My '89 4.3 just hit 150,000 miles and seems to still drive fine, but the transmission occasionally does some strange stuff. At around 38-40mph it will surge a bit when I'm just barely on the throttle. I'm guessing this is just the torque converter locking and unlocking since it still drives just fine if I jump on the gas hard. It also does something similar at very low speeds on really steep hills, if I'm just giving it a little gas to crawl up the hill it'll buck a bit, as if it's trying to shift to second, but then dropping back down to 1st. Giving it a bit more gas holds it in 1st and it acts normally. Are these worrying signs? My old '88 blazer always shifted a lot and seemed to race to overdrive, then downshift whenever I touched the gas, so it seems pretty normal to me.

As far as I know the truck may still have the original fluid in the transmission, I'm only the second owner and the first owner kept pretty complete records and I don't see anything about a transmission fluid replacement. The fluid still smells fine, and it's full at the correct level on the dipstick. Obviously I need to do the change though, and I plan to as soon as we get a dry weekend day here in Washington.

My question is on the gasket for the pan. I'm a decent mechanic and have worked on several different cars without issue, but this is my first time doing a pan drop on an auto. I know I need a gasket for the pan, but my Chilton's manual says to use "a new gasket and sealant". Is this sealant some sort of RTV? Is it pre-applied to the gasket? Do I need to put it on both sides of the gasket?

 

Do not use any sealant on the gasket. I have an 89 S15 Jimmy and have changed the transmission fluid at least half a dozen times in the life of the vehical. Use NAPA/Felpro/OEM gasket and you will be fine with no leaks. I would change the filter as well. When you remove the filter there is an O-Ring seal on the filter tube make sure it comes out with the old filter. Might need a scribe to remove the old seal. The new filter comes with a new O-Ring for the filter tube.

 

Great, thanks!