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Jake Brake questions
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Marshsll
the proper term is to have an Detroit/ Allison shop to awake “pre-select 4th downshift for jake brake. Once you’ve hit proper rpm, it will slam you into 4th at about 56. After one coach doing this, we prefer the proactive approach to using transmission pad to down shift manual thru gears to slow bus
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Not trying to start a war here. I got the information I need…..Thanks to everyone for your comments. My coach needs a trip to DD/Allison for a downshift routine program change. I’ll use the manual gear selection in the mean time to figure out just how aggressive I want to be.
Thanks again……
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Thanks Jim. Just saw your latest post.
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I don’t know if others do this, but when I manually downshift is momentarily step on the accelerator, look for a little boost and then push the downshift button. You can’t even feel the downshift. Of course I do that when I am in the proper speed for the gear.
To use Jim’s example of 4th, I make sure I am at 50 or below so am not at the peak of the RPM range.
Also, for a hard braking event if the retarder is engaged it will assist with braking at a force proportionate to the braking force automatically. The retarder stick can be in the zero position, but as long as the dash switch is on in that case your brakes are being assisted.
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Is it possible to have two programs for jake downshifting? Could the mode button be used to select the second profile? I am currently preselected to fourth gear and I like it that way. I do have to watch the fourth downshift as it will go straight to 2350 RPM and that makes me uncomfortable. I manage by watching the tach and turning off the jake at 1800 RPM and then bleeding speed, reengaging, and then manually downshifting as needed. I rarely touch the service brakes before the 15 MPH cutout using this technique. I am asking about the dual mode option as my wife also drives. I would like the added safety of knowing in a panic stop she has all the retarding force she can get.
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Does DD/Allison have a safety built in so you can’t accidentally down shift to low?
I have this recurring nightmare of some jurk cutting in front of me and I push the down arrow fast to many times, the trans goes to 1st @ 55Mph then there is my oil and parts scattered on the road while the idiot drives away clueless to what just happen
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Chuck, as someone stated earlier, if you shift down to first gear going 70 MPH, the only thing that will happen is the transmission will shift to 5th gear, and won’t shift to a lower gear until it is safe for the engine to do so.
When I first joined this forum, I found it to be a godsend of Prevost information. Jon in particular has a wealth of knowledge of everything Prevost. It was disappointing during our previous discussions on the use of the Jake brake to see Jon not only perpetuating the erroneous assertion that you can never exceed 2,100 RPM on the series 60 Detroit Diesel (DD), but also refusing to get the facts from the source, namely Detroit Diesel. The 2,100 RPM limit has been debunked in previous posts. There are three RPM limits for the Detroit Diesel. The manual states maximum allowable RPM is 2,100. On the side of the engine it states the NL (no load) limit is 2,250 RPM, and the DD manual lists the never exceed RPM as 2,500. The never exceed RPM for those of us who know engines, is known as the redline. Since the 2,100 RPM limit is obviously not the maximum in all circumstances, it is obviously the maximum RPM limit while under power. The 2,500 RPM (never exceed) speed is programmed into the engine/transmission computer to prevent the engine from overspeeding. Even Jon said in a previous post that if you allow the engine to get to 2,500 RPM while using the Jake brake, the transmission will upshift to the next higher gear. Why do you think this is? Well, it is because the transmission was programmed this way to protect the engine. If you choose to believe that the engineers programming the DD/Allison combination are a bunch of idiots who had no idea what they were doing, that is your business, but how many of you feel that way about the car/truck you drive every day?
If you choose to use a 2,100 RPM limit while using the Jake, again, that is your business, but rest assured there is no reason not to go up to 2,500 RPM while on the Jake. The higher RPM will give you a significant increase in braking power.
I do not know what the corresponding limits on the Volvo engine/transmission are, but rest assured they are properly programmed to ensure engine RPM limits will not be exceeded. Anyone who believes DD/Allison/Prevost would allow an $800,000 shell with a $1,500,000 conversion to have an operator blow the engine by shifting down too far, has to be a special kind of stupid!
1999 XLV X-6872, liberty #440 -
Per, I wish you had taken the high road and just stated your position without making our difference of opinion a part of the narrative.
Anybody that wants can drive their bus or set up their bus as you have. Anybody can accept what you state as their guiding principles for how to drive or manage their bus. It is theirs to do and drive as they wish.
But Detroit couldn’t make it any plainer than how they say 2100 is the limit. You have picked a 2500 RPM never exceed out of a single statement somewhere in the Detroit publication and are accepting that as your limit because someone at Detroit verbally said 2500 is OK. Get it in writing and we will make sure your 2500 RPM redline is posted here, but until you produce a statement from Detroit, in writing on their letterhead or in a service or owner’s manual for our model engines I have to accept 2100 as my limit for the engine.
Everyone else can decide on their own what the limits are.
Since I did not contradict what you said but explained to members how and why you use 2500 as your limit I will close this thread if we get into another debate.
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Well…..I started the thread, and didn’t expect a debate of specs and RPM’s. Simply asking a question on Jake Brake operation. I have learned everything I need from this forum (downshift on Jake Brake reprogramming is possible), so I’m good with closing the thread as long as everyone else is.
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Jon,
From page 25 of the Detroit Diesel series 60 owner’s manual:
“When descending a hill with Cruise Control OFF, do not allow the engine to exceed 2,500 rpm under any conditions. Failure to observe this precaution can result in overspeeding and serious engine damage.”
In addition, the placard on the side of your engine states no load limit is 2,250 rpm.
Those are the facts. As far as your high road comment goes, I find it laughable after the name-calling and insults you have dished out. Close the thread if you wish; too bad you are more concerned about hanging on to your old trucker’s tales than getting facts out to the members of this forum.
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From myself and all the brother truckers on here it’s time to say good bye to this piece of shit.
Later
bv
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