Jake brake position

[doc]

08 Essence, Freightliner chassis, 425 Cummins

The jake has a two positions that it can be activated in. There is a neutral which is vertical and then can be moved forward or to the rear. Bith activate the brake. I cannot see the difference, but why would there be two positions if both do the same thing? Or is there something I am failing to see?

[doc]

08 Essence, Freightliner chassis, 425 Cummins

The jake has a two positions that it can be activated in. There is a neutral which is vertical and then can be moved forward or to the rear. Bith activate the brake. I cannot see the difference, but why would there be two positions if both do the same thing? Or is there something I am failing to see?

[GaryKD]

Hi Doc,
Dumb question; could this be for a high or low activation of the feature? I've deen this on other coaches.

[doc]

I wondered about that. When activated, the Allison shows '2' as the target in both positions. I usually just flip it to the front and it slows us down OK. I guess I just need to call Freightliner and get the lowdown. (It is just easier to ask here ) Thanks for the reply Gary

[Pigman]

You have an engine compression brake on the 425 Cummins. The front position should be for the full effect of the brake and the rear position for only half the braking. On a good hill check it out closely. When we got our rig, both positions were set up for only half braking. I had Gaffney check it out, and they reprogrammed it the way it was supposed to be.

They also had the MMDC messed up. It and the speedometer was showing about 4 MPH less than the GPS was showing or than what I was getting by calculating time between mile posts. I guess the calibration guy was out to lunch the day mine was supposed to get checked. They fixed that issue too.

John

[Gary RVRoamer]

The two positions are for the two brake "speeds", called High and Low. Mine is wired to two separate switches, one is On/Off and the other High/Low and "High" is actually the lesser amount of braking (go figure!). One engages engine braking on 3 cylinders and the other on 6 cylinders. Both will target the same lower gear (normally 2 but can be programmed for any gear you like).

You won't notice the difference in braking except on long steep grades, probably 5% or more. Then the 6 cylinder braking (the Low position on mine) will slow you noticeably more than the 3 cylinder mode.

[Route 66]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">High/Low and "High" is actually the lesser amount of braking (go figure!). </div></BLOCKQUOTE>

Couldn't you swap the wires on the high and low terminals to make the switch work properly?

[Gary RVRoamer]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Couldn't you swap the wires on the high and low terminals to make the switch work properly? </div></BLOCKQUOTE>

Yes I could and had originally planned to do that, but once I learned which was which, it didn't make any difference. I just think of them in terms of "High gear" or "Low gear"

[doc]

That makes a lot of sense and I should have figured that out.
As soon as this weather gets better I am going to take the coach out and experiment a little to find out which way is the 'high' and 'low'.
Thanks
doc

[DonGee]

A class I attended at an FMCA Rally said the tranny shows second gear but in reallity it does not shift down.. Can't immagine it going into a lower gear at 60 MPH.

Don,WIT 70041

[Gary RVRoamer]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">the tranny shows second gear but in reallity it does not shift down.. </div></BLOCKQUOTE>


The gear displayed on the Allison panel is the "target gear". The transmission will downshift toward the target gear as engine RPMs permit. It will eventually downshift all the way to the target gear, step by step, if upper gears slow the rig down enough to allow it.