Sorry, this is a little long.
We are on our vacation and along Interstate 5 between California and Oregon, you have to drive across the Syskyou Mountains. Going up the grade was no problem. Everything looked good. The coach never seemed like it was really working that hard as the california side of the grade is less extreme than the other side. As we came down the big grade on the Oregon side, I used the grade brake which kept the transmission in 3rd gear. I kept the speed around 40mph and the engine speed less than 3800 rpm. I used the brakes about evey 1-2 minutes to slow the coach down to 35mph. For those who have traveled this hill, It is a long steep one. Towards the bottom of the grade, I got the 'Check Transmission Temp' warning on the Workhorse panel. Luckily we were almost at the bottom of the grade. Once we got to the bottom, I started looking for a place to turn off and let things cool down but the warning went away. When we did stop as soon as we could, I took a look at things and everything looked good. Fluid looked ok and still the normal color. We have a W24 with a 2100 series Allison built in mid 2007. The Coach weighs 21240lb wet and ready to travel and we are towing a 2007 Saturn VUE that had less than 1/4 tank of fuel. We had somewhere less than 2500 miles at the time. Does anyone have any knowlege as to why this would have happened. Anyone think I did any damage? Was I wrong in my use of the grade brake? BTW, I am not a fan of it because I feel it downshifts too much. Any recommendations as to what Can I do different when I go back over that hill?
Anoter note. I was passed up by 2 other Workhorse powered motorhomes going probably 50 down this hill towing which scared me. I figured 40 was more than fast enough and it felt like these guys were passing me like I was parked. Am I nuts to go that slow? I would rather be more cautious.
Again, any advice/comforting words... would be be very much appreciated.
Thanks

Do you have a braking system on the car you pull?

Yes the transmission will get hotter going down hill that it will up, if you are using it to saved your brakes. I found this out last summer crossing Trail Ridge Rd in Rocky Mt Nat Park. I got 224 degrees going up from Estes Park to the Alpine Vis. Center and 270 going down the West side. I have now instaled Mobile 1 Syn fluid and I am going to try it again this summer.

quote:

Originally posted by RV 4 2:
I kept the speed around 40mph and the engine speed less than 3800 rpm. I used the brakes about every 1-2 minutes to slow the coach down to 35mph.

I was passed up by 2 other Workhorse powered motorhomes going probably 50 down this hill towing which scared me.

RV 4 2, Personally I think you might be going too slow to dissipate the amount of heat that is being built up in the transmission at 35 MPH.

Your 2008 motorhome's Allison already comes with Transynd so I wouldn't be concerned about the fluid.

There is nothing wrong with doing select shifting and going to a lower gear, perhaps 2nd gear at 4300 to 4400 RPM, and letting the motorhome seek it's own best speed on the grade without you excessively getting on the brakes. If you begin to slow down too much you can always up shift to 3rd. Depending on the conditions of the grade whether the road is straight or whether the road winds down with a lot of curves I would target a speed of 50 MPH and I would rather have that speed going for me and pushing a lot more air through my cool pack. Using the brakes, stab them hard for about 1 to 2 seconds and continue the repetitions until you achieve a controlled speed.

Going too slow under a heavy load isn't a good thing. Going down hill under compression at a slow speed puts a lot of load on the drivetrain more so for the tranny. Get some more forward velocity and get more cooling air through the cool pack and I can just about guarantee you that the over heat condition on the tranny will not reoccur.

One other method of overheating the transmission is when the motorhome is backing up or if you get stuck and are attempting to rock the vehicle out - why because the tranny isn't getting enough cooling.

Keep your energy levels high, use engine compression to your advantage and stay off the brakes. There's nothing to fear but fear itself.

IMHO, 35-40mph is not too slow for descending a steep grade and I seriously doubt you damaged your transmission.

I'm quoting Allison's In Chassis Maintenance 1000, 2000 manual below.

When the light is "ON" shifts may be restricted by the Transmission Control Module (TCM) when the TCM senses abnormal conditions as follows:

The transmission may be locked in the range it was when the problem was detected.

The transmission may continue to operate with inhibited shifting.

The TCM may not respond to the shift selector requests.

Direction changes and shifts from neutral-to-range may not occur.

You had none of these occur.

Also, whenever the CHECK TRANS light is displayed, the TCM logs a diagnostic coed in memory. These diagnostic codes can be accessed through the PC-based Allison DOC diagnostic system software.

You may want to stop at an Allison shop and have them look for this code.

I recommend getting a ScanGuage II. The ScanGuageII will allow you to see real time transmission temperatures.

Have you checked your fluid level? Make certain you use the proper procedure when checking the level. If you add use only Castrol TranSynd.

I'll add I weigh 22,900# plus toad and I've never had the check trans light come on and I use the grade brake. I would continue to use the grade brake as Allison's software will protect your transmission and make the proper down and up shifts.

I'm in the motorhome on my cellphone. When I get back home I'll place the Allison manual online that I quoted from or you can get it from Allison's website.

-Tom

"The people that don't believe in evolution are the ones who need it most!"

Sarver, PA/Crystal River, FL/Indiana, PA
2005 Suncruiser 38R, W24 chassis, no chassis mods needed
2008 Honda Odyssey EX-L, Roadmaster Sterling tow bar
FMCA 335149, WCMC, Mystic Knights of the Sea, On the Road Again

The same warning message was displayed as I was just finishing a long, straight descent going eastbound on I-70 west of Green River, UT. I had the 'Grade Brake' enabled and was in 2nd gear doing about 42MPH @4200RPM for about 10 minutes. I was very comfortable with that speed and did not use the service brakes to slow down. As it was, I was able to stop within a minute after seeing the warning message. A look under the coach for fluids dripping and also a check of the transmission fluid level showed everything to be normal; the message cleared after several minutes. I continued on without incident, going up and down Vail Pass and Eisenhower Tunnel (going eastbound) the next day with no further warning messages being displayed. I also did not experience any of the conditions that Tom N has listed.

After talking to the WH roadside assistance folks, I decided to take the coach to the local WH service center and have them take a look. BTW, WH called the local service center to help facilitate an appointment - I thought this was a nice display of good support. The WH service center pulled error code "#P1820 - Trans Component Slipping" and said I would have to take it to the local Allison tranny shop as they (the WH service center) didn't have the equipment or experience to do any further diagnostics. I will be doing this in the near future.

About 6 weeks earlier I attended the WH rally in Tucson. During one of the technical sessions, grade braking was discussed. If memory serves me correctly, we were told to let the grade brake system do it's thing and the TCM would protect against any adverse conditions. I also had my coach weighed (outfitted and loaded for travel) while in Tucson and I was 1600lbs below GVWR.

One of my next thoughts was to buy a ScanGaugeII specifically to monitor tranny temperature. But I could not definitively confirm that the unit will properly measure this parameter. I e-mailed the ScanGauge people and while they said they have heard people have been successful measuring tranny temps, they themselves have not confirmed this performance. It would be very helpful if anyone can confirm this or not.

I don't know how accurate the ScangaugeII is for the temp, but it does work. A few Days ago, I was pulling a grade into a 40-50 mph headwind in New Mexico. The temp outside was 106. My tranny temp was running as high as 190 degrees while running out of OD. I saw this again doing the same thing pulling out of Needles in 110 degrees and no head wind. Same near Mojave at 104 and very strong side to head winds. Each time it go that high, I slowed down a bit and tried using OD as much as possible and it came right down to no more than 170. Normally I see it in the 154-160 range. The ScangaugeII is a great accessory.
Joe

OIL TEMPERATURE MEASURE AT CONVERTER OUTLET TO COOLER
350 degrees F is the maximum temperature. This is the normal place to install a temperature gauge or signal. The temperature in this location will vary significantly with each vehicle startup or hill. If the temperature reaches 350 degrees F, reduce throttle. To lower the transmission temperature with the transmission in NEUTRAL, run the engine at 1,200 RPM for 2-3 minutes to cool the oil. DO NOT allow the converter outlet temperature to exceed 350 degrees F.

OIL TEMPERATURE MEASURED IN THE SUMP OR OIL PAN
• 150 degrees F – Minimum operating temperature for continuous operation.
• 180–200 degrees F – Proper oil level checking temperature
• 200 degrees F – Maximum oil level checking temperature.
• 285 degrees F – Maximum sump/oil pan temperature for short duration, such as a long hill climb.
• 300 degrees F – Metal parts inside transmission begin to warp and distort in varying degrees, seals melt rapidly and transmission fluid life is extremely short due to oxidation and distress.

Just completed a trip from San Diego to Yosemite, including going over the Grapevine. No towing. This was my first trip with the ScanGuage installed. Weather coming home was pushing 100, on flat terrain running 60-65mph sump reading was steady at 183, when ambient was lower on the way out sump ran app 165. Going over over the grapevine, temp got as high as 210, engine temp got up to 215 for a moment. I am running a 50/50 blend Dexron and TranSynd. I am curious to hear more comps on trans temps along with ambient. I am v. happy with the ScanGuage, fun gadget.

DriVer,

Do you know if the Allison transmission on a 2007 W24 chassis is delivered standard with the ability to provide a measurement point and data for the sump/oil pan temperatures as opposed to having a gauge/signal at the converter outlet? If so, is the sump/oil pan temp what the ScanGaugeII will read and display?

Alternatively, how involved is it to add a temp sensor to the converter outlet and connect that output to a temperature gauge?