What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

40" Tires Requirements

S

SVPAM_SVPAM

Registered Member
Joined
Apr 19, 2020
Posts
9
Reaction score
0
Location
FL
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
icon_wink.gif
 
Welcome aboard!

How much do you want to cut on the fenders?

You will need 4-6” lift and possibly some body lift. You may get away with 6 lug axles, but it won’t take much to snap them, 40s are heavy. The 8 lug parts for the front axle don’t add any real significant load bearing difference, and the axle shafts are the same as a 6lug

You will need brake lines, shocks, new drive shafts
I don’t personally recommend spacing the trans down, as it changes the front driveline angle

9” or 10” isn’t a significant difference, and wheel choice may dictate what you get
 
Bent77 said:
Welcome aboard!

How much do you want to cut on the fenders?

You will need 4-6” lift and possibly some body lift. You may get away with 6 lug axles, but it won’t take much to snap them, 40s are heavy. The 8 lug parts for the front axle don’t add any real significant load bearing difference, and the axle shafts are the same as a 6lug

You will need brake lines, shocks, new drive shafts
I don’t personally recommend spacing the trans down, as it changes the front driveline angle

9” or 10” isn’t a significant difference, and wheel choice may dictate what you get
Click to expand...



So do you think that 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 ? As I mentioned I don't want to go extreme lift. I need the minimum that can handle the 40" tires.
The 40" tires are going lift the car enough !

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 ?

For gear ratios what about 4.56 or 4.88 ?
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 performance

For engine 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 do I 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/

Do I have to get steering reinforcement kit ?

Suspension hangers ?
 
Ok deep breath. That’s like an entire build thread of information....

Let’s start here. I have a 77 k10. No body lift, 5” suspension lift, cut and reconfigured the wheel wells about 3” on the back of all 4, and cut the fang’s off of the front fender. 37” Tires still hit

4.88 or 5.13 would be my recommendation, and those axles may be a 3/4 ton, which would be as I described above

Have time to read some build threads?
 
I would swap in 8 lug axles if you have them already.
For lift go 4 inches, then buy ez inches, and push the front axle forward, a 40 will get into the firewall with that short of a lift.
 
Man that's going for the hail mary pass with pushing for 40's. Bent's pointing you in the right direction, but the really short version is if you want anything to last you'll have to reconfigure the entire truck to work around the 40's.

1/2 ton axles aren't enough. Got to go 1 ton's and by that we mean Dana 60 upfront and a 14Bolt full floater out back. Even then the front will need fortification with 35 spline outers and matching hubs. Gearing those axles is going to require 5.13's to get them turning decently. Steering is going to suck with those big tires so plan on switching to cross-over steering and hydro assist. Lift really depends on how much sheet metal you want to cut. Leave it lower and you'll end up cutting more. Get the suspension higher and you'll still have to cut, just cut less. As far as the engine goes it's going to need all the help it can get to try and turn 40's. It may be a 454, but chances are it's a SMOG era big block with low compression heads and teeny cam sucking air through a quadrajet. Combine that with a dump truck sm465 trans and it's going to bring the suck with crappy gear splits and no OD for the highway with the engine screaming at 3,450 rpm at 80mph.

I'm going to ask the question nobody has yet though. Not to be an ass, just curious. If you aren't going to do any "aggressive" off-roading why need 40's? Is it going to be wheeled at all? Mall Crawling? Daily Driver? Again, not trying to beat you up, but 40's really shine off-road if the truck is built to handle it. On the street, without changing the steering to crossover with hydro assist those tires are going to be a royal bitch to turn at low speeds. In the end it's your truck and it makes no difference to me what you do to yours. Just giving some insight on some of the ramifications to going that big.
 
Mall crawling fire road 4x4 cruiser?

6 lug axles and 40s = mall crawler, not much height needed, minimum trimming w/4” lift
40s and actual off-roading = much more time/money, taller lift or lots of trimming and axle placement

Realistically, what are you using it for.
 
I can see that DANA 60 are the most recommended for my application

From which trucks I can pull this axles ? front and rear from same car ? what else I should get from the same truck to install in mine ?
Shall I look for K30 only ? which year ? it gonna help in my search
What if the K30 got dual rear tires ?

What do I need to install it in my Jimmy ?
 
80 mph as a regular cruising speed with 40's, is stupid. Your thoughts on engine sound great for a street car that is a cruiser, not great for what you allegedly want to do here. Holley makes great carb's, just not for off road. Thumper cams are great for cars and coffee, not 'wheelin.

IMO, if you want 40's and you want it streetable, safe, and capable when you want to wheel it you need to begin with the diff's. Dana 60 front, 14 bolt or Dana 70 rear. Not only will these handle the 40's just fine without breaking, but they have the brakes you need to be able to keep you able to stop in a normal enough distance, more than once. Transmission will dictate gearing, and final gearing will determine your comfy cruise speed (which still shouldn't be 80 mph)

Geared right a decent small block will do the job, but bear in mind 40's are heavy. It won't be fast. I would look at a truck big block and keep it close to stock. an 8.1 is a great choice, and I'd keep the fuel injection too. Way more reliable, and it won't stall off road.

Actual lift could stay in the 5"- 8" range. You will need to trim aggressively and even then it will be a tall rig.

Transmission choices. If it's already a three pedal rig, the SM 465 it has is good other than lacking overdrive. I'd limit gearing to 4.56:1 with that trans or you won't want to be on the highway with it at all, never mind 80 mph. NV4500 is an option, it shifts a little nicer than the 465 and has overdrive. It's not a bolt in swap, nor is it a cheap swap. with a NV4500 5:13's or 5:38's are at least an option.

Auto's. TH400 will live, again the lack of overdrive should limit your gearing choices to 4:56. 4L60, or 700R-4 I would not even consider at the size and weight of the rig itself and as importantly the weight of the tires. 4L80E is a good option, strong and overdrive so you can run deeper gears...but again it's not 100% bolt in and isn't exactly cheap.

My question is...how much money do you have?
 
SVPAM_SVPAM said:
I can see that DANA 60 are the most recommended for my application

From which trucks I can pull this axles ? front and rear from same car ? what else I should get from the same truck to install in mine ?
Shall I look for K30 only ? which year ? it gonna help in my search
What if the K30 got dual rear tires ?

What do I need to install it in my Jimmy ?
Click to expand...

K30 trucks with single rear wheels would be the target truck. Ideally, you'd get both from the same truck so the gear ratios match. A K30 14b will not just bolt into a Blazer/Jimmy since the shock mounting and axle perches are not in the same spot.

I'd pass on one with dual rears because both will require to be converted to SRW spec and that's going to add more cost to the upgrade that isn't needed if you just buy the right axles.
 
It's been a long time since I thought about it, but a van-width 14BFF (G30?) is the ultimate find.
Same track width as a D60, so you don't need to use rear wheel spacers to get the F&R track widths to match up.


-G
 
Dunno why matching track width is important to a lot of folks. I can’t see it while driving :)

And quite please about the 700r4 and 40s, ok. I don’t want mine hearing you. (At least it’s 4.88, should be 5:38 though)
 
Gibby56 said:
No lift needed for 40’s. Just trim to fit :hack:
Click to expand...

Are you sure about that ? Have you tried it in your truck ?
The I will be fine with 2 or 4" lift kit only and fender trimming

Off course with axles replacement
 
ZooMad75 said:
K30 trucks with single rear wheels would be the target truck. Ideally, you'd get both from the same truck so the gear ratios match. A K30 14b will not just bolt into a Blazer/Jimmy since the shock mounting and axle perches are not in the same spot.

I'd pass on one with dual rears because both will require to be converted to SRW spec and that's going to add more cost to the upgrade that isn't needed if you just buy the right axles.
Click to expand...

So what are the best fit axles and cheapest one I can find it in the salvage yards ? so I can focus more into these models
K30 ? C30 ?


My target should be DANA 60 in the front and 14 bolts rear, correct ?

What about K20 axles ? will not do the job ? or it's still weak than the DANA 60 that comes in pick up's ?
Or I can get the rear 14 bolts K20's axles and look for the DANA 60 front from pickup ?
In all ways I have to replace gear ratio to 4.56 +


Thanks man
 
SVPAM_SVPAM said:
So what are the best fit axles and cheapest one I can find it in the salvage yards ? so I can focus more into these models
K30 ? C30 ?


My target should be DANA 60 in the front and 14 bolts rear, correct ?

What about K20 axles ? will not do the job ? or it's still weak than the DANA 60 that comes in pick up's ?
Or I can get the rear 14 bolts K20's axles and look for the DANA 60 front from pickup ?
In all ways I have to replace gear ratio to 4.56 +


Thanks man
Click to expand...
K20s will be a 3/4 front axle, and the spring pads on the rear 14b will have to be cut off and moved. You will most likely not find them in a salvage yard. But you may get lucky

Yiou certainly can mix and match, but the gears may not be the same. Also, these axles came from CUCV trucks

Don't be surprised if you get to $5k buying just axles, wheels, and tires
 
Bent77 said:
K20s will be a 3/4 front axle, and the spring pads on the rear 14b will have to be cut off and moved. You will most likely not find them in a salvage yard. But you may get lucky

Yiou certainly can mix and match, but the gears may not be the same. Also, these axles came from CUCV trucks

Don't be surprised if you get to $5k buying just axles, wheels, and tires
Click to expand...


Hi Bent

I have theses axles pulled from 83 Suburban Manual ( front & rear )
What do you think ? It will work fine and strong enough in this project ? I can see that K30's are rare

900x674-1_-5e6e450acab7e.jpeg




900x674-1_-5e6e450b7a2a8.jpeg



900x674-1_-5e6e450c0ea69.jpeg




900x674-1_-5e6e450ca2524.jpeg
 
You must log in or register to reply here.

Latest Posts

Top Bottom