Re: water pump for a 478 with air brakes
 

What model; Allison is in your GMC terry? tom

Re: water pump for a 478 with air brakes
 

That's a great question! I have tried to figure that one out myself. I've not found any markings on it, it's a manual shift, meaning there is no electronic's.

Trans had a hyd PTO at one time as well. Here is a link to some photos:
https://www.flickr.com/photos/terry_warner/

I took these photos when I first brought Chug home.

Terry

Re: water pump for a 478 with air brakes
 

Amazon came thru with the gates pump that is brand new! Arrived here today, however the fedex guy got stuck in our driveway. epic snowstorm last night and today and we are at 7800' so had to get the tractor out to get him back on our gravel drive. No problem however as It's the right pump and it's new and here.

Terry

Re: water pump for a 478 with air brakes
 

glad you got it terry. truck looks awesome in the pics. thought maybe you had a later Allison it in it. tom

Re: water pump for a 478 with air brakes
 

That transmission is the MT series, probably an MT 40 or 41. It's a 6 speed, direct in sixth with locking torque converter and more than likely has a grade retarder.

Re: water pump for a 478 with air brakes
 

super nice piece terry. keep it going. ive seen those MT flexplates on Ebay for the V6s. im pulling the non synchro Spicer 4 speed out of the bus in the next couple weeks. plan is an Allison 2100 5 speed auto overdrive trans. main issue will be if torque converter hub will pilot into the crank end bore. tc hub may need to be machined. will need to have a custom flexplate made. I haven't seen the late Allison on a V6 but im sure its been done. tom