On Friday, 2/25/11, I'm buying a 97 Blazer from my neighbor and I was told it needs a new trasmission, although it does still run in 1st and 2nd and, as common, revs at shift. I was just going to pick up a tranny from the boneyard (supposably 3000 miles for $200 from a truck that was in an accident. Too good to be true?). Anyways, I started wondering if the transmission is fine, I'm looking for someone to talk to about it so I know what to do and check out on Friday and I will have more information on Friday night. I was also wondering how difficult it would be to swap the tranny. I'm mechanically inclined but I'm no expert. Thanks for your help.

 

If you know for sure the other transmission is good, you can go with that one (easiest). Other than that, simply dropping the pan should should tell you most of what you need to know.
If the fluid is rust colored or dark when drained into a container and has a smokey/very strong smell... it's burned BAD. If it's burned at all it's more than likely bad. Some of it depends on how much it was attempted to be drove above 2nd gear. I've smoked 3 and 4th before and limped it home locked in 2nd(to prevent spread of clutch material) with fluid almost red still. Also look for metal flakes and black specks/chunks. They will be parts of bushings, clutch steels, or clutches themselves. Any of that is automatic rebuild or replacement.
While you have the pan off, you can pull the solenoids and use some jumper wires to test them with 12Vdc. A+B solenoids are about 1"square and sit side by side on the tail end of the transmission. I actuated mine and blew into them. One way they were straight through and the other they directed air out the filter. Or something like that. If you don't want to do that you can ohm them out, but I don't know what sort of range they should fall in. Anything between open and a dead short may be good. But you would not know if they were just stuck.
Finally, you can drop the valvebody if you want to give it a try. With that off you can use a small pick or watch screwdriver to check valve operation. If you are not careful, you can create a burr on the spool bore and the valve cannot shift through it's range of motion or can become stuck in place. Not easy to fix unless you want to buy a handful of oddball reamers. I told that to a friend once and I had to spend a few hours with a small file and a reamer trying to fix a burr almost 2" down inside a hole.

I think with that you should be able to make an educated guess from looking at those things. If you do drop the valve body, I recommend a book in case a check-ball falls out of place(that reminds me that I need to scan some photos that may help in the future). Also, you will need a set of valvebody gaskets because they will tear. Not sure where to tell you to look for them, but they shouldn't run more than a few dollars. Assuming you find something wrong that would warrant reassembly and trying it.

 

I'm looking at it on friday but I'm almost starting to think it could be the VSS or maybe TPS? Or am I just hoping?

 

VSS has a great deal to do with shifting in general. TPS I believe affects line pressure to prevent slipping. If more throttle is used, more power is made, therefor more pressure needed to prevent slipping. TPS will also affect engine operation as well. Both would probably be worthwhile to check out as well.