Removed Valve Cover, and What Did I Find?

Glennman · February 24, 2025, 04:27:19 PM

I took my valve cover off today, and I discovered that I have Jake Brakes! There is no indication that I have them otherwise. No switches, nothing. They are all wired in, as would be expected, with those little white wires and the harness leaves the valve cover at the rear and goes from there.

How it the world would I find out if they work or how would I hook them up? Does it have anything to do with the ECU? I have a call in to the local motorcoach tour bus outfit hoping they might be able to steer me in the right direction. Any suggestions from you all would be much appreciated!

Iceni John · February 24, 2025, 05:35:43 PM

I don't know what version of DDEC you have, but my Bus's DDEC II permits the Jakes to operate by grounding DDEC wire 508 (Engine Brake) when in No Fuel condition (i.e. coasting). That wire grounds my Jake relay's pin 85; pin 86 gets power from the main CB panel, and then it powers my Jake switch from pin 87 (pin 30 is connected to 86) that actually controls when I want the Jakes on. One thing to note that's very important if using a relay, is that there's a diode between relay pins 85 and 86 to suppress voltage spikes when the relay operates: any such spikes could damage the ECU if they passed back along wire 508. There is no lockup signal from the transmission - only the DDEC signals the Jake.

John

luvrbus · February 24, 2025, 05:55:13 PM

They are controlled by the ECU wire 581 and wire 582,you should have switch off and on,and another low ,med and high,you probably just have Jakes on 4 cylinders on the D so there is no high, my switches were on the upper dash to the right, they may not be active check with your Pro/Link ,some buses used in commuter service were never activated because of city laws ,mine were on all 6 cylinders .They are wired through the ECU to prevent over speed of the engine ,if you are cruising say 75 mph they won't engage fully or maybe not at all till the speed drops DD replace a ton of series 60 where the rod went through the block because of over speed of RPMs so they made a safety net with programing

Glennman · February 24, 2025, 07:32:36 PM

I have the DDEC IV.

The Jakes are model 795 and serial number is TC028457 (at least the "front" one is).

The Jakes are in 2 sections under the valve cover. One is the "front" which is over 4 cylinders, and the other is the "rear" which is over 2 cylinders. The "rear" is actually toward the transmission and the "front" is toward the bumper.

On the dash, there is about a 1-inch diameter red momentary button. I've pushed it while idling, but never while driving (I have been afraid to try it while driving). I doubt that it would be for the Jakes, but I'll be looking into every possibility.

luvrbus · February 25, 2025, 04:10:33 AM

Wire 953 is the power to switch it should be a 2 switch like a Jacobs P/N 017328 ,wiring and switches can change on 25 year old bus ,but wire 622 cavity A and wire 621 cavity B for Jakes should never change

Jim Blackwood · February 25, 2025, 10:32:57 AM

Well how cool is that? Makes me want to go out and look for wires.

Jim

Glennman · February 25, 2025, 10:30:32 PM

Quote from: luvrbus on February 25, 2025, 04:10:33 AM
Wire 953 is the power to switch it should be a 2 switch like a Jacobs P/N 017328 ,wiring and switches can change on 25 year old bus ,but wire 622 cavity A and wire 621 cavity B for Jakes should never change

Back when I was figuring out how to get my systems up and running after removing my wheelchair lift, I learned quite a bit about the wiring, but I'm not clear on where I would find the wires you speak of. Where would I find 953 power wire, 621 cavity A and 621 cavity B (I'm not sure where those are or what "cavity A and B" mean). Do the 621 and 622 wires run the different levels of the Jakes (low, med and high)? Thanks for everything!!! I'll be looking into all this and share my results.

I heard from one source that I'll have to have my ECU parameters set to activate the Jakes after I figure out the wiring connections.

luvrbus · February 26, 2025, 08:15:04 AM

Once you figure out rhe DD reasonability and the OEM reasonability wiring it is not compilated when I get time I have it on 20x12 sheets that will show the cavity and wire numbers I will try to post you photos lol that could be a challenge for me

Glennman · February 26, 2025, 09:08:27 PM

Quote from: luvrbus on February 26, 2025, 08:15:04 AM
Once you figure out rhe DD reasonability and the OEM reasonability wiring it is not compilated when I get time I have it on 20x12 sheets that will show the cavity and wire numbers I will try to post you photos lol that could be a challenge for me

That would be great luvrbus! Much appreciated.