Using the Allison 6-speed on grades? - Montana Owners Club

GRHooper · 05-29-2010, 04:23 AM

[left][font=Tahoma][size=2]We're brand new rv'ers and pull a 2009 Montana 3605RL with a 2007 GMC Sierra 2500HD diesel. This is a great truck, 6.6L Duramax with the Allison 6-speed transmission. We're in Gallup, NM and preparing to drive to Phoenix via Flagstaff. Mountain grades are something we haven't experienced with the RV yet, nor have we needed the manual transmission feature because we've just been on flat surfaces.

What is the best way to use the manual speed of the Allison 6-speed transmission today? As I say, we're headed to Flagstaff and then to Phoenix. Thank you!

clarkandsheila · 05-29-2010, 05:15 AM

Do you mean the Tow/Haul? Use the Tow/Haul feature all the time when towing.
The trans will stay in each gear longer as you accelerate. When you are getting on the highway the rig will accelerate quicker. It will kick down a gear or two much sooner on hill climbs.
When going down grade, step on the brake and it will downshift and help hold the rig back.

The T/H makes things a lot easier on the engine. The only time I don't use the T/H is when I forget to push the button.

I have the '06 Ford with T/H and the whole rig runs better when used.

Parrothead · 05-29-2010, 05:20 AM

Jerry and Lisa,
We've made that trip several times. To and From CO and to Show Low, AZ and back, Flagstaff for the summer, etc. We are in Grants just east of you right now. That it a gradual climb into Flagstaff on I-40. We always use the "Tow and Haul" mode and let the trans do what it is designed for. We do have the 3500 which will make some difference. The T/H climbs well and keep the compression on the engine going down hill. An additional remark here is that Ed is not a fast driver, not slow but doesn't push it hard.
Have a great trip. The Flagstaff area is beautiful. We love it.
Happy trails.........................

dpam · 05-29-2010, 06:04 AM

I'm assuming your wondering if you can downshift your transmission manually. When towing in the Rocky Mountains (British Columbia) and Cascade Mountains (Washington State) there are alot of 6 and 7% downgrades with 30 mph curves at the bottom (especially the Cascades) so instead of having to frequently tap my brakes to get the tow/haul mode to downshift automatically I manually downshift with the toggle button on the tow/haul mode lever. In many instances I've manually downshifted into 2nd gear and left it there until I got to the bottom and then shifted up manually. The allison and duramax responded very well. Hope this helps.

Tom S. · 05-29-2010, 06:40 AM

Jerry, we have driven through several mountain ranges, from New York to Alaska (and places in between) and have never needed to use the manual setting. Put the trans in tow/haul mode and relax!

TLightning · 05-29-2010, 07:44 AM

I've made that Gallup, Flagstaff, PHX run...as others have said, don't bother with the manual feature. Turn on the Tow/Haul, put it in "D" and let the Allison do the thinking for you.

mlh · 05-29-2010, 02:59 PM

You are wright the 07 Duramax Allison is a great truck.
Lynwood

TAKPAK · 06-06-2010, 07:14 PM

GRHooper, we have a 2008 GMC 3500 w/dura and allison, and pull a 2007 3400 with it. IF, and I say IF I understand the operation of the tranny correctly, one thing that happens if you use the "manual" mode, is the torque converter does NOT stay locked up in the lower gears. My understanding is....by leaving it in tow/haul mode, the torque converter will stay locked up all the way down through second gear, thereby using ALL the engine compression to hold you back. Otherwise, in the manual mode, I believe you would be "free wheeling" a bit, without the torque converter lockup. We came down a long stretch of several miles and a 6 percent grade a year ago, and the T/H mode worked great. After you get used to the engine winding up to about 3400 RPM, it does a great job. Granted, you have to brake a bit to "tell" the system to "slow down" but it does work. The above info is what I've been led to understand how the system works from the dealer.

KDS MONY · 06-07-2010, 09:48 AM

We pulled our previous Monty with a GMC 3500 Duramax/allison dually and it did fine but as previously stated always use the Tow/haul. Also be sure your RV brakes are in good repair and properly adjusted. A little tip from past experience, I now tape the cover of the 7 pin connector around the plug end to insure that it doesn't come out. The cover is held in place by a small steel spring that will rust and eventually break, usually at the most inopportune time(like going down the 7% grade at Camp Verde) and vibration will eventually cause a disconnect. You really wnat the RV doing it's fair share of the braking on those big lond downhills, Best wishes, Jay and Kathy

Joeagrant · 06-07-2010, 10:00 AM

I personally use the tow haul mode all the time when towing, but I put the trans in manual and set it in 5th gear so that overdrive (6th) will not kick in. I works fine for down hills, and I have installed an exhaust gas temperature gauge so that I can tell it the temps are rising on an uphill clmb, and can then toggle down to a lower gear so that the exhaust will not get too hot. High EGT's will kill your engine.

KDS MONY · 06-07-2010, 03:31 PM

Joe, I think 5th is still an overdrive gear on the Allisons. I only use the manual function to stop gear searching when climbing a hill. I preferred to keep the torque converter locked up in the tow/haul when going downhill. But I'm not a transmission mechanic so maybe I'm wrong!!! Best wishes, Jay and Kathy

Joeagrant · 06-07-2010, 04:02 PM

Hey, I'm not a transmisssion expert by any means. I just know how it works for me. In the manual setting, the tranny still shifts as if it were in auto, when in the tow/haul mode, but just won't go into 6th. I don't like the lugging that I feel when it is running in 6th. I average 11 to 11.5 MPG when pulling the 37 foot Monty.

Tom S. · 06-08-2010, 02:39 AM

The Allison six speed ratios are as follows:

1st 3.10 to 1
2nd 1.81 to 1
3rd 1.41 to 1
4th 1.00 to 1
5th 0.71 to 1
6th 0.61 to 1
Rev 4.49 to 1

So yes, 5th and 6th gears are both overdrive gears.

Joeagrant · 06-08-2010, 04:07 AM

Thanks Tom.
The gear ratios are interesting. I notice that the ratios between 2 and 3, 3 and 4, and 4 and 6 are about .4 RPMS. It looks like Allixon slipped another gear in between 4 and 6 to ease the strain. But since the difference between 5 and 6 is only .1, I think that losing that .1 RPM by not using 6, is more benificial to the tanny so it does not have to downshift with the slightest increase in power demand when pulling loads. Shifting back and forth causes heat buildup in the tranny, I think, and that's not good.

KDS MONY · 06-08-2010, 05:44 AM

Joe, I understand where you are coming from, but my concern about using the manual mode is I think(but don't know for sure) it unlocks the torque converter which could lead to an overheating problem in the tranny when making a long pull. If it does not unlock then I think what you do makes a lot of sense and obviously it doesn't hurt your mpg significantly/ Best wishes, Jay and Kathy

Joeagrant · 06-08-2010, 07:02 AM

I guess we need an Allison expert to tell us just how using the tranny in manual while it is in the tow/haul mode affects it. The longest pull I have made is on I-64 in West VA. 6 or 7 percent grade about 5 miles long. I've had no problems going up, or coming down. The tranny never overheated, but I had to drop down into 4th gear to get up the grade without raising my EGT's too much.

KDS MONY · 06-08-2010, 08:29 AM

Joe, I'm familiar with that pull, it's Sandstone mtn at the New River. We pull it several times a year going to KY to see our son/daughter in law and now new granddaughter. When we were pulling the Monty with the GMC we did it in just tow/haul and by the time we crested the hill we were in 3rd at 2800 to 3000 rpm doing about 50 mph. The fan would be on and the tranny would be 195 to 200. Always felt like it was working really hard!! But never had any troubles. Now with the bigger rig and the big truck we don't go up any faster but the truck is in 4th at 1500rpm and doesn't really act like it is straining. I do see that you have the newer '07 with a Banks. We were running an '04 straight stock so that probably esplaines the difference in performance. I still would like to know if using the manual function unlocks the converter. Maybe somebody will educate us!!! Best wishes, Jay and Kathy

TLightning · 06-09-2010, 02:37 PM

The manual says to use the T/H when the GCW is 75% or more than the GCWR. That's what I do...works fine. The Allison is built for exactly how we use it. I put it in "D" and select "T/H" and let is work.

Tom S. · 06-10-2010, 01:21 AM

Not that it makes any real difference, but I have been in the plant that makes the Allison in Baltimore MD. In the lobby, they had a cut away of the transmission, and to a gear head like me, it is very impressive. Inside the plant was equally impressive with it's cleanliness, and the workers there were very committed to the quality of their product.

twindman · 06-10-2010, 07:20 PM

I have a 2004 2500 with a 5 speed Allison. If yours is like mine, if you have tow/haul on and hold the brakes around 3 seconds on a downhill, it shifts down a gear. Then if you do it again, it downshifts again. Some really steep hills require getting to 3rd (out of 5) gear. I was concerned that the rpms went up over the red line. But from what I have heard someplace, it doesn't hurt to over rev while coasting. Also, I think it was stated that you pretty much can't kill the Duramax. If it revs too high, it will actually shift back up. Of course that is bad when careening down a mountain!!! THat has never happened to me, tho. If I am at red line, I will tap the brakes for 2 seconds so it doesn't downshift again.
This may not be 100% accurate, but everything seems to work for me. I have gone down a 8 mile 8% mountain in Wyoming with almost no use of brakes. Of course, I was only going about 20-25 mph.
Good Luck!

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