85 Dodge Crewcab Tow Rig

[CKNAUTZ]

Hey guys, just picked this up and figured I’d start a thread for my build. Mainly gonna just be a tow rig and I kinda have a plan in my head for it but I figured it would be nice bouncing ideas off of others and I’m not exactly what you would call a purist so I think this is a better place for it than the dodge forums.

Here’s kinda my plans so far to get it started.
-24 valve Cummins swap with a mechanical ve pump.
-Nv5600 6 speed
-also needs more wheel and tire and it currently has 16.5s so something’s gotta change there. I’m thinking a 235/80r17 would fill it out a little better. Maybe some 19.5s in the future.

I have a line on an engine and trans that hopefully I can snag this weekend. Already have everything for the pump swap.

Now down the line I’m planning on a 4x4 swap. Not that I plan on off-roading a crewcab dually but just so I don’t get stuck on wet grass or on a slick boat ramp kinda deal. With that in mind I was curious how others like the Chevy IFS for there tow rigs? I’ve only ever had solid axle trucks but I’d like to keep this truck lower than my previous ones and I think that might be the ticket. End goal is a little taller than it currently sits. Probably around raising the front to be level with the current rear height. I may try and graft the frames together or just end up with a whole gmt400 frame swap . Kinda thinking 4 link and bags on the rear as well.

Would love to hear more tow rig ideas from y’all as well. I’m just starting the project so open to ideas of what you would include in a build.


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[YotaAtieToo]

Swapping to GM IFS is a pretty interesting idea. I'd lean towards the later suspension, only because I'm assuming they made updates as years went on.

I'd do some research on cummins into GM trucks to see how the oil pan cooperates with the ifs.

Obviously, you're going to get the go to "just use 05+ superduty axles" which you can't go wrong with. But if you're just looking for a highway cruiser, I can see the appeal of the IFS.

The GM IFS has been under diesels for what 30 years? I'd think it could be made to work perfectly fine.

 

[CKNAUTZ]

They make Cummins mounts for the gmt400 series which is why I was leaning that way. It’s tight but if you countersink a few bolts on the diff it clears fine with the kits that are available. I figured someone’s already done the engineering why redo it. Not a lot of people want to Cummins swap a platform you can get good Diesel engine in already(duramax). And yeah I’m sure there’s a lot of people that will still suggest superduty axles. Don’t get me wrong I think they’re fantastic but pretty overkill for my needs.

 

[u2slow]

I'm fiddling with a SD axle under a 92 W350 frame chunk. It's easy to make tall. More work to keep low.

The trick with the IFS 4wd will be keeping the engine vs axle vs firewall relationship happy. I'm guessing you'd like the wheels centered in the fenders. The cummins is nestled in tight to the firewall and low on a D-series dodge.

 

[u2slow]

Btw, A locking axle in a 2wd is a cheap & easy way to avoid nuisance stucks.

 

[YotaAtieToo]

Btw, A locking axle in a 2wd is a cheap & easy way to avoid nuisance stucks.

No it's not, I don't know why people post this. I have owned 2 stockish trucks with rear lockers and the rear locker almost never helps much, for tow rig type sucks. 4wd always makes 10 times the difference.

I'm talking like backing up a gravel driveway and spinning. Locker doesn't do shit, 4wd always helps.

They make Cummins mounts for the gmt400 series which is why I was leaning that way. It’s tight but if you countersink a few bolts on the diff it clears fine with the kits that are available. I figured someone’s already done the engineering why redo it. Not a lot of people want to Cummins swap a platform you can get good Diesel engine in already(duramax). And yeah I’m sure there’s a lot of people that will still suggest superduty axles. Don’t get me wrong I think they’re fantastic but pretty overkill for my needs.

Yes, you're right, I remember someone saying the cabs are the hardest to fit a Cummins is because that body style never came with an inline 6. But didn't remember issues with the frame.

I'd think dropping the dodge cab onto the GM frame would make the most sense. I'd still say go gmt800, for newer stuff like disc brakes and whatever else they did. Finding the right gear ratio might be tough either way. But I guess that's just how it goes with a project like this.

 

[u2slow]

No it's not, I don't know why people post this. I have owned 2 stockish trucks with rear lockers and the rear locker almost never helps much, for tow rig type sucks. 4wd always makes 10 times the difference.

I'm talking like backing up a gravel driveway and spinning. Locker doesn't do shit, 4wd always helps.

I post this because I run a locked 2wd CTD, and it works really well for me. You do need sufficient weight on the rear axle for the trailer aspect.

 

[YotaAtieToo]

I post this because I run a locked 2wd CTD, and it works really well for me. You do need sufficient weight on the rear axle.

And the wieght does more than the locker 90% of the time. I'd suggest adding 1k lbs to the bed for free before I suggested spending money on a locker.

My cclb F350 is helpless in 2wd, same wb as the ops truck. You aren't getting any wieght transfer unless you're climbing waterfalls

Doesn't matter anyway, sounds like he's doing 4wd.

 

[u2slow]

My cclb F350 is helpless in 2wd, same wb as the ops truck.

My cclb F350 also, despite the trash-lok... until I put a Detroit in.

 

[YotaAtieToo]

My cclb F350 also, despite the trac-lok... until I put a Detroit in.

It just doesn't make enough difference for me. Im cursed with steep gravel driveways and usually spin both tires backing up even with an open diff. My Detroit cucv, and my wife's F150 with the locker are no better. 4wd is the only answer for me.

Not even mentioning snow or ice

I'm not going to keep derailing, though, so I guess agree to disagree

 

[72blazer]

Very cool build



I’m getting ready to build a squarebody this summer. We are taking my single cab duramax and get the rolling chassis under the squarebody for all the updated gadgets. I decided to keep it 2wd to keep the budget within reason and because I’ve owned two diesel truck before and never needed 4wd unless I was doing 4wd launches or getting a friend out of the mud. I’ve loaded it with a backhoe and ran it through a really soft dirt field. I’ve also had it loaded with a trailer full of trash in mud with no problems. I think I’ll save my pennies for other mods.

 

[u2slow]

For shits n giggles... here is the 05+ SD axle under the dodge frame chunk. The crossmember is resting on the pumpkin in this pic.



The GMT400 IFS should save some height.

 

[CKNAUTZ]

U2slow… I had considered leaving it 2wd but knowing myself I’d f**k up and get myself stuck somehow. I currently live in Texas but I’m originally from Wisconsin and do travel back often so snow is also another thing I will encounter. And as this is a lifelong keeper I don’t mind sticking the time and effort into it. Also I’d like to try something a little different than everybody else. I’ve done 2nd gen and 3rd gen axles under a international travelette and a first gen before. Like I said this time I want it lower and it’s not really for off-road. Ultimately I’ve already decided it’s getting 4wd somehow and if I can’t make it work I’ll go straight axle. Once this project is driveable I’d like to find another older dodge to make a fun off road truck. That’ll most likely get sd axles.

YotaAtieToo… I feel the same on the 2wd with a locker. Been there. Done that. Poor results.

72Blazer…sounds like a sweet build. Are the 2wd front ends of the gm platform similar to the 4x4? I’m curious about ride quality of the ifs. I’m used to straight axle trucks.

 

[CKNAUTZ]

U2slow this is a gmt800 4x4 platform but they are similar to the gmt400. This is about a 2”front and 4” rear drop. Kinda around the rideheight I’m looking for and this is a pretty moderate drop from what I’ve found guys have had them even lower. I wouldn’t be able to get near this low with a straight axle with out riding on bump stops.

 

[u2slow]

I dismantled/wrecked a lot of S10 and GMT400 trucks 20-25 years ago. The ride height and IFS geometry is very similar 2wd vs 4wd. Basically the coil spring is deleted for a torsion bar, and that makes room for the half shaft. Knuckles have a unit bearing instead of a spindle.

 

[YotaAtieToo]

You couldn't get that low with upside-down portals on a straight axle

 

[Projectjunkie]

Gm if s is nice, beware the gmt800 and up use the modern "pull the front tires back really close to the door" thinking


Also, 4wd van guys gravitate to ford ttb to keep ride height low, as a van engine is low in the chassis, so a solid axle van is sky high, or riding on the bumps


Following along, my best friend built an 85 2wd dually crew Cummins on 19.5s, gets a ton of attention

 

[CKNAUTZ]

Gm if s is nice, beware the gmt800 and up use the modern "pull the front tires back really close to the door" thinking


Also, 4wd van guys gravitate to ford ttb to keep ride height low, as a van engine is low in the chassis, so a solid axle van is sky high, or riding on the bumps


Following along, my best friend built an 85 2wd dually crew Cummins on 19.5s, gets a ton of attention

Care to elaborate what you mean by pull the front tires back towards the door? I not quite sure I understand what your trying to say. TTB had crossed my mind but I didn’t know about the van stuff hadn’t thought to look there. Ironically this idea started because of vans. I’m a Mercedes’ technician but I mainly work on sprinters and the 4x4 versions are kinda what sparked the thought of ifs. They’re setup a little different though as they use a perpendicular mono leaf design similar to a corvette irs.

 

[YotaAtieToo]

I was going to suggest TTB, but any other hight but stock the camber is fucked. You could do a cut and turn or whatever guys do to lift them, but opposite



I kinda want to try TTB on full air bags one day. How much hate would I get for pulling my D60 out to put TTB in?

 

[rockota]

I was going to suggest TTB, but any other hight but stock the camber is fucked. You could do a cut and turn or whatever guys do to lift them, but opposite



I kinda want to try TTB on full air bags one day. How much hate would I get for pulling my D60 out to put TTB in?

I dare you

 

[u2slow]

Care to elaborate what you mean by pull the front tires back towards the door? I not quite sure I understand what your trying to say.

I get it. It's the modern cab-forward design with shallow-sloped windshields, huge dashes, and huge doors. The fender is really short/small between the tire and door.

AFAIK, most engines are still rear-sump, so the engine vs axle relationship only gets skewed so far. Still - you gotta fit up what you wanna do to avoid surprises.

 

[Projectjunkie]

Up to 93 dodge, gmt 400s, obs Ford's, and still super duty truck's put the front axle out front a ways, and you've got 6+" of fender behind the tire at the bottom, gives you room to play with.
Then they started with the 94 dodges, moving the axle center line back under the engine farther, it's why ford bodies on 2nd gen dodges look like shit, because you can't have your wheels centered in the fenders, and have a proper cooling stack, unless you move your motor mounts, which people cry about

Anyways, if you use gmt800 stuff, be aware that the axle center line and the firewall don't jive


Also on gmt800, 1/2 and 3/4t stuff can mix and match, and gmt610 van 2500 and 3500 stuff too
I put a 1500 diff and half shafts in a 3500 van with 8 lug hubs and brakes

It's almost a 9" ring gear, high pinion (higher strength)
I personally know guys drag racing 1500hp turbo silverados in 4wd, with stock diffs and shafts, so I was happy in a van with a 6.0 and 285s

But, you'll be stuck with 3.73s I believe, and IMO a cummins on 32" tires needs lower numerically gearing, my 97 5speed truck with 3.54s on 32" tires wasn't suited for highway trips IMO

Keep that thing at 1700-1900rpms cruising, use boost to roll over the little hills

My next Cummins 4wd build will use late model 3.31 super duty diffs

 

[arse_sidewards]

No it's not, I don't know why people post this.

Because they're idiots. But as someone from a desert shithole full of dry rocks you should be familiar enough with these idiots that you don't have to ask the question

I was going to suggest TTB, but any other hight but stock the camber is fucked. You could do a cut and turn or whatever guys do to lift them, but opposite

TTB camber is probably easier to deal with than retrofitting GM IFS into anything that didn't come with it.

I kinda want to try TTB on full air bags one day. How much hate would I get for pulling my D60 out to put TTB in?

Just like everything else TTB it would make all the idiots who slept through 8th grade geometry come out of the woodwork.

Also, 4wd van guys gravitate to ford ttb to keep ride height low, as a van engine is low in the chassis, so a solid axle van is sky high, or riding on the bumps

That's just because swapping a TTB into an E-series is pretty easy (since they already come with beams) and E-series conversions outnumber GM ~10:1 for reasons that boil down to "a bunch of little shit adding up".

If you just want a little help in snow or light mud GM IFS is fine, don't expect it to survive your best Duke boys impression like beams will though.

 

[CKNAUTZ]

I get it. It's the modern cab-forward design with shallow-sloped windshields, huge dashes, and huge doors. The fender is really short/small between the tire and door.

AFAIK, most engines are still rear-sump, so the engine vs axle relationship only gets skewed so far. Still - you gotta fit up what you wanna do to avoid surprises.

That’s what I was thinking you were referring to but I just wanted to make sure. From my research the wheelbase is actually a little longer on the gmt800 than my truck. I assume all that difference is in the cab design but I think if I line up the front wheel in the wheel well and build the body mounts around that I can move the rear axle forward a bit by 4 linking it and be good.

 

[CKNAUTZ]

Up to 93 dodge, gmt 400s, obs Ford's, and still super duty truck's put the front axle out front a ways, and you've got 6+" of fender behind the tire at the bottom, gives you room to play with.
Then they started with the 94 dodges, moving the axle center line back under the engine farther, it's why ford bodies on 2nd gen dodges look like shit, because you can't have your wheels centered in the fenders, and have a proper cooling stack, unless you move your motor mounts, which people cry about

Anyways, if you use gmt800 stuff, be aware that the axle center line and the firewall don't jive


Also on gmt800, 1/2 and 3/4t stuff can mix and match, and gmt610 van 2500 and 3500 stuff too
I put a 1500 diff and half shafts in a 3500 van with 8 lug hubs and brakes

It's almost a 9" ring gear, high pinion (higher strength)
I personally know guys drag racing 1500hp turbo silverados in 4wd, with stock diffs and shafts, so I was happy in a van with a 6.0 and 285s

But, you'll be stuck with 3.73s I believe, and IMO a cummins on 32" tires needs lower numerically gearing, my 97 5speed truck with 3.54s on 32" tires wasn't suited for highway trips IMO

Keep that thing at 1700-1900rpms cruising, use boost to roll over the little hills

My next Cummins 4wd build will use late model 3.31 super duty diffs

I agree about the 3.73 issue. It’s something I had already looked into and I’ve found 3.42 gears were actually an option as well it’s option code GU6. Which with my tire size and overdrive ratio should put me at 1850ish rpm at 70. Which will be better than my third gen with 3.73 and a .79 overdrive of the g56. On 35s I’m at 2000 rpm at 70. When I got the truck on stock sized tires it felt completely undrivable at highway speeds. It’s pretty crazy that dodge actually put that combo together. Also that’s some good info. It’s nice to find people with real world experience on some of these parts. As a dodge guy it’ll be my first go around with anything ifs.

 

[YotaAtieToo]

Because they're idiots. But as someone from a desert shithole full of dry rocks you should be familiar enough with these idiots that you don't have to ask the question

For christs sake, I didn't live withing 4 hours of desert. Slick clay, snow, loose gravel were the enemies of my truck in 2wd.

TTB camber is probably easier to deal with than retrofitting GM IFS into anything that didn't come with it.

Just like everything else TTB it would make all the idiots who slept through 8th grade geometry come out of the woodwork.

Ya, i mean just mounting pivot points and leafs or a radius arm mount seems pretty easy. 3.54s should be easy to come by.

That's just because swapping a TTB into an E-series is pretty easy (since they already come with beams) and E-series conversions outnumber GM ~10:1 for reasons that boil down to "a bunch of little shit adding up".

If you just want a little help in snow or light mud GM IFS is fine, don't expect it to survive your best Duke boys impression like beams will though.

 

[u2slow]

That’s what I was thinking you were referring to but I just wanted to make sure. From my research the wheelbase is actually a little longer on the gmt800 than my truck. I assume all that difference is in the cab design but I think if I line up the front wheel in the wheel well and build the body mounts around that I can move the rear axle forward a bit by 4 linking it and be good.

Don't get hung up on the overall wheelbase. Shifting the whole body fwd on the chassis to line up a wheel in a fender also means you're carving into the firewall. Factory head to firewall clearance is within an inch.

One advantage in your favour is the 94+ dodge situates the cummins ~2" further forward compared the front wheels. Part of what allows this is the revised oil pan used for 94+. It stands to reason the IFS4x4 stuff can be bulkier (than 2wd stuff) with the engine in the stock position.

Depending how wide the frame is on the GMT400, you're probably looking at a splice somewhere close to the front cab mount.

 

[Projectjunkie]

Don't overlook the express vans 02ish and up, I assume the cross member is lower than same year pickup, and I can walk you thru a 4wd swap with gmt800 stuff, its a pain in the dick, but it fits


Also, I'm not quite sure how they're doing it, but depending on how they're spec'd, the late model 4wd f250s are sometimes damn low, like double take and crouch down to see if there's a pumpkin, might be worth revisiting a solid axle

 

[arse_sidewards]

Also, I'm not quite sure how they're doing it, but depending on how they're spec'd, the late model 4wd f250s are sometimes damn low, like double take and crouch down to see if there's a pumpkin, might be worth revisiting a solid axle

It's all in the sheet metal. The frame is approximately where it's always been.

Late model superduties basically have a factory body drop compared to the old ones. The cab has a big step up between the door frame and the floor level like a van. The bumper, fenders and valence are also stupid low. Everything that shares the platform is the same. The 350s and bigger are just taller because more spring, taller springs, bigger blocks, etc.

 

[pennsylvaniaboy]

I think GMT 400 IFS would be money....I almost wonder in you could even adapt the a arms to the dodge mounts, and then add the torsion bars and crossmember, and diff and use the dodge steering setup.

or just do a frame swap, or front frame splice.....