transmission oil change

OK as I am nearing 25K on my truck the manual recommends changing the tranny oil at 25K. I changed the spin off filter at 10K. I talked to the dealer and they are quoting 245 bucks for a flush and fill. Stating that it is imperative to get all the oil out of the transmission and torque converter. When managed to get my jaw shut, he subtly reminded me that preventative maintenance not only keeps the warranty in effect, but the transmission is 6K not including labor. Then he smiles at me..."is it worth risking?"

I had planned on buying the Transynd and filters and doing it myself. Is this not advisable? Is there more to this than a 'regular' transmission oil and filter change? I know that there is two filters an internal and external, I assume both get changed.

What are you guys doing?

Wrong forum, but I'll move it:)


The flush isn't bad, and you can do it yourself (help is nice, but not required). Search the drivetrain forum. Lots of posts and some step-by-step instructions. If you are not replacing the pan (with the deep pan), just drain it. Allison recommends the internal filter be changed only during overhaul. Your fluid choice is good, but there are other options at 1/2 the price, and every bit as good, IMO. Check out Amsoil TorqueDrive. Any synthetic is better than any dino fluid. Mobil 1, Redline, Royal Purple, etc. are all good, but TorqueDrive is the only fluid (other than Transynd) that carries the TES-295 spec.

Honest, I had two minutes at work to post, and I did! I realize the err of my ways!

No problem. That's what we're here for. If you gotta post, just post. We'll sort the details later.

I'm going to use the Amsoil and this is a post I saved sometime ago.

" Drain the pan (don't remove, it has a drain plug) and replace the plug. Refill with about 8 qts. Don't worry about the fluid level yet, you're just going to pump it out. Remove the "from cooler" line at the tranny (top line), and install a hose onto it. You don't need the hose, but it's sure a lot less messy. Direct the hose (or fluid path if no hose) into a large container. Baffle the stream, as it can come out quite fast. I used a plastic Gatoraide bottle with the bottom cut off. With shifter in P, and E-brake on, start the engine, and keep at idle. Watch fluid stream (helps to have another set of eyes). As soon as it starts to slow down, turn off engine. Add about 8 qts, start engine and watch stream again. Shut off as soon as it slows down. Repeat these steps until you see a color change in the fluid, or you have added about 15 qts. Stop the flushing and replace the cooler line. Be sure it snaps in good and solid. Replace the spin-on filter, and don't forget to remove/clean/replace the magnet that should come out with the filter. Fill up to the "full cold" level, which should be about 8 qts. Bring the tranny up to operating temp. A short drive should do it. Drive in a manner that keeps the torque converter unlocked, like under 50 MPH, not in T/H. This will warm the tranny quick, and cycle as much fluid as possible. Recheck the fluid level, and fill up to the "full hot" level. Check for leaks. Drive it normally for a while (a couple days or warm-up cycles), then check the fluid level again. Done.

If you have a service station available with a passive flush machine and the connectors, you could go that route and avoid all the mess and disposal. Be sure their flush machine is PASSIVE. It's important to let the tranny do all the pumping. Using a powered machine can damage the tranny. Don't let anyone tell you different!

Good luck. "

Hope this helps.

Mark thanks for the details. Sorry I have been a little slow to get back here. This sounds like a real process. So that I am sure I am following your details, you are using the new oil to displace the old oil that is running through the gatorade bottle?

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Originally Posted by Stlheadake

Mark thanks for the details. Sorry I have been a little slow to get back here. This sounds like a real process. So that I am sure I am following your details, you are using the new oil to displace the old oil that is running through the gatorade bottle?

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I wrote that up some time ago. The plastic bottle is just to baffle the flow out of the cooling line. It comes out pretty fast, and will splash right out of a shallow drain pan.

After draining and filling the pan, the fluid pumped up will be fresh. Usually (I've done this quite a few times), there will be a noticeable change in fluid color once the old fluid is about gone. If you change new(er) fluid with like fluid, you may not notice it as easily. Going from dino fluid (OEM fill) to synthetic should be obvious. Good lighting helps.

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Originally Posted by DmaxMaverick

I wrote that up some time ago. The plastic bottle is just to baffle the flow out of the cooling line. It comes out pretty fast, and will splash right out of a shallow drain pan.

After draining and filling the pan, the fluid pumped up will be fresh. Usually (I've done this quite a few times), there will be a noticeable change in fluid color once the old fluid is about gone. If you change new(er) fluid with like fluid, you may not notice it as easily. Going from dino fluid (OEM fill) to synthetic should be obvious. Good lighting helps.

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This write up is exactly why I keep my subscription!

The last time I was in the local allison shop buying filters and transynd they had a sign up $170.00 for change over to transynd. I didn't ask them what was all involved but it would of been cheeper than what I did.

170 bucks for transynd and filter, AND I don't have to do the work? That sounds like a no brainer to me. I called another dealer (chevy) today and they told me that a 'regular transmisison flush is $130 bucks, so the Allison would only cost the difference in the more expensive Dexron VI' Not having any idea of what the Dexron VI costs I asked him to ball park he thought he could do the whole thing for around $160 bucks for dino oil!

I wasn't feeling great about his confidence in all of this since they don't sell the Dexron over the counter. He stated that they have a bulk tank so he couldn't really quote me a per unit price.

I'm done digging around. I have a local Amsoil dealer who is working up a price for both my truck and my dad's (both are ready). I'm going to use DMaxMaverick's write up on how to flush it, and I will be done! Good for another few thousand.

Thanks for all the info!

For what its worth, we pull the snot out of our Duramaxes, and use one method, every 10K oil change:

1) Drain what comes out of the transmission with plug removed;
2) If you are really energetic, with parking brake on, do a series of P-R-P-D shifts to get another quart or so out the drain;
3) Spin on a new filter, replacing the magnet on the new filter;
4) Add 7-8 quarts, rechecking level in next 100 miles driven.

If you had encountered severely hot tranny temps, or had scorched (stinky or dark colored) fluid, I'd certainly flush using the method above. I have never seen this happen, all of the fluid I have seen coming out of Allisons is happy and pink. Even with 240K on our 2002 with a trailerload every day, and moderate temps at all times.

I am certain that daily drivers and weekend warriors would be more than well served with this 'refresh' method. Not only is flushing yourself messy and time consuming, any time you take a fitting loose, its a potential leak when underway. Why bother.

More insight, I love it!! Mark, what do you think about switching from Dexron to synthetic? Wouldn't a flush be a good idea? I am VERY concerned about taking the cooler lines a part, I don't have the tool (not that getting one is out of the question). I hadn't thought about shifting through the gears to get that 'last little bit' out.

I like your process it is a hell uva lot easier and cleaner to do, and just change the synthetic a little earlier or is that even a concern? I pull our 14k trailer about twice a month maybe a couple hundred miles a month each trip. Nothing too big. Certainly not as serious as other trucks on the list.

Thanks again,

Removing the line is a piece of cake. It's O-ring sealed, so as long as you clean up everything, it should not leak. No special tools required, either.

Here's how.
Pull back the plastic collar at the connector. Use a small screwdriver or pick to remove the spring clip (it's like a staple, and should pull straight out easily). Hang on to it, or it'll take flight, never to be found. The line will come out, you may have to wiggle it a little while pulling. Not too much force, it doesn't take much.

Replace the clip immediately (so you don't lose it). When done, push the line back in until it clicks and the line is in solid. Give it a little tug and wiggle to ensure it is secure.

If you are replacing with like fluid as a normal service (not because it got too hot or is burned/contaminated), Mark's method is probably the best. If changing fluid types, I recommend a full flush. Basic logic applies here.


$170 for a Transynd changeover is a very good deal. As long as it includes the fluid and filter. If fluid is not included, then not so good of a deal. While you are at the Allison shop, pick up a few spare filters. They will be much cheaper there than at the dealer. Typically $10-15 vs $35+.

is there a specific place/cap to add auto tmission fluid in the allison or do you just remove the dipstick and use a funnel to add fluid? I dont remember seeing a specific place to add new ATF in the duramax/allison combo.

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Originally Posted by bradmd

is there a specific place/cap to add auto tmission fluid in the allison or do you just remove the dipstick and use a funnel to add fluid? I dont remember seeing a specific place to add new ATF in the duramax/allison combo.

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Nothing new here. Use the dipstick tube.

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Originally Posted by DmaxMaverick

Nothing new here. Use the dipstick tube.

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thx very much