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Thread: Bobcat 763 Traction Lock Issue

  1. #1
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    Bobcat 763 Traction Lock Issue

    I have a Bobcat 763, guessing early 90's, that is getting a traction lock hold circuit shorted to ground flash code (Traction LED blinks 3 times on the BICS). The failure happens when I have middle to upper RPMs, but not so much with just idling around. I don't have a service manual so I am at a lose as to how to go about trouble shooting this failure. I don't know what wire(s) are associated with the traction lock hold solenoid that go to the BICS but I did look at the wire harness in general and didn't see any wires that I suspected were shorting.

    I am not sure what solenoid is associated with the traction lock hold circuit.... thus I haven't verified it.

    Thanks in advance for any assistance you may be able to give.

    Regards,
    Dave

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    I should add a little more detail. The traction lock works initially and I am able to drive the machine. When I increase the RPMs the machine will lock while driving, almost throwing me out, and then the flash LED of 3 shows up. At that point I shut the machine down,restart it and the failure clears until the next time.

  3. #3
    Member TriHonu's Avatar
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    The traction lock circuit has a fuse, a relay, the brake solenoid, the Traction Lock Override button (if equipped), the brake switch on the floor and the BICS controller.

    The solenoid has two coils, a pull coil and the hold coil. It sounds like either the hold coil is shorting or the circuit that powers it.

    To get to the solenoid raise the cab. The solenoid is in the top of the chaincase below the seat. The solenoid has two power wires and a black ground wire. The power wire for the pull coil is red or white and the power wire for the hold coil wire is pink or red. The resistance for the hold coil is 0.4 - 0.5 ohms. The resistance for the hold coil is 10-11 ohms.

    The relay is one of the 4 or 5 relays mounted to a bar right above the battery. The Brake relay harness has 4 wires. Black is ground, Red/White, White, Pink/White. All the relays are the same type. The bar is labeled but be aware you can plug any harness into any relay. These relays can fail in the open or closed position.

    The BICS powers the relay to close the switch powering the pull coil in the brake solenoid. The BICS also directly powers the hold coil in the brake solenoid.

    I would start by checking the resistance of the brake solenoid coils, Brake Fuse and relay. You can switch the glow plug relay with the brake relay to check if your problem subsides. When my relays started to go I replaced them all and bolted an extra one on the back side of the mounting bar. That way if one goes bad I can just unplug the harness and plug it into the spare.

    Since it will start and go, It must be a short some where between the brake solenoid and the BICS controller. Not so obvious, it could be the brake switch opening when you bounce the loader.

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    My analysis continues

    Thanks TriHonu for the great information.

    Here is what I have done so far:
    1. Brake solenoid hold coil resistance is 10.4 ohms (normal)
    2. Brake solenoid pull coil resistance is 0.5 ohms (normal)
    3. Temporarily used the Glow Plug relay in place of Brake relay, no improvement.
    4. Disconnected the brake switch on the floor, no improvement.
    5. Since the hold circuit short is reported during higher RPMs, I suspected vibration maybe affecting the coil. So I removed the brake solenoid and attached an ohm meter to the hold coil leads. While watching the resistance I tapped the solenoid, vibrated it, etc.... nothing seemed to change the hold coil resistance.
    6. With the brake solenoid disconnected I started the machine and the BICS correctly reported the hold coil was open. Suggesting maybe the BICS is operating correctly.

    As I understand it the hold coil lead is coming directly from the BICS. Seems hard to believe a ground short is occurring somewhere along the wire as its in a plastic webbing all the way back to the BICS.

    Seems to me the brake solenoid is still somehow bad or changes resistance during operation. OR The BICS is malfunctioning during operation.

    Any suggestions on how I sort this out?

  5. #5
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    Another thought...

    The GND lead of the brake solenoid is not electrically connected to the case of the solenoid. What if the hold coil momentarily shorted to the case? My bench test of attempting to obstruct the hold coil resistance by vibrating the solenoid would have been affected by a short to the case as the case was floating at that point. However when the solenoid is attached to the machine the case would be grounded and therefore an intermittent connection would yield a lower coil resistance.

    Thoughts?

    Looks like I may need to go buy another brake solenoid and see what happens... Any idea on how much they cost?

  6. #6
    Member TriHonu's Avatar
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    What if the problem is the BICS momentarily loosing its ground and letting the traction lock solenoid snap shut?

    With the cab raised, you will find a group of ground wires near the cab hinge (behind your left shoulder as you're sitting in the cab). It is common for this connection to corrode and cause numerous issues. Try cleaning this connection to insure the BICS is staying properly grounded. If you have a recording multimeter, hook it up to the hold coil and set to record. Jiggle the ground wire group and see it the hold circuit is loosing power.

    You may want to run this by the Service Manager at your dealer. I deal with Lano in Ramsey. They have been very helpful when I have gotten stuck on a couple wiring issues.

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    check to make sure the alternator is not over charging also it may be causing that

  8. #8
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    just thought of this and disregard the alt post they have a foot brake on those i believe there is a metal tube that runs under the kick plate and the wires a re known to be rubbed or cut there look at that harness and make sure the wires are not cut i got burned by that before so look there it should be right behind the kick plate on the right side of the machine also look at the solenoid by the brake petal also

  9. #9
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    Thanks bobcatmechanic!

    I have isolated the foot brake by disconnecting it from the circuit. This eliminates the wiring that goes through that metal tube and the switch itself. I still had the same problem of the traction lock hold circuit shorted to ground under higher RPMs.

    I have yet to check the BICS ground connection as suggested by TriHonu.

  10. #10
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    How does the trac lock solenoid operate?

    I have bought a new solenoid and have off chaincase cover, but piece on the old solenoid that goes down in chaincase is missing. I need to know what keeps that piece from falling out of solenoid?

  11. #11
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    it is magnetic

  12. #12
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    which piece there is a 1/4 bolt a small washer a wedge 2 springs and a about 1/2 around solid rod if any is in the chain case start fishing with a magnet if any gets in your chains or bearings its bad news look under the rear drive sprockets in the back corners is where the pieces usallly end up

  13. #13
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    the coil is magnetic and pulls the brake wedge assembly up when energised and then there is a hold circuit in it to keep it up

  14. #14
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    I think it is the alt. because it only happens at hi rpm's.

  15. #15
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    I'm having a similar problem with our 763G, It will not let the brake release after start up. Machine will not move at all, has a code of 17 06(may have that wrong) which says the traction lock solenoid is not grounded. Checked the ground and it seems to be OK. I'm not very familiar with the Bobcat BICS system as this is the only one I've ever worked on.

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