Is there an older model Allison Auto with O/drive?

[Aussiecoach]

Hi

I have a bus with 350Hp mechanical 6V92TA and a six speed overdrive spicer 1463C. I am thinking of installing an Auto and was wondering if there were any older model Allison autos that had an overdrive that I could use as I have a rear axle of 3.71:1?

Or any other suggestions would be welcome?

Thanx
Glen

[luvrbus]

Yep the Allison 60 and 70 both have overdrives 6 speeds

good luck

[Aussiecoach]

Hi luvrbus
Is there any more model details you can give me as a google of Allison 60 or 70 doesn't return anything? Obviously I know nothing on the subject.

Would these be suitable to install with a mechanical 6V92?

Thanx
glen

[luvrbus]

Try AT 70 it will bring it up you see manuals for the the AT 70 on ebay sometimes

[junkman42]

I have a HT70 Allison which is a true 6 speed and is far more overdrive than You need for the axel ratio You mentioned.  My coach had a original diff ratio of 4.77 I presently have 4.00 and it is way too tall for My 8v71!  I have been told that the HT70 is a weak tranny but have found that it was mated to 12v71 engines used in the logging industry in Canada!  The Stewart and Stevenson shop foreman in Texas told Me that They overhaul this tranny on a regular basis as They are used in off road equipment!  Anyhow pretty old device My tranny has a retarder and with it engaged and the Jake's on You can back up a hill in drive LOL.  John L

[gus]

Glen,

That six speed is ideal for a bus if it has a nice low first gear.

I would never trade that for an AT!

[Aussiecoach]

Thanx guys

Sounds like the HT70 maybe an option but gearing might be too high and maybe availability of parts and the size of the HT70 might be a bit of a challenge. Might have to change the axle and go with the more common HT740 or 750.

Gus do you know what the ratios of the 6speed are?

Can you use one of the newer Autos with a mechanical engine?

Thanx Glen

[luvrbus]

Yep the newer Allisons work with mechanical engines you run into the same problem they need a low rear gear or they don't lubricate and run hot so 6th is locked out go with a 740 and 3:36 gears or the 750 CR is a good option but no OD in either

[TomC]

The HT740 is the most reliable Allison transmission ever made, period.  It is used in all hot rod vehicles with many times 1,000-2,000hp.  You mechanical 6V-92TA with 350hp puts out about 1,000lb/ft torque.  You want to cruise the 92 series between 1600 and 1800.  If you gear your bus with the HT740 (direct 4th-no overdrive) to cruise at 65mph @ 1600rpm, with 12R-22.5, you would need a 3.08 gear ratio-that would give a true 1618rpm @ 65mph.  If you bus weighs 40,000lb and with the Allison first gear of 3.692 with 2:1 torque converter, with the 3.08 your startability will be almost 26%.  Over the road trucks need 16%, and off road trucks 21%. So you're good with the HT740.  The HT740 is an aluminum case transmission. I believe the HT60 and HT70 are cast iron case-much heavier. 
With your 3.7, the HT740 with 12R-22.5 will give you 1944rpm @ 65mph-a bit fast but doable.  Changing the rear end ratio is usually at least $2,000.00.  Good Luck, TomC

[Aussiecoach]

Thanx again guys, I appreciate your Knowledge and you taking the time to educate me

TomC if I run 11R 22.5 Tyres do the calculations change much? would the 3.08 still be ideal and what would my current rear end give me at 65?

Thanx
Glen

[TomC]

In general, the 12R-22.5 is a 485rpm (revs per mile) and the 11R-22.5 are 500rpm.  Hence with the 3.08 with the Allison HT740 and 3.08's, your 65mph would be 1668rpm-still good. 

With your 3.7 ratio and the 11R's, your 65mph will be 2004rpm-which is a bit fast for continuous on a 92 series (will burn extra fuel). Keep it at 60mph and you'll be at 1850.  Good Luck, TomC

[Aussiecoach]

Thanx Again

If anyone has a good 740 or 754 for sale let me know, I have access to a container that gets packed out of Gardena CA

hanx
GlenT