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Thread: Pinion angle when using m105 springs and zero degree perches. Should I use shims?

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    4 Star General tobyS's Avatar
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    Thanks Shannon for taking those photo's. It's difficult to see the driveshaft angle in relation to the angle of the pinion, but it appears to point about straight to the output of the TC, somewhat up hill. Picture 3 makes it look like it could angle up 10 degree.

    When I search pinon angle, most of the threads are concerning axle wrap, especially when using the large tires. That is understandable, because they increase the torque on the axle a lot. The solutions were mostly a torsion issue and I didn't see any discussion of the pinion angles, except as it relates to axle torque (wrap) making it worse.

    My friend with a machine shop builds funny cars...ha, ha,...and we talked about the pinion angles. His recommendation was to keep them as parallel as possible.

    That large lift you have would seem to have a huge twisting effect (long lever) on the spring aka wrap. Have you ever had any "wrap" issues....you seem to say no but it sounds like your use is on road mostly. Several threads turn into builds of torsion bars with those high lifts.

    I went with plating my frame (with L 11" x 3" x10') and getting 3" of height there, so don't need near the height that you have under the spring. The torque will not have as much leverage on my spring like the large lifts do. I have 2 3/4" high perch (axle housing to bottom of spring).

    I'll use the 9" height I measure the spring bottom to the frame to calculate the axle to frame dimensions. I have 3" + 2 3/4" + 9" = 14 3/4". My front is 12" so I have 2 3/4" higher at the rear than the front. Is that too much??..now's my time to reduce the perch height if it is. Wheelbase is 165".

    Shannon, will you measure the front axle to frame and back axle to frame on yours? Does your truck sit higher in the back than the front and would you change that if you were at my stage?
    Last edited by tobyS; 03-02-2019 at 19:38.

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    I was told by several driveshaft places to never exceed 3 degrees for cruising and high RPM uses.

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    tobyS (03-12-2019)

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    That sounds reasonable letssled. I moved my project to this thread;

    https://www.steelsoldiers.com/showth...ng-and-air-bag

    Check out post number 8. I calculated the pinion angle using no or parallel blocks for the perch with the 105 springs and come up with 4.17 degree, so the angle is not as bad as I had originally thought (6-10). With my 2.8 degree blocks, that makes my pinion angle under 1.5 degree, which I'm very happy with.
    M35A3 4x4 "Money Pit"
    M929A2
    (14) 5 tons bought and sold

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    Hey Toby, whats your transfer case output angle? Letssleds guy was most likely talking about no more than 3 degrees deviation from end to end of shaft. In other words, you want your transfer case shaft and pinion as parallel as possible, at ride height.
    M925A2

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    Thanks Jbulach. The transfer case seems level with the frame for both front and rear outputs. I don't think it is tilted back...that's not mentioned in what I read that I can recall (I'll do some searching). Yea, it would be relative to the angle of the TC.

    If you have info that it is tilted let me know, not that there is much I could do at this point.

    I must have been fairly accurate on the estimates for my spring angle, ending at about 1.4 degree in relation to the frame, it has a visual but low angle up with the weight of the truck on the springs. I'm very happy with the angle and think it was worth putting the 2.8 degree block in

    Rear of truck on springs, no payload, is 2" higher than the front. That may leave room to rebuild the front springs and come up an inch....will have to see it on level ground and consider some new front weight. Front rebuild will include an 809 series hood, getting the fan back from the radiator, frame and plow connects..... so will need stronger front springs on phase 14 of this project, 13 is putting air lock diff in the rear while 15 will have to be the powered 105 trailer. "Money Pit" is living up to it's (don't know sex yet) name.
    M35A3 4x4 "Money Pit"
    M929A2
    (14) 5 tons bought and sold

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    Jbulach (04-15-2019)

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    Quote Originally Posted by tobyS View Post


    Front rebuild will include an 809 series hood, getting the fan back from the radiator, frame and plow connects..... so will need stronger front springs on phase 14 of this project, 13 is putting air lock diff in the rear while 15 will have to be the powered 105 trailer. "Money Pit" is living up to it's (don't know sex yet) name.

    This is as good a thing to spend your money on as anything else is. Plus it keeps you out of the bars and pool halls ! Or worse, those Indian reservation Casino's !

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