[prairieschooner]

Jake Brake Fixed! I wanted to document this for others that may have this problem in the future.
The problem was Voltage Drops that didn't show up until tested under load. There was about .5 Volts Drop across the Glass Fuse so I installed a Spade Type Fuse Holder in it's place. There was an even bigger problem with the Dash Switch that showed 1.2 Volts Drop but only intermittent so that was replaced as well.
Since I needed to Adjust the Micro Switch that is Piston Activated at the Buffer Location I simply made sure that it was in the Closed Position. This activated the Solenoids inside the Valve Covers and put the System under Load, this made it so that I could find the Voltage Drops. I then removed the Valve Covers and began to test Voltage at the Solenoids, low at 9.8 Volts! Now to the Front Fuse Block (#16) and then working my way back, to Dash Switch, to Front Terminal Strip (#36), to Rear Terminal Strip (#23), to the Buffer Activated Micro Switch (No Fuel Closes N.O) then finally to the Solenoids.
After the repairs I had full voltage at the Solenoids. I then Adjusted the Micro Switch by Sliding it In until I could hear it "click" and confirmed that it was now Closed using the Volt Meter on the Solenoid, then moving the Switch Back until I could hear it "click" again confirming that it was now Open using the Volt Meter on the Solenoid. ***With the Valve Cover Off you can actually see the Solenoid Pull In when Raising the RPM and then Decreasing the RPM.
Here is the Wiring as I found it on my '82 with Detroit Diesel.

Jake Brake Wiring.pdf Size: 38.84 KB  Downloads: 30

[encantotom]

steve. thanks for documenting your repairs. great work

tom

[whatsnewell]

Steve, seeing I have an '82 also, with the same 6V92, this information will be invaluable in the future should I begin to have the same issue. So far it works just fine, but time and chance happen to us all.

[prairieschooner]

You bet Clarke, not just for us but others as well with 6V92 and 8V92 and earlier 71 Series as well as some Cummins or Cats. This does make me re-think leaving it on all of the time. This would make the Solenoids come in every time we decelerate. I am thinking of turning the Jake Brake off when on a long run and not when needing that extra help.

Those Solenoids are most likely the same ones used on Cummins and Caterpillars though so may be readily available.

[Retro]

Great info Steve!!

[77newell]

Steve's diagram of the wiring is exactly as my 77 coach was wired. Be aware that if you have a two stage Jake setup, the positions of the micro-switch and the dash switch will be reversed, with the dash switch being a three position (off, half the cylinders, all the cylinders).

Also be aware that the "buffer switch" assembly performs two functions on the Detroit mechanically governed two stroke engines: 1) it turns the Jakes on and off, 2) minimizes or eliminates "rolling" (a small amount of hunting) of the engine speed at idle. Whether or not #2 is true with other mechanically governed engines is unknown to me.

Steve's description is really helpful. I would reiterate one caution. When you have finished messing with the adjustments and are testing how it is working, rev the engine up only enough so that when you drop it back to idle the Jakes kick in. If the adjustment is such that the Jakes come on before zero fuel is reached the sound generated, at least on my engine, was loud and I'm sure it was an indication of extraordinary stress on the exhaust parts. I would not want an extended period of that happening. When operating correctly, the sound of a two stroke in Jake mode is one of the coolest on the planet to my ears;GRRRRRRrrrrrr!

[prairieschooner]

I used the Troubleshooting manual that Michael Posted earlier (Thanks Michael!). Not being sure how long that Manual will be available online I posted it here under Documentation along with my hand drawn diagram ***This Manual is for the 71 and 92 Series Detroits as well as some Cummins and Caterpillars;
http://newellgurus.com/Thread-Jacobs-Bra...e-Shooting

I think that if I have another issue with the Jake I would start at the Fuse and then go straight to removing the Valve Cover. The Operation is fairly Fast so I couldn't use my nifty Digital Meter to Check the Voltage so I had to go to my trusty Simpson 260. But better still is that you can actually see the Solenoid Pull In and then Release! The valve cover seals are rubber so they are reusable with no issues. ***The Components inside the Valve Cover are Hydraulic, but don't let that scare you because as I have been able to find out most of the Troubles with these Systems are Electric.

As 77 stated you do NOT want this Engaged when the Throttle is Depressed and I would NOT want it Engaged when at Idle. Still really easy to lift the valve cover on the passenger side of my 6V92 and watch the System Operate.
PS The Manual suggests that you Adjust the "Buffer Switch" at 100,000 miles and with only 125,000 miles I can see why.

[ccjohnson]

Almost like a "Harley" sound Jon!

[whatsnewell]

Love the Jake sound a 2 stroke makes......silky smooth.....like putting a hot knife through warm butter.

[Tf175]

I know this thread is a few years old , but it's applicable to what I have going on with my 86 coach with 8V92TA . Back in July I tried the Jake brake for the first time , got no response . After researching this deal , I think that the two times I actually tried the Jake I wasn't going fast enough , probably only 35 or 40 mph  , coasting in drive. In any case I have been going over the electrics of the system and have found the following: With console switch on , I have battery voltage (12.7 ) going into the lower (common) terminal of the buffer switch. 
The wire going to the driver's side valve cover is connected to the center ( N.O.) terminal of buffer switch . The wire to the other valve cover was disconnected.
Using a thin strip of metal between the buffer shaft and switch plunger I was able to trigger the switch , sending power to the N.O. terminal. Therefore the switch was working. 
I removed the micro switch only , leaving the actual buffer screw unchanged so the adjustment will not be affected . The micro switch is held in place with two machine screws on a slotted bracket .
While cleaning the switch I managed to tear the protective boot on the plunger so I went in search of a replacement switch . The original is an Omron , Z-15 series . Jacobs only sells an upgrade which requires removal of the whole buffer screw , a little more than what I want to get into at the moment. Ended up finding a replacement on Ebay , a Pacbrake unit p/n PO 1218 , identical switch , not Omron.
The buffer screw is hollow with a spring loaded plunger to activate the switch . The plunger is very close to flush with engine off . 
I installed the switch using Prarieschooner's method of adjusting it. I can't see why this won't work provided the mechanical parts are working , but I worry about premature activation due to the very short travel of switch (.010") before it clicks . 
I am wondering if there is gap that should be set between the switch and the plunger . Also wonder if anyone might know the travel of the plunger when the governor moves it in a no fuel condition .
Appreciate any and all input ,
Thanks, Chris