Discussion in 'Introduction' started by Tremek, Jul 20, 2017.
Thanks 74 Shortbed and 73 C10
My $.02 - If your main interest is drive-ability and you have big changes in elevation, I would suggest the 6.0l and 4l80/6l80/6l90 swap. That would probably be fairly expensive if you pay someone to do the work, but would be a great learning experience if you did the swap yourself. If you have to purchase a 4l80/6l80/6l90 transmission and computer, you may have as much invested as a Gear Vendors overdrive would cost, but that also depends on what shape the turbo 400 is in. If your engine is in good shape and you do go with a "bolt-on" TB fuel injection, I don't believe your mileage would change much from a well tuned carb, but you would have better tuning capabilities. I would suggest doing a lot of research as to which TB you pick.
Quick update -
At the end of last month I both sold my CTS-V, and picked up an intermediate second car (truck) - a one owner '03 Suburban 2500 with Quadrasteer. This serves a couple functions; a) it was cheap, b) it's in great shape, and c) it has an LQ4 and 4L80e in it already. We're also in the process of moving and doing some significant rehab to the next house, so the Suburban's a good fit for all this chaos for now.
Once we're moved - I'm thinking I'd like to pick up a second LQ4 to build on a stand, swap on LS3 heads and an L92 intake and maaaaybe some FI of some variety, and then swap THAT motor into the Suburban, and start the process again with the 200k+ motor I'll pull out of it. Said motor +another 4L80e can then get prepped to drop into the '77.
Overall I have to play the long game, as the house stuff comes first, but once we're in the next house I can get the truck there as well and begin working on the non-drivetrain stuff.
Hey guys - have a good update:
This weekend I went over to Dad's and we got the truck running. It hadn't moved in a couple years since it had developed a fuel leak and Dad didn't want to touch it. I got under it, figured out what was going on, and after a new battery and a splash of gas down the carb it fired right up.
At some point in the recent past, Dad had a shop bypass or modify the diverter valve system for the saddle tanks, and some of the hose clamps that were going to the hard line on the frame rail were loose. Easy fixes (but insert "damn PO!" here.)
It looked like something had also been gnawing on the hose between the hard line and the mechanical fuel pump - replaced that too.
Nevertheless got it running, verified nothing else was leaking in a concerning manner, and got it underway and out of Dad's neighborhood, and down the road a few miles to the house we're moving into and renovating.
Dad had the original title from '83 when he got it (I was an infant):
Yesterday I went back over to dig into what the truck needs and found some fun stuff in the glovebox:
At any rate, it moved under its own power and is in a more convenient place for me to work on it now.
Current punch list is as follows:
- New tires - the 16.5" tires on it are 15+ years old and there's dry rot. It looks like it ought to be a 8x6.5 pattern, so I'm going to swap what I currently have on the 2500 Suburban onto it and upgrade the Suburban's wheels/tires.
- Brakes - the pedal is soft every 3rd push on the pedal. Need to diagnose, probably bleed them and check the drums and pads
- Oil/fluid changes.
- Rubber/bushings everywhere - it's all dry and shot, all of it. Are there comprehensive kits out there I could go after to save some money?
- New shocks - the units on there have to date back to at least the 80s and look shot/corroded.
- Cosmetics and nice-to-haves like pulling and cleaning behind door cards, fender rust, etc.
- A trailer hitch - thinking a Class IV that bolts to the tail of the frame - any reason to not go this route?
After all that - I'm thinking higher compression heads, a cam, fuel injection, and a 4L80.
Any thoughts on the punch list or performance stuff would be appreciated. Looking forward to revitalizing the beast. Thanks!
I read your entire thread and just can't understand why you want to do all the mods to this truck. I love it just the way it is.
All of the engine work and transmission swapping will get you a net gain of 2-4mpg empty (6.o and 4L80 = 16mpg with 3.73 gear) vs the 12mpg your truck should get with a good tune. Towing will see a 1-2mpg net gain with same assumptions.
The altitude problem is an argument for efi, I understand that part. Perhaps you could buy a cheapo O2 meter and log a few trips to find the weak spot and tune/adjust for it.
My 2500hd Classic 8.1L gets 13.6mpg with 3.73 and an Allison 6spd auto. My 2004 Sub 2500 with 8.1L 4L80 and 3.73 got 14.1mpg. That is highway with cruise going 70mph max. The 2500HD gets 10.6 in town and the Sub got 9.5mpg on the same route. The old 1986 Sub 454 TH400 3.73 got 10 in town, 12 highway empty, and 10 towing anything and everything.
Nothing but love for the truck and it is your project, just throwing out some ideas.
BTW, replace every fuel and vacuum line with modern line rated for ethanol contact.
You may run into a clearance issue with the center hole on the newer wheels fitting over the hubs on the rear axle. Iirc, the 4x4s had more of a problem with this on the fronts, not sure if it applies to the rears also though. I'd do a test fit on one of the back wheels before you got too far.
Good call on the hub bore clearance, I'll change a rear first and see if it fits.
Didn't make any more progress on the GMC yet, but did get the 17s I bought for the Suburban mounted and aligned, so now its former 16s are waiting for when I can get some free time to start thinking about the GMC.
The Suburban is actually turning out to be a nice DD. Starting to run out of things to get working/repair on it before I get to the mysterious (Quadrasteer not working) or the annoying and/or expensive (exhaust smell in the cab when not on recirc - possibly related to broken header studs?) At any rate it's good that the C25 is the third car and therefore not mandatory to having running at any given time.
Posting a brief update: moved over the winter, got way deeper into the Suburban above than intended (heads off - old heads had exhaust manifold studs broken off, and then we discovered cracks between the valve seats on the rear cylinders, so new heads - ARP head studs, fixed all the leaks, new timing chain and oil pump, LS9 head gaskets, upgraded trunnions on the rockers, hardened pushrods, better truck intake, bigger/newer throttle body, bigger injectors, cam, tune, headers and full exhaust, etc - the LQ4 is mostly refreshed and maybe ready for a PD blower) - and am now finally coming back to the ‘77.
Yesterday started getting into it and picked up a carb rebuild kit, belts, plugs, wires, an air filter, some vacuum hoses, and some 9/16-18 lug nuts to see if I can get the Suburban’s former wheels on the beast.
Hoping to get it running and able to get smogged and tags this week; running under its own power will make it a lot easier (and motivating) to start working on maintenance items.
Another update: the truck lives! (But not with some concern - more in a moment
Last week my buddy and I decided to start working on the beast; we did cap, rotor, wires, plugs, a few vacuum lines, a carb rebuild kit, and a few other minor things, and took a chance and added some good gas into the tank and tried to get it to crank. One plug wire re-check and backfire through the carb later, the beast fired up!
First things we did were to let it idle for a bit and adjust the carb (only minor adjustments - float seems to be right) and then kill it to throw on my Suburban's old wheels and tires. 2015 rubber versus 2002, and it bolted right up with new lug nuts without any issues whatsoever.
Cautiously taking it out onto the road, I drove it over to Walmart initially intending for them to change the oil, but they didn't have time so we picked up two gallons of Rotella 10w-30 + a FRAM filter and did the oil change back in my driveway. Also pulled off the bed shell and cleaned out the bed, no rust through the bed and overall it looks pretty good.
Both before the oil change and after, however, with revs, we could hear what sounds like a concerning knock of sorts as the motor revs. At idle, it's more or less inaudible, but with revs it gets louder.
We grabbed a mechanic's stethoscope and tried to figure out the general location of the noise; it sounds loudest from the top-front center of the motor.
Could this be piston slap? Stuck lifter (do these '77 454s have solid or hydraulic lifters?) Rod knock? Would very much appreciate input on what you guys think is the best path to diagnose the beast without hurting it further. For what it's worth it seemed to drive normally, but I also didn't put my foot into it.
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