A3 transmission questions

[abh3]

I've done my duty and searched the forums and have only learned the A3 has an Allison, some Google-ing reveals it's an Allison 1545... Now, that's a 4 speed with a 1:1 top gear (industrialautomatic.com), in fact I have one in an International bus behind a 9.0 that's going to be parted out. How does the A3 exceed 45 or so mph without an overdrive? What am I missing here? An auto Duece would be neat...

 

[EdMontana]

I've done my duty and searched the forums and have only learned the A3 has an Allison, some Google-ing reveals it's an Allison 1545... Now, that's a 4 speed with a 1:1 top gear (industrialautomatic.com), in fact I have one in an International bus behind a 9.0 that's going to be parted out. How does the A3 exceed 45 or so mph without an overdrive? What am I missing here? An auto Duece would be neat...

M35A3 specifications for transmission:

http://www.tpub.com/content/misc_manuals_2/TM-9-2320-386-10/TM-9-2320-386-100033.htm

 

[bottleworks]

RE: Re: A3 transmission questions

Keep in mind that the A3's have Cat engines not the multi. So, It's not quite apples to apples. The A3's have larger diameter tires compared to the stock A2.

 

[cranetruck]

This may be informative...

 

[abh3]

I'm sorry Cranetruck, I'm missing something, that's the gear selector in an A3, some text was lost.

A stock Cat 3116 isn't going to rev higher than the multi so it's just the 14.5R20 tires on the A3 that make up the groundspeed difference? Is the transfer-case moved back or is that why A3s have the weird front end, the longer Allison slushbox? A 3116 isn't that much longer than a Multi, maybe the radiator is bigger as well...

Thanks for the info

 

[gringeltaube]

The Cat's operating speed is 2700 rpm according to specs. Auto tranny in D is 1:1 (downhill & wind from astern if no lock-up converter). TC high is 1:1, diff. gearing 6.72:1, same as A2.
The 14.5R20 singles only add 6% compared to the A2's 9.00-20.
So if an M35A2 makes 56mph@2600, it would be just 49mph@2700 for the A3, at best.
So here comes my theory...: the only way to keep up with the A2 is reving its engine close to 3100rpm....!

Anybody knowing better?

G.

 

[abh3]

What i'm wondering exactalacily, just better worded...

 

[m16ty]

The Cat's operating speed is 2700 rpm according to specs. Auto tranny in D is 1:1 (downhill & wind from astern if no lock-up converter). TC high is 1:1, diff. gearing 6.72:1, same as A2.
The 14.5R20 singles only add 6% compared to the A2's 9.00-20.
So if an M35A2 makes 56mph@2600, it would be just 49mph@2700 for the A3, at best.
So here comes my theory...: the only way to keep up with the A2 is reving its engine close to 3100rpm....!

Anybody knowing better?

G.

This is very interesting (I'm assuming you did your math right). Maybe someone with a A3 will chime in and give some info. I've never drove an A3 but I would think it would do more than 49mph. That would seem like a downgrade instead of an upgrade over the A2.

 

[jasonjc]

I past one on the hyway and it was doing 55-60 at least.

 

[EdMontana]

G.[/quote]
This is very interesting (I'm assuming you did your math right). Maybe someone with a A3 will chime in and give some info. I've never drove an A3 but I would think it would do more than 49mph. That would seem like a downgrade instead of an upgrade over the A2.[/quote]


Hummmm, waiting on my SF-97 (going to 4 MONTHS NOW! ), so my driving was very limited so far.

The only thing I can tell you is that comparing my A3 with my A2's is like compare a Caddy with Jeep's ( I enjoy drive both ). I would say without doubt that the A3 is far faster not only in top speed but also in achieve the speed because of the auto transmission, I was very impressed first time in how fast it got speed....and most importantly, it STOPS!..... as fast as my 08 Tundra 4X4 w/ four disk brakes

.

 

[m-35tom]

55 mph in an A3 is 2956 rpm.

 

[m16ty]

So are the transmission specs posted above wrong? Where is the A3 getting it's speed? I don't think they changed out the ring gear and pinion did they?

 

[sierra117]

Not sure where you found an a3 that'll do 55-60 mine does about 52 running about 2900 rpm and that's with my foot down as far as it'll go granted there is a bolt sticking up underneath the gas pedal

 

[quickfarms]

Without lock up plan on the RPM's being about 200 higher do to the slipping

 

[Hoefler]

Standard A3 tire outside diameter is about 43". So, 43 x 3.14 (pi)=135.03" or 11.25 foot. So for every wheel revolution, the truck moves forward 11.25 feet.
Engine at 2,700 RPM and 1: 1 ratio to rear end and 6.72 rear end ratio, we get 401.78 revolutions of the wheel at 2,700 RPM.
401.25 revolutions x 11.25 feet = 4,520 feet of truck travel per minute. 4,520 feet x 60 minutes = 271,205 feet in an hour. There is 5,280 feet in a mile so,
271,205 ft divided by 5,280 feet = 51.36 MPH with our without a tail wind! Now, running with the larger 395 Goodyears at 46" diameter, the A3 can run 54.84 MPH. 46" x 3.14 =144.44 divided by 12=12.03 ft per rev x 401 revs = 4,826 foot per min x 60=289,602 divided by 5,280 ft = 54.84 MPH.
I have the big Goodyears on my A3 and typically run at 2200 RPM which puts me at 45 MPH.
The front of the A3 hood-grill is longer due to the radiator and intercooler depth.
Did the math here for others to use by simply plugging in there numbers to determine just how fast their buggys are driving.
Pete

 

[glcaines]

Without lock up plan on the RPM's being about 200 higher do to the slipping

There is no slipping in an A3. The 1545 transmission locks up.

 

[Z71]

Can someone explain why they did not pick a 5 speed automatic with an overdrive gear for this application? Larger 5 ton trucks can easily run 65 MPH with large singles. You would think that they would make all these trucks capable of the same speed when traveling in a convoy on an interstate.

 

[Jeepsinker]

That logic makes too much sense. Easier for them to just tell everyone to run 40mph...

 

[welldigger]

Can someone explain why they did not pick a 5 speed automatic with an overdrive gear for this application? Larger 5 ton trucks can easily run 65 MPH with large singles. You would think that they would make all these trucks capable of the same speed when traveling in a convoy on an interstate.

There isn't any room for a bigger tranny.

 

[welldigger]

Not sure where you found an a3 that'll do 55-60 mine does about 52 running about 2900 rpm and that's with my foot down as far as it'll go granted there is a bolt sticking up underneath the gas pedal

The a3 bobber me and a buddy built would do 58-59 at redline with 14.00-20 xzls. This was verified with gps.