Drain And Replace Auto Trans Fluid Or Flush And Fill?

Wayne02 · July 23, 2009

2000 GMC sierra 2500LD, 6L, Auto, 4x4 SLT, 87,000 miles. The truck does do some towing and hauling with maybe a 85/15% commute/tow haul split.

I have the truck up on the hoist doing some service right now and was wondering what the recommended change-out frequency is for the auto trans fluid and filter on these trucks?

I do 90% of my own work on vehicles and have always drained the fluid by removing the pan, and replace filter and fluid. I'm aware that this method may not exchange all of the fluid in the system, but I can't recall this method to have produced any negative affects on any of the vehicles I've done this on.

However, reading the wonderful internets I see comments on how much better having a shop do a flush and fill on the transmission is, and I assume they use some sort of machine for this that will exchange most all the fluid in the system?

What say you?

Flush and fill vastly superior to drain and fill? Worth the cost and hassel to have a dealer or trans shop do this service? Or not...?

Thanks

crepitus · July 23, 2009

txab · July 23, 2009

Google search results....

Several posts to read.

DBVille · July 23, 2009

Well, since you asked a pointed question, I'll actually answer it.

I would not take any vehicle past 50,000 miles on tranny fluid. Probably more like 30,000 max.

I don't flush - I drop the pan or just drain the fluid. Partially because of the stories I have heard about cars dropping trannys after a flush, and partially because I am afraid of the job being relegated to the newest guy in the shop.

Wayne02 · July 23, 2009

Well, since you asked a pointed question, I'll actually answer it.
I would not take any vehicle past 50,000 miles on tranny fluid. Probably more like 30,000 max.

I don't flush - I drop the pan or just drain the fluid. Partially because of the stories I have heard about cars dropping trannys after a flush, and partially because I am afraid of the job being relegated to the newest guy in the shop.

Thanks. I'd have to check my records but I believe the trans was last serviced at about 45-50K which I had done at the dealer at the time because it was still in warranty, and it was in the dealers for something else. Once out of warranty I try to do the work myself if possible. Sounds like this subject is about like the old 9mm vs. .45 discussions and I need to just pick one and get it done.

randyf · July 23, 2009

Serviced the tranney on my 05 Suburban.

I changed the filter and did the home fluid flush.....

I took the bolts out of the transmission mount and jacked it up a little..... I used a screw driver the push the transmission bracket over and work the pan out......its a real pain!

Installed new filter and replaced pan.

Filled with Dextron VI

I removed the grill (easy took just a couple of minutes) I have a trans cooler in front of the radiator...it had both lines on the bottom, I took off the one on the passengers side and attached about a 1 1/2 foot tube to the line....when you start the motor the fluid pumps out......do a quart or two at a time.

Repeat till the fluid changes color.....ouch!!! mine took 14 quarts!!

Dirty Chris · July 23, 2009

Same method, step-by-step:

http://denalitrucks.com/forum/viewtopic.ph...ht=tranny+flush

The benifit is you use the tranny itself to pump all the old fluid out, replacing it gradually with new fluid. Since you're using the tranny pump, there is less chance of forcing something loose (with a machine) that might lodge itself in the wrong nook, cranny, valve, etc.

Starrman · July 23, 2009

Same method, step-by-step:
http://denalitrucks.com/forum/viewtopic.ph...ht=tranny+flush

The benifit is you use the tranny itself to pump all the old fluid out, replacing it gradually with new fluid. Since you're using the tranny pump, there is less chance of forcing something loose (with a machine) that might lodge itself in the wrong nook, cranny, valve, etc.

gotta be registered on that forum to view the post

WaterGuy · July 24, 2009

I take mine to my local guy who has been doing GM trans for 37 years.

He drops the pan and "reads" the piles of debris. He can tell me exactly what is normal and what is not as well as what part(s) is making the piles.

He is the guy that the other trans shops go to for help.

He does have the machine that does the power flush. It even does a systematic momentary reverse of the fluid. The machine usually has dust on it.

That said, just do a drop pan and filter change and top off. Unless you have burnt (or other issues) fluid then a full exchange is required.

jvmorgan · July 24, 2009

Hopefully Nick will chime in on this question I am wanting to switch to AmsOil in the transmission and do I need to do a complete fluid switch of are they compatible in mixing them together?

Wayne02 · July 24, 2009

Thanks for the replies. I guess what I'll do is drop the pan, change the filter and unless there is anything that looks bad I'll just refill with 4 qts of Dexron VI. From the dipstick the fluid looks fine and I have not had any problems.

If I go this route that means there will be Dexron VI mixed in with the existing Dexron II or III that is in the system currently. Assuming you can't buy III anymore? From my reading, it appears that VI is backward compatible so that should not be a problem???

Also, when I purchase the trans filter, I assume it comes with a new round seal as well? Does it come with a new pan gasket or do I need to buy that separately??

Thanks

Wayne02 · July 25, 2009

I was able to find Dexron III but had to go to two different stores.

That very back bolt on the pan that is buried under the trans cross-member looks like it will be near impossible for me to get back in. I was able to break it loose with a small end wrench, and then turn it out using one finger from each hand but I don't know if my big fingers can get that thing back in there to get it started. (Assuming the pan will drop with the trans cross-member in place)

Also noticed that one of the two bolts from the rubber trans mount to the cross-member has broken off inside the nut, seems to be tight but there is little thread engagement. The other bolt is quite long. If I'm going to drop the cross-member to change to pull the pan I might as well replace the trans mount at the same time. Of course today being Saturday who knows if any dealership parts places are open or would have one in stock...