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91 cummins In a 85 Crew cab- Frame Stength?

21K views 24 replies 13 participants last post by  SHORTY3375 
#1 ·
Though im still gathering misc parts and dreaming bigger.
I have a 85 Crew cab 4x4 short bed 60's front and rear 1 ton. The plan is to put the 91 cummins diesel into it that i have.
My question is should i strengthen the frame, box the frame, or double the frame. This truck would be a daily driver and a tow rig. I read that Drew had frame cracks due to the weight, Has any one else had this problem?

Any one else done this conversion in a crew cab? That has put some miles on it?

I know plenty have done the Ramcharger conversion, but im only concerned about any crew cab conversions.

Thanks for the help.
 

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#3 ·
4wheelinstud said:
mrpeal did one but now drew owns the crew cab...

Scott
Yeah Drew is the one i listed above about haveing frame cracks. His rig is a big offroad rig. Im looking for guys that have more settle daily drivers.
 
#4 ·
Hey Eric (It's Eric ja?) - if you bolt up the body nice and tight (per 'factory') you won't have any problems with frame strength with a 'driver'.  Even an off roader will be okay but the weak link becomes the cab - it'll develop cowl cracks first then they'll go down the door frame, etc. 

I am doing a serious off roader crewcab cummins trail machine, and I am fully boxing the frame with 3/16" hot rolled steel plate almost entirely from the front to the back end of the cab, maybe a couple feet more.  I'm fine with the back end of the frame twisting with the bed but the cab and the front section need to be stronger.  I'm also starting with a '92 "diesel" frame (ex cab long bed).  With as much weight as I'll be carrying and a 38"-44" tire and with what I have planned with the truck (just about anything I can find including the fins and cracks of Moab), boxing the frame was a no-brainer.

I would definitely recommend longer leaf springs for your rig - that'll definitely help with absorbing the twisting the frame will be trying to eliminate.

Suerte amigo!  {popcorn}

- Sam
 
#5 ·
Yup Its Eric  ;D
Thanks Max For the info. I have read that some guys have made extra cab mounts to support the Crew Cab on the frame. Im Trying to keep this "little" project as bolt on as possible. So i Will go through everything to see what condition the frame and cab are in now and see if new hardware at the proper torque spec will work. I will be going with poly cab mounts to help the process.
Trust me i have thought very hard about longer springs on this project. I run 52's fronts and 63's rears on my M880 and it rides like a cadillac. But I was hopeing that if i just upgraded to set up aftermarket First Gen cummins springs in the front it would handle the job. The most lift i would like to do is 4 inchs. So its not going to be a skyscraper by any means.

My biggest concern is the frame around the frame bushings in the front and the steering box. I can easly box or renforce the steering box frame but wasn;t sure if i need to go further, after seeing what happen to Drew's Frame on his Cummins Crew Cab.

The only thing that has me at a stand still on this project is the transmission. I want to run a 5spd either a Getrag but perfer a Nv4500. But i have yet to get one yet for the right price. I have a2wd getrag but the shift plates and shifter are wasted. I guess as a last draw i could go with a auto, but really don't want to go that route
 
#6 ·
ProjectM880 said:
...aftermarket First Gen cummins springs
...there really isn't such a thing as "Cummins" leaf spring, and really there isn't much of a difference between 1/2, 3/4, and 1-ton leafs. And best I can tell...in all my years of messin' with leafs...the only difference is the number of leafs per pack, and it seems whatever you order all seems to have the same number of leafs....unless they're custom made of course. In other words, you likely won't find a leaf spring specifically for a 1-ton Cummins front end - you'll just find Dodge Ram springs, period. And I'm likely not even going to use a "Dodge" springs again as they're all too short - i want the longer ones for both the ride and the flex, and that means going Chevy....and they're cheaper - bonus {cool}.

What I might suggest is grab hold of a set of the 52" ProComp rear Chevy leafs, at the lift you want, do the 1-time fabrication/modification to the frame mounts, remove the bottom leaf (plus the 20-ton overload, as so many seem to come with ::) ), bolt it up and run it. I bet it rides awesome.

I'm fully planning to eliminate at least the lower leaf, maybe the two bottom leafs from my 56" Chevy 4"-lift procomp pack for my front leaf setup. I proved that the just 3 of the original 5 leafs in the 13511 spring pack will suspend Nacho's heavy front end, just 3. But, while removing leafs will gain a better ride it will also lend to spring wrap. To counter that I'm planning a simple wishbone setup, front and rear, to swing with the fixed (non-shackle) end of the leaf springs.
If you get the 4" lift spring, and remove a leaf, and set a 6bt on top of them, you'll already be at a 2" lift, which will nicely put you 'in' the spring {cool}. Have you seen the threads about having the truck riding 'in' the spring verse riding 'on' the spring?

ProjectM880 said:
The only thing that has me at a stand still on this project is the transmission. I want to run a 5spd either a Getrag but perfer a Nv4500. But i have yet to get one yet for the right price. I have a2wd getrag but the shift plates and shifter are wasted. I guess as a last draw i could go with a auto, but really don't want to go that route
yahh, trannies are often the single most spendy...and critical...part of a big project. If you really want a 4500 I say just have faith and patience and keep scrounging and you'll eventually score one.
 
#7 ·
The Reason I said Cummins Springs, is because when i look up supension kits they usually have then separated by gas engine 1 tons and Cummins Diesel 1 tons. Such as here http://rockymountainsusp.com/dodge74_93_1Ton.htm

The Reason for going with a spring that fits is purely for the ease of bolt on and go. I completely understand the reasoning behind 52" springs in the front and the benfit that come with them. Like i said i run 52 Chevys on the front and 63 chevys on the rear of my M880 and i love it. It just took time to fabricate it and it is also a strickly offroad vehicle. Im not as comfortable fabricating key suspension components for a truck that i want to go 70mph down the highway. But I will look to see if i can find a better way to fabricate the mounts for my use. I know you and a few others have done this mod so i will reference yalls build post for pictures.

Have you ever seen a front sway bar setup with crossover steering on a 72-93 dodge with leaf springs? Still looking for a way to do this also, another reason i was asking about frame strength
 
#8 ·
Hey Sam do you know if a Crew cab short bed frame is the same length as a ex-cab long bed frame? the reason i ask is i found a complete 92 4x4 ex-cab long bed cummins with a Nv4500 4x4 . So i was wondering if i could just mount my crew cab and bed on that frame?
 
#9 ·
I think they are, or within +/- 2 inches or so.  I'm using a '92 ex-cab long bed frame to do my crewcab short box truck, and even though I'll likely 'bob' the bed a bit I will not have to do any length changes to the frame.
 
#10 ·
Mad Max said:
I think they are, or within +/- 2 inches or so. I'm using a '92 ex-cab long bed frame to do my crewcab short box truck, and even though I'll likely 'bob' the bed a bit I will not have to do any length changes to the frame.
I didn't realize those military beds were short beds. I thought they were about the same as a Long Bed. Hhmmm There are alot of those military truck bed trailers around here. i might have to look into that.
 
#15 ·
Frame specifications from the 1975 FSM.

Model Wheel Base    Depth    Flange Width    Rail Gage    Section Modulus    R.B.M.*    Rear Overhang
Conv. Cab
D100 115 6.06 2.27 .156 2.86 91520 38.25
D100 131 6.06 2.27 .156 2.86 91520 42.25
D200 131 6.17 2.32 .210 3.88 124160 42.25
D2/300 HD 131 7.20 2.73 .194 5.02 160640 42.25
D300 135 7.20 2.73 .194 5.02 160640 42.25
D300 159 7.31 2.79 .250 6.56 160640 48.25
W100 115 6.12 2.30 .188 3.43 109760 38.25
W1/200 131 6.17 2.32 .210 3.88 124160 42.25
W300 125 7.20 2.73 .194 5.02 160640 48.25
Club Cab
D100 133 7.16 2.72 .176 4.57 146240 38.25
D1/200 149 7.20 2.73 .194 5.02 160640 42.25
D300 149 7.23 2.75 .210 5.47 175040 42.25
W100 133 7.18 2.72 .188 4.75 152000 38.25
W1/200 149 7.23 2.75 .210 5.47 175040 42.25
Crew Cab
D200 149 7.20 2.73 .194 5.02 160640 38.25
D2/300 165 7.31 2.79 .250 6.56 209920 42.25
W200 149 7.20 2.73 .194 5.02 160640 38.25

*Resisting Bending Moment based on 32000 psi minimum yield strength of siderail steel.
 
#16 ·
i bought a skyjacker lift kit 6in diesel lift kit. THE WORST THING I HAVE EVER DONE. it was 1200. the ubolts where all the wrong size. then they told me i didnt put it together right and that i was the only one to complain. I will do procomp chevy springs every time now. I am every steering towards a chevy steering box, rear 14bolt.


Skyjacker springs where to short to just bolt on i had to make new perches because they where to short and the shackles didnt fit. I will never buy them again. they seem to be stock springs arched an sold for 1200. I am interested in a chevy link if someone has one?
 
G
#17 ·
Most of the frame cracks in my crew cab originated from a panhard bar that was not properly attached or reinforced to the frame.  The panhard was trying to swing in an arc while the leaf springs were going straight up and down.  Constantly flexing on the frame at the mounting point.  But the panhard had to be there because without it I was getting death wobble with the crossover steering. 

I could also see my frame flexing at the steering box.  I had to put an extra crossmember in at the steering box. 

You know stress there is a problem.  If not noone would sell steering box braces.  Ram assist helped the flex and the death wobble. 
 
#18 ·
ProjectM880 said:
Hey Sam do you know if a Crew cab short bed frame is the same length as a ex-cab long bed frame? the reason i ask is i found a complete 92 4x4 ex-cab long bed cummins with a Nv4500 4x4 . So i was wondering if i could just mount my crew cab and bed on that frame?
I believe they are the same length, but the ext. cab frame kicks up before the crew frame does. i.e. the cab won't sit down on the frame, unless you do a body lift maybe and I've seen guys cut "pockets" into the floor of the cab for the frame to sit into. Looks like crap.

I'd say just swap the engine into your crew frame
 
G
#19 ·
scatpack_69 said:
I believe they are the same length, but the ext. cab frame kicks up before the crew frame does. i.e. the cab won't sit down on the frame, unless you do a body lift maybe and I've seen guys cut "pockets" into the floor of the cab for the frame to sit into. Looks like crap.

I'd say just swap the engine into your crew frame
Or do a body lift.
 
#20 ·
Eric, take it from me, I highly suggest just swapping the diesel drivetrain into the crew cab. I really think that's the right way to do it. The front frames appear pretty identical. I promise you it will not be "bolt in" procedure to put the crew cab onto a Club Cab frame... http://www.cumminsforum.com/forum/89-93-powertrain/319345-crew-cab-under-construction.html even after he trashed the cab floor to avoid a body lift, he couldn't get the bed to line up and had to redrill all the bed mounts and chop some off of the rear of the frame... The stupidest part is he had a perfectly good crew cab short bed 4x4 frame sitting there, he coulda literally bolted the drivetrain in from the donor and been on the road, instead he literally cobbled the entire build, in my opinion anyway... I'm bigblue12V on there BTW. I'm the one giving him crap for his retarded methods...

I've never seen anyone have problems from a crew cab frame with a Cummins in it. Not that i've seen a lot in person, only one as a matter of fact, besides mine, but I've done a LOT of research on the internet before I started mine.

Like Steveinaz, I wanted a long bed 4x4 crew, my crew cab is also a 77, my donor was also a 92, D250 Club Cab. We decided the best route was to use the rear frame half from the 92. The frame on the 92, behind the cab where we spliced, ended up being 7" tall and my crew cab was 6" tall there... so we slid the 7" tall 92 rear frame over the crew cab's frame rails, overlapping them by almost 2'. Then once we were satisfied it was as square as can be, we welded it together and shimmed the bottom with 1/2" plate, welded that all up, and bolted the frames together for insurance. You can see pics of this on my build thread...

The wheelbase is supposed to be the same on a club cab long bed and a crew cab short bed, 149". You SHOULD be able to drop the entire diesel drivetrain right into the crew cab and almost bolt everything right up. I think you'll want to switch dash and harness also while you're at it. About the only snag I can think you might have is fuel tank... Your harness and fuel lines from the club cab donor truck will be just the right length (I had to lengthen mine being long bed) but you'll have to use the diesel sending unit in the gasser tank, or notch your cab like the guy on Cummins Forum did, which didn't appear to be a big procedure. That would give you the advantage of a bigger tank than the truck already has. The diesel sending unit may fit right in the stock tank in the crew cab now I don't know. Since I went long bed, the donor's fuel tank bolted right in.

Good luck buddy! I look forward to seeing the build thread for this one. Your stuff always comes out nice!
 
#21 ·
ProjectM880......the wheelbase is the same on a SB crewcab and a ex cab LB....you can use the frame on the CREW cab...it will be fine! If you choose to swap the crew cab over to the ex cab frame you will have to use a body lift....you want alot of info on doing your project....check out mine..I just finished a 81 crewcab shortbed 4x4..to a 92 cummins...The thread is LONG...but should be very useful! And Im still running the original 60s front and back!
http://www.cumminsforum.com/forum/89-93-non-powertrain/182113-81-crewcab-cummins-swap-project.html
 
#23 ·
Chalk up another Diesel Drivetrain into a crew cab here:  It is a '72 Crew cab Short bed Adventurer. I run it on 37" tires on stock ford budd 16.5" wheels and stock leaf springs.  It does great off road for what it is - Have been snow wheeling a handful of times and it makes it as far as the toys and 4 runners do.  Had to replace one cab mount that was cracked when I got it.  The frame is 7" tall vs. the 8" tall one on my 1993 W250 Club Cab Diesel.  Also I calipered out the gauge and the '93 is a smudge thicker as well.  I'm not worried about the frame at all though.

No cowl cracks at all though - the upper cowl had no "opening" as we usually see on the later trucks.  The open end was on the bottom.

 
G
#24 ·
PapeCAT said:
Chalk up another Diesel Drivetrain into a crew cab here: It is a '72 Crew cab Short bed Adventurer. I run it on 37" tires on stock ford budd 16.5" wheels and stock leaf springs. It does great off road for what it is - Have been snow wheeling a handful of times and it makes it as far as the toys and 4 runners do. Had to replace one cab mount that was cracked when I got it. The frame is 7" tall vs. the 8" tall one on my 1993 W250 Club Cab Diesel. Also I calipered out the gauge and the '93 is a smudge thicker as well. I'm not worried about the frame at all though.

No cowl cracks at all though - the upper cowl had no "opening" as we usually see on the later trucks. The open end was on the bottom.
How about at the back of the cab between the bed and cab?
 
#25 ·
The frame strength should not be a problem I rolled my old crewcab destroyed the body brought it back home pulled the body off did a complete body swap and never had any troubles never twisted or or anything I would say you will be fine .

right now I am in the process of doing another build this 1 is longbed also but it's not going up as high as last 1
 
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