I've got a 2004 2WD 1500, which size rear end is it?
I thought it was an 10-bolt 8.5 rear end.
Tried to buy something for it and was told it was an 8.6...??

EDIT: Nevermind, I got some good information by searching. Turns out GM changed in 2001 from an 8.5 to 8.6, but some parts are still universal, but some aren't...

 

I thought that they changed in 99....(why do I think that I'm going to be buying to sets of bearings when I do my trutrac darn it!)

 

you have a 8.625" rear end

 

You might be right... After re-reading, might be 2000, I'm not sure...lol

My concern was I bought a true-trac for an 8.5 rear and and 4.10 gears.
Then, went to get the install kit and was told it was 8.6, not 8.5- I got a lil' nervous.

 

yep pre 99 is the old 10 bolt 8.5" rear
99+ is the newer 8.625" 10 bolt rear

 

Either way it shoulld fit. Only the ring gear diameter changed. Hence the 8.5" or 8.6" dimensions. IIRC, carriers and ring gear bolt pattern are the same.

 

the install kit is different between th 8.5 and 8.6...i know because i ordered the 8.5 one and Ron emailed me telling me i need the 8.6

 

I was wrong apparently, the ring gear is the same size at 8.5" but the install kits are different just like GMCtrk said. 8.6 is always 30 spline and came on 99 and up trucks (NBS).

 

Yep, Ron straightened me out, too.