1990 GMC Suburban ... Cummins Powered

[greguw]

Thanks buddy , it will look alot better once I put some big meat under the truck .

[Dieselwrencher]

Yes it will but I know how it is working on those big trucks when the big tires are on them. I know climbing up and down on mine is a PITA after a while.

[greguw]

Got the fender wells modified around the intercooler tubes and painted and installed over the weekend . Looks the original style battery trays will work so thats good . Trimmed up my gauge face plate to fit the Autometer carbon fiber gauges ... Looks pretty good .
Looks like the wiring will be next then start some of the body .

[greguw]

Still waiting for some back ordered battery trays , could come in tomorrow . I got the exhaust fabed up and welded over the weekend , I went with 3" straight piped for now ... Had the Gavanized tubing sitting around the shop .
Had to put the rear tires on to make sure the clearance was correct with the tire ... putting the tires on is like oping presents be for xmas ...LOL I just want to keep them on ...LOL
The 42's fit the wells pretty good .... What do you think ?

[y5mgisi]

Looks very much bad ass! Exhaust looks good too!

[68Timber]

Looks great and I'm sure I'm not the only one that wants a ride in that beast.
What are your plans for paint?

[greguw]

Had the Flu last week , so it was a slow week for being productive . M managed to fine tune the exhaust and hangers . I used the standard big truck hangers ... they look like the regular hangers just a little more beef to them .
So I opted to mount them on studs that I also cut thick rubber washers out of coolant hose ... I used locking nuts to adjust the tension on the hangers . If you have the to tight the viberation will transfer threw the body and it just really sucks , I went thrru it with other diesels I put exhaust with .
I also added a 4 inch stainless tip ... Blacked out the exhaust , looks pretty good and sounds great , not much viberation transfer at all .
I was able to drive it a few feet back and forth in my shop ... clutch feels great , steers and stops ... and no major leaks , I was really concerned with the rear main seal ... its nice and dry .
I bought a over flow bottle from ebay and it was junk , I ended up plastic welding up my old one and that seems to be holding up nice , shes all toped off with coolant ... took over 5 gallons ... no leaks .
The final engine component I need to fab up is the air filter , I'll be dealing with a small space ... I new this was going to be a custom fit ... I might be able to squeeze one of the Big Honking Air filter with a tight elbow coupling .
Next week I will hit the electrical also .
Heres a few pics ... done for the day .

[flomulgator]

Amazing looking rig. I stumbled here because I have a 1991 turbo diesel Sub with plenty of work on it, but that has some persistent issues that would disappear with a 6BT Cummins. Since this is the most thorough, well thought out and written up job I've seen on the net so far, I thought I'd ask you a couple questions. If these answers are buried in the thread just tell me to hunt harder.

1. Frame thickness: you mentioned 88-90 is best. Is a 1991 frame thinner? It is still the old body style.
2. How necessary is the plating you did? Looks like you are building a serious Off-roader. Mine would maybe do some light trails but mostly Forest Service roads and a lot of freeway.
3. What is the minimum lift necessary for a 12v Cummins? I already have 33" that I like and that's pretty high. I don't want to add too much suspension lift.
4. I have a 3/4 ton axle swap (8 lug, 8.5" up front 14b, 9.5" out back), would these be strong enough for the Cummins?
5. Thoughts on Gear ratios for the Cummins?

Any insight would be valuable, as we have owned this vehicle from day 1 and want to keep it in the family for as long as the frame and body hold out. A Cummins just might take me there.

[kieth]

I just stumbled into this build thread and saw the lengths you went to to reinforce the frame on this vehicle, If you ever do one of these again you might try having frame formed in a U and when you put it in place huckbolt it into place instead of bolts. They never come loose and never need to be tightened. I do big truck work and we use a lot of hucks since they are so much stronger than bolts and never need maintenance. Kieth

[greguw]

I did consider the hucks ... The bolts were there just for assembly and lining stuff up ... Everything is welded in place , plus the bolts are grade 9 ... there almost ARP stud strength over 200,000 psi , not much stretching going on there .

The frame thickness was best around 88 to 1990 ... yes that was the old body style . Think it ranged from .190 to .210 ... the K30 were the best for the cummins conversions , there .230 ... allmost a 1/4 thick . They all flex with the weight of the cummins . If your not hard core offraoding its not a big issue .

I have seen guys get away with 3 inch lift ... biggest thing is the front driveshaft contact with pan ... its close . really depends on the motor mounts you run . I did the 1" aluminum body lift and that was perfect from my build .
I have the custom deavers ... really now with all my weight I am 8 to 9 lift body and all my springs did settle but are going to ride and work better than stock .
The 8 lug will be fine ... unless your wheeling then dana 60's are pretty cheap right now .
Gears depends on your transmission ... with 33 to 35 3.73 or 4:10 would be fine ... stock these 12 valves max out at around 2200 rpms .
I have put a lot of time in this build , its going on a year now , my big concern was a rust free truck . Truck was a little more than I though , I owned a automotive shop for 20yrs so I can build just about anything ... I forgot how much time and money goes into toys like this ... I'm over 30K and will dump another 3k in paint and body .
Todays my birthday and I will be picking at the truck for a couple hours today ... I have been doing 3 hrs everyday and say 6 hrs on weekends .
Not to sway you away from doing your build , these trucks are alot of work and its not cheap to build a diesel .

[y5mgisi]

I'm over 30K and will dump another 3k in paint and body .

Its pretty insane huh? You think "30k is so much money!" then it turns into 1000 here, 3000 there, 1500 there, 500,500,5000 etc! The real effed up part about it is thats not even including your labor! And the even more effed up part is that when its all said and done you would be lucky to sell the thing for 12k tops! Makes me question this darn hobby sometimes!

[greguw]

Yep 30k is nutz ... stuff just adds up . could have just put the cumins in the stock burb ... you seen the pic's I started with ...
Once the project starts it just adds up ... I could have spent more time tracking down used parts , most of the time stuff is all ready beat and my time working my job VS. time to hunt for parts was not worth it for me .
I'm at the point that I don't look back , its like buy and new truck that no one has and the cool factor is ... pretty cool ...LOL
Truck is worth more in parts than whole ...
3k for a rust free suburban .
3k for a 1996 12valve with low miles .
4k for a built dodge cummins NV4500 with 205 .
2k in suspension .
5k into axles and all the new parts
4k tires and wheels
2k in NOS body parts
1k in fasteners
1600 driveshafts
Right there is 25k and thats not encluding all the misc crap ... I don't even think about anymore ... it was the last one I build .
To be honest I did not mind spending the money its just the time ...I run a business so for me to find time is pretty tough these days .

[Dieselwrencher]

Greg, Happy Birthday! I saw where you said these 12v's max out around 2200 rpm's. It's 2400 on VE's and 2600 on P pumps stock. And you're right, they sure eat up a lot of money. Keep up the good work. You're getting so close.

[Dieselwrencher]

That little stuff you never think of is probably in the $2500-$5k range. That's how it goes for me.

[greguw]

Happy 4th guys ... Figured I would run the grill at my shop and make the best use of time while the food cooks before I run over to moms .
Its been allmost 1 yr since my first post on this thread ... seems like 2 years ...LOL
Got all the wiring done under the hood ... I hooked everything up from the rid heater to the fuel heater ... I put everything on switched controlled times ... don't need that stuff in the warmer months .
The single wire alternator kicks but 200 amps at 14.5 volts , ran #4 feed wires to both batteries ... fused everything with links , maxi and little blade sealed ... lot more wiring than a basic 12 valve , I used the solenoid and the Hi-ram relay but connected everything thru a high load solenoid .
Its a turn key machine !
Still have all the gauges and inside wiring to deal with ... Going to button up the dash stuff during the week and going to try and take her out for a road test next weekend ... can only runner her so much and my shop fills with diesel ... LOL

Have a nice holiday everyone .

[Dieselwrencher]

Greg, I hope you had a great 4th as well! The wiring looks top notch! Congrats. I was at Good guys this weekend and saw a vendor that had a 8 or 12 circuit add on kit and I am going to get one of these to try on the next 12 valve swap.

[greguw]

Thanks buddy ... If you look at the last pic I posted I went with a 8 circuit Painless wiring water proof block , has the dual relays for higher loads ... summit racing had them .
I'll use them for the gauges and other accessories ...
Was picking at the dash wiring ... weirdest thing I can't find a wire for the Ebrake , found it on the ebrake peddle , its a tan and white but as for locating it any where else its hiding .
I'm just going to do a red light under the dash to indicate brake is on or problem with the proportioning valve . .. its just a ground I will find it .
Going to get all the wiring sorted and lots of crap that previous people have add ... Plans are still set for a test drive this weekend .

[Dieselwrencher]

Isn't it amazing how probably 85% of these trucks' wiring harnesses are molested under the dash? Every one I've worked on or parted out was, except for a minute few.

[greguw]

What sucks is the dash was cut in the radio hole ... now I either have to find a radio that fits the hole or fab up a filler plate ... sucks because interior is basiclly all there .
Just did a change in the electric fan wiring ... went back to the paper work on my fans and the Hayden controller .
It is a dual control unit but not rated for the amperage my fans will draw ... was not that big of a deal I added two 30 amp relays ... just took the out put feed that went to the fans and plugged them in as the control power for for the relay ... I ran a new feed power for both relays and just connect them to a 50 amp maxi fuse .

[Dieselwrencher]

That was a nice save and should keep those fans running for a long time.

[greguw]

Found some time to tinker with the truck ... The Tachometer was kicking my butt ... I was using a HEI module with a magnetic pickup to trigger and thats common with ford and dodge guys .
For some reason I need to send power via a resister to the tach connection in order to get the tach to pick up the signal .
It will work from idle to around 1100 rpm then the tack goes flat and back down at idle its fine again ... I know I am in the ball park .
The biig news is I pulled her out this morning ... sucks because I had to move a ton of crap , its worked out .
I'm in a larger industrial park so I was out driving and checking everything thing for leaks and any problems ... one stupid leak to do with the autometer sender ,,, few cranks of the wrench and it was fine .
Truck rode nicer than my new dodge cummins 4x4 ... it rides like a big caddy ... brakes are perfect , shifts great but with the small tires the gears are pretty short but got the feel .
Had her running for over an hour with out any problems .,.. Hydro steering is awsome ... Its best handling lift truck I ever rode , no bump steering at all ... Its a 30k truck ...LOL
Going to move forward , still have to research the tach thing , but moving on to the body .
Going to pull the windshield and side glass to start preping for new glass and paint .

[CowboyProtectionUnit]

subscribed.... lol doin a cummins swap asap after i get my truck

[Mrtn15]

Subscribed! Those wheels are monster!
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[greguw]

I'm going for that lifted low rider look ...LOL Check page 5 for tires .

[Dieselwrencher]

Very nice. It's a nice feeling when they can back out and see the sin light for them selves! Good luck on the tach!