[prairieschooner]

OK so while heading to a TT Park I noticed that the Jake Brake wasn't working-----No Sound when letting off of the throttle.
I have already checked the DC Voltage at the Forward Terminal Strip and Fuse Block as well as the After Terminal Strip----Purple Wire in our case. Checked with the Engine Running and the Switch Off--No Voltage, then the Switch On Voltage (nominal 12 Volts).
Having not had to look into this before I could use some direction on a 6V92 Jacobs Brake.
thanks in advance!

[whatsnewell]

Wish I could help Steve.....haven't had that problem yet, but would be very unhappy if I did. What do you mean by "nominal 12 volts" when the switch is on?

[Fulltiming]

Steve, a quick check on the internet resulted in a couple of information sources but they seem to address the Detroit Diesels with DDEC and I suspect yours is mechanical. There may be something in these that help in any case. The first one seems to focus ONLY on DDEC so it is likely the least useable:
Detroit Diesel DDEC Wiring

The second reference seems to hold more promise since it is focused on the Jake itself:
Jacobs Troubleshooting Guide starting about page 35.

The third reference is an installation manual but does address the non-DDEC systems. Jacobs Installation 71A and 92A

[encantotom]

jim ellis just had his mechanical jake brake fixed. jim, any advice?

tom

[prairieschooner]

Does anyone know what model Jacobs Brake these older 6V92 Detroits used (1982)?

Thanks Michael, the troubleshooting guide in the 2nd link discusses how to test the solenoid with current draw. I'll get my amp meter on it once it gets light out and get some readings. In any case this will be a learning experience understanding how it works. I may also try starting it up with the Switch Off and the Energizing/De-Energizing the system a few times for giggles.

Clarke, nominal 12 Volts DC in my case is around 12.7 Volts with the Diesel Running and the Alternator Charging ....I did have the Battery Merge Switch on because we are going to be Dry-Camping and wanted to charge the house bank.

I really don't want to take much apart until we get back from Doheny State Beach. I'll just limp along and pay close attention.

[prairieschooner]

OK found what I believe to be the Buffer Switch but having trouble locating the Control Module. Anyone know where this could be hiding?
Still too early to fire the diesel.

[77newell]

I've had some experience with this on my 77 coach. Hopefully this will help. The dash switch supplies 12 volts (when in the "on" position) to the buffer switch. The buffer switch turns "on" whenever the governor enters a no fuel situation (this would occur when the engine is over-running the governor setting). When the dash switch and buffer switch are both "on" then power is sent to the solenoids inside the rocker box covers to alter the timing of the exhaust valves so that braking occurs. The adjustment of the buffer switch is critical. If it adjusted too far out then no braking will be available. If it is adjusted too far in you will have fuel being injected by the injectors while opening the exhaust valves early. If this happens very long you will hear your wallet getting lighter.

If I recall correctly you can(with the engine stopped and the dash switch "on" mechanically trigger the buffer switch to ensure it is operating. This switch can occasionally die and you don't want to mess with the adjustment until you are sure it is working. If it is working, then you want to make tiny adjustments. If you go slow you will not harm the engine. In my case all it took was 1/8-1/4 turn to go from too far to just right. I would suggest downloading the manual from the Jake website which will show pictures of the process I just described. Adjusting inward will make the Jake come on earlier and adjusting out will make it come on later or eventually not at all.

It is a very simple system, there is no control box, just a couple switches and some solenoid valves.

[prairieschooner]

Thanks 77, you stated that there is NO CONTROL BOX? then that is why I couldn't find it! Do you have a link to the correct Jake Brake Page?
Sounds like my problem would be the Buffer Switch and since the Adjustment hasn't been messed with I'll start by checking it. From what you stated the Buffer Switch is a normally Open or Closed Switch that is Activated by the Governor (+ 12 Volts DC to the Dash Switch, then when On +12 Volts DC to the Buffer Switch, then when Switched +12 Volts DC to the Solenoids?)

Advice as to where to get a new one?

***Quick Update***
Found what appears to be a Limit Switch with a Plunger type Assembly on the Governor. Had Detroit Slobber on it so I cleaned it with a Electrical Cleaner. I used my Volt Meter on it and have + 12 Volts DC coming into the Switch. Started the Detroit and brought up the RPM and then let off of the Throttle to try and read the Voltage when the Governor went to No Fuel but the Digital Volt Meter isn't fast enough to get a good reading so I'll need to wait until I get my Analog Meter on it.

The Rubber Boot on the Limit Switch looks to be in poor condition so I will be replacing it when I return from this run.

[77newell]

You found the right switch and it is normally open unless sending current to activate the brake action. The switch assembly is probably best gotten from Jacobs.

Manual is copied here: http://www.jacobsvehiclesystems.com/file...-Guide.pdf

You want to check out the section on the buffer switch. let me know if you need further advice.

[folivier]

Steve does your dvm have a hold function? That should show you the peaks.