Grumpa’s 72 GMC Denali
 

This thread is to document the build of a truck that my grandfather-in-law purchased new and has been in the family ever since. “Grumpa” as he was called by most of the family for his ever delightful demeanor, handed the truck down to me in 1999 with a little less than 80k original miles on it. Shortly before inheriting the truck, I had rebuilt the engine for him due to a cam lobe failing. But otherwise the truck was pretty well bone stock save for upgrading the wheels away from the split rings that had been on it for many years and a Chevy bumper my father-in-law had installed after the original was damaged. Grumpa left us in 2002 after 89 good years, but he lives on in the old truck.

I started upgrading some things soon after, starting with the charging and ignition systems, then suspension and exhaust followed that. The truck was my daily driver for several years until I could afford transportation that was more suited to my needs at the time. I last drove the truck in 2008 and since then the truck has followed me around the country as an un-started project. In 2016, two years after I moved my family to Alaska, I brought the truck up here and stored it in my shop while deciding what to do with it. By now some rust had started to show in the usual places, and many other areas of the truck were in need of attention.

Knowing the truck needed to be preserved before it deteriorated further, but also wanting to improve the trucks performance and dependability, I decided that modernized powertrain and electrical systems were in order. Being in heavy equipment repair and maintenance all of my career, at first I really wanted to graft a Cummins into the truck but it just didn’t feel like this was the right direction for Grumpa’s truck. No particular reason, just sentimentally it didn’t feel right I guess.

After much contemplating and internet searching I got the bug to do an LS Swap. Many discussions with buddies who had done similar projects, and after seeing so many of the trucks on this site that had been swapped, I knew that the LS swap was the way to go. I wanted to do it right, and wanted a result that Grumpa would be proud of when it was finished. In October 2018 I finally found the right donor vehicle for the project, a 2007 Yukon Denali with 117k on the clock. The aluminum blocked L92 and 6L80 were just what I was looking for in terms of modernizing the drivetrain, yet keeping with a theme that would still reflect the trucks heritage. Hence the name for my project, Grumpa’s 72 GMC Denali.

My goal is to have the rolling chassis assembly largely completed by ‘Break-up’ (that is Spring in Alaskan). And then take the summer off from the project while we hunt, fish, and boat. Next year’s plan is interior, electrical and body work.

1: Throwback pic of the truck at my old place in Wright, Wyoming when it was still a daily driver.
2: Bringing Grumpa home to Alaska in 2016
3: Getting ready to start the teardown in October 2018
4: SPID: Many years ago I removed the second battery and discarded the battery tray for it, I regret that nearly every time I look under the hood. Per the SPID the truck originally shipped with bucket seats but I never heard what became of them, it had a bench seat for many years before I got the truck.

Re: Grumpa’s 72 GMC Denali
 

With winter coming on and the boat put away for the season it was time to get started on the teardown. By the end of the first weekend I had the 72 pretty well stripped down.

Re: Grumpa’s 72 GMC Denali
 

Next up was tearing down the axles and getting the old engine and transmission out of the way.

Re: Grumpa’s 72 GMC Denali
 

Finishing up the axle and transfer case teardown. I was quite surprised when I found the inner race of one carrier bearing to be in early stages of failure. The truck originally was equipped with an open diff but I went back in with a Trac-Lok to help put the torque from the L92 into forward motion.

Re: Grumpa’s 72 GMC Denali
 

This post basically gets the project up to present time. Last weekend a buddy came and helped me strip the donor vehicle of the goodies I would save for future use on this project. I saved the radiator, electric fans, front clip and engine harnesses, engine, trans, pedal, front seats, speakers, amp, and air compressor. Hopefully there isn't too much I missed. A fella I work with bought the remainder of the Denali from me so I know where to go in case I forgot to pull something off of it (which I've already thought of a couple minor things that would come in handy).

After throwing a battery in it, the Denali fired up and ran really nice so I was pleased to have a good set of components to start with. I bought the SUV at a salvage auction down in Anchorage and had not had it off the trailer before last Friday so really didn't know what I was going to find.

Re: Grumpa’s 72 GMC Denali
 

Looks like you have a Great plan together.
It's always a good feeling when you
can own a vehicle
With Good History.

Re: Grumpa’s 72 GMC Denali
 

Im in .

Re: Grumpa’s 72 GMC Denali
 

nice story about getting your grandpa's truck, keep us updated with pics on your progress, thanks, I love these old 3/4 ton 4x4's I have a 72 K20

Re: Grumpa’s 72 GMC Denali
 

Made a little forward progress this weekend and finished the rear axle assembly.

Re: Grumpa’s 72 GMC Denali
 

Slow and steady progress continues. Front gear set is done, calipers are rebuilt and front axle reassembly is progressing.

Stopped on the way home from work last week to snap a picture of Mount Denali at sunset at 4pm. That view is one of the best parts of my drive home, on the days she is visible some 120 miles South of here.

Re: Grumpa’s 72 GMC Denali
 

Wrapped up assembly of the front axle this weekend. It feels like progress is painfully slow but it is moving forward. I’ve been sandblasting and cleaning each part then painting most of the pieces with POR15 then topcoating that with enamel prior to assembly.

My adapter kit to bolt the 6L80 to my NP205 arrived Wednesday from Advanced Adapters and I took the transfer case housing to a machinist to get the input bearing bore enlarged to fit the bigger bearing on the new shaft. Hopefully it will be done soon and I can get the t-case reassembled quickly.

I picked up a set of Camero exhaust manifolds from a fella on LS1tech that look like they’ll fit well and engine mounts arrived on Friday. Will be starting to clean up the engine very soon then on to building a crossmember for it to ride on. Then I can work on fuel delivery and wiring after that.

Right now I just need some warmer weather to get the frame outside and sandblast it for paint.

Re: Grumpa’s 72 GMC Denali
 

doing an awesome job !

Re: Grumpa’s 72 GMC Denali
 

Hey Highcountry. Just realized you are located in in Fairbanks as well! I read through your build - looks like you have made some progress this winter. These things always take longer than planned. I hope to see your truck running around town after you finish it! Are you going to do a body resto as well or just a mechanical? If you ever need a hand I would be happy to help out and would love to meet another forum member! Was that your craigslist add selling the 1972 350/350 combo a while back?

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Good to see another Fairbanksan on here Cruiser! We’ll have to catch up and compare trucks one of these days. It’s going to be a good while before the truck is back on the road, but hopefully by break-up next year it’ll be ready to go. This year I am focused on the chassis and hopefully next year is the body. It’s fairly straight and very little rust so it should go pretty quick. Thanks for the offer of a hand, I may have to call on you one of these days! I did post the motor and trans on CL and it sold quick, then I think the buyer took what he wanted and relisted the rest of it.

Last weekend I got the L92 and 6L80 cleaned up but found some metal in the engine filter and rocker area so that’s going to need some further investigation, hopefully it is a simple fix. I also pulled the tcm out of the trans so it can get reprogrammed and started to prep the suspension for reassembly. Machine work on the t-case input bore is taking longer than anticipated but there’s plenty of other items to work on but I’m hoping to starting fabricating engine mounts in another couple of weeks.

Re: Grumpa’s 72 GMC Denali
 

Not a lot of progress to report since the last update, had a few days under the weather with the flu, took a trip to Anchorage one weekend and caught up some honey-do’s that were starting to pile up last week. But, I did manage to get the rest of the suspension parts painted and ready for install. Got my t-case housing back from the machine shop last week and yesterday I got it reassembled. Went to bolt it to the trans and it’s not wanting to go all the way together but I ran out of time to investigate the cause any further.
We’ve had some warmer weather here lately, even saw a day or two where the mercury managed to climb north of freezing for an hour or two. Hopefully it will stick around and I’ll be able to get the frame drug outside and get it sandblasted for paint this coming weekend.

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Well, it's hard to believe that nearly three months have passed since my last post, but there has not been a lot of progress on the build since that point. Spring came early to Alaska and with our summers being so short the last place I want to be is inside, so this project is pretty well on hold until after Moose hunting season wraps up (September).

I did manage to sort out the issue with the transfer case to transmission with a few phone calls and emails to Advance Adapters. Based on their advice I had to short both the transmission output and the T-Case input by about 3/16" each, and now the interference issue is gone. There is still plenty of spline engagement so no worries there but I will say I was nervous when I started cutting!

My goal for the project this summer is to have the frame painting complete before it gets cold again so it will likely be a while before I add more to the thread!

Re: Grumpa’s 72 GMC Denali
 

Looking good so far! I'm considering an L92/6L80E, one just posted locally for me, and will definitely follow along and possibly hit you up for some questions if I do get the combo that was just listed. I have a '72 K20 as well, so very similar install.