Change ATF or not ?

[Bill325]

I've previously posted the problem I'm having with my 2000 GMC 4L60-E automatic trans. After it heats up ( takes about 25 miles) the 1-2 and 2-3 shifts become very hard and harsh. There is a service bulletin describing a harsh 1-2 shift ( bulletin 01-07-30-023B) and they recommend replacing the valve body. Before I get to that stage, however, I'm proceeding in a more conservative manner. I've replaced the engine TPS , just in case it had a bad spot when it gets hot. I don't yet know if that helped . My next plan is to change the ATF and filter in the pan . That gets rid of about half of the old ATF, and if I drain the pan a second time after a few miles, I can cut the old fluid percentage down to about 25%. I'm worried, however, about all of the advice I see online about problems that can occur after changing high mileage AFT. ( Mine has 120,000 miles.) My truck seems to have been taken very good care of by the previous owners , although I have no service records. There has never been a trailer hitch on the truck , and it was garaged daily. I would bet that the ATF and filter have been changed at least once before. I plan on using Dexron VI instead of the factory fill Dexron III . My hope is that I might, by some miracle, fix the harsh shift problem by changing the filter and fluid. There are also some " high mileage vehicle" ATFs on the market , such as by Castrol, that contain seal swellers among other things. Any advice on this subject ? Thanks.

 

[Molson02536]

I've previously posted the problem I'm having with my 2000 GMC 4L60-E automatic trans. After it heats up ( takes about 25 miles) the 1-2 and 2-3 shifts become very hard and harsh. There is a service bulletin describing a harsh 1-2 shift ( bulletin 01-07-30-023B) and they recommend replacing the valve body. Before I get to that stage, however, I'm proceeding in a more conservative manner. I've replaced the engine TPS , just in case it had a bad spot when it gets hot. I don't yet know if that helped . My next plan is to change the ATF and filter in the pan . That gets rid of about half of the old ATF, and if I drain the pan a second time after a few miles, I can cut the old fluid percentage down to about 25%. I'm worried, however, about all of the advice I see online about problems that can occur after changing high mileage AFT. ( Mine has 120,000 miles.) My truck seems to have been taken very good care of by the previous owners , although I have no service records. There has never been a trailer hitch on the truck , and it was garaged daily. I would bet that the ATF and filter have been changed at least once before. I plan on using Dexron VI instead of the factory fill Dexron III . My hope is that I might, by some miracle, fix the harsh shift problem by changing the filter and fluid. There are also some " high mileage vehicle" ATFs on the market , such as by Castrol, that contain seal swellers among other things. Any advice on this subject ? Thanks.

EPC (Electronic Pressure Control) solenoid starting to fail. Easy fix in pan. Fix as soon as possible or hard parts will eventually break. This can be checked with a scan 2 reader and also if you do a transmission line test as the transmission goes through the gears.

The transmission fluid i use on my toys is http://www.castrol.com/liveassets/b...GING/local_assets/downloads/t/TranSyndPDS.pdf http://allseasondieselperformance.com/images/Allison-Transynd.gif

We use it on our fleet of coaches and in our GMC transmissions.

Good luck and hope this helps/
Molson02536