[360]

After having driven a S60 with 6 speed Allison I'm a bit perplexed by something.  My understanding was that the optimal range for using the Jake was around 2000 RPM up to a safe maximum of around 2200.  When cruising along at 65 or so and heading down a long slight grade in which the coach itself will not hold itself back in 6th without either braking or the Jake the Jake wants to downshift 2 gears into 4th and that takes you to darned near 2500 RPM.  One would assume that the controller on the unit would not let the trans downshift to an unsafe RPM for the engine, but I have not seen an reference in anything I've read that it's ok to operate at that high of an RPM on a regular basis?

I can't for the life of me understand why it's programmed to drop to 4th automatically as there are so many times that a less agressive breaking would be preferred.  Would to be so much better if it either stayed in 6th initially with a slight uptick in speed triggering 5th and/or braking on top of that should make it drop to 4th.

[Richard]

As built by Newell, it downshifts to 5th. Newell’s idea was not to jar the passengers. Some owners have had the ECM programmed to downshift to 4th for more aggressive braking off the bat.


I don’t know the RPM number, but I do know that on some pretty steep descents, I have had to tap the brakes to get the tranny to downshift all the way to the gear I selected.

The jake should come on immediately if you lift your foot off the throttle, unless the owner did a little magic with the wiring to get the jake to activate off the brake pedal. I have modified my jake wiring so that I can choose if the accelerator or the brake pedal activates the jake.

[360]

Makes perfect sense, it must have been reprogrammed. 5th would have been perfect for my liking and then a manual move to 4th if needed after braking or it will automatically go to 4th upon braking that would be fine too so long as the RPM's stay in line. 4th was jarring for sure and excessive on all but the steeper grades.

[encantotom]

i had mine reprogrammed to downshift to 4th.

tom

[360]

Tom, what do you feel is a safe max RPM while using engine braking? Do you also think the controller will let that downshift to 4th initially take to to above a safe operating range? To clarify, I'm not talking about a runaway train situation where it gets away from someone and they over rev, i'm talking about initial engagement of the engine brake.

[encantotom]

from what i understand and have witnessed on mine is that the tranny is smart enough to not downshift until it is in safe rpm range.

it has been a while so i dont remember what that was.

tom

[RussWhite]

I also had mine programmed to 4th. Would never go back and the Allison is way smart enough to handle it. But, as with many things, your mileage may vary and do what works for you.

[TJ Clark]

Low experience user here....


In my travels through Flagstaff and on to Spokane. I experienced plenty of hills.

One in particular I had inadvertently switched off the Jake. by the time I found the fault (fat fingered driver) and switched on the system, I was doing 70 and gaining fast on the cliff ahead.

It activated and slowed my increase in speed but it was still climbing. I jabbed the breaks a few times and the system down shifted to 4th from 5th at about 2500 rpm. I was still passing them yellow signs with the truck tipping over that and the 45MPH title at about 55, so I selected 3 and jabbed the breaks a few times and the system then shifted to 3rd again at about 2500 rpm.

That got me under the posted warning speed and my comfort level returned.

On the next down hill I made sure the Jake system was on well before the summit and at the summit I lifted to crest off power.

I felt more confident that way.

Fine system and it sounds great too.

My PRODRIVER display has a screen that looks to display the MAX RPM, mine reads something like 3400. Was like that when I got. it.

[360]

Hey TJ, I've had one of those moments before in a semi where you think you're on a runaway train for a few seconds, fun times. Your post is another version of exactly what I was talking about. I just surprises me that the system allows the coach to rev to 2500 while braking.

I love the idea of engaging in 4th, so long as that means if I'm cruising down a long extended grades with my Jake engaged at 2500 that i'm doing zero harm. I'm for sure in the camp that I don't think the engine management would let it grab a gear that would do harm, but I'd love a more detailed explanation as to why sustained 2500 rpm is just fine while braking, where we know 2500 would not be considered fine when not braking.

[Deper10]

I am having an issue with my Jake brake. It was working just fine two weeks ago when I took a short 30 mile run, but yesterday it did not seam to be working. I think it might be a fuse so I am going to go back today and see if I can find anything. What I want to ask is in a steep downhill grade, 8%, what gear should I use especially if the Jake is not working. Yesterday I used 3rd gear which started out OK but quickly ran up to 2500 rpm so I had to keep pumping the brakes to try and slow down. It also felt like the transmission shifted up to 4th, even though I had selected 3rd gear. The grade was only about a mile long but when I reach my storage space, the brakes were heated and I could smell hot grease at the right rear tires. Any thoughts on what that could be. It does not do this when under normal operating conditions.

Dario Perini

#581  2001 45'8"