1979 GMC Sierra Classic c3500 Dually

[JT_Trucks87]

I’m sure this name has been used for a yellow squarebody before, but I would like to introduce my newest project that we have started calling “top banana”. I have been wanting to do something different for several years now. I have been a die hard 4x4 guy my entire life but we are stepping into the lowered 2wd world with this one. The truck is a 1979 Sierra classic c3500 dually that was bought new at Speight Buick GMC on Santa Monica BLVD in Hollywood California. The truck spent its early life in California before going to Las Vegas for close to 20 years. I acquired the truck from a friend of mine that owns a body shop. He bought it as a parts truck circa 2014 and decided it was too nice to part out. He threw a motor and transmission in it and enjoyed it for a few years. Fast forward to 2020 he decided that he wanted to do a 4l80e swap. The transmission was built, a converter was ordered, a vintage air front runner setup was installed and the truck was lowered with a 6/8 drop. As so many large projects do it got put on the back burner so he could serve his customers and grow his business. I have bugged him about this truck since around 2018. Well in April of this year he reached out and I bought the truck on the spot. There’s a laundry list of things to do but I am in the process of resurrecting this ole lead sled. The plan for the truck is get the Big block fired back up, install the US Shift quick 4 stand alone harness for the transmission, have anew driveshaft made, figure out shifter linkage, full vintage air setup, new tires, and I am going to swap the grill to a 73-74 style. I’m a big fan of roundeye squarebodys but it just so happens that the 79-80 front grille is my least favorite by a mile. I’ll have lots of update pictures to come but here’s the truck as it sits right now.

[JT_Trucks87]

Here’s a few pictures after I got the truck home. And the second picture is after just a little cleaning with soap and water.

[JT_Trucks87]

Here’s a picture of the vintage air front runner setup hanging off the front of the BBC. Second picture is a comparison of 79 grille vs 73-74. I have gathered all the parts and brackets to complete the swap after I hang the front clip back on the truck.

[SCOTI]

I like it.

[rodstored-72]

agree!! keep us posted on the progress...

[JT_Trucks87]

Moving forward with vintage air install. Headers on, fired the motor for the first time on Tuesday. Had a slight hiccup from the truck sitting for so long but she purrs like a kitten now. 4l80e dipstick installed. Dropped the pan and everything looks good in the transmission. It’s as advertised and never been ran.

[JT_Trucks87]

Need to give a big shout out to my friend Travis Utz at Utz speed shop for all his hard work on this truck. He has stepped in and helped me jumpstart getting this truck back on the road as I have had very little time to get anything done on any of my trucks this summer. If you are on the west side of Missouri and need a mechanic Travis is your guy. This whole process has been a challenge from day 1, but things are coming together the vintage air install is all but complete and our new SLOSH TUBZ are installed. I decided to have the underside of the tubs sprayed with bedliner. The US Shift quick 4 standalone controller for the 4l80e is in and wired with TPS sensor and monitor installed. new slip yoke and carrier bearing installed. The exhaust is done, just waiting one a few hoses from vintage air and some transmission lines and the cooler and we will be in business! Gonna be a neat rig to cruise in with the 454/4l80e combo on a 6/8 drop. The front fenders look different because I polished around on them a bit before install. The whole truck should match patina wise once I work the cab and bed over!

[JT_Trucks87]

More pics

[PowerdbyChevy79]

Subscribed!!

[JT_Trucks87]

I’ve been plugging away getting some little stuff done on the truck. As usual I am pretty slow with getting anything done but I finally have a hood, grille and bezels on the truck. I also replaced all the lenses on the truck and fought a couple grounds for the cab lights but got that squared away as well. I fought getting the hood lined up and ran into several issues with the WAMrods that replaced the hood hinge springs. Most of that was mistakes made on my part. Overall once I worked through the issues I’m really happy with their product. The gas shocks are nice and smooth. Check them out if you want an upgrade for the 73-80 hood hinges. I do not recommend buying the hinges from classic parts though. They are pretty flimsy compared to a GM set. Overall I’m happy with progress. Next thing is getting a bad brake light switch fixed and polishing around on the truck. Here’s a few pictures of my progress.

[JT_Trucks87]

A couple more pictures

[JT_Trucks87]

Getting closer everyday.

[SCOTI]

Looking good....

[Willowrun]

Gotta love a corporate blue big block. Following along!

[JT_Trucks87]

My oldest son and I took the truck on its first roadtrip over the weekend. We put around 250 miles on the truck in two days. The truck ran great and cruises 80 down the interstate at around 2700 rpm. Only hiccup we had was coming up a pretty rough two lane we lost an exhaust hanger. (Which happened to be the only one still holding on). I have known I needed to make a trip to the exhaust shop but this has expedited that trip! Oh well it was nothing a couple hose clamps bought at a truck stop couldn’t solve.

[SCOTI]

Not a bad trip then....

Gearing & tire size/s?

[JT_Trucks87]

Originally Posted by SCOTI

Not a bad trip then....

Gearing & tire size/s?

As far as I know the truck still has the 4:10 gears. I am running 235/85//16 on the back. I believe 4th is .75:1

[SCOTI]

Originally Posted by JT_Trucks87

As far as I know the truck still has the 4:10 gears. I am running 235/85//16 on the back. I believe 4th is .75:1

That's what I calculated for (4.10's, 31.7" tire, .75 final trans ratio @ 2607rpms).

I was always hoping the combo would yield ~2500 @ 80 w/the lock-up converter dropping rpms down a bit. Still way better than 3krpm @ 70mph w/o the 4l80e.

[JT_Trucks87]

Originally Posted by SCOTI

That's what I calculated for (4.10's, 31.7" tire, .75 final trans ratio @ 2607rpms).

I was always hoping the combo would yield ~2500 @ 80 w/the lock-up converter dropping rpms down a bit. Still way better than 3krpm @ 70mph w/o the 4l80e.

I agree. I have a 1987 V30 454/400 and 1971 K20 350/350 both with 4:10s and lemme tell ya they are howling at 65. I bought this dually with the intentions of being able to hop in it and go the next town over or hop in and take off to California if I wanted too. So far it’s everything I thought it would be. Just need to keep getting the small stuff sorted out!

[SCOTI]

I'd say goal achieved.
😎

[JT_Trucks87]

Got the license plate lights working tonight. With those fixed and operational all the exterior lights now work. Onto the next little project.