Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 07, 2025 ...

How to manage steep descents safely

March 09, 2024, 06:55:58 pm

Looking for a previous thread or help with how to manage steep descents safely using the retarder, engine and brakes. We are on our first trip in our 2001 U320 and may encounter some steep grades when we drive through Flagstaff next week. I have pulled a large fifth wheel with a one ton Ford dually and always felt secure and under control with the exhaust brake,however, it didn't take long to discover the U320 is a different animal and requires different management on steep grades. Thank you in advance for your help.

Quote Selected

Re: How to manage steep descents safely

Reply #1 – March 09, 2024, 07:05:40 pm

Retarder: Transmission Retarder Operation -How Does It Work? - All Things...

Learning the the retarder useage reply#25

Might start here?

Quote Selected

Re: How to manage steep descents safely

Reply #2 – March 09, 2024, 07:07:43 pm

Don't have a retarder so I can't help with that.
If you're going to use US17 south to Camp Verde, it's not MAY encounter rather WILL encounter.
Saw a couple of trailers with smoking rear tandems.

 Folks here know their stuff.  Take their words of wisdom to heart.

Quote Selected

Re: How to manage steep descents safely

Reply #3 – March 09, 2024, 07:19:57 pm

Quote from: Tommy D – March 09, 2024, 07:05:40 pm

[Other link]

Learning the the retarder useage

Might start here?

Original content on the Forum that was copied from the Forum and the old Yahoo Group into the other link site is here: 

https://www.foreforums.com/index.php?media/file/retarder-operation-how-does-it-work.3404/

and here  https://www.foreforums.com/index.php?media/file/allison-automatic-retartders.3436/

more here  https://www.foreforums.com/index.php?media/file/wteciii-retarder-controls.956/

Quote Selected

Re: How to manage steep descents safely

Reply #4 – March 09, 2024, 08:19:44 pm

DW just suggested......
 If you have a toad and second driver, consider disconnecting (even if toad has brakes) before you hit the hills if you're lacking in experience.

Quote Selected

Re: How to manage steep descents safely

Reply #5 – March 09, 2024, 08:37:17 pm

In using the retarder you want to keep the revs high for the best cooling. In long hills I would
not use any more of the retarder than the second notch with the joy stick and be in a low enough
gear that the second notch will hold the speed  without using the brakes. Keep an eye on the
temperature gage and don't let the temperature get over 250.

Quote Selected

Re: How to manage steep descents safely

Reply #6 – March 09, 2024, 09:22:24 pm

Yup use the Allison down arrow to select a gear that puts the engine at the higher end of it's RPM range (max coolant circulation) and keep a close eye on transmission temperature. If it continues to rise, SLOW DOWN.

Yes, it takes more braking HP (irrespective of whether that braking HP comes from an exhaust brake, engine compression brake or transmission retarder) at higher speeds-- so SLOW DOWN. And the need to generate less braking HP= LESS HEAT in the transmission.

If you do need to use the service brakes because you are continuing to accelerate or transmission temperature is continuing to rise, step on the brakes firmly and long enough to slow you down and allow you to select a lower gear.

You will still be faster than the loaded 18 wheelers on that same grade, so no worries about traffic.

Quote Selected

Re: How to manage steep descents safely

Reply #7 – March 09, 2024, 10:32:09 pm

Thanks everyone!!  Appreciate the advice and links!!!!

Quote Selected

Re: How to manage steep descents safely

Reply #8 – March 10, 2024, 02:02:39 pm

Basic ROT:  go down a grade in the same gear it took to go up the same grade.  Works for me anyway.

Quote Selected

Re: How to manage steep descents safely

Reply #9 – March 10, 2024, 06:49:03 pm

. "Keep an eye on the
temperature gage and don't let the temperature get over 150".
 
  Pete.  I'm thinking you meant 250.

Quote Selected

Re: How to manage steep descents safely

Reply #10 – March 10, 2024, 08:49:30 pm

230 is my limit.

Quote Selected

Re: How to manage steep descents safely

Reply #11 – March 10, 2024, 08:51:33 pm

BTW that is transmission temperature, not coolant temperature.

And 250 degrees F is a good conservative number on Transynd/668.

Quote Selected

Re: How to manage steep descents safely

Reply #12 – March 10, 2024, 09:53:27 pm

For Dash tranny temp sensor, Foretravel has installed their own temp sensor into one of the big elbows that are on the back of the tranny that move fluid from transmission to and from transmission cooler. Heard that to not scare owners, they use the elbow on the cooler line RETURNING fluid from cooler. Many want the real temp of the hot fluid leaving the transmission, so they relocate the sensor to the outbound line where temps are real (hotter). Better yet it would be nice to know both in & out temps, but that would require adding a new wire from transmission to dash. Speaking of these elbows, there was a time when one of the big elbows was facing down so the two hoses could pass each other on the way to the transmission cooler. The downward elbow could be seen as the lowest part of the engine and subject to road damage. The fix was to put an extension coupling on downward line's elbow so the elbow could be located further forward and then go around the other line without having to face downward first. Check yours out. . .

Quote Selected

Re: How to manage steep descents safely

Reply #13 – March 15, 2024, 06:34:44 pm

I found that having silver leaf really helps manage retarder use on Long descents. You really see the temperature go up quickly while the transmission temperature goes up slowly. And as old guy suggestion the second detent and a low enough gear to keep you within a decent range of speed while keeping your RPMs high. I usually stay behind and with the trucks unless I feel it's safe to go around them meaning very few automobiles. Better to take it safe and slow. I remember following one truck in Mazatlan with its rear brakes on fire. He had no idea.
There's a good thread here that I initiated about this very topic.

Quote Selected