Transmission Flush

[aediaz]

Dear GM Technician:

I have a 2002 Chevy Avalanche 1500 with the Z71 package. I bought it last year with 61,000 miles on her. I have now about 65,000 miles. I'm changing all the fluids of my truck because I don't know in what conditions the previos owner drove the truck and I don't have the service record. Know I need some advice about the transmission, I call my GM dealer to change the tranny oil and they told me that with my mileage all I need is a transmission flush and change the filter when the truck get 100,000 miles. I heard from people who owns Avalanche that after they had the Transmission flush they got problems. Others recomend to just drop the pan and change the oil and filter.

Please, provide me some advice!

Thanks

[Z45]

There has never been a reason to flush a transmission with a flush machine other than to make easy money.

 

 

[Fyrcaptain]

I believe that a lot of the problems you hear about come with the use of the high powered cleaner that they use before hand (BG and I am sure a few others).

I believe a low pressure flush / fluid exchange without the use of a pre-cleaner is the way to go with, after a pan drop and filter change.

[jdelrizzle]

Hey rob, what I am about to say is going to piss you off but I'm going to go ahead and say it.

I have been on this forum for almost a year and I've read and learned plenty of things in regards to my truck, I have read time and time again, DON'T do tranny flushes, they'll screw your tranny up! I even read one thread were you put, you people don't get it don't flush your transmission, blah blah blah. I understand your a high speed transmission guy, former GM tech, etc, but I am almost certain had the CLL3 guy said something like I got my tranny flushed at jiffy lube you wouldn't be saying the flush had nothing to do with his tranny blowing up, I understand it's your opinion, I'm just saying.

[Silverfoxbody]

I agree,drop the pan and change fluid and filter. On my old Suburban when I dropped the pan I drilled out the pan and installed a dran plug for more frequent changes of fluid and replaced the filter every other change.You can det that drain plug kit at any parts store.

 

 

I am unsure what is the HOT OUT cool line on that trans, but the best way to drain is to undo that fitting and run the engine will the ATF is all pumped out into a pan, then drop the pan, much less of a shower.

[bassadict69]

Someone needs to inform our local GM dealers about this...when I had mine done, I called everyone one of them in town, and ALL of them only would do the flush. They all told me that changing the filter was unnecessary & that the machine would flush it.

 

I ended up getting a local shop to do the flush & filter change!

[corgnon]

I recently performed this service on my 2002 Z17 Suburban, just before 100K miles. A couple of observations:

 

• My pan has the drain plug BUT it wasn't coming out! Of course, I stripped it and had to drain the pan the old fashioned way. The recommendation to drill a hole and install a plug is a good one.
  
• You need to remove bolts that attach the range slector bracket to the pan. These are overhead bolts that are not very easy to get to and they require something like a starz or torqz. I did not have the proper tool and even if I did I'm not sure I could get to these fasteners. So I ended up dropping the exhaust from the manifold in order to fully remove the pan.
  
• There is a seal in the transmission that probably will not come out with the filter. If so, don't bother removing and replacing it unless you have the proper seal puller. With out the right tools you can scratch up that bore.
  
• The recommended Amsoil sight that describes a full transmission flush is: http://www.amsoil.com/faqs/ATF_and_Filter_..._Procedures.pdf
  
• I found the best place to flush the fluid is at the transmission oil cooler. Since you have a Z71, you should have the tow package, which includes extra cooling capacity. This will be a small heat exchanger in front of your radiator and AC condenser. You'll need to remove the grille, which is actually very easy to do. Disconnect the right side connection and run the engine to pump the old fluid out. I was flying solo so I had to do this in iterations (drain some fluid then add some fluid). You will easily notice the change in color when the flush is complete.
  
• Now here is my biggest recommendation of all. You should also replace the gear oil in both the rear and front differentials AND replace the AUTO-TRAK fluid in your transfer case. I was very surprised how worn the gear oil looked.
  

Good Luck!

[ChevyTech77]

Then, at the next engine oil change, pull the engine oil drain plug, drain half the old engine oil, put the plug back in, put a new oil filter on it, and top of the engine oil too.

 

Same way of thinking, just sayin.

[lbilan]

I've read what everyone has said and it seems to be in my best interest to just drop the pan, replace the filter and add new fluid. I have a 2500HD with 102,000 miles on it and has never had the transmission oil changed. I have it at the GM shop and they suggested the flush and fill and not replacing the filter. I bought this truck new, have never had a problem and knew the trans had to be changed at 100k. I've used this truck to haul our tractor/farm equipment. Never thinking this service should have been done sooner. Now with this many miles and the GM guy just saying to flush and fill, I don't want to lose this transmission, I have no problems at all with this truck and love it. I've had the radiator flushed and filled and kept up with oil changes, what is everyones best oponion for me to do.

 

P.S. Husband it out of the country on business and he's left me in charge with this?

 

Thank you

Leah

[Stevens03]

And the word flush is such a dirty word when it comes to transmissions. I cringe every time I read it. I like to use the term swap. Really I think one of the best ways is to disconnect the cooling lines and use the transmissions own pump to suck in new fluid and pump out the old fluid. 2 bucket method. That way you get 99% thru the torque converter too and your not "stirring" up any possible loose debris. And why the dealership wouldn't change the filter is beyond me.

 

I've seen guys do reverse flush's that loosened crap up and cause the trans to fail shortly after

[peteking]

And the word flush is such a dirty word when it comes to transmissions. I cringe every time I read it. I like to use the term swap. Really I think one of the best ways is to disconnect the cooling lines and use the transmissions own pump to suck in new fluid and pump out the old fluid. 2 bucket method. That way you get 99% thru the torque converter too and your not "stirring" up any possible loose debris. And why the dealership wouldn't change the filter is beyond me.

 

I've seen guys do reverse flush's that loosened crap up and cause the trans to fail shortly after

 

OK, I've seen the 1-bucket method, where you disconnect the return line on the radiator, connect that via a tube into a bucket. Then you pump out the old fluid, stop, dump in a few quarts of new fluid, and repeat. Where does a second bucket come into play?

[C & A s Dad]

Orangeman, good advice and this is what I did. Only I was able to remove my trans gear selector bracket pretty easy and the pan came right out. When I was going back up the clearance between the pan and the exhaust crossover pipe was close but it fit back in without any problems. I was replacing my OE cooler with a larger one at the time so I had hoses attached to my cooler lines. The longer hose allowed me to reach a container so I did not make a mess. The Amsoil site provides a good blow by blow of this process.

 

If you do this again and you have clearance issues, you may be able to remove the bolts and/or nuts from the rear trans mount and simply lift up on the trans a little to clear your exhaust pipe. Not sure about this but it may be easier than fooling with the exh pipe.

[txab]

Then, at the next engine oil change, pull the engine oil drain plug, drain half the old engine oil, put the plug back in, put a new oil filter on it, and top of the engine oil too.

 

Same way of thinking, just sayin.

 

Not really. Not trying to start an argument, but you can't arbitrarily make the engine oil to trans oil comparison, IMHO.

 

Transmissions aren't exposed to hydrocarbons and moisture constantly like an internal combustion engine is. Having been responsible for and seen the data on over 80 trucks that our company uses, doing a pan drop regularly does just as much as a flush with no pan drop. If there is material in the pan, it is examined. Every vehicle's transmission fluid is tested, engine oil as well on regular schedule. We've got trucks that have 250k + miles with 4L60, 4L80, etc... that have survived. Have a couple of them broken? Yes, but not due to a fluid related failure.

 

With Dex VI out, we have started changing out all fluid on each unit, mainly because oil reports are not consistent with Dex III and Dex VI mix. After re-reading and seeing that the poster has an older, pre-synthetic filled trans, I'd go for a complete change WITH a pan drop and filter. After that, just pan drops, unless some other condition warrants it. But if she did just do a pan/filter drop now. I would still sleep well knowing what I know.

 

On my personal vehicles, all are full synthetic now and will only receive pan drains/drops and the filter screen only if necessary.

 

 

Best thing for all, is do do whatever makes you sleep well at night

 

 

Now if you BBQ your transmission regularly, there is a different story......