Chevy automatic transmission

94chevyg20

I bought a 94 chevy g20 van a few months ago with a bad transmission. A local shade tree mechanic replaced it with a used one. I have been driving locally for the past few months with no problems. The other night I had to go on a 6 hour trip. I checked the fluids before I left. Oil good. Antifreeze good. About an hour and a half later I stop at a rest area. Take the time to check my fluids again. Oil good antifreeze good. Oh s$&@ I forgot to check the trans fluid. I check it and the stick is dry. I always keep a quart of oil and trans and some antifreeze just in case. I put my only quart of trans fluid in and go toward the nearest walmart. As I get back on the interstate I can only go 45 mph cause it's not shifting into third. I don't want to do anymore damage to it or the engine so I baby it at 30-35 to walmart about 15 mins away. 15 at normal speed lol. I get some trans fluid and some lucus trans fix. Hope this helps. I head for home. Still 45 at its max. I put another quart in and no better so I decide to cripple it home with the hazards on. About a half hour the van makes a huge swaying motion. Not really a jerk but more like a big wave hitting the back of your boat hard lifting you up and pushing you back down powerful but smooth. As soon as his happened I the van increased in speed 5 mph without me pressing any harder on the gas pedal. A few minutes later it did it again and I gained 10. A few more times and I was cruising comfortable at 65. I had to slow down for a speed trap town and when I got to 45 it started raising he rpms on the engine so I slowed to 15 and stopped at the light. When I started back to driving again it took forever to get above 15 and that was when it started swaying again. Several times and I'm cruising 55. I've been watching my gauges the whole time and the temp and oil pressure have been normal. A few miles from home and my oil pressure drops from around 40 to just above the red line starting to touch it. I'm so close to home and it's so late I just wanna get home. I keep my eyes firmly on he temp guage. If it it moves even a little I'll pull over but it stayed cool. Almost home and each stop makes it slower. Temp still good. 100 yards from home and it acts like it wants to die but crawls on its belly to my drive way. I'm done for the night. When I go to look at it he next day my oil dipstick is bone dry and the trans has way extra. I realize that when I put the trans fluid in at the rest area I put it in the oil instead of the trans and I think I checked the trans without the engine running. Had a lot of things on my mind I guess. I topped the oil back off. The engine seems to be running fine for its age and miles. Over 300,000 btw. I put it in reverse and it grabs then in drive and it grabs. I'm kinda scared to drive it to mechanic. I can always get pulled if it doesn't make it. It will be raining the next several days and I'll wait til it dries up before I try to cripple it anywhere. What makes me scratch my head more than any other thing in life (except for politics lol) is what the heck happened. The trans was running perfect until I put the trans fluid in the oil. I can reason Mabey the trans fluid thinned down the oil and the engine burned it up faster. But WHY did he trans have problems immediately after? Anyone else have a trans problem like this? If so what was the resolution? Ty

thecardoc3

The transmission controls rely on engine controls. If the engine performance is reduced it causes drivers to press the accelerator further which as far as the transmission is concerned means you are commanding it to downshift to increase torque such as during a hard acceleration. But with the engine not performing correctly you get stuck in a lower gear with the engine racing. So it might not have been a transmission issue at all in the beginning. Now?????

94chevyg20

Checked oil again before cranking it up. Idled for an hour. Engine sounds normal. No knocks taps etc. goosed it a few times. It's still got power. Reverse was perfect. Put it in drive. Felt strong until time to shift. Wouldn't shift. 25 mph max. Circled the block and back in the drive. If it's the engine causing the problem what could it be when it still sounds and feels good as ever until time to shift?

thecardoc3

What it "could be" isn't the way to approach this. It isn't uncommon for the information someone gives a tech about a symptom that their car is presenting initially misleads the tech when what he/she observes when testing the car doesn't match how the issue was described by the owner. At this point the contradiction between whether or not the engine truly has power or not isn't settled and shouldn't be without first hand input. Even if it is a transmission issue depending on what transmission your van has it could have electronic or the older style mechanical controls.

No matter what, the fluid in the transmission needs to be flushed out. Engine oils are thicker than most transmission fluids and have completely different additives that won't play well with the seals and clutches.