Trying to save my transmission

I recently purchased a 4WD '99 Silverado. The truck is very clean and looks to be well maintained except the transmission fluid is brown and gritty. I was wanting to change the fluid and filter, but have heard that is not suggested due to the detergent in the new clean fluid breaking loose dirt deposits which could clog the valve body.

I am considering draining the fluid, changing the filter, straining the used fluid and reusing it, substituting a quart of new fluid for old. Then over the course of the next year, periodically draining a quart or two of old fluid and adding new fluid. Hopefully this would allow the new fluid to slowly break down the dirt deposits in a way that wouldn't be as likely to cause problems. What are your thoughts? Thanks.

I recently purchased a 4WD '99 Silverado. The truck is very clean and looks to be well maintained except the transmission fluid is brown and gritty. I was wanting to change the fluid and filter, but have heard that is not suggested due to the detergent in the new clean fluid breaking loose dirt deposits which could clog the valve body.

I am considering draining the fluid, changing the filter, straining the used fluid and reusing it, substituting a quart of new fluid for old. Then over the course of the next year, periodically draining a quart or two of old fluid and adding new fluid. Hopefully this would allow the new fluid to slowly break down the dirt deposits in a way that wouldn't be as likely to cause problems. What are your thoughts? Thanks.

the fluid and filter needs to be replaced. drop pan replace filter. then fill to the proper level about 5 qts of dexronVI.

DO NOT USE DEXRON III .

YOU CAN DISCONNECT THE TRANNY COOLER LINES before starting the engine. and with about 10qts of fluid add new to return line as the old fluid come out the other line with the engine running and the tranny in park.

now you will have most all old fluid removed with a new filter. monitor the fluid condition and you may luck out.

dexron III is a defective fluid to begin with .. when this fluid gets old it becomes acidic. the brown is actually gray metal eaten away by the acid in the fluid.

Thanks jcat. I never knew that about Dexron III. I forgot to include in my first post that the truck has 170,000 miles. When I talked to two different transmission shops about the problem, they said with that many miles, they wouldn't risk changing the fluid at this point, of course they get paid if the transmission quits working.

Thanks jcat. I never knew that about Dexron III. I forgot to include in my first post that the truck has 170,000 miles. When I talked to two different transmission shops about the problem, they said with that many miles, they wouldn't risk changing the fluid at this point, of course they get paid if the transmission quits working.

when you drop the pan you will know if is a very worn transmission ,with how bad the filter and pan bottom is littered with debris.

also with what I stated before, I use a product called transmedic. this on older 10 plus year old , very high mileage transmissions cleans and help[d seals stop leaking.

many years ago when I used dexron III I would add a 12oz bottle of this product then run the vehicle a thousand miles and the drop pan/replace filter fluid. this helps keep things clean and condition seals. 1984 vehicle original tranny no leaks 380,ooomi. the tail shaft bushing got worn at the 275,ooomi ..very easy cheap fix.that was the only repair.

since 1998 I use mobil synthetic tranny fluid . no failures good product about 10.oo a qt,,,.