who knows their allison transmissions???

[lapeer20m]

i keep searching and can't find the answer.

according to the previous owner the new bus has an mtb743 automatic trans. I want to know how many speeds it has. I think it's an MT743...the B equals retarder i'm pretty sure.

perhaps he's mistaken and it's an ht743?

thanks

[crazycal]

I don't know about the others, but I don't think you're retarded.


I think there is a R after the model number if there is a retarder.

[crazycal]

Checked a book. The 700 series is a HT. I think the middle number is the number of gears.

[lapeer20m]

i can hear/feel the trans shift from first to 4th gear. I found the axle ratio, and the tire size is easy enough to come by as well as max rpm for a 6v71

max rpm: 2350
axle rato: 4.56:1
tire height: 41.3 inches
final drive ratio: 1:1

max speed 63.34


unless that trans has overdrive which is very unlikely, someone is not telling the truth when he states it'll cruise an indicated 70 or 75 mph on the speedo which he believes to be an actual 80 -85 mph. I tested the speedo vs my gps and found the speedo to be off less than 4% ie: when speedo sais 50 mph the bus is moving almost 52 mph according to gps.

wonder how i can identify the transmission....perhaps i can find a tag on the unit when i crawl under there.

GRRRRRRRRRRRR!!!

[lapeer20m]

i crawled under there and found the tag. Allison on their website states that the tag for there transmissions is 2" x 3" on located on the right rear of the transmission. That helped a lot. After scraping off oil/grease from the tag (it is a Detroit Diesel under the hood) i discovered it is an:

MTB647

I belive it is a variant of the MT647.....probably not so far removed from the 643.

[lapeer20m]

here is a photo of the transmission tag





this is a four speed transmission with a final drive ratio of 1:1

[the_experience03]

That be an AT545 as best as I can tell.

[Elliot Naess]

I like this site for Allison information:
http://www.industrialautomatic.com/html/onhiway.htm

Click on "HT-series" to see the HT-700s.

Edit:
Some key info from that site:
http://www.skoolie.net/forum/viewtopic.php?f=6&t=1824

[Jarlaxle]

WHOA! 2350RPM is too much for a 6V71 engine! Even 2250 was fire apparatus only! Keep it down to 2100RPM for normal use.