6V92 Jake Brake malfunction

[oldmansax]

My 6v92 has a 2 stage Jake Brake that doesn't work; however. when I start the coach cold, one side of the Jake Brake is on. After it runs 40 seconds to 1 minute (depending on how cold it is), Jake goes off and engine runs fine. The only test I have done is to remove 1 wire from the buffer switch to see if that made any difference. It didn't. I have tried starting with Jake switch off, on LO, and on HI, and that made no difference either. The Allison trans has a retarder and a switch for JAKE, OFF, & RETARD. That makes no difference either.

Any ideas?

TOM

[Geoff]

If there is no electrical power to the Jakes and the are coming on, then one or more of the Jakes is mechanically sticking.  The side that is sticking needs the valve cover removed to see what is going on when starting

This situation is not good if the piston comes up and hits the valves.
 
--Geoff

[bevans6]

Interesting problem.  Here is my conjecture:  Jake brake comes on when two things happen - solenoid that controls oil flow is open, and there is sufficient oil pressure to activate the cylinders that press down on the valve bridge.  If it's happening at start up, oil pressure will be really high until oil starts to heat up, could be forcing the solenoid open, leaking past the solenoid to the cylinders (apologies if that's not the correct term), or something like that.

Brian

[Bill Gerrie]

Remove the wires at the head as 12 volts could be shorted to the wire somewhere. Other than that you will have to rebuild the Jakes. Kits are available.

[luvrbus]

Tom,under the solenoid are 2 o-rings 1 has blown or the solenoid it self is bad is what I always find causing that   

[oldmansax]

Well, it looks like I need to find someone  to pull the valve covers & look. I'm not up for that yet.

Thanks to everyone for the help!

TOM

[oldmansax]

'Nother question. Will the tune up kit from Pacbrake, part # P69201, have the O-rings I need?

TOM

[Iceni John]

'Nother question. Will the tune up kit from Pacbrake, part # P69201, have the O-rings I need?

TOM

I used that kit when I overhauled my Jakes a few years ago.   As far as I can remember, it has two or three O-rings for each solenoid, plus new shuttle valves and oil crossover tubes and lots of other fun stuff.   It's not an especially difficult job to work on the Jakes, but you will need the special Jake tool afterwards to reset them to the correct height.   While I was in there I also readjusted the valves and replaced all my fuel crossover tubes' O-rings, even though none were leaking.   Getting the valve covers' silicone gaskets to stay in place when reinstalling the covers was about the trickiest part of the whole job!

John

[oldmansax]

Thanks John. Looks like a job for a good shop that has the tools. I can't fold myself up like I used to!  LOL!

TOM

[chessie4905]

If one of those threaded jumper tubes has backed off,( locknut wasn't properly tightened) it will cause loss of operation. That happened to mine when acquired.

[Iceni John]

If one of those threaded jumper tubes has backed off,( locknut wasn't properly tightened) it will cause loss of operation. That happened to mine when acquired.

One of mine was broken completely in two, and another was cracked and probably would soon break as well.   Result  -  no oil pressure for one bank's Jakes, so they didn't work at all.   The other bank's solenoid had two damaged O-rings, so not much was happening there either.   And one shuttle valve was sticking slightly because of a burr in its bore, so I had to smooth that off.   I noticed another few PSI oil pressure after I fixed the Jakes, so I guess the broken tubes were bleeding off some of the engine's not-high-at-best oil pressure!

I would like to change (remove?) the muffler so my Jakes sound like this, but it may then attract too much attention!  https://www.youtube.com/watch?v=Wz_VJB3y89M

John

[luvrbus]

With broken cross over tubes or the o-ring between the tube they won't engage,that has to be in good shape for a Jake to engage,control valves just control the flow of oil when the solenoid opens Jakes are simple

[Geoff]

If this thread encourages anyone to work on their Jakes, please be sure to first back off the threaded jumper oil feeds.  If you don't, and loosen the 1/2" hold down bolts, you can easily break the oil jumpers and they don't grow on trees.

[luvrbus]

If this thread encourages anyone to work on their Jakes, please be sure to first back off the threaded jumper oil feeds.  If you don't, and loosen the 1/2" hold down bolts, you can easily break the oil jumpers and they don't grow on trees.

What breaks the jumper tubes most of the time is people over tightening the jumper tube to the master or drone,hidden some place in one of my Jake manuals or a service bulletin it says to leave a 0.010 clearance when tightening.I always use a feeler gauge for the gap and haven't had one break in years now,plus I always install new jumper tube seals regardless of what they look like   
  

[chessie4905]

Yes, set the required clearance on these. Set them tight and they'll fail when engine heats up and the major assemblies expand toward each other.