allison transmission

[pokgunner]

This is the first time I hae ever used a forum of any kind so hopefully I am doing it right, if not sorry.  It also looks like I am too late to ask Allisonman, but hpefully someone else can help.

My  2010 motor home sits on 2009 freightliner chassis with a front engine Cummins and a 1000MH Allison.  I took it to the Cummins service center (which is also an Allison service center) they said the engine was programmed for 300hp because at the time Allison would not warranty the 1000MH for more power.  But by now Allison warrantees the same transmission 340 hp and 600 ft-lbs.  So Cummins reprogrammed it to those figures. 

I still am not satisfied and plan to have the Cummins reprogram the engine for 390hp and 400 ft-lbs. But the pinch point may, or may not, be the 1000MH.  Replacing it with a 2500MH or 3000MH, besides costly, introduces a host of interface problems also costly to resolve.  There are several transmission performance shops that beef up an Allison 1000 (no MH) to handle tremendous amounts of  torque and hp.  But when I tell them I have a 1000MH, all but one said they can not help me.  The one that said he could quoted $5,000 and said I would have to ship the transmission to him for the build up.  He is about 800 miles from me

What are your thoughts about the 1000MH behind 390hp and 400 ft-lbs?  Should I:  1) just be sure that I keep the 1000mh cool (add a radiator), or 2) beef up what I have, or 3) bite the bullet and go to a MH3000?

 

[Terry A. Brewer]

Are you sure you would  even have the space to replace your 1000 with that 3000 transmission?

My 4000 MH transmission is so much bigger than the 3000MH  transmission, and that is my reason for asking.

 

[pokgunner]

Actually space is the least of the problems with going to the 3000MH.  The unit is not a pusher so I have the space.  I would have to custom build the mounting.  The bigest problem with the 3000mh is dollars followed by computer, electrical and plumbing interfaces.  Just havig the 1000MH beefed up would be a no brianer decision but I worry as to why I can find only one shop willing to do so and guarantee the work.

 

[34footer]

  But by now Allison warrantees the same transmission 340 hp and 600 ft-lbs.  So Cummins reprogrammed it to those figures. 

I still am not satisfied and plan to have the Cummins reprogram the engine for 390hp and 400 ft-lbs.

Why would you go from 600# of torque to 400# of torque?
J

 

[Gary RV_Wizard]

I haven't seen this engine factory rated over 350 Hp - is the 390 hp a custom re-program? What is the peak torque?

I don't see the payback for this upgrade. You are talking many thousands of dollars to gain 40-50 hp on a chassis that already performs well with the stock 300 or 340 hp.  I guess its just the "need for speed".

 

[yolo]

If it ain't broke, don't fix it. 

 

[34footer]

If it ain't broke, don't fix it. 

That's the 6.7 engine....he might blow it up.  :'(
J

 

[pokgunner]

As I said I am new to using a forum and did not expect this many responses, this quickly. 

In response to 34 footer; I made a typo the reprogramming would go from 600 to 800 ft-lbs.

In response to Gary RV Roamer; the Cummins Service center is who told me they can reprogram it to 390hp, as of several months ago. 

A general response to every one else;  If my unit including toad and passengers is barely under the GCWR, I can not maintain 45 mph over about a half dozen grades on Interstate 5, between Redding and Portland.  For two of the grades I cannot maintain 40mph.  My home is in the mountains, and there is a county road grade that slows me to less that 25mph. Last fall I drove over 200 miles out of my way as I was afraid to even attempt going up the grape vine grade north of LA. 

The modification I am gong to do is expensive and could result in ?blowing it up?.  That is why I am trying to figure out the best way to proceed.  The expense is less than selling the unit and going back to a pickup and fifth wheel.  In hindsight I never would have ?moved up? to a motor home.  We spent 6 months looking for a mid size motor home  (under 30 feet)  with enough power to load if for 3 weeks of dry camping and towing 5,000LBS.  We thought the unit we bought was the closest available to what we wanted.  We knew going in, that it was 3 feet longer than we wanted, but did not suspect it to be as gutless. 

The advertised hp and torque to weight ratios are, when compared to the pick up and fifth wheel I use to own, with in 10 percent; but actual performance is more like 35% less.  Cummins has diagnosed the engine and can find no problems with it.  They clim it is typcial for the motothome maufacutuers to use too small of an engine.    However next week I am driving it 250 miles to the closest place that can put the unit on a chassis dyno to be sure that at least 80% of the advertised power is getting to the wheels, before I make any modification.

Note that the same engine is commonly sold in much bigger rigs, with GCWRs over 40% mine.  Except they are all pushers, mine is front engine.  The other differences are they have the DEF smog control and I have the DPF, they have much shorter exhausts and shorter drive shafts.  However when it comes to gearing, from the crank to the size of the tires they are  quite close to mine, varying by no more than 7% depending on what gear the transmission is in.  While my original post was about the Allison, if any one can explain why a front engine 6.7 Cummins should be expected to perform so much worse than a pusher with the same engine, I would be happy to hear it. 

But for now I feel like I must increase engine power and the weak link in doing so is the Allison.  The topic of my original post.

 

[Icemaker]

This is probably the dumbest suggestion yet on this topic..but..
Why not use an under-drive to get a lower gear or use a different final gear rear..??
Since he is willing to spend so much money fuel mileage is, apparently, not an issue.