chevy 4500

[woodmills1]

when I did an oil and filter last week I noticed the allison transmission in my 2005 chevy 4500 has an external filter.   I bought the filter, and changed it the next day(almost didn't see the magnet that sits on top the filter) but wasn't happy about the trans fluid color, a bit brownish at 25,000 miles.  well low and behold there is a drain in the trans pan.  so here is my question

should i drain the pan and replace the fluid?
if so, what fluid and how much

I didn't get an owners manual with this used truck

[wooddog]

Hi woodmills1 Draining the will not get alot out, There is a filter inside that you can get from you gm dealer  Drop the pan change the filter and see if there is alot of clutch dust or dark kind of slug in the pan If the truck was hailing heavy stuff or plowing It may mean the forward  clutches may be wore a bit, Put new oil in it start with about 6 liters  run the truck and top up as needed, don't drive it till It is at least on the full cold mark, Then drive till up to temp and recheck and top up, Should be ok then.

[wooddog]

I forgot put only dextron from your GM dealership Its the only that should be put in that trans. And it is a synthetic oil..   

[woodmills1]

thanks for the tip

I drained it and the dipstick said dextron I put 9 quarts and will wait 1000 miles and filter and 9 quarts again, it was not good lookin fluid I took out >:(

[stonebroke]

You could see if BG systems can flush it. They pump fluid though until it is all clean.

Stonebroke

[ScottAR]

Dextron VI is the allison spec fluid.   It is synthetic.