Allison Trans

[Porscheguy]

I was told by International that all of the Allison 2500 Transmissions were 5 speeds. Does anyone actually have a 6 speed? I have the 5.29 gears and definately a 5sp. I would love to bring down the rpm but the dealer says I would have to go down to a 4.?? and did not know how that would have an effect on the ability to tow or climb hills. Has anyone done any conversions?

[Texas TC]

When I first got my coach, it was and early model, it had 6.17 gears and 75 mph was at the engine red-line of 3200 rpm's. International/Gulf Stream paid to change the gears to the current standard of 5.29. The drop was about 500 rpm's at cruising speed so now 75 is 2700.

Now that I have put almost 38000 miles on the coach with the 5.29, I don't think I would want to go to a higher gear in the rear. I don't particularly like to cruise at 2700 but agree with International that the power would be suspect on severe grades if the engine rpm's were down. When I have tried to lower the rpm's by slowing down, I have noticed that the transmission is constantly going into a lower gear.

I have been cruising at 2700 for most of the miles on the coach. Even though it is high, I feel it should not hurt the engine in the short term. If we were going to try to put 200-300000 miles on these engines, I might be more concerned. But the way we use these things, we would probably be really pushing it to put a 100000 miles on them in 10-15 years and this engine, IMHO, should last that long without any major issues.

If you are worried about engine noise, I will assure you that after 30000+ miles, it gets quieter and the power actually increases.

I wish someone would try a 4.88 (?) gear and give us their assessment but I am concerned about the loss of power by raising the gear. If I remember correctly, when I saw the invoice to change from 6.17 to 5.29 in 2007, it was around $2500.00 from International.

[Porscheguy]

When talking with the service writer he said between $2500 and $3200 and that would include changing the computer so the trans would still shift properly.
I spent the last couple days putting Dynamat everywhere. I hope this will help, there was a small amount installed before I bought it. I tore the entire interior apart and then went underneith.
I still would like to know if anyone does have a six speed trans. I would consider installing one if there is a great difference.

[schmittm]

Here is an option that I am considering. It is an overdrive or gear splitter that can be added your transmission. It would give you that sixth gear and lower RPM or it would give you a gear in-between 4th/5th to help towing. Take a look at site.
http://gearvendors.com/

[Texas TC]

I checked out gearvendors a couple of years ago and they did not have an application for the Allison 2500MH transmission. If that has changed, I feel this would be a good solution for those who desire to lower the rpm range to try. However, if International says the computer must be re-set when changing to a higher gear, I am not sure what it would do to the shift points and power when shifting the overdrive application in gear with the gearvendor product.

I recently test drove a new Winnebago class A coach that had a 340hp Cummins engine with the Allison 2500MH transmission. One of the things that I wanted to know was the engine speed while cruising the freeway. I was surprised to find that the rpm's at 70 mph was still around 2500 which is very close to what we are turning the VT365 in our International chassis coaches.

After 40,000 miles with most of those miles towing a Jeep and many miles in altitude, I don't feel that we would have enough pulling power if the engine speed were reduced. I really do not worry about the engine speed anymore even though, as I have documented before, I consistently cruise at 75mph and higher.

[schmittm]

I will let you know if this works on the tranny. Not sure why the computor would be a problem, but will find out.
As far as engine speed, I am not worried about that either and agree if the RPMs were any lower it would hurt the towing. I was thinking of this application to lower RPMs on cruising flats and then to help split the gears when climbing hills and Mountains.
I pull ski boat that is 5500-6000lbs and if the gears were any lower taking off from a dead stop would be harder, it is real slow to get going and then th power builds. I also would not be able to maintain 55mph on steep hills with lower gears.
The other comment I got from International is that they design their engines to run at higher rpms, unlike the automanufactures that pic a lower RPM point partly because it keeps the noise down.