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Transmission Flush

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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

Edited by DuPont 24

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I am not a Tech but make my living in the Auto Parts Industry. There is nothing wrong with using a trans flush machine to draw the fluid from the trans as long as the tech drops the pan and replaces the filter. You cannot "flush" the filter in your truck. It contains a paper filter media similar to an engine oil filter and it cannot be flushed. My suggestion to you is to drop the pan, clean it, replace the filter and put it back up with apprx 5 qts of fresh fluid. If the fluid appears dark or smells burned or you just want to change all the fluid, you can do this without a machine. You can use the transmissions pump to pump out one qt at a time until you have replaced all of the fluid. Amsoil's website offers step by step instructions as to how to do this and it is very easy. If you are not comfortable in doing this, take your truck to a Prof Tech and let him change the filter and the fluid.

 

Please do not let someone talk you into "flushing" the system without dropping the pan and changing the filter.

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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.

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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.

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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!

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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!

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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.

Edited by C & A s Dad

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If you decide to flush, keep the old filter in, flush, and fill. Then drop the pan and drain 5 qts and change filter, bolt up and install 5 qts fresh fluid.

 

When you flush, you loosen up debris in the valve body and crap gets stuck in the check valves...thats the problems you hear about.

 

The best way is to simply drop the pan every 50K, drain 5 qts or so and change filter each time and bolt it up and top it off..you will not have any problems....

 

Flushing loosens debris...if you decide you want a full flush, drop the pan afterwards and you will pull out 90% of any debris, change the filter etc....

 

That's what a dealer tranny tech told me to do...

 

I just drop, change filter, and top off each time ...no flushes for me ....

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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.

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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!

 

I've got an 05 1500 Crew and noticed this same problem when I went to change the fluid/filter this past weekend. I ended up bolting the pan back up and decided to check around (like here).

Does anyone have any magical secret as to what size/type these fasteners are?

Is there an easier way to get to these?

Anything would help...

Thanks.

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They are Torx and I think a T 15 but I cannot remember. Some people bend the bracket out of the way but I do not recommend that. The torx screws are not that bad to get to but you need the proper size that will fit on a 1/4" or 3/8" drive ratchet. I do not remember for sure, but I do not think you have room in there for a torx srewdriver.

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I used the Amsoil home flush method at the tranny cooler and it worked great. I dropped the pan and changed the filter first, then topped off the pan with fresh fluid before performing the flush procedure. My logic for changing the pan and filter first was when you put fresh fluid in by the fill tube, it goes straight to the pan, so I think performing the flush procedure before you drop the pan and change the filter is somewhat self-defeating because you'll just be dumping fresh fluid into the pan on top of the old fluid already in there, which will further dilute the new fluid. My thought is that by dropping the pan and changing the filter first you are dumping new fluid into the pan on top of new fluid and minimizing the blending of old and new fluid, as well as pushing out the old fluid as you go. Somebody please correct me if my logic is flawed.

 

I believe the proper size Torx bit is the T-40. I used a 3/8" rachet with a socket-type Torx bit and had no problems. Just be sure that you work the bit around a little and get as much dirt and grit out of the top of the bolt as you can before you go yanking on it, or you'll mess up your bit and/or bolt. I also made sure that I used one hand near the head of the ratchet pushing the opposite direction to help hold the bit straight up and down while torquing it loose.

 

I also found on my Z71 that disconnecting the front drive shaft and letting it hang down freely gave me more room to work with. I just put the t-case in 4x4 mode, loosened up the U-joint strap bolts that I could get to first, then had my girlfriend turn the ignition on (did not start it) and put it in 2wd mode while I turned the shaft around to the other side, girlfriend put it back in 4x4 mode and that locks the driveshaft so I don't have to struggle with holding it while loosening or tightening the staps.

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I have 2000 1/2 ton, I take my truck to the shop have them flush it, put in new tranny fluid drive the mile home drop the pan and replace the filter and add about 5 qts of fluid as far as the torqs head bolts on the shift linkage bracket, they where a pain in the a$$, so I replaced them with hex head metric bolts, makes it a lot easier to remove and replace. :D

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When I drop my pan I use a pry bar and bend the bracket. Its just enough to tilt the pan down. I've done this twice. I straighten it back, but I'm not sure its needed. Mark.

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