BAC Forum
General Boards => Technical Support => Topic started by: Jerry Emert on September 28, 2017, 06:08:54 PM
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This is not new but I'm curious. When going down a steep grade, I can often smell the brakes. I am aware that I am not supposed to ride the brakes and I don't. I have evolved from sharp hard brakes for a second or two to bring speed down to a lighter application a little more often to maintain slower speeds. They don't always smell but sometimes do. I do use the Jake but have to hold speeds down below 50mph because when it slams into 4th gear it over speeds the transmission above 2100 RPM if over 50MPH. When using the cruise control the Jake usually does not downshift but the braking is not as efficient and it will sometimes slam into 4th and I see RPMs of 2400 RPM+. So I try to manage the Jake very closely causing me to look like a one armed paper hanger while descending steep grades. I realize I added a little more info than required for the original question but was trying to anticipate the questions and comments about the proper way to descend (no sarcasm intended.) Are smelly brakes the norm? Thanks for your patience.
Jerry
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I have never smelled my brakes. In fact, I rarely use my brakes except for final stopping from a slow speed or to slow down on a downhill section of a highway of 4% or steeper. When I use the brakes going down a steep hill I use multiple and soft toe-touches to take off perhaps 5 mph. Again, as I have opined many times here on the Forum, I do NOT like your brake programming. Mine was like that and I had the programming changed ASAP at a Kenworth shop in Pasco, WA... and at no charge... but I was lucky on that score.
Recently, the coach had its 2-year physical at Eagle Freightliner. The coach has just over 70k miles and the brake pads were at 50% or so.
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Jerry, In my 40 plus years of driving Lowbeds with Heavy Equipment loads I would use this procedure of going down the hill the same speed I would go up it. I know I would be hauling more weight than our rigs but it is a good rule of thumb since we are all on vacation when driving our coaches. Not to mention I am responsible for all the upkeep on my coach. imho
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After replacing all brakes years ago I had the Allison reprogrammed in order NOT to have to use the service brakes to avoid the transmission 'slamming' into 4th when selecting the Jake brake. I now have Jake in all gears and never smell the brakes.
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The RPM limit "on compression" is not the same as under power. Check the book. With the Cummins we had, it was 2400 downhill and 2100 uphill. I suspect the Cats are about te same. The best braking was at about 2300. The Allison/Cummins programming made it impossible to hurt anything. If it touched 2400 going downhill, it shifted to take care of the engine.
If you are smelling brakes, they are hot and you have little left if you need to actually use them to stop.
On a six percent freeway grade is about 45mph up and about 47mph down without ever touching the brakes.
Be careful out there!
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Thanks all. I guess I will bump up the priority of the transmission reprogramming some. We have been non stop since retirement 19 months ago. Haven't really had much time except for normal maintenance and repairs. Brakes don't seem to be fading when I smell them and as I said I just use them lightly most of the time. I rarely hit them very hard. Just had chassis maint. done about 6 weeks ago and they said the brakes looked almost new. I've checked for high temps on occasion and they are all pretty equal. As for descending at the same speed as I climb, most of the climbs don't slow me much and when I hit the top I usually have to brake to under 50 to use the Jake. Thanks again for your help. 30K+ miles on this machine in the last 3 years and I am still learning.
Jerry
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Jerry, For starters I wouldn't let that Cat rev over 2K, one of the 1st times I turned on the "Engine Brake" at 65 mph and it shifted into 4th gear and I looked at the tack which was somewhere around 2400 I said this is not going to work. I had the Allison reprogrammed to not shift down, there was two things the tech had to turn off in the program. Now I can have it on at 65 or 70 coming off a slight hill or a west Texas whoop de do and so shift and manually shift down as needed. When downshifting from 4th to 3rd I have to be careful as you can over-rev the motor because there is a big split between those two gears. Western Canada has so really nice grades 8 and 9% which I can go down and never touch the brakes.
If I do use the brakes I just apply light pressure to slow a bit. My 06 also has disc brakes which make a big difference.