Jake brakes keep blowing fuses

[RickB]

Hey all,

At the risk of all of you finding out just how truly and completely incompetent I am with all things electrical here goes... 15 amp automotive fuse is inline between the Jakes on the motor to the front electrical bay just underneath the drivers window.

The switch on the dash says High Lo so I'm guessing I have the two stage jakes but mine have only worked on Hi since I bought it.I have no idea how to tell the difference between single stage and two stage jakes, do any of you know how to tell the difference?

Is there any reason I should be popping this fuse almost immediately and is a 15 amp auto fuse big enough for this application?

Does this really need to be fused?

It's most certainly an add-on by the original converter and he seemed to be a bit fuse happy all over the bus.

We are planning a trip to the mountains later this fall and I will NOT do the Rockies without properly functioning jakes so i need to get to the bottom of this before then.

Thanks in advance for all the helpful advice that I know you electrical geniuses will share. You are a good bunch of bus freaks and I'm proud to be one of the tribe.

Rick

[OneLapper]

Rick,

Do you have a multi meter?  If not then the read on....

The first area I would suspect is the wiring into the cylinder heads. Check for bare wires that are grounding out.  After that I would pop the valve covers off and look at the wiring to each of the the solenoids. The oil tends to crack the wire insulation over time.

A meter will make this easier, the approach is different. You would check for continuity.

Mark

[luvrbus]

No difference in the Jakes for 2 stage vs single stage Rick it is all the wiring look on the switch if you have a supply wire and 1 wire leaving the switch you are a single all 4 masters come on if you have 4 wires you have a hi and lo

What type buffer switch do have any idea ? they do need a fuse to protect the buffer switch and wiring going to the back check your wiring going from the switch sounds like you have a bare spot.

Hard to give advice on Jakes here the bus nuts get creative with the wiring so many ways to wire one.

Unplug the wires at the head if it doesn't blow the fuse remove the valve cover you have a wire broke and shorting out or check it with a meter me I just unplug the wire

Do you know if yours has the stands the wires plug into or a 1 piece harness on each side ? a 15 amp is plenty (Jake calls for a 10amp) and it will blow if your buffer switch is bad also

[Lin]

Yes, fuses are really important.  Right now you have a problem popping fuses.  It is quite possible that if there was no fuse, you would have a bigger problem.  Multimeters are cheap.  Get one and check for continuity between your Jake supply wire (not the switch hot wire) at the switch and ground.  If there is continuity, you have a short.  If so, you have to go through the process of finding it.  It can be a nuisance but most likely the fix will be very cheap.  That is of course, if it is the wiring.  If it is the buffer switch itself, then you have a part to buy.  Now, if you have high idol and want to keep it, that buffer switch is very expensive.  Most just get a regular buffer switch without high idol and never miss it.

[luvrbus]

Forgot to ask you Rick is fuse blowing without the engine running ?

[bevans6]

First thing you need to do is trace the wiring.  With two stage jakes on an MCI 8V71, if they are wired per the manual, the power starts out in the back engine bay panel, goes up to the jake switch on the buffer on the governor, goes up to the front of the bus to the control switch which sends it back to the jake units on the cylinder head.  Low is one head switched on, high is both heads switched on.  The schematic is available on line, google MC-9 Manual and the link pops up, it's on one of Walker's web sites.  The other way MCI wired jakes on 8V71's is single stage, and the wiring is quite different.  Power starts out at the front main electrical panel, goes to the dash switch as a simple on/off function, goes back to the rear power panel and up to the jake/buffer switch, and is sent directly to the jake units on both cylinder heads so they all turn on at once.  From what you describe, I'd guess you have this sort of setup.  I suspect the kit came with a switch label that had high/low on it, my switch has the same label but is set up as single stage.

I suspect a chafed wire creating a dead short somewhere, probably in the cylinder head wiring.  Trace your wiring, and then disconnect the cylinder head wiring and see if you can just turn on the bit that goes to the buffer switch without the actual jake solenoids and wiring connected.  Use a meter to look for dead shorts to ground in the jake wiring on the heads.  Use an ohm meter to measure the resistance of each coil (two on each head, take the valve covers off, look at the wiring) The resistance for each coil should be between 30 and 50 ohms, but blowing a 15 amp fuse instantly pretty much indicates a dead short somewhere, and the solenoids themselves have a habit of failing open, not shorted.  Even if you have one bad solenoid you can just disconnect it and get the other three running, so it's not all or nothing.

Here I spent 15 minutes at 6:30 in the morning writing all this out and it's all here anyway:  http://www.jacobsvehiclesystems.com/files/file/Troubleshooting-Guide.pdf  Oh well, I hope this helps.

edit: according to that pdf, the fuse should be a 10 amp in line.  According to my rusty memory 4 coils at 30 ohms each in parallel would be 7.5 ohms, E/R = I, so 28 volts divided by 7.5 ohms equals 3.73 amps maximum normal load for all the jake coils on at once.

Brian

[RickB]

Thanks guys, I'll check the wires today for any obvious abrasions and if I find the problem I'll probably go to a 10 amp fuse.

Clifford, I haven't checked to see if it happens when it's not running I'll do that as well

RB

[luvrbus]

Rick do a little maintenance while you are working on the Jakes replace the jumpers seals and check for broken cross over tubes , set the clearance not hard to do.

If you need parts like the harness,seals and  cross over pipe contact Derrick Thomas (thomasinnv) he found a outfit back east parts for Jakes are a fraction of what DD charges he posted the name here but I cannot find the name using the search feature on this board

good luck

[RickB]

Well it's not gonna be as easy as I had hoped. Pulled the instrument cluster and fixed the shoddy work that a previous owner had done. Heat shrinked the wires and checked for obvious issues in the engine compartment ( I was amazed at how loose some of the connections at the junction on the rear of the block tightened them up good) got myself covered in oil and diesel, sprayed the hi idle buffer switch with brake cleaner and got it clean and.... it popped another 15 amp fuse in about two seconds parked in the driveway. So, when we get a cool morning I'm gonna pull the valve covers and see if there's an obvious bare wire.

I have a friend that's a mechanic and he said these kind of issues sometimes take more time to identify than rebuilding a motor. Hope that's not true with this. As far as the continuity tests I think you all have underestimated my ignorance when it comes to all things electrical (think I can put batteries in a flashlight as long as they have the + and - signs and you'll be in my hemisphere.

Clifford the jakes were adjusted when my rack was run about a year ago. 5000 miles tops since then, they were working great until this electrical gremlin reared it's ugly head.

I forget all the time just how dirty these darn things get. It's really almost comical, I brush one square inch of cloth against anything back of the last bay and I'm throwing another pair of good shorts away.

The good news is Grant Goold had a good used entrance door window that he sent me and I found a dual pane drivers peninsula slider in Craigslist for $150 and I got them both installed today. Felt good to win one for a change.

Rick

[luvrbus]

Rick before you pull the valve covers disconnect the wires going to the heads if it blows again the short is not in there if you are idling the engine or just have the switch turn on without a running engine there should be no power going to the Jakes unless you have a faulty buffer switch they cut the power at around 900 rpm and disengage the Jakes

good luck

[bevans6]

Clifford beat me to it!  What he is suggesting is what I suggested in my original post.  Basically break the circuit in half, once you get it traced out, and see if the fuse blows with all the cylinder head stuff disconnected.  On my bus it's two spade connectors on the buffer switch, could not be easier.  Take the jake solenoids and wiring off the circuit and see if it still blows the fuse.  If it doesn't, use your meter to check for the short.  If it does, start going backwards towards the source of power, keep isolating the circuit down.


Brian

[Lin]

Funny thing.  Took the bus out today and the Jakes were not working-- the fuse had blown.

Anyway Rick, I do not underestimate your lack of electrical expertise.  Rather, you are overestimating the complexity here.  The stuff you listed you just did is more difficult than testing continuity.  If you get or borrow a multimeter, the instructions will tell you how to do it, or you can find a Youtube video.  Like many tasks, the first time you try it is seen as a challenge.  Once you're passed that, you will be amazed that you did not try it sooner.  Further, basic electrical testing is a mandatory skill in this hobby.  If you do not learn it now, there will be a failure somewhere in the future that will make you wish you had.  It seems that now you are without Jakes at home.  That's a lot better than trying to learn when you are without lights somewhere else.

My wife had always said she was terrible at math.  When she decided to back to school for her BA, she was required to take college math courses.  Once I could get her to stop repeating how terrible she was at math, it turned out she was quite good at it.  As an old friend used to say, "You will never learn any younger."

[luvrbus]

You have to much wire Lin lol

[Lin]

Clifford, no doubt you are right about that, but since my Jakes are 12v and I ran it from a 24v dash switch, they are powered through a relay off a center tap on the coach batteries.  That is the fuse that blew, so even with less wire, it would be an issue.  I am not positive how I blew that fuse, but I think I shorted it out when wiring for my mister.  So there you are-- if I followed your advice about misters, this would not have happened!

[luvrbus]

Lin ot but there are 4 couples going to Idaho the last week in July you and the wife need to go with us then you can test the misters and Jakes seriously give me a call and get out of this miserable heat for a few days or week 112 in Scottsdale today