Hi Guys

I need you to help me technically and to suggest products / package
For 1978 GMC Jimmy 4WD stock manual trans with 454 swap with Stock 6 lugs axles

I am planning to go for 40" tires and I don't have a problem on fender trimming

1- What modifications I need in the car ? Chassis, body, wheel spacers, shorter front or rear axles ? Anything required for safety ? I am looking for minimum lifting possible to install the 40" tires. I will not go that much aggressive in off roading

2- I am thinking of superlift lift kit https://superlift.com/product-detail/K424
What do I still need ? do you suggest another brand ? I am looking for min lift kit that can handle 40" tires to be more durable and safe
What do you advice ? Note that lift kit comes with raised steering arm


3- What about drive shafts, 6 lugs axles upgrade to 8 lugs ? , transmission spacers , steering upgrade, suspension hangers, dual steering dampers, suggest pinion and ring ratio ?


4-I've selected tires 40X13.5X17, what is the recommendation for wheel selection ? 17 X 9 or 17 X 10 ?


Thanks for your help

 

If you trim the fenders enough, you don't need any lift at all. But that kit you linked should get you by with minor trimming, if any. Especially if you're not planning on any aggressive off-roading. Your stock axles are fine for cruising shopping malls, but you'll want to upgrade to at least a 14-bolt semi-float rear axle for anything more than that. The front Dana 44 will be ok with mild use. If you break axle shafts, you can upgrade to chrome-moly. You'll also want to change the differential gears to 4.56 or 4.88, depending on how much you plan to drive on the freeway. You'll also need to have your driveshafts lengthened and add a good steering stabilizer. I would probably install a reinforcement kit for the steering box, since those tires will put a lot of stress on the frame.

And, to answer your last question, I would probably mount those tires on 10" wide wheels.

Check out Off-Road Design, too. They're not exactly cheap, but they are the square-body Chevy experts, IMO. Besides offering tons of good products, they're also good people who don't mind answering questions on the phone.

 

Thanks Tom

So 2"or 4" lift kit with minor fender trimming is going to be OK ? What about body lift ? is it recommended in my case ? or I go for lift kit only ?

I have 8 lugs front & rear axles from 1983 Suburban Manual Trans. I can use them even before I start the project, what do you think ? Is it much stronger than my stock 6 lugs ?
Moly or 14 bolts are expensive

For gear I can go for 4.56 or 4.88 no issues, but why ?
My highway drive is maximum 80 MPH
I have 3 speeds manual trans. But I may go for manual 5 spds 90's trans if this better

For performance I'm not planning for high HP I am looking for torque for off road application
LT headers, Holley carburetor, Solid cam thumper comp cams, valves, springs, timing chain, pushrods. Stock cylinder heads

How I can length my drive shafts ? is it extension ? or better to customize it in the work shop based on actually dimensions ?

For steering stabilizer I am thinking to get this kit. It should fit with both 6 & 8 lugs
https://skyjacker.com/shop/steering-...izer-dual-kit/

For steering reinforcement kit, can you help to send me link of this product

What about suspension hangers, any recommendations ?

Sorry for the long reply

 

So 2"or 4" lift kit with minor fender trimming is going to be OK ? What about body lift ? is it recommended in my case ? or I go for lift kit only ?

The kit you linked to was 8". A 2" or 4" kit will require major trimming. For reference, my last K5 had 7" of lift (6" suspension plus 1" body lift) and still required substantial trimming on the front fenders to clear 37" tires when rock crawling.

I have 8 lugs front & rear axles from 1983 Suburban Manual Trans. I can use them even before I start the project, what do you think ? Is it much stronger than my stock 6 lugs ?
Moly or 14 bolts are expensive

The Suburban rear axle is probably a 14-bolt. It will be MUCH stronger than your current axle (10 or 12-bolt). The front axle from the Suburban is probably a 10-bolt, but it will have slightly better brakes and heavier-duty components at the wheel ends. Properly running 40" tires isn't going to be cheap.

For gear I can go for 4.56 or 4.88 no issues, but why ?
My highway drive is maximum 80 MPH
I have 3 speeds manual trans. But I may go for manual 5 spds 90's trans if this better

Your current trans (should be an SM465) has a very low first gear, which is helpful, but your truck will still be a dog with stock gears. If you go with a 5-speed, I would recommend an even lower ratio (5.13 or even 5.38) since you won't have as low of a first gear, and the overdrive will bring your RPM down to a reasonable number on the freeway. For reference, my S10 has the same transmission (SM465) with 37" tires, and I'm running 4.88 gears. I recommended 4.56 to you, even though you have bigger tires and a heavier vehicle, because your 454 has a lot more torque than my V-6.

For performance I'm not planning for high HP I am looking for torque for off road application
LT headers, Holley carburetor, Solid cam thumper comp cams, valves, springs, timing chain, pushrods. Stock cylinder heads

The best low-end torque will generally come from a stock engine. Cams, etc. usually add torque at higher RPM. Not down low where you want it. Small-tube headers are an exception and can add low-end torque. This is even more important if you aren't planning on running low ring and pinion gears.

How I can length my drive shafts ? is it extension ? or better to customize it in the work shop based on actually dimensions ?

You'll need to measure the length after installing the lift and either have new shafts made from scratch, or have your current ones re-tubed with longer tubes.

For steering stabilizer I am thinking to get this kit. It should fit with both 6 & 8 lugs

https://skyjacker.com/shop/steering-...izer-dual-kit/

That kit should work fine.

For steering reinforcement kit, can you help to send me link of this product

I would get this

and this

I had both of those on my K5

What about suspension hangers, any recommendations ?

Offroad Design also makes some nice upper shackle hangers, but they're pretty expensive and probably not necessary. You might want their shackle kit, though, because the front shackles are a weak point.

Sorry for the long reply

Not a problem!

 

What about axles ?

I have 1983 Suburban 8 lugs front & rear axles ( Pls. check photos )

Does it work with this project or shall I look for K30's axles ? I think it's DANA 60 front & 14 bolts rear
Which is much stronger than DANA 44 that comes in the Suburban 4WD

Somebody is advising that 40" tires can fit with major fender trim only
And it's recommended to replace axles. Is it correct ?

In this case I can go for 4" lift kit, with 8 lugs axles and customize drive shafts based on actual dimensions

 

I have 44" tires on my 82 k10 suburban with a 6" lift and major trimming. It still rubs offroad. I'll find a pic.

 

Before trimming.



What I had to cut.









So you can make 40s fit with 6" lift. I'm going to add a 3" body lift if I don't tear it down to use the drive train in my Jimmy or another project.