Adventures in troubleshooting - Jake brakes

bobofthenorth · November 02, 2009, 11:38:34 AM

Maybe I should have titled this "clueless in Kelowna"

So we came over the connector from Merritt to Kelowna yesterday --- with no jakes. I don't recommend trying that. Anybody who has driven that route will understand when I say that we spent literally hours chugging along in 2nd gear. Some of those grades go on for over 10 miles. So this morning I set about figuring out what was wrong. Long story short I found a heavy draw and traced it to a wire that fell off one of the solenoids on the left side of the engine. All is good again. Thanks to watching Oscar I & II last winter in Luke's shop & Joe last spring in Lakeland I wasn't afraid to jump in. Fools jump in etc etc but I got everything put back together and it still runs. So that's good.

But what is puzzling me is the ohms on the two banks. In the course of troubleshooting I ohmed out both sides. The right side comes in at 56 ohms. Now I didn't take the valve cover off so I couldn't test the solenoids separately. On the left side however the individual solenoids come in at 16 ohms and 9 for the two combined. So here's the question: how come one side reads 9 ohms for the two solenoids combined while the other side reads 56? Are there different solenoids with different resistance and perhaps I have some bastard combination of solenoids? It seems to me that the side with the least resistance is going to be doing all the work.

stevet903 · November 02, 2009, 12:08:59 PM

Where were you connecting the ohmmeter? If you were using the front panel connectors, one side may be going through a relay coil as well as the solenoids under the valve cover to turn on the "Cyclops" center brake light when the Jake is activated. If you were using the wire going into the valve covers I'd say you have a bad solenoid on that side. Here is a table from the jake troubleshooting guide located at

http://www.jakebrake.com/support/parts-and-service-literature.php?engine_mfr=3&engine_model=29&jacobs_product=26

RESISTANCE (OHMS)
P/N VOLTAGE COLD HOT
016440* 12 VDC 9.62 to 10.75 11.8 to 14.3
016441* 24 VDC 31.5 to 38.5 38.2 to 50.0
016442* 24 VDC 31.5 to 38.5 38.2 to 50.0
D/L
020239* 12 VDC 9.0 to 10.0 11.5 to 14.0
018674 12 VDC 9.5 to 10.5 11.5 to 14.0
013472* 24 VDC 34.9 to 38.7 43.3 to 51.3
SCREW
003784, 12 VDC 19.8 to 22.0 24.0 to 29.5
004205,
003433,
002689
003784, 24 VDC 19.8 to 22.0 24.0 to 29.5
004205,
003433,
002689
* Current Production Solenoid Valves
D/L Dual Lead

Using the parallel resistance calculator here http://www.1728.com/resistrs.htm , you can calculate what the resistance should be with the two solenoids. According to the chart, none of the readings make sense. Don't feel bad, when I had my solenoids out to replace the o-rings, none of the resistances matched the chart either, yet they were all pretty close to each other.

bobofthenorth · November 02, 2009, 12:15:15 PM

Thanks Steve - I was measuring right at the valve cover so it appears I have a high resistance solenoid but I must either have 2 of them or else there's another broken wire under that valve cover too. My thinking was similar to yours in that I don't really care what the "correct" value is --- I just don't think there should be that much difference from side to side.

bevans6 · November 02, 2009, 12:20:34 PM

I don't have an answer for your basic question, but the solenoids are just a switch, on or off. Once they switch on, they do the work, it won't matter to the Jake if the solenoid has 16 ohms or 100 ohms dc resistance in the energising coil. If the jake gets turned on, it will do it's share of the work.

Maybe the ones on the 56 ohm side are wired in series, it seems the ones on the 9 ohm side are wired in parallel, which is what you would expect. You wouldn't expect them to be in series. The 9 ohm pair will be drawing 3.1 amps, which seems in the ballpark to me. The other pair will be drawing less, only 0.5 amps.

I am going to go out and measure mine, I am curious now!

Just got back in, mine were 18 ohms per side, measured by disconnecting them from the buffer switch. Total dc resistance for both sides was 9 ohms, more or less.

Edit - per the chart, most of the 24 volt solenoids are in the 31.5 to 38.5 ohm range, so mine at 17 ohms for a pair in parallel are pretty ok, do you think?

Brian

bobofthenorth · November 02, 2009, 12:50:03 PM

Brian my concern is that in a parallel circuit the high resistance side might never come on. After further reflection though I think I may just split the circuit and run the solenoids with 2 cube relays. I know that both sides work if they get power and the relays will isolate them so they both can operate. I have to make a run later today to get ready for the big inspection tomorrow so I'll have a better idea as to whether I'm just worrying about nothing. It also occurred to me that I may have 24 volt solenoids on the high resistance side but its all just speculation until I get motivated enough to pull that valve cover and I'm not excited about doing that because the turbo is on that side.

bevans6 · November 02, 2009, 01:20:24 PM

I think the relays are a good way to go. Makes sense to isolate them, also to reduce the current in the jake switch.

Brian

Rick 74 MC-8 · November 02, 2009, 02:03:20 PM

Bob I need to replace the solenoids on the drivers side bank myself. how bad of job is it have the same problem the wire is broke at the coil does the coil just come off by itself like most or is there more to it

Thanks
Rick 74 MC-8 8V71n

stevet903 · November 02, 2009, 05:39:08 PM

Check page 14 of the installation manual ( http://www.jakebrake.com/service/pdf2/003879.pdf ) to get a picture of what it looks like under the valve cover. If the wire going to the solenoid is broken you can crimp a new ring terminal on the end and reconnect, or repair the break in the wire if it is in the middle. If the solenoid is open, you will need a 12-point 7/8" socket to remove (I think!!) if it is an old style solenoid or a regular six-point 7/8" if it is the new style. Each solenoid has three o-rings that you should replace as well. Check carefully for 3 - one tends to hang in the bore and can get left behind - you may need a small pick or piece of wire to remove. This is not that difficult of a job once the valve cover is off...

bobofthenorth · November 04, 2009, 11:00:14 AM

Quote from: Rick 74 MC-8 on November 02, 2009, 02:03:20 PM
Bob I need to replace the solenoids on the drivers side bank myself. how bad of job is it have the same problem the wire is broke at the coil does the coil just come off by itself like most or is there more to it

I think actually replacing the solenoids would be a bit more of a challenge. For starters you are going to have to pull the oil lines to the solenoid in question and I think you are going to need to regap the valves BICBW there. If I was inclined to change solenoids myself I would want some senior observer/advisor present. I subscribe to the "fools jump in" theory of tackling projects but there is a level of foolishness past which I try not to go. If you just have a broken wire that shouldn't require replacing the solenoid - from what I saw anyway.

(edit) Sorry about the acronym. After re-reading Steve's post it sounds like the solenoid probably threads out without affecting the bridge adjustment but I'm sure somebody who actually knows what they are talking (typing) about will chime in with the right answer eventually. One of my favorite signs in the world is on the ski school at Bridger Bowl in Montana - "amateurs teach amateurs to be amateurs".

lostagain · November 04, 2009, 11:52:46 AM

BICBW?

bevans6 · November 04, 2009, 12:21:35 PM

BICBW = but I could be wrong.