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.

K5 3/4 ton IFS build

KOW with Keys

Newbie
Joined
Apr 8, 2018
Posts
1
Reaction score
2
Location
Joplin, Missouri
To preface this I've been researching this for 5 years and I need some things lined out by K5 owners before I start to build my own in a few years. I know these questions have all been asked before, BUT NOT LIKE THIS. The little kid in me is thinking this will be what the K5 was intended to become before it's untimely demise. I'll tell the build first then explain why for all you who won't read the why before the what.
1980-1989 K5 body, 1992-1999 2 door Tahoe(Blazer) Chassis, 3/4 ton GM 14 bolt IFS front end, Ford 8.8 inch rear, LS 5.3 v8, 4l65 or 6l80 or NV4500 Trans. 4 inch Suspension lift, 2 inch body lift. 35 inch tires(BFG K02)



So, understandably K5's are a beast off-road. Could they be better, more comfortable, more reliable, FASTER? We all have a rivalry with the Bronco and it's twin traction beam. We all know that the TTB has too much going on and are costly to build and repair. GM's IFS was just as capable, however it had some setbacks. Everyone knows IFS's weakest link is the tie rods and occasionally the CV axle. On the other hand, custom IFS are expensive. Being a mechanic myself I've noticed that the second gen Toyota Tundra IFS is similar(identical in size and structure) to the 3/4 ton Chevy IFS. Well, apparently through research and a date with a tape measure, I've found that 3/4 ton IFS in the OBS Chevy's will bolt to the 1/2 IFS Chevy's with a cradle drop found in 4-6 inch lift kits. So why all this for IFS, as a general rule most off-roaders(when honest) use is that solid axle can negotiate more extreme terrain although with less speed and more discomfort and the threat of death wobble at high speeds. IFS can do similar work with more haste and more passenger comfort at the cost of strength, performance, and a minor amount of stability. So if you're not rock crawling and occasionally envy the 4runner in front or behind you on the trail then this mod would make a degree of sense(although extensive). I've found that so long as you have a solid rear axle and pick a good line you really have no loss.
EVERYONE knows the GM 10 Bolt just ain't strong enough for anything beyond OEM applications where lockers and limited slip is involved. All the same everyone can agree the GM 14 Bolt and the Dana 60 are BIG and you will sacrifice ground clearance for strength and guarantee beating the diff off of even easy obstacles if you run anything under 37 inch tires. An alternative dare I say (through gritted teeth) Ford 8.8 inch rear axle, strong enough to run 35-37 inch tires, and still small enough to go places and not add a ton of weight.
What I'm unsure of is the Transmission. Most people prefer automatic due to the ease of control. I want to know that this is the same even if you have a granny 1st gear. I'm also between 4 and 6 speeds. And to tie it off I know the 4l60 is everywhere which is why I considered it an option due to it’s commonality and low cost, although due to it's low HP rating the 4l65 upgrade would be needed.
Lift kit, 6 inches vs 4in+2in. From what I've seen when you get to 6 inches it tends to be too much for tie rods, axles, and u joints. However I've seen and known 4 inch lifted vehicles to almost never have any issues. Most people claim that 4 inches just ain't enough to clear 35-37 inch tires. So the 2 inch body lift could make up the difference without having to modify wiring and brake lines, this may also be the difference when adapting the K5 body to the Tahoe Chassis. This would also allow the frame to protrude out from under the body, this allows for easy installation(fabrication) of rock sliders.
Last tires, most IFS tend to fail with 35 inch tires and up. It’s also not uncommon for even IFS to have death wobble with 37 inch tires. With the beefed up IFS it’s my belief that 35’s will be a walk in the park seeing that most IFS set ups out there are just modified 1/2 ton setups or smaller. If you work on any of these and see the difference you will understand that GM’s HD IFS and Toyota Tundra’s IFS are insane. The issue with death wobble and road force translation can also be halted by the reduction in tread width. Everyone wants to run big wide tires, give me a break. My S10 Blazer could go almost anywhere on stock tires and OEM EVERYTHING(if you ignored the repair bill that is). It’s been tested, tested again, and retested, that running a stock width(or just narrower) tire and still having height will still wield the same or greater tire flex and tread contact, all while reducing torque going into your steering system. Even better for the budget though is that these ‘pizza cutters’ typically cost less and weigh less saving your budget on two fronts. This is especially helpful seeing that the IFS will disengage the driveshaft and the Ford 8.8 is a light/more efficient axle, saving fuel that much more.
SO this K5 estimated weight 3800-5000 lbs, estimated horsepower 300-450hp, estimated fuel economy 18-22mpg(numbers) or 17 mpg being my guess. WHAT DO Y’ALL THINK? Should I go for it or just build another look alike K5 like all the classic off-roaders or overlander's out there? With great risk comes great rewards?
 
I say go for it because it’s one of the most off the wall things I’ve seen lately.

Personally, having wheeled an IFS 4runner and a solid axle blazer, I’ll take axle over IFS any day for crawling.
 
I will watch you build it. Different is cool.

That said, over the 30+ years of GM IFS there have been many attempts at using them off road and they have not worked well. Its not just rock crawling that breaks them. I would love it if there was a recipe for a super tough IFS that doesn't break the bank. Nobody seems to have found it yet.

I think you are extremely optimistic on fuel mileage for a V8 full size on 35's or 37's.

I really hated all the body lifted trucks I have had. Nothing ever felt solid. I would rather do about 4 inches of lift and then modify fenders for clearance. I guess if you have to build mounts for a body swap you could adjust the height without using blocks. 4" is plenty to clear a 35 or 37 if you are willing to do some work to the wheel wells. The stock wheel opening was designed for a little 29" tire, just open it up. A 6" lift works fine with leaf springs and a solid axle but not so much for IFS.

Do these trucks have the same wheelbase?

There are a bunch of go fast in the dunes guys here that really send it with their trucks. None of them are IFS.

Why not build the Tahoe? They are cool too. Heck of a lot easier than a body swap. I have been looking for a clean barn door Tahoe for a while.

Again, I fully support different builds. I don't think IFS is worth the hassle for off road. My '05 2500 rides way better than any of my squares. Its getting the 3rd front end of its 130,000 mile life. It doesn't get heavy 4 wheeling, just lots of dirt roads. I am not impressed with GM IFS lifespan. My squarebodys ride like a brick but the axles hardly ever need parts.
 
Actually I like your idea.
I have beat the living shit out of Toyota IFS. Not so much with GM IFS but a bit… not as bad as everyone on the solid axle train says they are.

Definitely ride is way better!

It’s only money and time to make it work!

Give her shit!
 
Why not the 9 inch if going Ford rear? It's proven and tons of options. Isn't the 8.8 a c-clip like the 10 bolt?
 
You stated that you wanted a K-5 body from 1980~1989 but I think you meant 1981~1991.

On the 4L v/s 6L trans let your choice of what year motor and harness comes from to determine which trans if your not set on one or the other.

And the selection of an auto or stick is very much a personal choice on driving style.
The lower first gear of the 4500’s 6.34 or 5.61, depending on which version you get, will be a great benefit off road but your driving style and skill set should determine which way to go.

Like a few others have said you might want to truly consider doing a little more investigating/research ( other than what the internet says ) on the real world durability and strength of the 8.8” in a vehicle that weighs more than a Jeep or something comparable - I think your modified K5 project is going to weigh a little more than you think it will.

If you do plan on the 8.8” what are your wheel lug pattern plans as compared to the 9-1/4” high-pinion HD 3/4 IFS front that are eight-lug units?
This is where a GM semi-floater 9-1/2” will be much more user friendly w/o giving up any amount of ground clearance to fret over while being much stronger than a 8.8” that is only marginally better than a GM 8.5” and almost identical is size and strength of the 12bolts at 8.875”.

As others above have mentioned the IFS set up does ride good but has draw backs in the articulation department, ball joint issues ( even the bigger 2500/3500 versions ), ground clearance problems plus the torsion bars hanging down so low on a lifted IFS chassis that already has frame rails that are extremely low also the axle disconnect system on these front ends have many issues in durability, strength and engagement problems.

If your plans are to basically only go wheeling where you took your go-anywhere stock S-10 with IFS , low frame rails and under axle rear springs than ground clearance may not be an issue on this build project but there are lots of off road situations ( not rock crawling ) where such low hanging components will not be in your favor no matter what level of driver skill set you may obtain.

Not trying to wiz on your dream at all but you asked for input and these are things that should be considered and addressed before any progress is taken.

Nothing wrong with an off the wall build but consider why it is not commonly done by those in the know and experienced off roaders - and not just the hardcore solid axle setups kind of guys.

Ya might want to consider taking a ride in a proper multi-link coil over solid setup sometime if extreme ride comfort is your goal.
It just might open up your options and give you even more of what you are after.
An IFS setup can be really nice but there are drawbacks to be considered - there is a reason that the aftermarket has only embraced this system to a limited degree.
Not saying don’t do it but just put a little more thought into the big picture. Good luck on it.
 
Last edited:
Im all for building what you want....
8.8 is not any stronger than a gm 8.5 aka 10 bolt, they spin tubes, bend and break shafts just the same as an 8.5 when you put 35's on them and full size weight, plus you will be stuck with a 5x5.5 lug pattern.

Are you using the torsion bar front end or covering to coil over's to support the ifs, of using torsion bars the ride and articulation really isn't that good and it leaves lots of stuff to hang up.

Twin traction beam is actually a really simple set up and parts aren't very expensive, you just have to maintain it.

Having owned, driven and wheeled both a k5 and 90's 2dr tahoe the ride was better with quality leafs than stock ifs.

If you are going to go thru the trouble of grafting frames use a 99 and up 1500 front end at least, they have actual support other than drop bracket lifts and stock parts.
 
3/4 ton IFS is 8 lug

8.8 is 5 lug

Other than that, I’m curious to see how it comes together
 
Here's a past build I remember Fred Williams doing to see how well 3/4 ton IFS would do when built up. It was called "Project Red Sled". Any of the 1991 chevy articles are about it.
I remember when he built that and tried to make the IFS tough. Didn't work so well. I think he was one of the first to really try and work with the IFS on a real build. He recently did a Toyota with IFS. It worked well but had some real expensive parts on it.
 
I remember when he built that and tried to make the IFS tough. Didn't work so well. I think he was one of the first to really try and work with the IFS on a real build. He recently did a Toyota with IFS. It worked well but had some real expensive parts on it.
Nate on the Dirt Lifestyle YouTube channel did a newer ifs Toyota on 38s not long ago to develop a special suspension kit with Marlin Crawler I believe.
 
Almost finished with my project k5. Sounds like something close to what you’re wanting to build. 1988 k5. Ls6.2, 4L80,
Atlas transfer case, 3/4 ton Dana axles with drivers drop transfer case. 37” tires, 6” lift.
I purchased AMP steps 6 months ago and just installed them today. Wiring them tomorrow. Dakota dash, Holley terminated x wires and vintage air. Need to update pictures
 
Like someone else mentioned, taking a ride and at least a look at a linked and coilover solid axle system could be an eye opener for you. Ride quality is really good, especially with light front axle (10b or D44), strength is totally adequate for 35s and install is flat out easy compared to what you propose. Durability is also really good. Way better than leaf spring stuff and it'll be better than the IFS you're proposing. 12-14" of vertical travel is on table and you won't touch that with IFS till you're pushing the width or playing with centering up a custom diff. Run some of our custom leaves in the back with all the shock you want to afford and you'll cover a lot of ground quick and comfortable.

All that said, nothing solid axle is like IFS when you're going fast. I've spent time in all levels of U4 cars and co-driven really good UTVs in Baja races in addition to a lot of solid axle time so I have a pretty good perspective. IFS has a chance of handling better in slower speed chatter like washboard because of the lighter unsprung weight but it's really when you kick the speeds up that IFS shines. For milder overall use with not much hard terrain, IFS will be nice BUT, the cost is pretty huge relative to the performance gain with the project you laid out.

On the IFS side... We've played around with some GMT400 and 800 stuff too. You'll probably want a uniball upper arm with welded adjusters or heim joint arms. Urethane bushings in the lower arms aren't really that great, you need a pretty hard bushing there that is custom stuff at this point. The best aftermarket steering will be just enough for what you're going. We've gone past what you talk about with 37s and a locker an have found the limits. Torque strength of the GMT800 diff and axleshafts is pretty good for 35s as long as you check travel and steering at all the limits and your system will not deflect from those limits. And if you break shafts, RCV is always the go to. It is assumed that you'll be running a coilover so you have a good shock and can easily tune spring rates. There's nothing inherently wrong with torsion bars but most guys won't research available spring rates to get them right and or will need a bar that's not available. And they're a little cumbersome to mount too.
You might consider starting with a newer platform that would let you work with the blitzkriegs and dirt kings of the world for IFS upgrades. Those guys are all about the go fast but the durability can play down pretty well. You'll find about anything 8 lug is a bastard child but there are some suspensions out there for GMT800 and newer.
 
Top Bottom