Which way to go with my '91 K2500

[Steve@OldSub.com]

I have a tired '91 K2500 extended cab short box as if those body details make any difference to my question.

Its got over 190,000 and though it runs reasonably it has a broken exhaust stud that annoys me. It also is no powerhouse pulling a trailer. Its not a real clean truck but body is mostly straight and interior is serviceable. It does leak through the drivers door enough the carpet stays wet all winter.

This is a six-lug truck with a 700r4. And that's the part that is driving me to consider my options, the 700r4 us beginning to fail.

I figure I can replace the 700r4 with a stock trans which will cost more than I expected and just keep driving it until the next issue,

I can replace the 700r4 with one of the expensive modified versions which will cost what the truck is worth or more, but will set it up for an upgrade in the power area.

Or I can sell this one and buy another.

I have a TBI 454 with TH400 available and have thought about giving up OD and swappng this this stuff in.

I also have a Cadillac 500 with TH400 available and have toyed with swapping this stuff in.

In theory I can put either of those motors in front of a modified 700r4 though it takes a very stout tranny to stay alive behind the Cadillac and I do use this truck to pull a trailer.

I will eventually need to replace the truck if I don't fix the engine and transmission. I suspect I'll have trouble doing either engine swap cheaper than I could trade up a few years and perhaps get a big block truck with a 4l80e. Add the cost of a modified 700r4 to this truck and its almost certain I could buy nicer truck for less.

This truck was purchased and has been used as a tool. It was never intended to be a hot rod or project of any sort. But now I'm torn between fixing and then hot rodding the truck I've got and just moving on to a little better truck.

What would you do?

[ChevLoRay]

Interesting issues.....

I take it money isn't necessarily the object du jour, but it is of concern. What to do....what to do....Of course, there's no substitute for cubic inches. Your issue is more transmission-related, anyway. As I have been lead to believe, based on the comments I have read and seen, the 700R4 is an overdrive version of the TH400. So, does that mean that one swaps for the other? It may, then it may not. Driveshaft issues may be the thing of concern. Will the 700R4 driveshaft slip in to the tailshaft of the TH400? What about the length? Too short....or too long?

I have a TH400 in my '69. I'd love to have an OD gearbox....but right now the truck is disassembled and the drivetrain sits in my garage. Not burning any gas, right now. But, that transmission and the original 350 that it was hooked to, towed a 26-ft travel trailer. So, the same gearbox, behind that Caddy 500, should also haul the mail.

Is the Cad ready to run? What kind of mods are you going to have to do to get it installed and operable? I assume it's a carbureted engine, so the TH400 should be comfortable with it, when you have the kickdown linkage working right.

I don't know if I answered your questions, but I did offer my opinion.

[Steve@OldSub.com]

I have finite resources like most people, but feel to start with the budget may not drive to the smartest allocation of those resources. Better to have thought all the issues through including the cost.

I'm not willing to spend a pile of money on a new truck and while spending $1000 or so on this one right isn't a big problem I'm resistant to spend twice that for the better built transmissions.

The 700r4/4l60/4l60e is closer to the TH350. The 4l80e is more like the TH400.

Running the 454 or 500 in front of the 700r4 is probably asking for trouble someday in the future unless I pop for one of the more expensive built versions. Even then it might be risky. I do use this truck to tow a trailer.

If I swap to the 454 its already bolted to a TH400 and transfer case and I see swapping the whole works now as one option to solve my current transmission problem and it solves the weak motor issues too.

Since there parts are coming out of an '89 1-ton I do expect some differences and since the donor truck is a different wheelbase from the target truck I'll need to make at least a rear driveline to make that work. Since the donor truck was wrecked in the front I'll be buying things like the big radiator new if I go this route.

Cadillac is said to be good but I've not run the particular motor that would get used in this swap (I'm already working on a Caddy swap on another truck using a motor I drove into my shop). So there is a possible expensive question mark there and that is too complicated a swap for me to want to get into it right now.

I don't really want to change trucks but as I write and think about this its beginning to make sense to me that I trade up. I just don't enjoy the whole car buying game, dealing with individuals or dealers either way.

Thanks for your comments.

Anyone else have suggestions?

[Otsa580]

The 454 th400 options sounds good if you can just slide it in. It might be cheaper than buying a new truck.

I hate buying vehicles from dealers also. Pain in the rear!

[ChevLoRay]

I agree. If the 454/TH400 is a composite ass'y, it sounds like a no-brainer. Of course, there's always the details to deal with.

[TennesseeZ]

Personally, I'd probably stay away from either big engine/non OD transmission combo on the gas mileage issue. I'd consider finding a good used TH700 at the Pull-A-Part or locally on CL, and driving the truck a couple more years, or fixing it and selling it and moving up to a 97ish with the 4L80

[Steve@OldSub.com]

Originally Posted by TennesseeZ

Personally, I'd probably stay away from either big engine/non OD transmission combo on the gas mileage issue.

It was worrying about gas mileage that got me into the truck in the first place. While its done as good as 17 on the highway and the big block truck never broke 10, I've not been happy with the performance and don't have a problem feeding the truck a little more to get the grunt I want....

You may have persuaded me to do the big block swap.

This is not my only vehicle and performance when I'm working it is more important to me than how much fuel it uses in the process. It may only get driven a couple thousand a year as a big block truck but its not driven 5,000 a year now.

However before I commit I need to really figure out what its going to take. If its a weekend job plus waiting for driveshafts and exhaust I'm probably okay. If its a month of weekends I don't think its worth the time and trouble and looking for a newer big block truck with a 4L80e might become my answer.

While I don't often drive it far when I need it I need it. That is probably what would keep me from doing the Cadillac swap because I suspect the elapsed time that the truck would be unavailable could extend outside my comfort range.

I don't see a way through this that doesn't include spending one or two thousand in 2010. The price tag doesn't have to climb very high before trading up does start to make more sense to me.

This dialog has helped me clarify my thinking and I appreciate all your comments and responses. I think my next move is to research the likely sale price of the '91 and the current going price of 3/4- or 1-ton trucks with a big block and a 4L80e.

But if I find a screaming deal on a big block with a TH400 I won't turn my nose up at it. At my relatively low annual usage it could take a long time to make that OD pay if the price differential to acquire is very high.

Thanks for the help!