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1989 Chevrolet 3 4 Ton Pickups Base Fleetside 131.5

1989 Chevrolet 3 4 Ton Pickups
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January 21, 2013, 11:48 am

Allen L

Question: Need opinion on changing automatic tranny fluid

This vehicle has a 305 engine with automatic transmission. 4wd. It is mainly used as a plow truck around the farm. It has about 250k miles on it now. I got it at an auction several years ago. Generally it is running good. Every once in a while I will think it shifts odd or "hard"..mostly it does good.

Anyway...I have no idea when the last time the tranny fluid was changed. Anyway...lots of guys on line say at this point not to change the fluid because it will hasten problems coming. Other guys say change but don't "flush". And others say it really doesn't matter.

I'm leaning towards changing, new filter, but no flush so as not to "shock" the system.

Thoughts?? Goal here is to keep truck running as long as possible without a rebuild. If it broke down now I would probably rebuild. If I could get it to work another 3 or 4 years....and many more miles...I may skip it and put the plow on something else.


January 26, 2013, 8:24 pm

Ron W
Expert Mechanic

I would recommend you change the filter and transmission fluid. I don't recommend flushes.

And it is true that sometimes when you service a transmission that hasn't been serviced in a long time, they can fail. It's not from the service, you just removed the gunk that was holding it together. The transmission would have probably failed anyway, cleaning it out just made it happen slightly quicker.

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