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Jake Brake
I just purchased a 2001 Featherlight Vantaire 45′ with tag.
It has the DD60 with allison 6spd.
During the test drive I checked the Jake on both low and high setting and while the dash would indicate that it was working, I did not feel the deceleration I was expecting.
I’m trading a Monaco DP with an exhaust brake and it seemed to have better deceleration.
I have read that the engine/trans affect of the jake should work better than my old exhaust brake but it did not seem that way.
The dealer tole me that it was likely programmed by Allison for 4th gear but could not confirm or that it was working correctly but offered to check codes but told me not to expect a very noticable deceleration. It does not seem right to me.
Should I expect to see a noticeable deceleration and if so would it only be at certain speeds or gears? I have no experience with a jake or a Prevost.
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16 Replies
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I have the S60 with Jake brakes. I’m pretty impressed with them. If you open the driver window you should hear the typical jake brake noise when you get off the accelerator.
I have gone down mountain passes and never touched the service brakes. You’ll need higher RPMs (>1500) and a lower gear to have the most braking action.
You’ll have to watch RPMs going down steep inclines in low gear and keep them below 2100-2200. The transmission will upshift to protect the engine around 2300 and then your coach will accelerate smartly down the hill given the reduced braking action in the higher gear.
The only time you’d not have a very noticeable braking action is if you are gliding along in 6th gear at low rpm.
Gerald
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In the rear electric box (over the engine) it is likely you will have two posts for the Jake brake. They will be identified on the diagram and wire list. On an XL or XLII the listing and diagram is on the inside of the LH door. I am not sure where to find that on an H.
If you run a jumper (12 volt) from the 12 volt post in the electric box to either of the Jake brake posts with the engine idling you should hear the engine lug down. Both posts should react the same way to the application of voltage. Doing that bypasses the switch at the dash and confirms the Jake brake within the engine is functioning. If you do not get the loss of RPM on the motor on one or both of the Jake circuits, look for the problem to be with the wiring to the solenoids under the valve cover. They are simple to replace if they have failed, but usually the problem is a broken wire or loose connection. If the engine lugs down as expected look for the issue to be at the Jake control on the dash or the wires or connections from that point back.
As was pointed out when you lift off the accelerator with the Jake engaged you should hear the distinct exhaust sound a Jake brake makes when it is working. It might be as simple as the heavier Prevost is less affected by the application of the Jake so you may not get the feel of deceleration you got on the previous coach.
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You would be very impressed with how well a Jake works as opposed to an exhaust brake. Make sure you selected the high position at the switch. You can also see a boost on your turbo gauge when the jake is engaged in the high position.
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When we first tried the Jake on our 2006 Marathon I was extremely unhappy having traded our 2000 Marathon with a trans retarder. I took the coach to the Ocala, FL Detroit/Allison facility where the tech told me he could make the Jake slow the coach just like the transmission retarder did. Knowing more than this young man, I bet him a lunch at MacDonalds that he couldn’t…I lost! Using his laptop, he analyzed the transmission setup on my coach, then down loaded the transmission setup program from Allison. Using an xcel matrix he had me check off the gears I wanted the Jake to be activated in. I chose 6 down to 2. It was strictly a software change.
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Good info George and I was there when you swapped the 2000 for the 2006, great time at Lake Toxaway!
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Most Prevost conversions will not be programed to downshift when the Jake is activated (off throttle, engine over 1,000 rpm, & Jake switch on). An exception to this are Royale conversions when owned by Monaco and most Country Coach conversions. Most regular motorhomes with a true Jake or simply an exhaust brake are programed to downshift, sometimes to as low as 2nd gear. While this will provide more braking force, it can also cause the coach to slow far more than desired on slight grades. My personal preference is to have the coach remain in the gear selected, and the driver can manually select a lower gear if needed. The Allison transmission will not initiate a downshift until the coach speed has dropped to the point that a lower gear would not cause an overspeed of the engine. I have driven Monaco products with the 600H.P. Cummins ISX that will almost put you through the windshield when the Jake is activated, and the transmission programed to try to get to 2nd or 3rd gear downshifts. This makes it difficult to drive smoothly, and most people end up applying throttle, then releasing the throttle, resulting in a very rough drive. The Detroit Series 60 is not as effective on the Jake as some other engines, particularly the very large displacement engines such as the ISX Cummins or C-15 Caterpillar. I find that on some descents with a very heavy coach, you may need to use the service brakes occasionally to maintain a safe speed. It is critical that the service brakes are used for short periods (3-5seconds) then given adequate time to cool before applying again.
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The key to a smooth use of the Jake brake is to not let off all the way on the accelerator, but to feather it back so the Jake will disengage but the transmission will not upshift. Just takes a bit of pracitice. When we get our Prevost, I will have the tranny reprogrammed to go to second as a target gear.
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When you are on cruise control that won’t work , it will try and shift to second all the time most jakes come on in sixth if you change it to 4 th it’s a pain in the ass so try second let me know, how it works out going up and down hills
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Most of the time I turn the cruise off when I get to the downhills, and turn the Jake on as needed. If the Jake gives me too much braking, I ease off the trottle so it stays in the same gear, but the Jake is not engaged. Of course you can tailor the Jake position to the hill ( I have a 3-position Jake), and then use service brakes as needed.
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Our Monaco down shifts to 3rd upon activation of the Jake. I usually leave the Jake on low and switch to high Jake on steep down grades. With the Jake on high the coach will slow down even on an 8% grade.
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whether the coach has a jake or a retarder it has likely been programmed to downshift upon application. With later model coaches some are programmed to drop down to 5th, some down to 4th.
They can be programmed to go to 1st if that is your preference, but the downshift will only happen to the programmed gear if the coach speed is within that gear’s range. In other words if the top speed in gear for 4th is 55 mph, and the coach is at 60 mph it will only downshift to 5th and will not drop into 4th unless the speed drops below 55.
The use of the retarder or jake takes a little getting used to and it is to a great extent fully controllable by the driver who has the ability to determine target speeds, setting of the jake or retarder and gear selection manually or allowing it to be selected by the programming or cruise control.
With today’s coaches and a skilled driver who anticipates his needs can go many miles in areas with steep grades that slow the coach going uphill, and never touch the brakes on the downhill side.
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My jake matches the gear selected automatically or manually and disengages on 1st gear. No crazy down shifting for me.
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The jakes on my 2 stroke does the same. Automatically downshifts where it wants to. Kicks out at first. Here in the flatland or slight hills don’t really use the brakes that much. Can really feel it tugging slowing down.
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Tom Mine does the same
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My experience with that symptom turned out to be a bad switch. The rocker switch on the dash.
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