overdrive blows fuses

[joncon]

I got the fuel pump working on my J and now the overdrives not working. I drove it this morning and everything was fine. This afternoon it wouldn't go into overdrive. When the overdrive engages it blows the fuse on the firewall relay. I blew 3 30amp fuses trying it ouIt had a 30 amp fuse in it already instead of 20. I checked the relay with a 9volt battery and it clicked. Also checked the wires for bare spots where it could be shorting out. Any ideas? It's Fid's dad's old grey 51 J

[joefrazer]

Something in the circuit is causing a high current condition when the system engages. It has to be either a bare wire somewhere in the circuit, or one of the components has gone bad. My experience with OD units leads me to believe it's either in the relay or the kickdown switch. I've had this sort of trouble with both in the past.

[joncon]

Well, I don't know what I did but it's working again, just gave it a test drive and it worked OK.
I moved the wires around, looking for a bare spot, and must have moved it into the right spot. Does anyone make reproduction OD wiring harnesses? I noticed several small bare spots but didn't see any touching anywhere.

[Fid]

I can't believe a relay or kick down switch would cause the fuse to blow as the fuse is only inline with solenoid.  A sticking solenoid, which means it's not throwing in  fast enough to break the pull-in contacts, will cause an over current and blow the fuse. A bare wire to the solenoid touching against the car somewhere will short it and blow it.  I once had an OD solenoid plunger seal which was leaking and grease would run down into the solenoid causing it to act like a plunger inside resulting in it pulling in too slow and not breaking the pull-in contacts fast enough. That was causing it to blow fuses. Also, any foreign material in solenoid itself could cause a short if it touches the windings or the contacts.  If it happens again, pull the solenoid and inspect it.

[joncon]

Thanks for all the info. hopefully it won't happen again. I hadn't driven it since last October, sometimes funny things happen when they're not driven for awhile.

[HJ-ETEX]

I have seen this on several OD cars. Typically, the OD engages once, then doesn't engage the next time. The fuse is blown. If you were to examine the fuse after the 1st time it engaged, you would see the metal in the fuse is already damaged. If you happened to look at the ampmeter when the OD successfully engaged that 1st time, the needle may have swung over past 15 amps discharge.
What is happening is the solenoid is slow to engage and it is drawing a lot of current in the process. I can't say that removing the solenoid and generously lubricating the shaft and the hole in the transmission would solve this.  However, one fix is to use a 25 circuit breaker instead of a normal fuse. This is going to require some non-factory wiring to bridge around the fuse on most KF relays.

[joncon]

I moved the wires around a little and it works fine now. Must have a small bare spot. It started blowing the fuse after I was working on the speedometer cable, so I must of moved one of the wires.
I've driven it several times since then and it's worked OK.

[Richstape]

I had the same problem.  A new relay fixed mine.

[Fid]

Richstape, I'm curious, did you lightly shake the relay you had that was blowing fuses?  And if so, did it rattle?  After rethinking my comment, I can see where a  relay would blow a fuse. Sometimes the brass rivets that hold the contacts on the "spindle" inside it corrode away. If they do, and the "spindle" falls and touches against the cover it would blow the fuse.  If it was lodged that way, it would blow the fuse instantly but if it wobbled back and forth enough (which I don't think it can) and touched the cover, the fuse would blow.  In either case, lightly shaking it, it would rattle inside and you'd know  something was wrong.

[Corsairdeluxe]

I have several o.d. relays ,checked out and guaranteed, if anyone is in need. I have one ceramic socket also.

[Richstape]

FID,
When I was having the problem I did not have time at first so I replaced the fuse with a 30a circuit breaker.  It still popped the breaker but it would reset on its own, so I got by like that for a while.  When I finally got around to diagnosing it I first replaced the solenoid.  The problem did not go away.  After checking all of the wires and switches to not be the problem I bought a new relay and installed it.  The problem never returned.  The relay was $185.