Allison question...

[kbyounger]

I have an 06 Silverado. Bought it as the second owner with 314,000 miles on it. It was previously owned by a survey company with mostly highway miles. I have no maintenance records at all. It now has 345,000 miles on it. I pull a 7500 pound camper with it.

As far as transmission maintenance, I have changed the spin off filter with every other engine oil change. I have done nothing with the internal filter or the fluid. I have heard various ideas about changing the internal filter and fluids (change both - don't touch them - drain and refill the fluid only).

I want to do what is best for the tranny. What is recommended, when there is no previous records of maintenance? Change the internal filter and fluids, or simply drain the fluid and refill, leaving the pan and filter alone? Is it true that changing the fluid, with so many miles (perhaps) on the old fluid will harm the clutches or tranny in any way? Thanks for helping me figure this out...

 

[Mike L.]

Change the internal filter also.

 

[JoshH]

You're doing a great job if you change your spin on filter every other oil change. If you're running conventional ATF (non synthetic), I would do a drain and fill every other time you change the spin on. If you have 340k+ miles on the original internal filter, go ahead and change it too. You don't really have to change it much, but with that kind of mileage, it sure wouldn't hurt.

 

[Bdsankey]

As others have said, drain and replace the internal filter and fluid. I wouldn't be worried about damaging the transmission due to new fluid. I also change my spin on every 10k miles.

 

[kbyounger]

Thanks so much. I have heard so many times, to do nothing when in doubt about past maintenance. And new fluid will hurt clutches... Seems like the filters should catch anything floating around in the fluids...
I cannot imagine changing filters and fluid would be bad...
Again, thanks much...

 

[Mike L.]

Truth is:
Back in the old days ( '50s, all the way to the late '90s ) the atf was not that good and neither were the clutches. The addative package in the fluid would quickly burn away and the fluid would oxidize and create a varnish inside the trans. The friction clutches would start to flake and and restrict the filter. Changing the fluid after this would start to wash the varnish and oxidation down to the bottom and help flake off what was left of the friction material. It would plug the new filter and get caught up in the valve body and stick valves. Many times the car or truck never left the hoist and the shop performing the service got blamed. After all, it did drive in and now it won't drive out.
This no longer happens with new clutch material and the new fluids starting in the early 2k's to the present. But is was a potential problem back then.