Allison slipping since fluid change

[Heavy Metal]

I recently switched my 2008 Duramax Allison to Transynd after reading many rave reviews. Previously I was using non-synthetic. Perhaps it is just coincidence but after a few hundred miles my Allison started slipping and seeming to be getting worse. Sometimes on cold start-ups, but mostly on really hot days, load or no load, it slips for a while, then takes hold, then may slip again after a while. both tow mode and drive. Is there any reason to think going to synthetic triggered this and should I : a. go back to dino oil. b. change to different fluid. c. change transynd again. Truck is 2008 Crew cab LTZ dually with 240k on it.

[DmaxStoreJimmy]

When you switched did you just dump the pan and fill? Did you change the spin on filter? Have you had somebody hook up a scanner to see if there are any codes?

[Heavy Metal]

just changed the spin on and drained pan.

[Heavy Metal]

have not checked for codes. That will be Friday when check on my fuel system issue.

[Mike D]

just changed the spin on and drained pan.

Sounds like you may have incorrect fluid level. How much fluid did you ad? Also did you drop the pan or just drain from plug?


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[Heavy Metal]

HI Mike! I just drained from plug. Filled to hot full with engine running. I had it checked this weekend and there were no codes. Should first step be a dropped pan change and another new filter?

[Mike D]

HI Mike! I just drained from plug. Filled to hot full with engine running. I had it checked this weekend and there were no codes. Should first step be a dropped pan change and another new filter?

Do you have the factory shallow sump pan that comes on the truck new? Do you recall how much fluid you added?


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[Heavy Metal]

Yes, truck is bone stock. Did not measure exactly. Bot the Transynd kit , started at about 7 quarts and and topped it off.

[Mike D]

Yes, truck is bone stock. Did not measure exactly. Bot the Transynd kit , started at about 7 quarts and and topped it off.

Hmmm. Slipping seems very unusual with what you did.
Curious if you have checked the Tcase fluid and condition?


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[Heavy Metal]

2WD (sadly)

[Mike D]

2WD (sadly)

Well it seems very strange. Get the fueling issue resolved first. That may be all that's needed. The Allison shifting is highly dependent on fuel pressure. I have seen people change a valve body just to realize all they needed was a fuel filter.


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[Heavy Metal]

Had no idea the two were related. Ordering this week. Thanks Mike!

[Andremaxproblems]

Did you figure out your problem? I have a 2005 lly and I just did a fluid change with external filter only. Used the transynd and now after service it won't go into R hot or cold. It does however go in if I shift it though the gears for 10 min. Any help would be appreciated

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[Mike D]

Did you figure out your problem? I have a 2005 lly and I just did a fluid change with external filter only. Used the transynd and now after service it won't go into R hot or cold. It does however go in if I shift it though the gears for 10 min. Any help would be appreciated

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The symptoms Heavy Metal has are different than what you have. I just responded to your concern. Take a look when you get the chance. We will help you get it figured out. 👍


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