M915a1 Jake brake electrical problem

[Hooty481]

Picked up my new to me truck from Andy in Missouri on Friday. When we got there I test drove the truck. Only thing that didn't work was the Jake brake. We did some testing and here is what we found.

Switch on the injector pump is closing circuit when the pedal is released.
Switch in the floor is closing circuit when it is pressed.
Hooked 12 volts straight to terminal on heads and Jake brake worked.
Not getting any power to wires that plug into head when Jake brake pedal is pressed.

Is there anything else that I can check. All circuit breakers are pushed in. If someone new which tm and what section had the wiring diagram it would be helpful.

Does anyone know of a relay or anything that I am missing?

 

[Castle Bravo]

Page 2-62 of TM 9-2320-283-20-1 is what I used to troubleshoot mine. Page 2-63 has a logical diagram of the jake brake electrical system. It should tell you all you need to know.

 

[Hooty481]

i printed the trouble shooting pages off and they are like spanish trying to understand. im gonna check everything again tomorrow and see if i can come up with anything. if anybody has any other ideas let me know. or a better way to understand the tm.

 

[73m819]

what about the low/med/high selector on the dash, power in/out from all three postions, are you getting power in/out of the floor switch, are you getting power in/out of the ip switch.

The 915 that I drove for Ziggy, the jake stopped working, it turned out it was the ip switch, by passed it, jake worked great

Really do not need the ip switch because of the floor switch, civi jakes have a on/off as well as the three postion on the dash, with a switch on the clutch pedal and one on the ip

 

[cundupa]

Not sure on the allison trans, but the Cat trans has a switch to tell the jake that the trans is in gear. Allison should have something like that.

 

[Castle Bravo]

This diagram is what I used when I troubleshot (troubleshooted? ) mine.

All of the wires you are interested will have a 52 number with a letter after it. In the diagram, the last letters designate the color of the wire. WH = white, GY = grey, etc.

The high-med-low switch in the dash works with only three connections because low runs 1 solenoid, med runs the remaining 2 solenoids, and the high position runs both positions. (1 + 2 = 3)

Attacking the problem systematically is the key. It sounds like you've done a lot of that already. You've eliminated 4 of the 6 items in the line. I would check the low-med-high switch in the dash itself and then if that yields no result, look at the bulkhead connector.

There is no transmission pressure switch in the Jake system on a M915A1 according to this diagram. The M915A1 that I drove would run the jake in neutral at idle RPM, which to me, says it does not have a switch.

I bypassed the foot switch by connecting the leads to each other in the foot switch. That made it easier (read possible) to do by myself. Electricity and I don't get along well at all, but I was able to figure this one out.

 

[Hooty481]

Ok so everything tested good. All switches were good. It appears that there is a connection issue somewhere from the wires that to the selector switch to where they run out through the fire wall. It works part of the time and part of the time it doesn't.

Also it seems that the turn signals work part of the time and the head lights work parts of the time. So maybe there is a plug that isn't making good connections. Is there some sort of grease I can use for the terminals to make sure they connect good?

Also got a problem with the low air warning buzzer and warning light. The buzzer has never made a sound and the light works when it wants to.

All wires are nice and clean truck has 18600 miles on it since over haul in 2006 in Texas. Oil pressure gauge also reads part of the time and the other part it is at 0.

Must be a bad ground or something. Anyone have any idea where to start?

 

[Hooty481]

Ok so everything tested good. All switches were good. It appears that there is a connection issue somewhere from the wires that to the selector switch to where they run out through the fire wall. It works part of the time and part of the time it doesn't.

Also it seems that the turn signals work part of the time and the head lights work parts of the time. So maybe there is a plug that isn't making good connections. Is there some sort of grease I can use for the terminals to make sure they connect good?

Also got a problem with the low air warning buzzer and warning light. The buzzer has never made a sound and the light works when it wants to.

All wires are nice and clean truck has 18600 miles on it since over haul in 2006 in Texas. Oil pressure gauge also reads part of the time and the other part it is at 0.

Must be a bad ground or something. Anyone have any idea where to start?

 

[R Racing]

There are 2 connectors on the drivers side that come thru the firewall. check them.

 

[Hooty481]

Found that low air buzzer is getting power but it is burnt up. It would make a buzz for about a second if you smacked it with a wrench. I took it apart and was hot and had melted part of the housing.

Haven't got to run the truck anymore as the bearing was going out on the idler pulley for the water pump belt. Once I get the new bearing and seal we can fired it up and see if the new buzzer works as it should.

 

[Hooty481]

Replaced buzzer yesterday only to find out that the new one was bad to or my truck burnt it up too. It would buzz for about 5 seconds and then stop and you could smack it a little and it would start again. always had power to it even when it wasnt buzzing. any ideas on what to check. going to pick up a second new buzzer today and try it.

turn signals... they were working when we got the truck. not the indicator on the steering column is working and the flasher is ticking but none of the lights are flashing.

jake brake is working good right now. seems kinda like if you fix one thing 3 more things wont work.

 

[CGarbee]

The 915 that I drove for Ziggy, the jake stopped working, it turned out it was the ip switch, by passed it, jake worked great

Yep... I'm really glad that you fixed that...

 

[cornrichard]

The headlight switch or plug is probably bad. The switch can't carry the load of the headlights and all of the marker lights. You can rig up a relay so the switch just runs the headlights and the relay carries the rest. More info here http://www.steelsoldiers.com/5-ton-up/67474-headlight-switch-m915a1.html All 4 of my 915a1 trucks had this problem.

 

[Danl]

Danl M915A1

This is easy do you have power [12 Volts] befor Floor switch ,YES OK. No than there is a fuse done in do you have power befor the throttle swith yes OK no than the floor swith is done in do you have power befor retarder seleter switch Yes ok No the throttle switch is done inIs there power after Retarder switch no tarder switch is done in Yes than engine retarders are done in You said the Jake worked when you put power to the solenoids so the done in MF is fuse, foot switch or throttle switch or tarder switch good luck and it is easy thankyou

 

[mdmorgan]

My M915A1's jake brake works in low, but does not work in med or high. So, I know the foot switch works and at least the low positions of the switch works. I do notice that when I depress the foot switch in med or high, there is a draw on the electrical system, lights dim, dash fans slow down but nothing from the engine. I don't really know where to go from here. I was going to short the solenoids to see if they were bad but I don't know where they are. I have looked through the -10 and the -20 and I can't find where they mention the solenoids.

 

[ichudov]

So, which ones of the "M929 series trucks" have Jake Brakes? I have an M927 and M931A2. Thanks

 

[Castle Bravo]

So, which ones of the "M929 series trucks" have Jake Brakes? I have an M927 and M931A2. Thanks

Probably none of them do from the factory. There is a jake brake for a NHC-250 engine, but I don't think there is one for the 6CTA8.3 engine.

One of the TMs contains mention and diagrams of an exhaust brake for the 939 trucks.