I would appreciate any thoughts or opinions on the various temperature ranges for VMSpc caution settings. I have yellow and red upper limit settings for the retarder, but they are totally arbitrary. I have found no information as to what would be reasonable settings. My retarder temp normally runs between 190 and 200 degrees and can easily spike up to 240 or above on steep downgrades.
Thanks,
Richard
Richard
This is a good question. Inquiring minds want to know. I have not done a lot of mountain driving, just Arkansas hills.
My retarder temps run close to what transmission is until it is used then goes up pretty fast. I try and not let retarder temp get over 220-230. I think I read that somewhere on here.
There is fine line between using gears, retarder, and brakes on downhills. I think that you need to set them up before you have started down hill and your speed is to fast to start with.
I have also heard and I try to do this on long and steep downhills use the same gear down as you came up the hill.
Anyone that has better info please make corrections to what I have said. I want to do it the best way also.
This is just my two cents
Retarder temps run about 10° warmer than the transmission temps. I set the warning light to turn yellow at 235° and red at 250°. If you are using synthetic oil in the transmission then it is more tolerant of higher temps than organic fluids.
The yellow indicator lets you know you have reached a temp where you should be paying attention to it. Stepping on the service brakes will make this temp go up fast. If you get to this temp on a down grade maybe it is time to slow down a bit, downshift and reduce retarder a notch. Increased RPMs will increase cooling of everything.
If you get warm enough to make the red indicator come on do something now to reduce load and increase cooloun.
Does anyone now what the stock Foretravel temp alarm is set at? I've seen 250 degrees and never heard a peep.
Don't know if any information here would apply. Page 46 uses 300 deg as max for stall test.
http://www.waghornswood.net.nz/Manuals_01_18/Vehicles/Allison_Automatic/Mechanics_tips_md_hd_b_series_Allison_on_highway_transmissions.pdf
The FT alarm is activated via the retarder temp sensor directly.
Depending on the software of your trans, it is 281-285 F
I have the repair manual
See chart from book
Here is my post on the faulty retarder sensor
Allison Transmission Fault Codes, Retarder not working (https://www.foreforums.com/index.php?topic=35951.msg342961#msg342961)
That sounds correct.
Yellow at 235, pay attention, slow down, and downshift
Red at 250, entering the danger zone, hit the brakes enough to use the actual brakes, slow more, consider another downshift. Really watch the rpms too.
I occasionally hit 260, but just for an instant.
Alarm at 280 and change. Time to hit the brakes hard. But not for long.
I have heard the alarm a few times, back before my VmsPC was installed.
Keep it under 300 and probably no damage done
And at some temperature, the retarder shuts itself off.
At 300 deg. retarder starts shedding.
Post from 12 years ago seems to explain a lot.
Retarder...this time from the manual (https://www.foreforums.com/index.php?topic=4261.msg16815#msg16815)
Are we talking retarder temperature or transmission sump temperature as shown on the bottom of the chart? Silverleaf can show both. Doesn't the alarm on our FTs alarm at sump temperature?
You're correct on all 3 points. The retarder gives you an extra layer of safety but at the end of the day you're managing a heat energy equation that is unforgiving if you get the wrong answer.
When going down steep grades, I always select a gear lower, two if necessary. When the retarder temp starts to rise , push the joy stick forward, that turn off the retarder.When off it will dump the hot oil and replace it. In one minute I reapply the retarder.. Retarders were not made to hold the whole load continuously....
it works for me on my motor home as well a commercial 650 HP Cummins with 62000 kg or about 135,000lbs of load.
Safe travels,
Dave
Dave