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Hi, I wondering if anyone out there knows the mods to make my 84 GMC Jimmy fullsize flex...I've seen some that are crazy, want mine to do the same. Also would like to know if anyone has any 3 speed with low trannys, or a 4 speed, as well as a front drive shaft? Thanks!
 

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I'm not a pro but from my understanding there are a few things you can do. The first thing you can do and my next mod is call a shackle flip, it basically flips your shackles on your rear springs from underneath the spring to on top of the spring, this allows the spring to flex out much better. Now I'm not recommending this next suggestion I have only heard of it being done but you can remove leafs. I think the proper way of doing this is going to a spring shop and have new packs made all the way around with thiner leaves. The thinner leaves allow for more flex without loosing ride quality/height. That is about the extent of what I know correct me if I am wrong.
As for the trany, check craigslist van saw a couple on there the other day, you are talking about an SM456(Muncie) 4speed. What year is your jimmy, what's in it for a transfer case and front diff?
 

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I have the off road design shackle flip and 6" shackle on the rear of a 77' k25 with the stock 52" rear springs. I can stuff the rear wheels no problem and on the road body roll is negligible (no swaybar in the front).
 

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4 link for ultimate flex. leaf springs... dont cheap out...Alcan or Deaver
 

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If you're feeling really ambitious, you could fab up a 4 link setup. You'd get a lot more flex out of them than leafs, if you build it properly.
 

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You have to do an exhaust flip 3.8 link and that thing will fix like crazy. Thats your only option, don't listen to any of these morons.

Also don't forget to change your spring bearings, they leak down and prevent flex!
 

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You have to do an exhaust flip 3.8 link and that thing will fix like crazy. Thats your only option, don't listen to any of these morons.

Also don't forget to change your spring bearings, they leak down and prevent flex!
That may be fine if you have an IQ below room temperature, but for real results, you need coils.
 

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What if we're in Australia and using fahrenheit.. IQ might not be so low in that case.
Well we're in Canada, so I don't see any issue with my remark.:finger_1:
 

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What if we're in Australia and using fahrenheit.. IQ might not be so low in that case.
FYI Australia has been metric for decades, actually before Canada.:shakehead:

Now regarding the OP's question, if you have the coin Off-Road Design makes some pretty trick suspension systems for the GM 4x4's. Like Ringding stated they have systems that will offer tons of flex and their front four links are sweet and worth a long look too (they have all the math/measurements sorted already). They also have some other goodies for GM's worth looking at too.

Remember though, no matter what system you use a double roller muffler bearing will always be required along with forged piston return springs to keep the engine equilibrium in balance when flexed out...:)

Cheers D
 
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