Allison 4500RDS, Any thoughts?

Go for it, you will not be diappointed. Though, you should look into the bigger ISX. What vehicle are you going to be getting this in? What HP and torque rating is your ISX? You would have much better luck with a Detroit and Allison combo. Remember, if you go to a Detroit Allison shop its a one stop shop. Let us know what you find. More information would help, thanks.

 

We are starting to see more Allison's in more bigger trucks in aus.
I havnt seen one on a highway truck but some truck and dogs run them.
I own 8 Allison's, 6 3200, and 2 4400 series. Myself I don't really like them, they run hot, use alot more fuel and they can't really handle partial throttle, they seem to hunt and can't make up there mind what gear they want to be in. Facter in that you are up for a oil and filter change ever year and it isn't cheap, about $1000 in aus not sure how much over there.

Benifets. They are quick, real quick. They keep the engine on boost during up shifts so they don't place a lot of strain on the driveline.
They are easy to drive, any monkey can drive one, and they are really hard to break. That's the reason we buy them.

The only thing that will kill them is heat and poor maintenance.

Put it this way, I drove one for 3 years, and I have just got my new truck which is a manual and don't regret it.

 

Keep in mind, the over drive gears on these transmissions are very tall. Is this a 6 speed automatic? I know on motor coaches that run ISX, ISM, Series 60, C13, etc. They have B500 automatics, with a tall rear end, drivers report driving mountainous terrain in 5th gear as the RPM's will only rise a little. But they pull good. I'm sure the 4500 series probably has different gearing inside of it.

Remember, as far as I know you just change the oil and filter on the transmission and the specified interval. Traction in snow, sand or starting on a hill from a dead stop is awesome. Watch this video: https://www.youtube.com/watch?v=6W8ahYBdYIE

There are more reviews from Allison too, like this one: https://www.youtube.com/watch?v=ncZ8ciI7v2s

Here is their channel: https://www.youtube.com/user/allisontheautomatic/videos?view=0

This will help you decide more. Don't be deterred. Don't forget how awesome it is to use your jake brakes with one of these.

Here is another one: https://www.youtube.com/watch?v=jAn0VIyqNuc

 

Yes it is just an oil and filter but the oil is $100 per Liter for the synthetic oil which is the only oil to run, yes you can run mineral but it only last half as long.

They don't climb steep hills quite as good as manual, because of the large gap between ratios one is usually to tall and the next to short, so you find yourself locking it in a lower gear often. But they are much easier to drive.
Yes the traction is great becuase of the linear delivery of power.
If you are taking off heavy on steep terrain, it can take awhile after applying the throttle for the truck to move until the torque converter can build enough pressure to move. This builds up extreme heat in the tranny which takes along time to dissipate.
Also on a lot of trucks the tranny fluid is cooled through the radiator, so it places more strain on the cooling system, but some trucks run an extra external cooler.
My Manual trucks run 5 to 10 degrees cooler than the autos, my autos run at 100 degrees often when working hard. i can't remember when one of manuals ran anywhere near that hot.

They do run large overdrives but like u said the final drive is tall. I think ours run a 6.29:1 in the auto which is like a 5.11:1 in a manual. Just the ratios that Allison's run nothing to really worry about.

BTW. The jakes work nowhere near as effectively on the auto compared to the manual. Just remember that there is no mechanical link between engine and driveline. Yes there is a lockup in the tranny but it still isn't a direct linkage.

 

You will not get good fuel mileage with an Allision 6 speed transmission for OTR. The way the Allision is designed they have the engine running at higher rpm's while cruising down the highway. The three that I have driven with the setup you have talked about were very nice in an in town setting. Even if you went with the 15 liter with an Allision you still wouldn't get that good of fuel mileage. The one big thing that I dislike about these transmissions is that when you have the engine brakes on the transmission will downshift when you let off of the accelerator and it will throw you forward and the engine will hit higher rpm's. If it were me I wouldn't spec it with an Allision for OTR.