Axle swap

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Phils67
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Axle swap

Post by Phils67 »

Has anyone here swapped a J20 front axle into an early FSJ without changing the post style front leaf springs? If i am measuring correctly the cast spring perch on the main housing will interfere with the u-bolt when i weld the new perches on. The diff i am building is a 78 front passenger drop that was originally SUA and im going SOA. Just seems like ill have to offset the perch a half inch for u-bolt clearance and i dont want any issues when i go to install it. Feedback is appreciated
1967 Gladiator J2000, 1998 4.0L OBD2, T18, D20 twin sticks, D44HD/D60, Detroit lockers, 3.73s, 4wheel disc brake, FSSR, Dakota digital, etc.
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66stepside
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Re: Axle swap

Post by 66stepside »

Phils67 wrote:Has anyone here swapped a J20 front axle into an early FSJ without changing the post style front leaf springs? If i am measuring correctly the cast spring perch on the main housing will interfere with the u-bolt when i weld the new perches on. The diff i am building is a 78 front passenger drop that was originally SUA and im going SOA. Just seems like ill have to offset the perch a half inch for u-bolt clearance and i dont want any issues when i go to install it. Feedback is appreciated
I swapped in J20 axles on my 66, but it was necessary to relocate the front springs.
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66stepside
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Re: Axle swap

Post by 66stepside »

Phils67 wrote:Has anyone here swapped a J20 front axle into an early FSJ without changing the post style front leaf springs? If i am measuring correctly the cast spring perch on the main housing will interfere with the u-bolt when i weld the new perches on. The diff i am building is a 78 front passenger drop that was originally SUA and im going SOA. Just seems like ill have to offset the perch a half inch for u-bolt clearance and i dont want any issues when i go to install it. Feedback is appreciated
I swapped in J20 axles on my 66, but it was necessary to relocate the front springs.
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Phils67
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Re: Axle swap

Post by Phils67 »

Did you go sua or soa? What were the reasons you found it necessary to change the spring mounting, same reasons im thinking?
1967 Gladiator J2000, 1998 4.0L OBD2, T18, D20 twin sticks, D44HD/D60, Detroit lockers, 3.73s, 4wheel disc brake, FSSR, Dakota digital, etc.
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66stepside
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Re: Axle swap

Post by 66stepside »

Phils67 wrote:Did you go sua or soa? What were the reasons you found it necessary to change the spring mounting, same reasons im thinking?

I went spring under. It was less risky to relocate the springs than mod the axle to fit.

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I joke around and say if I had a do over button, I would of bought a newer j truck and just did the rhino conversion on it to make it look older! Haha. But, it’s a hobby, so what can ya do but build them the way you want?
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Phils67
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Re: Axle swap

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I really don't want to move the springs. I ordered perches already so i'll have to mock things up before i weld them on to see how it all lines up. I guess only time will tell. Trial and error. I will update as it goes. And yeah, sometimes i wish i had the newer chassis. Ive looked at some before and opted to just build what i have. Mine was still in saveable condition
1967 Gladiator J2000, 1998 4.0L OBD2, T18, D20 twin sticks, D44HD/D60, Detroit lockers, 3.73s, 4wheel disc brake, FSSR, Dakota digital, etc.
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66stepside
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Re: Axle swap

Post by 66stepside »

Phils67 wrote:I really don't want to move the springs. I ordered perches already so i'll have to mock things up before i weld them on to see how it all lines up. I guess only time will tell. Trial and error. I will update as it goes. And yeah, sometimes i wish i had the newer chassis. Ive looked at some before and opted to just build what i have. Mine was still in saveable condition

Ya gotta do what ya gotta do.
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Kaiserman
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Re: Axle swap

Post by Kaiserman »

When I swapped a Dodge Dana 60 under the front of my 71 the outside edge of the spring perch (cast into the diff) on the passangers side landed right about in the middle of where my new spring perch needed to be. I ground the diff down just a little bit and modified a new spring perch to fit over it, then welded it to the diff and tube. Haven't had a problem in about 10 years. J20 should be similar I would think.

I prefer post mount front springs and will never move them on anything.
1971 J2500 Gladiator Custom-Cab Platform Stake on 126" wb. B350/T18A/D20 D60/D60-3 w/locker 4.10's Ramsey 8klb PTO winch, Day-brook dump. 225/95R16's
1969 J3800 Gladiator 3407Z Camper Truck. B350/T18A/D20 D44/D60-3 w/4.10's
1968 Wagoneer Custom 327/TH400 Mostly Stock
1987 Cherokee Laredo 2-Door 4.0L/AW4 4" lift OEM swing out tire carrier and brushguard
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Phils67
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Re: Axle swap

Post by Phils67 »

The J20 front also had the cast spring perch. If my measurements are correct it puts the perch on top with a tight fit to the step down on the casting. I played afpubd with it a bit and found if i fill the 3/8 gap on the bottom side i csn use a 3.5" 9/16 u bolt on the inner side and it will be good and secure, and use a 3" u bolt on the outer side. I'll just have to make a custom spring plate to secure them to. This may work out ok
1967 Gladiator J2000, 1998 4.0L OBD2, T18, D20 twin sticks, D44HD/D60, Detroit lockers, 3.73s, 4wheel disc brake, FSSR, Dakota digital, etc.
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