'89 Suburban transmission

I'm considering buying an '89 Suburban 5.7L with automatic overdrive, but the trans is out of it. The price is VERY reasonable but I'd like to know more about which
transmissions will fit as far as different years, etc. and the extent of how much electronic controls there are on these and the potential for problems due to incompatiblity from various years, etc. In other words I'm considering getting a used trans from a salvage yard instead of rebuilding the one it already has. I presume it is a 700-R4. Any input appreciated.
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I have no use for used major components, consider buying a rebuilt trans from an auto parts store * not a transmission shop *
OD trans use a low axle ratio, if it were me, I'd run a Turbo 400 and suitable rear axle
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"451CTDS" wrote:

Kinda silly to give up the best of both worlds, a taller effective cruising gear with OD and a deeper rear axle ratio for more power too and a deeper first gear (700R4s 3.06 vs the THM400s 2.48) and lack of locking converter on the THM400 too. So tell me again why??? ALso the 700R4 in that year is not electrically controlled except for the lockup of the converter which is controled by the ECM. And I might add that I have a 89 4x4 burb that I bought new and it has 175k miles on it now and the tranny still works like new.
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OK, how many people post about balky turbo 400's ? Answer ... none How many people post about their newfangled transmissions failing ? Answer ... too many
I agree with the fact that an OD trans gives better mileage, particularly on the highway. For the city work I do, an OD would be a waste. I'm pretty much old school, for me high performance means lasting a couple hundred thousand miles.
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"451CTDS" wrote:

Just about every tranny problem in a 4x4 is from overheating due to improper cooling and/or too tall of gearing with big tires. Also some tranny failures are from user mods and my favorite is shift kits. It will tear out the imtermediate sprauge in a 700R4 or the 4L60 (which is just a electronically controlled 700R4) just about every time if you beat it. The typical routine is they install a lift, add big tires then a shift kit and do not change the axle ratios or beef up tranny cooling and when the tranny fails it is the trannies fault, never the owners. There is NOTHING wrong with the design of a 700R4 built 1987 or later (or a earlier one brought up to 87 specs) and it is a good tranny. Keep it cool and have the correct axle ratios for the load and it will give you a long trouble free life. The THM400 was a good tranny in its day but I would never go back to one for a newer OD model. I wish that GM had made a non electronic version of the 4L80 (which is a THM400 with OD added) but they never did which leaves the 700R4 the best choice for GM older truck mods. Also I would like to se them put a deeper first and second gear in the 4L80/85 to but then that would start to invade the Allisons tuff with its aprrox 3.1 first gear ratio and make it less attractive.
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