Two Position Jake Brake Switch - Any difference between up and down?

[GTHill]

So my coach has a two position Jake Brake switch. Is there a difference between pushing up (M) and down (Blank)? Thanks for all of the continued help!

GT

[Ted III]

If the 2003 is the same as my 2005 you should have a high & a low for your Jake brake. There is a substantial difference and you should be able to feel the difference immediately.

[Old Scout]

Not sure when WRV went to a high/low/off position jake brake, our early 2003 only has two positions--on and off. Off is obvious while the "on" position results in a pretty harsh application of "high" jake braking. Let off the throttle and a slight application of the brake pedal should induce a noticeable braking effect--if not, your jake is AWOL.

[GTHill]

Mine is a three position rocker switch. The middle position is off. I can push the top or bottom in and the Jake works. I'm not sure if I've ever actually tried to see if there is a difference in the intensity of the two positions.

I'll try it on the way home. Oh, and my accelerator pedal does turn it off, which is a nice feature for sure.

I read in another forum that some coaches came with cruise control that would actuate the Jake when needed. That would be nice for sure.

GT

[Old Scout]

Soooooo--you really dont have a "two-position" switch??????

[jerry davis]

There is a definite difference in the high and low if you do indeed have a three position switch. Shortly after purchasing our coach I took it to Cummins because there was no discernible difference in the two positions. Now there is a real difference.......so much so that I seldom use the high setting. I leave it in low most of the time.

[gator67]

There is a definite difference between the high and low setting. There is a good description of how the Jake brake works at http://www.svfd.net/SVFD%20Files/Art...a%20diesel.pdf. According to something I read, on the low setting, effectively, the engine is retarded by losing 3 cylinders of power. On the high setting, it loses 6 cylinders of power. When I'm in 2nd gear on the high setting I can stop dead on an 8% grade.

[D & D Rich]

If your coach has the 2 stage Jake Brake, and three position switch, Low/Off/High and doesn't work in both modes it may be a program issue.

During Dessert Rat Rally 2005, I watched Mike Young, Cummins Northwest Yakama, WA hook up his laptop computer to the data port and reprogram the Jake Brake to work on both High and Low. I'm sure that's what Cummins did for Jerry Davis. Mike Young said for some reason WRV had the Jake Brake programmed for only one stage, (I don't recall which now).

I'm not sure of the year WRV went to the 2 stage Jack Brake, but my guess would be when they started using the ISL 400 engine.

[GTHill]

Just as a quick update, my Jake brake does have the two stages. My switch has an (M) at the top and that is the stronger of the two stages. The bottom of the switch is blank, but is a weaker Jake. Thanks for the advice!

GT

[Renipladlo]

When I first purchased the coach, mine would not work. So I had Cummings look into it, the wiring connection was switched with the Battery Boost Switch. So now the thing she works well. Rock it forward or up, and that is high braking, middle is off, and down or in, is low. I use high for real steep hills or medium traffic in the city. It immediately shifts the transmission into 4th and brother you can feel it. We were in traffic in Salem, OR, and the lady in front of me jetted ahead, and so I moseyed in behind her, and glad I had it in high, she just stood on the brakes, and I was sure I was going to hit her, but it stopped in time, but jostled some dishes in the kitchen, which the BH was not please about.

[takepride]

GT:

We have the same model. My coach has the three position switch and works as designed. Interestingly, under the dash is the wiring and plug labeled "Pac Brake", just dangling disconnected. The plug and wiring in use are labeled "exhaust brake".

My switch labels are "High", blank and "Low".

[dgerstel]

Takepride,

I think that in 2003, the 400 ISL was an option and the 350 ISC was the standard engine. The ISC used the Pac brake and the ISL uses the Jake brake, so the wire loom would be wired for either.

[takepride]

That makes perfect sense! Mystery solved.

[EngineerMike]

When we took delivery at the factory in 2007, september-ish, there was no Jake. I sent it back to the chassis shop where they claim to have remade the ECU connector to fully push 3 pins in place, and voila! there was Jake. However it took me a while to realize there was only one stage whether switch was in Lo or Hi. Been doing some research at rallies, in engine bays, at Cummins, etc., and here is the current update:

1) I had my engine ECM read by Mike Young of Cummins Yakima at the Salem Rally last year to discern if there was a programming error. No error, he could read parameter set for 2-stage engine brake. Further he could read Jake-Lo Commanded when I flipped the switch to Lo, and Jake-Hi Commanded when I switched to Hi. He concluded either a) wiring between ECU and Jake was not installed properly, or b) Jake is busted. He offered that they had had some type b) problems from time to time.
2) Each bank of 3 cylinders corresponds to one "stage" of jake, i.e. one 3 cylinder bank engaged = Lo, all 6 cylinders of Jake engaged = Hi. There are two bullet connectors on the RH side of engine, each about at the front or rear quarter point, near the level where the valve cover splits from engine. The female/wire connection of the bullet simply pulls off & snaps back on. You can get to the rear one easily thru engine hatch to see what it is & how it works. If you apply 12V to the stud going thru the "Pass-Thru" into the head (the bullet), you will hear the solenoid that is supposed to be controlling the Jake bank of 3 cylinders "click." On my rig I can hear each of the two bullet connectors report a "click" when I apply 12V; one is slightly higher pitch click than the other. On other coaches some have same pitch click, some have discernible difference like mine.
3) took rig to Cummins West in West Sacramento w/Jake complaint. They did shop-test of applying 12V and got "click" and concluded all was well, both banks "work". I asked if they road tested, and Oops. So shop foreman road tested; couldn't discern difference. They told me there was a "recalibration" which is their word for ECU programming change, which rendered all calls for Jake to Jake-Hi, so that was what I was getting. Yeah, right.
4) I tested jake under way on I-5 subsequently, at freeway speed. To do this I split the wire-loom at the 2-pin Delphi connector near front of engine (you can trace the loom forward & down from the forward bullet connector on head & find this 2-pin connector), and installed a purpose-built connector & loooong pigtail (wife wanted to know why she was tripping over wires coming from engine) so I could drive & volt-test at the same time (probably a ticketable offense, so I had DSW do the volt readings). Commanded Jake-Lo thru the dash switch- got 12V to rear 3 cylinders (nearest engine hatch) but no voltage to front 3 cylinders. Commanded Jake-Hi at dash switch and got 12V to both banks. I.e. rumor of recalibration = B.S.
5) I ran coach up to 75mph on the straight w/Jake-Lo "ON" and let off the gas, jake engages & engine/trans downshifts; I snapped the Lo/Hi switch to Hi and there was a momentary disengagement of the Jake as switch went thru Off, but once back On there was no change in the degree of retarding.

Conclusion: Hi stage on my jake is busted. Need warranty work.
This affects at least two other 2008 rigs in the early round of ULSD-only engines. I'm posting here in case anybody else is having this issue.