angl...linometer/dp/B07GH7Y5ZM/ref=asc_df_B07GH7Y5ZM I have one like this, and I also have the old needle type.

    Looks like you are past the long-short spring question. I own a '77 J10 if I can help with pics or something. Warning - it's a rusty beater.
     
    Last edited: Oct 24, 2021
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  18. Oct 24, 2021
    timgr

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

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    No gas tank skid plate. That's another one. My truck is missing a skid plate too. Being a CJ owner from way back, it always puzzled my why anyone would not get the $50 (?) skid plate option. I guess truck buyers imagine different service for their Jeeps than CJ buyers. My J10 buyer used the truck to service bee hives.
     
  19. Oct 24, 2021
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member 2021 Sponsor 2020 Sponsor

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    I prefer avalanche snow slope indicators...or geologists brunton compasses with dip inclinometers...must be my heritage...:D
    [​IMG]

    Sounds good will let you know...from the last I heard, the leafs were going back on with no shims at all, and things were looking good. I requested a pic of the finished geometry, but haven't heard back. I was hoping to stop by last night to see it in person, but didn't happen....maybe tonight or Monday after its all back together for the third time.
     
  20. Oct 24, 2021
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member 2021 Sponsor 2020 Sponsor

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    agreed....I haven't even begun looking, but I'd like to figure out a gas tank skid for the 58 wagon...
     
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