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Retarder Tranny Temp – How Hot is Normal
All
my other buses and MH’s had Jakes except for a Foretravel and no
Retarder. We’re in the CO Rockies and after going through the
Eisenhower Tunnel westbound it’s a long way to the bottom and 6%
grade. Used 4th gear and toggled back and forth between the 2nd and
3rd position on the retarder and held it to a safe speed. Towards the
last mile the tranny temp got to 250 and the light came on. Didn’t
get any hotter and cooled off quick at the bottom. The hottest I have
seen prior is 225 in the east. This also got the engine temp up to
208 for a brief time. No heat issues up hill, the cooling in these
XL2’s is great.So
I assume that is a normal occurrence with a retarder on a reaaalllyy
long down grade. My transmission is the HD4000MTH-R. Allison gives
the following max temps for this transmission using the retarder:Sump
Fluid
250Fluid
to Cooler
300Retarder
out Fluid
330So
my question to the experts, which temp is being shown on the XL2 info
center? And, what has been your experience with retarder temps of the
same vintage as mine? -
9 Replies
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That is a long hill you have to becarful or you might get brakes to hot on the way back Tom let me know how fast she goes up that hill and how hot she gets just for kicks
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No heat up hill Peter, runs cool with manual shifting to maintain a good speed and rpm. After reading a little more, the tranny will automatically reduce retarder output as temps climb. The dash light appears to be a warning to the driver who may not be paying any attention to the tranny temp gauge. Kind of a “hey dummy, your tranny is getting hot.” It also stayed in 4th gear near the bottom until a certain temp was reached and then shifted into 6th gear.
I only fanned the brakes once, so next time, a little more breaking may be needed to keep the temp in check. The downside is, by braking, you’re getting harder retarding at a time when you’re trying to cool it off. That leaves you with the option to turn off the retarder for a quick brake and then turn it back on. Trial and error….
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I don’t believe the tranny temp is what held you in 4th at the bottom of the hill. As long as the bus is pushing the engine the transmission does not automatically upshift. As soon as the road levels and the cruise control or your foot calls for power the tranny upshifts. If a lot of power is required it will hang in the lower gear, but usually the bottom of a descent has a long transition before an upslope.
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Tom,
From our seminar at United Engines in OKC, they advised that the transmission temperature had a “maximum upper limit” of 300 degrees. My notes don’t state where that is exactly measured from, but I made it my mission to see to it that my transmission temperatures never saw that number on anything I had a display for.
The highest temperature I ever saw displayed while using the retarder was 225, although I never drove the bus down steep grades for any significant distances.
Likewise, the transmission temperature always seemed to recover rather quickly after the use of the retarder.
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I think Jon is right about the upshift. If I recall the Allison manual correctly, the retarder will stop retarding if it gets too hot — at some temperature above when the light comes on. The temp-protect override remains in effect until the fluid cools or unless it senses that the vehicle is going too fast. At some point the transmission decides to risk harm to itself and turns the retarder back on to slow the bus and protect the occupants. Pretty courageous, for a machine…
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Where are you guys seeing the trans temp displayed? I haven’t seen that anywhere on mine. Does it show up on shifter indicator or where?
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It was for sure locked up in 4th gear at the bottom and the selector was in 6th gear with the retarder turned off. It stayed that way with no throttle input for a little ways on level ground while the temp decreased and then eventually went into 6th.
The temps are displayed on the info center in the gauge mode and will display oil temp, tranny temp and dc voltage.
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Tom, for some reason, mine in guage mode only shows engine oil temp, volts, and I am assuming coolant temp…..but, maybe the symbol I am seeing is Trans Temp? I’m going out to the shop now to look at that again.
that may explain why I am seeing different temps.
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Per Allison at a Foretravel rally, they measure at the sump. To volatile to measure at the retarder but you can with Silverleaf. I was just out in CO and used 3rd gear and had no issues with temps coming down. I was 215. I didit a week prior and was 248 in 4th gear.
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