Cummins Powered Suburban

[Signgonzo]

Howdy, don't know if I'm in the right place to post this, new to the forum. Just purchased a '77 Suburban that I will do a frame up rebuild on. This is my third Suburban project and by far the most complicated. I'm a 62 year old retired Trucker and this will be the truck I always wanted but never had the time or money to build.
So far the plan is 12 valve Cummins, NV4500, NP 208, and I don't know what axles yet.
I know I'm not the first guy to do one of these so if any of you guys have done one, I would really appreciate feedback as to what pitfalls I may encounter. You know, one of those "if I had it all to do over again" kinda things.
Thanks for you input,
Signgonzo

 

[muddysub]

Howdy, don't know if I'm in the right place to post this, new to the forum. Just purchased a '77 Suburban that I will do a frame up rebuild on. This is my third Suburban project and by far the most complicated. I'm a 62 year old retired Trucker and this will be the truck I always wanted but never had the time or money to build.
So far the plan is 12 valve Cummins, NV4500, NP 208, and I don't know what axles yet.
I know I'm not the first guy to do one of these so if any of you guys have done one, I would really appreciate feedback as to what pitfalls I may encounter. You know, one of those "if I had it all to do over again" kinda things.
Thanks for you input,
Signgonzo

with that kinda weight over the front end, you're probably going to want a dana 60 front axle. they can be hard to find and a little pricey but with what you've got planned, its the best choice. while you're at it, throw a 14 bolt rear axle in there, those are plentiful and cheap.

what are your plans for suspension? the cummins is gonna drop the front end some, so a set of lift springs would probably be a good idea. not sure how tall you want to go there.

are you building an off road/camping rig or a highway cruiser to pull a trailer and do some traveling with?

 

[76zimmer]

12V=1 tons!

Welcome aboard your in the right section for a truck build up.

I'll be following the build, I'm doing a 12V/47RE swap on a 76CC over the next 9 mo.
Good luck, post up alot, and we love pics!

 

[Signgonzo]

Sounds like good advice

Yeah, I figure the Cummins to be 300 or 400 lbs heavier than a mouse or a rat motor. So I will be beefin' up the front suspension. Really looking forward to doing all that with the body off for a change. Will do a little lift to improve looks and angle of departure, but I am too long in the tooth for a big lift. Me and granny gotta get in the damn thing.
This rig will be my daily driver and do a little heavy haul once in a while. I live in the beautiful Okanogan Highlands in north central Washington so there will be some off road on hunting and fishing trips, but my hardcore off road days are gone. Over three million miles in a truck and the old back is toast.
The Suburban is a 3/4T but I am pretty sure it doesn't have a Dana 60. Still trying to figure that out.
Thanks for the help fellas, I'll keep you posted.

 

[drew4x4]

the 77 3/4 ton probably has an 8-lug dana 44.

 

[jt512]

Welcome

Since a 12v anything is cool in my book I will definetly follow along, and like already said D60 up front and I don't know that I'd mess with a 208, a round pattern 205 is a simple swap behind a nv4500 or even a 241 would be a good choice.
Looking forward to pics and if you have any questions there are quite a few of us that have done or are doing cummins swaps

 

[76zimmer]

Yeah, I figure the Cummins to be 300 or 400 lbs heavier than a mouse or a rat motor. So I will be beefin' up the front suspension. Really looking forward to doing all that with the body off for a change. Will do a little lift to improve looks and angle of departure, but I am too long in the tooth for a big lift. Me and granny gotta get in the damn thing.
This rig will be my daily driver and do a little heavy haul once in a while. I live in the beautiful Okanogan Highlands in north central Washington so there will be some off road on hunting and fishing trips, but my hardcore off road days are gone. Over three million miles in a truck and the old back is toast.
The Suburban is a 3/4T but I am pretty sure it doesn't have a Dana 60. Still trying to figure that out.
Thanks for the help fellas, I'll keep you posted.

help for D60 I.D.... http://coloradok5.com/forums/showthread.php?t=271314&highlight=d60+thread

 

[Signgonzo]

T case options

Welcome

Since a 12v anything is cool in my book I will definetly follow along, and like already said D60 up front and I don't know that I'd mess with a 208, a round pattern 205 is a simple swap behind a nv4500 or even a 241 would be a good choice.
Looking forward to pics and if you have any questions there are quite a few of us that have done or are doing cummins swaps

I hadn't thought about the 241. I'll look into that. Ultimately it boils down to what I can find/afford.

 

[Signgonzo]

Duh!!!

76zimmer; thanks for the link, very cool. The D44 and D60 are stamped on the punkin'. Who'd a thunk it!

 

[Signgonzo]

Gear ratio

Axles will be the first thing I try to locate, but I gotta do the math to figure ratios and tire size to come out with the right RPM to keep the Cummins happy.

 

[jt512]

What's your planned tire size?
With the manual behind a 12v, just for conversation sake, 35" tire - 3.73's are nice, 37-38" tire - 4.10's do well, which are both common ratios for stock Dana 60 /14 bolt axles.
Not sure How familiar you are with 12valves, but, if you aren't very ...definitely read up on the KDP (killer dowel pin) and at the very least a 3 or 4,000 rpm governor spring kit (GSK) , at least sliding the fuel plate and AFC cover forward should be mandatory for these engines along with a timing pump to the ~16* range.

 

[ba3jbrown]

You've made the right choice for power. Suburbans should have came with a Cummins to begin with. I did the same conversion to an 89' burb. It is a 3/4t and came with a semi float 14b rear and dana 44 frt. Both were 8 lug. During the conversion I replaced the rear with a 14b ff with 4.10 and used the 44 for awhile. The front did not like the weight and it drove funny and felt soft. I was very gentle with it. I've since replaced it with a d60 and the front feels more firm and drives better. I also started out with a 47rh/np205 combo which runs great. I've been acquiring parts for the nv4500 swap. Convert to hydroboost if your burb isn't already as that make a world of difference and start lookin for hydroboost brake/clutch pedals now as they are hard to source in good condition. Best thing to do is purchase a dodge donor truck if you don't already have an engine/drivetrain. The nv4500 have np241s which is also good combo but chain driven. The dodge np 205 which is gear drive came in 23 and 29 spline with the latter used behind the Getrag but also bolts up to an nv4500. Of course the 23 spline are easier to find. Don't be afraid of the Getrag either as it is a well built unit. Ve pumped cummins are the simplest and get the best fuel mileage. I am getting 20-22 with my setup. You'll need at least a 4 inch lift but better to have 6 inch for oil pan clearance. This is great site with lots of info. Good luck! Brian

 

[Signgonzo]

What's your planned tire size?
With the manual behind a 12v, just for conversation sake, 35" tire - 3.73's are nice, 37-38" tire - 4.10's do well, which are both common ratios for stock Dana 60 /14 bolt axles.
Not sure How familiar you are with 12valves, but, if you aren't very ...definitely read up on the KDP (killer dowel pin) and at the very least a 3 or 4,000 rpm governor spring kit (GSK) , at least sliding the fuel plate and AFC cover forward should be mandatory for these engines along with a timing pump to the ~16* range.

Yup, I did the math today and I'm thinkin' D60 with a 3:73 or even 3:54.
Don't care for tires much taller than 33" to 35" and I prefer to keep them narrow as I can. I learned that when I lived in Alaska for 17 years. Wide tires suck in deep snow IMHO. Plus I like to keep the unsprung weight down when I can. I understand the KDP thing and I will probably govern it at around 3000 rpm. It's too easy to zing one with the manual tranny (or when you get pissed off in a mud hole.) Thanks for the info.

 

[Signgonzo]

Hydroboost?

I agree with ba3jBrown, with all the Cummins Conversions going around I can't figure why Dodge is the only truck manufacturer to get the news. I always said you should be able to buy a pickup or SUV the same way you buy a semi tractor; buy the cab/chassis of your choice and name your engine and drive train combo, except Mack of course.
I am clueless on the hydroboost thing. What is it and why do I need it?

 

[ba3jbrown]

Instead of vacuum assisted brakes they are hydraulically assisted with pressure routed from the power steering pump through the hydro unit and into the steering gearbox. The other reason to use it is diesels do not produce vacuum and have either an electric or mechanical pump. The cummins year models you seek will have a mechanical mounted under the fuel injector pump with the power steering mounted on the back. You have to have the mechanical vacuum there to drive the power steering pump. I took the diaphrams and lifters out of mine and blocked off the ports. I'm sure someone has made a prettier mount for the ps pump I just haven't seen it. I installed an electric vacuum pump from an F250/F350 on my firewall to operate the hvac. Overall the hydroboost seems to have better braking than vacuum. I also have disc brakes on all four. I just recently installed a AAM 10.5(14b FF) rear end from an 03' Sierra HD that has the parking brake in the disc. I removed the load valve in the back and replaced the proportioning valve in front with an adjustable. All these changes made a world of difference in braking. Also, I like the 4.10 with 35s. I tried 3.73 with the 47rh and my fuel mileage went down. My setup seemed to like the 4.10 due to the rpm range on the engine and got better mileage. Btw, the newer axle spring perches are wider which required to be cut off and new perches welded on. A bit of a pain but well worth it. Brian

 

[Signgonzo]

Hydroboost

ba3jbrown; Yeah, after I asked the question about hydroboost I went online and learned a little. This is my third Suburban, I had a '79 which I sold and got an '84, which I gave to my son when we left Alaska and I did not know about this. Like my pappy used to say, "You learn something every day... if you pay attention."
I am getting a boatload of good information from this forum.
Thanks for your reply.