Hello people. Noob here. I recently bought a 04 chevy 2500 crew cab with the 8.1 and allison. I have been on these forums a lot gathering information about this. Read a lot before I bought it. Its a fun truck I purchased due to the respect for the 496 engine. (wanted to have something more powerful that my BIL's v10 f250 :))

I want to switch to synthetic and read all about the hoot method for the Allison transmission. Me and my mechanic (buddy) are a little nervous about doing this.

Local auto places will either do a flush which I do not want or a straight drop the pan and replace fluid.
I was wondering if there was anybody that would be able to help me do the hoot method. I live in the KCMO area. We can discuss cost etc if there is anyone interested.
Thanks for your help.

http://www.dieselplace.com/forum/showthread.php?t=239630 here you go :)

It's really easier than a writeup would have you think. The main thing is to make sure you don't get fluid all over the place (some large pieces of cardboard are really helpful) and pump out a little, then refill; then pump out a little, and refill, etc. Don't try to do too much at one time. Make sure you have plenty of fluid on hand before you start - maybe a 2 or 3 quarts extra.

I live in Topeka (Berryton address) and am at home during the daytime if you really need more help. You can find me in the phone book or Whitepages.com.

One more suggestion - wait till the weather is a little nicer.

The Hoot method is not technically difficult, but you should read all of the instructions, assemble fluid, tools and equipment, and give yourself some time. Don't try to cut corners. But if you are still intimidated, just drain the pan (you don't have to drop it), change the filter (be sure to replace the magnet on top of it), and refill the pan. Drive it for a few days and repeat. Not entirely as good as Hoot, but close enough for most purposes — and Allison agrees.

I guess there are shops around that can do a flush without pressuring the fluild out of the transmission. They have a machine that can be placed in between the trans cooler and the pan and drain and fill fluid at the same time with the truck on. Would that be acceptable. That is essentially the same as the hoot method right?

yep....thats the hoot method in a nutshell.....make sure if they effe up though, that they will cover their mistakes...its not cheap to rebuild an ally

I guess there are shops around that can do a flush without pressuring the fluild out of the transmission. They have a machine that can be placed in between the trans cooler and the pan and drain and fill fluid at the same time with the truck on. Would that be acceptable. That is essentially the same as the hoot method right?

Allison does not recomend the use of a fluid exchange machine. If you don't want to do the hoot method just drain the pan and refill. If changing out to TES 295 it will take two pan dumps with filter changes to effect a 100% concentration needed for the extended service intervals.

By the way -no need to remove the pan to drain fluid on Allison -it has a drain plug.

Anyone that lives in the KC area want to earn some extra bucks or a case of beer or some computer help? :)

Allison does not recomend the use of a fluid exchange machine. If you don't want to do the hoot method just drain the pan and refill. If changing out to TES 295 it will take two pan dumps with filter changes to effect a 100% concentration needed for the extended service intervals.

By the way -no need to remove the pan to drain fluid on Allison -it has a drain plug.

Yes,it has a drain plug,but unfortunately the pan is recessed by the plug,so if you just remove the plug,app. 2 qts. of dirty ATF will be left behind.If you drop the pan to get all the fluid out,then you can also clean the gunk on the bottom.

Just make sure you snap in the retun line into the tranny!!!!


Don't ask me how I know this. It's a simple job to do just make sure to snap in the line as mentioned above.

It really is a piece of cake. The main thing is getting prepared and having everything in place. Take your time.

To start with, it's a great write up, really helped me. First off, use safety glasses!
A. If you have a 4" down pipe, you'll have to loosen the v-clamp, hanger bracket, and/or flange to get the cooler line out of the tranny. Also, there is a plastic retainer bolted on the side of the engine. It helps to remove the retainer off the stud to aid in moving the return line.
B. I used clear 5/8" vinyl tubing with a 1/2" pvc elbow. The elbow with a short piece of tubing will fit between the line and side of the tranny. You only need a clamp on the return line. I didn't want to bend the line much. I did it off the passenger side with a driver.
C. The drain plug is recessed into the pan, so there will be at least 1 quart remaining in the pad when you drop it. Have a tray under the pan in preparation of a spill.
D. Keep a tray under the open cooler line on the tranny because fluid will over flow from there.
C. From what I researched, the capacity does not include the cooler or the lines.
When you get to the point of pumping out the remaining dirty fluid:
1. Plan to have your driver run through the gears right away.
2. Plan to shut down the engine after 1.5 quarts. Shortly after shut down you'll get another .2 quarts or so.
3. Only pump out approximately 3.5 quarts. Reason being, the fluid you add is mixing with the old. There is no dark brown flow followed by a bright red flow. Near the end, it's mixed.
I had 5 gallons on hand (20 quarts) and ended with about 2.5. I pumped out, on 3 attempts, about 6 quarts. I had added 2 quarts after each pump attempt. IMO, I pumped out at least 1 quart that MIGHT have resulted in 1 or 2% gain in clean fluid to dirty fluid. I guess my tranny is about 98% pure. That's good enough for me! Good luck!

Yes,it has a drain plug,but unfortunately the pan is recessed by the plug,so if you just remove the plug,app. 2 qts. of dirty ATF will be left behind.If you drop the pan to get all the fluid out,then you can also clean the gunk on the bottom.

Absolutely right! But my response was aimed at someone who was considering taking the truck to a shop and being hooked up to flush machine due to being "unsure" about tackling the job due to his skill set/comfort level.

If someone wants to switch to TranSynd without the hoot method ---it is as simple as doing two consecutive pan drains via the drain plug with filter changes in a 25K time period. This is straight from Allison's technical information. Is it the "best" method? No -but for someone faced with the OP's choices and inferred skill set -it might be.