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Should i keep or sell my '90 Suburban V1500 4x4 350 V8 with 700r for a '89 V2500 Suburban 6.2 Diesel

campfire said:
I had the same thought. The driver door doesn't seem to match, and so many other things are screaming HALF TON. That may or may not matter to the O.P., but it's worth finding out now vs. later.
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You're right..... it does say halfton ...
campfire said:
@82355 : Martin, does this ring any bells? I was thinking that the 6-lug 3/4-ton wheels didn't start until the GMT-400 years. :dunno:

FWIW, I didn't see the reference to 6-lug wheels in that options brochure. You'll have to point it out to me.

I will again suggest you check the VIN, just to see what the truck started out as. It's a bit on the strange side for a 3/4-ton. It's trimmed out very nicely, it has 6-lug wheels, and O/D shifting indicators shouldn't have been available for 3/4-ton Suburbans. Plus, you have already been told that it has been through some modifications (a pretty labor-intensive transmission upgrade, to say the least). So you have a bit of an oddball truck here. IMO, it's worth checking the things that you can check before you decide to buy it. Check the VIN. Check the weight rating on the door tag. Check to see which rear axle you have. Check to see that it's actually a 4L80E. Assuming that it is, what sort of computer is running it, and where is it getting its VSS signal from ('89 would have been mechanical speedometer originally)? Has the speedometer been converted to VSS to match the tranmission? Why does the quarter panel not match? Has this truck been crunched at that corner? Lots of questions come up when I think about it.


I still think it's worth jumping on if it all pans out. But the time for asking questions is now.
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Maybe I should ask for the vin number.... That will tell everything
 
82355 said:
You are correct. No 6 lug 3/4 tons Suburban's from 1973-1991.

Martin
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Come to think of it,.....even if it isn't a 3/4 ton suburban and it's a half ton instead , at least it does not have all the extra weight which can help with fuel mileage. Besides, its not like I tow like talking about . and at least the condition of the vehicle is good along with a strong 4 speed transmission and 4wheel drive. Not to mention it being a diesel
 
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blackandgold51 said:
Come to think of it,.....even if it isn't a 3/4 ton suburban and it's a half ton instead , at least it does not have all the extra weight which can help with fuel mileage. Besides, its not like I tow like talking about . and at least the condition of the vehicle is good along with a strong 4 speed transmission and 4wheel drive. Not to mention it being a diesel
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As said before, if it's in good shape I would jump on it. A 4L80 with good 1/2-ton gears will probably be an awesome highway cruiser (until the trailers get heavy, but it sounds like that's not an issue for you). I just want you to know (ahead of time) if you're being lied to by the seller. If he's intentionally lying about the weight rating, I become immediately suspicious of everything else he says about the truck. Even if he's just misinformed about the weight class, it's a sign that he doesn't know the truck well enough.

Swapping in a computer-controlled 4L80E into a non-computerized truck is not a simple swap, and I would want to see some proof that he did a quality job doing the conversion. There's no Vehicle Speed Sensor on an '89, so he has either converted the truck to have one (which messes up the mechanical speedometer, as both sensors occupy the same location), or he's not running an electronically controlled transmission. So if he has done the work he claims to have done, he has a lot of time and effort into this truck. I (and many others on this board) could go on for hours about how much headache it is to inherit someone else's shoddy project. It is worth the time to make sure that he did a quality job (or you'll pay for it later in extra headache). And to make sure that he actually put a 4L80E in instead of a mechanically-controlled 4L60/700R4. Most folks could not tell the difference.
 
campfire said:
As said before, if it's in good shape I would jump on it. A 4L80 with good 1/2-ton gears will probably be an awesome highway cruiser (until the trailers get heavy, but it sounds like that's not an issue for you). I just want you to know (ahead of time) if you're being lied to by the seller. If he's intentionally lying about the weight rating, I become immediately suspicious of everything else he says about the truck. Even if he's just misinformed about the weight class, it's a sign that he doesn't know the truck well enough.

Swapping in a computer-controlled 4L80E into a non-computerized truck is not a simple swap, and I would want to see some proof that he did a quality job doing the conversion. There's no Vehicle Speed Sensor on an '89, so he has either converted the truck to have one (which messes up the mechanical speedometer, as both sensors occupy the same location), or he's not running an electronically controlled transmission. So if he has done the work he claims to have done, he has a lot of time and effort into this truck. I (and many others on this board) could go on for hours about how much headache it is to inherit someone else's shoddy project. It is worth the time to make sure that he did a quality job (or you'll pay for it later in extra headache). And to make sure that he actually put a 4L80E in instead of a mechanically-controlled 4L60/700R4. Most folks could not tell the difference.
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Iagree
 
I'd wait for a 91 with the factory 4l80e

I feel strongly that they never should have made these older burbs in half ton configuration.

The swapped trans into a 1/2 ton doesn't make me feel good. Too much needed to do it right.
 
dhcomp said:
I'd wait for a 91 with the factory 4l80e

I feel strongly that they never should have made these older burbs in half ton configuration.

The swapped trans into a 1/2 ton doesn't make me feel good. Too much needed to do it right.
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Don't know what your area or his area is like, but finding such a burb around here would not be trivial. I don't think I've ever seen one, neither in person nor on Craigslist. :dunno:
 
The 91 3/4 tons aren't that rare around here. The diesels are But they exist.
 
Define efficient?

I got 15-17 mpg on flat highway with a 91 350, with the 4l80e and stock 235 highway tread tires, but it must have been downhill with a tailwind. Lack of torque really kills your mileage when the tires get bigger. Flat ground, I was getting 12-13 with my 33x12.50 bfg's.

Stock other than tbi mods, headers, exhaust.
 
dhcomp said:
Define efficient?

I got 15-17 mpg on flat highway with a 91 350, with the 4l80e and stock 235 highway tread tires, but it must have been downhill with a tailwind. Lack of torque really kills your mileage when the tires get bigger. Flat ground, I was getting 12-13 with my 33x12.50 bfg's.

Stock other than tbi mods, headers, exhaust.
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Efficient as in fuel mileage.

And as for turque , so the better the turqoue the better the mileage?
 
blackandgold51 said:
Efficient as in fuel mileage.

And as for turque , so the better the turqoue the better the mileage?
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No, more torque does not equal better mileage. And mods to increase torque generally decrease efficiency. I think his comment was about running larger-than-stock tires. Large tires decrease engine speed for a given vehicle speed, so you are operating lower on the torque curve. This doesn't have to be bad (if engine speed stays inside a happy range), but if it gets too low you will be steadily downshifting and that will have a negative effect on both efficiency and transmission lifespan. More pertinent, IMO, is that larger tires are typically heavier (causing you to waste more fuel in stop-and-go situations), often have more rolling resistance, and the extra elevation increases aerodynamic drag. So large tires & lift kits should not be on your todo list if you're aiming for mileage. But that's pretty much common sense.
 
As said in the other thread, one of the largest things you can do to get good mileage out of a stock rig is making a good choice gear-wise. You don't want to be winding the engine up fast on the road. Lower cruising engine speed = less fuel wasted (at the cost of having less power available). There is a reason that 1/2-tons often came with 3.08 & 3.42 gears and 3/4-tons often came with 3.73 & 4.10 gears. If you don't need the extra power, it's just burning fuel for no benefit. So you're going to have some compromise between cruising efficiency and power generation. Given your needs, I think you would be just fine over on the cruising end of the spectrum. But most of the 3/4-ton rigs out there are not geared properly for that use.
 
I don't know. I might just keep what I have and just convert it to a diesel later on. Plus the 700r4 transmission has been fully rebuilt on my suburban two years ago.

The gear ratio is good where it has a quick acceleration off the line.
 
blackandgold51 said:
I don't know. I might just keep what I have and just convert it to a diesel later on. Plus the 700r4 transmission has been fully rebuilt on my suburban two years ago.

The gear ratio is good where it has a quick acceleration off the line.
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Things to keep in mind if you go that route:

Coming from TBI is good, as it means that you already have a return line for the injection system. You may need a lower-pressure lift pump (not sure what operating pressure is for that TBI system, but ours is supposed to run ~7PSI)

Diesel 700R4 governor weights are heavier than gasoline 700R4 weights. Aside from that the cases are identical. There are some great tranny guys on here than can talk you through switching yours out (I'm not one of them). If you don't switch them out, the transmission will shift like a gasoline rig (running the engine speed up higher than it should before shifting). You probably would also like a lower stall speed on your torque converter.

The 6.2 engines come with a larger radiator.

6.2 engines do not generate manifold vacuum, and their supplemental vacuum pumps are undersized for running vacuum-boosted brakes (they operate HVAC & smog equipment). All factory 6.2 trucks came with hydroboost brakes.

You will probably want to add a fuel filter & water separator combination.

Your TBI computer will probably be unnecessary if you swap.

Stock glow plug controllers often fail. They're easy to fix, but many trucks (including all of mine) are converted to have manual buttons operate the plugs.

That's all that comes to mind quickly, but I'm sure there are other quirks. Definitely make sure you have a plan for each of these issues before you start yanking things.


What gear ratio is your truck running? If you're geared for quick acceleration off the line, you are probably on the towing end of the gear spectrum. Throwing a diesel at a low gear ratio is not going to result in a happy engine, and fuel economy gains won't be as nice as they could be (though you should be even faster off the line). The diesel wants to spin slowly. If you don't have anemic gears in there now, you will probably be over-spinning the new engine, and yours won't be one of the 22MPG trucks (though it will probably still be 17 or 18MPG). If fuel mileage is your goal, that ~20% hit might make it worth regearing for the new engine.
 
blackandgold51 said:
Gentleman said with the rig that he did put a 4l80 in but also had it rebuilt. He says he has the receipt and 1200 dollars on the rebuild
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So why aren't you jumping on that rig? Much, much easier than converting your existing rig, and it probably comes with more appropriate gearing than yours does (though that's just a guess, since we don't have real numbers). The 4L80 is likely to outlast your 700R4, and you won't have to worry about swapping out governor weights or any of the other stuff that gets swapped out during the diesel conversion.
 
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