Jake Brake Circuit Breaker Size?

[Geoff]

Apparently some Class 8 trucks and motorhomes already have "auxiliary brakes" activating the brake lights.  But you can defeat this feature by reprograming the ECU.

[richard5933]

I think I got as much done on this project this season as I wanted before the weather turns. As soon as the weather breaks at the end of winter I'll take the bus to the shop where they are going to do the install on the Jakes themselves.

1) I've got the switch installed on the dash.
2) Installed the new circuit breaker on the driver's panel. Went with 8-amp 24v breaker. Advice here was 6 amp, only other reference I saw was for a 10-amp on a 12v system. The 8-amp was the closest that Luke had that would fit into the breaker panel.
3) Wired in a NOS relay to control the Jakes.
4) Installed the bump on the engine bay door.
5) Cleaned and painted the new tall valve covers to match the engine.

I'm not going to bother with the brake lights for now. I can always add them later. Also decided to have these installed as a single stage system. Again, that could be changed if necessary later on, but from everything I've read here and elsewhere the single stage seemed to be the way to go. Especially since all the variations in the GM manual for wiring indicated a single stage system.

Shop is going to rebuild all the Jakes before installing to make sure they are work as well as possible. They've already inventoried and inspected all the parts to be sure I've got what I need to do this. Seems like I do, including a NOS buffer switch with fast idle option. My goal was to get as much prepped as I could - no need to pay them to do what I'm able. I may not know how to install Jakes, but I can run wire and install switches and such.

Unless anyone can point out something I missed in prepping for this, I'm going to call this a successful prep for my first big project next year.

[sixtyseven]

I agree with BK about the lights, I think it's safer without brake lights connected.   I rarely use my first stage, it's nice to have when I do but like you said I would wait to see after you use them a while.   If you do decide you want 2 stage later it is possible to do it with only 2 wires with some added relays.   As far as the debate about jakes on a 2 stroke, I guarantee you will love them, The only time I ever use my brakes on any hill is when that jerk cuts in front of me

[chessie4905]

After installation, you can see what a two stage would be like by disconnecting one cylinder head temporarily.
Btw, if your engine doesnt have the individual spring loaded rack fingers, now would be a good time to switch over, since things are going to be apart.

[luvrbus]

My biggest gripe about Jakes on a 2 stroke is they add to the oil consumption to a engine that is high to begin with,then the air drains drip more,plus people won''t spend the dollars to change to the o-ring fuel lines   

[richard5933]

Cherry on top...

Today I identified an unused spare wire going from the front panel to the rear. Would you believe it was right there at terminal #77, just like the book said it would be.

Now if I could just figure out an easy way to get the cover on the rear panel in the engine bay. I'm a small guy, but even I have to be a contortionist to get near enough to close it up.

[chessie4905]

If you pull the engine, it is real easy to access....

[sledhead]

ya  pull the engine it is easy to get at all kinds of stuff

dave

[chessie4905]

Yeah, that cover is just a little too high, a little too far back. Have mine off right now while checking some wiring and installing some brighter engine compartment lights.

[richard5933]

I suppose pulling the engine would make it easier...

The problem I have is that the screws are captive in the panel cover. Since there is no flex in the cover, it's difficult to get one screw started without the others getting in the way. Then there's the issue of the speed nuts flying all over the place. The position to reach the thing is just too awkward for me to stay in long enough to get the cover on.

I've ordered some 1/4-20 extruded nuts to replace the speed nuts. They are similar except that they have actual threads on them and generally work more smoothly. I'm also replacing the captive screws with removable 1/4-20 thumb screws. Hopefully this will make it somewhat easier, that is if I don't lose the thumb screws since they will no longer be captive. (Yes - I ordered extra).

Maybe it's just because I've not been sleeping. Maybe it's just the long list of little things I was racing to get done before the weather turns to total crap. Maybe it's just being bummed about parking the bus for a few months. Whatever it is, I'm glad I'm at the end of the list because I need a break from projects for a short time.

[Lin]

I must apologize for commenting about single verses two stage Jakes and not checking back to see if a followup was warranted.  This debate has appeared several times before though not quite as much as the oil debate.  I do not have the mechanical expertise to say why or why not a two stage system would work on a 2-stroke.  I only know what I have and can evaluate it.  First, my situation is different since we installed the Jakes when the engine was out while we were changing to an Allison 647.  I don't remember exactly how we wired it, but we did use two relays-- one for the first stage and one for the second that have separate dash switches.  The second stage switch is energized by the first switch, so stage two will only engage when stage one is on.

My first stage works great on moderate grades.  I can just leave it on and coast down the hill without braking.  Don Fairchild installed the Jakes, and there are others on this board that have said he adjusted them so they work better.  I would guess that it is something like Geoff is suggesting. The extra wire is not an issue; that's really talking about pennies.  Besides, I think we used a three wire heavy duty extension cord, so there are three wires anyway.

Clifford is right that I installed a valve to be able to lockup the 647 in 1st and 2nd.  1st is not much of any issue but second is since that covers a critical speed range on a serious grade with sharp turns.  The 740 transmission locks up in 2nd, but for some reason the 640 series is designed not to.  Actually, I think it would be better if it did not lock up in 1st.  Considering the cost of having a bus, I wouldn't say that I spent big dollars for the alteration.  I was surprised though that the valve we needed to do it was 3 or 4 hundred dollars.  The braided high pressure hoses were also an expense, so it did cost somewhere between $500 and $600 total.  As mentioned, if you had a 740 transmission, you'd be set.

I have never driven a manual transmission with Jakes, so I do not know how different the experience is.  Possibly, with the added gear control the 1st stage is less beneficial.  If you are using existing wiring, I can see going with whatever that wiring would allow.  If you are running the wire, you might as well run several more blanks for the Jake or just for future use.  I have always found that extra wires get called into service eventually.

[Geoff]

Lin--
Thank you for your time and effort in wtiting a detailed response! 

--Geoff

I must apologize for commenting about single verses two stage Jakes and not checking back to see if a followup was warranted.  This debate has appeared several times before though not quite as much as the oil debate.  I do not have the mechanical expertise to say why or why not a two stage system would work on a 2-stroke.  I only know what I have and can evaluate it.  First, my situation is different since we installed the Jakes when the engine was out while we were changing to an Allison 647.  I don't remember exactly how we wired it, but we did use two relays-- one for the first stage and one for the second that have separate dash switches.  The second stage switch is energized by the first switch, so stage two will only engage when stage one is on.

My first stage works great on moderate grades.  I can just leave it on and coast down the hill without braking.  Don Fairchild installed the Jakes, and there are others on this board that have said he adjusted them so they work better.  I would guess that it is something like Geoff is suggesting. The extra wire is not an issue; that's really talking about pennies.  Besides, I think we used a three wire heavy duty extension cord, so there are three wires anyway.

Clifford is right that I installed a valve to be able to lockup the 647 in 1st and 2nd.  1st is not much of any issue but second is since that covers a critical speed range on a serious grade with sharp turns.  The 740 transmission locks up in 2nd, but for some reason the 640 series is designed not to.  Actually, I think it would be better if it did not lock up in 1st.  Considering the cost of having a bus, I wouldn't say that I spent big dollars for the alteration.  I was surprised though that the valve we needed to do it was 3 or 4 hundred dollars.  The braided high pressure hoses were also an expense, so it did cost somewhere between $500 and $600 total.  As mentioned, if you had a 740 transmission, you'd be set.

I have never driven a manual transmission with Jakes, so I do not know how different the experience is.  Possibly, with the added gear control the 1st stage is less beneficial.  If you are using existing wiring, I can see going with whatever that wiring would allow.  If you are running the wire, you might as well run several more blanks for the Jake or just for future use.  I have always found that extra wires get called into service eventually.

[luvrbus]

Don is a good friend of mine and we communicate on a regular basis he set Lin's and TomC's Jakes on 0.55 instead of 0.59 like I use.Me i figure Jake and Detroit knew what the were doing so I stick with the 0.59 for 71/92 heads and the 0.65 for the 71 heads we each do things different.
I cannot tell the difference with different setting on a Jake I have tried different setting before and knowing the operation of how they work I need someone to school me on the advantage of a closer setting     

[bevans6]

Lots of people know this well, but I just spent a few minutes reading the manual so it's new to me.  I probably knew it just fine 6 years ago when I set up Jakes on my engine, but I can't reliably remember what I had for breakfast... 

Jake brake works by trapping high pressure oil between an activation master piston and a slave piston.  The master piston is activated by the injector push-rod, so  when the injector is fired (although in no-fuel, the cam still activates the injector) the Jake brake is also activated.  It activates by the master piston compressing trapped high pressure oil and causing the slave piston to press down and open the exhaust valve at a specific time - that time being when the injector is being fired.  The duration of the exhaust valve opening is somewhat fixed by the timing and profile of the injector lobe on the cam.  When the cam causes the Jake master piston to operate, the first thing that happens is the master piston starts to close and the trapped oil is pressurized.  The next thing that happens is the pressurized oil overcomes the return spring pressure in the slave piston.  Next, the slave piston opens a measured amount, and stays open as long as the cam is operating against the master piston.  Finally the cam event passes, the injector pushrod backs down, the master piston releases it's pressure, and the slave piston retracts to it's normal open position.  Adjusting the gap between the slave piston and the exhaust valve bridge to a smaller dimension will cause the valves to open fractionally sooner, open fractionally farther, and stay open fractionally longer, all contributing to a greater release of compression energy into the exhaust port.  Since the Jake is timed by the injector cam lobe, that event is quite short, so the theory would be that maximizing the release of compression is worthwhile, and that some compression doesn't get out in the short time interval allowed by the injector cam event.  The risk is that the injection event happens on the compression stroke, before TDC, the piston is rushing up the bore, and you are dropping the exhaust valves down the bore to meet the piston - almost!  Dropping them farther and holding them open longer would increase the risk of a piston hitting a valve.

[DoubleEagle]

So, therefore, listening to Cliff, Jacobs, and Detroit, is safer than trying to squeeze out a little more braking power.