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Generation One Brake locked up

Discussion in 'Medium-duty Truck Forum' started by waynebrv, Aug 3, 2013.

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  1. waynebrv

    waynebrv New Member

    Truck is a generation one GMC Topkick, 1981 model. It is a over-center bucket truck and has drum brakes, Bud 20" wheels. It has a Mico brake lock system, which is a system that locks the brakes in the applied mode, and releases by pressing the pedal and activating the release. The truck was parked in a parking lot in Baton Rouge LA and apparently, the Mico brake lock was applied. When I picked the truck up, two brakes were frozen, right front and Left-rear. Right front broke loose easily, but that left rear will not loosen. I bled both wheel cylinders on the Left-rear but it appears the pads are froze and rusted to the drum.
    Don't believe the r-front is part of the Mico brake system, only the rears. Also unsure whether the Mico Brake uses both wheel cylinders on the drum, or just one.

    Here is what I have tried so far: I jacked the left rear duals up about 2", and the truck is still on my trailer, and the right rear is chained down tight, and the truck is chained at all four corners in 30 degree tie down. Fired the truck up, put it in reverse and popped the clutch trying to break it loose. It spun the right rear dual...

    My next move will be to pull the tires on the left rear, and drop the LR onto shoring material wood blocks. I will then chain the RR to the trailer. Then I am going to take the pressure washer and blast the drum, and try popping the clutch again in reverse,

    So now for the question. Any better suggestions on how to break the shoes loose from the drum?
  2. waynebrv

    waynebrv New Member

    The brakes are now all unlocked. Pulled the tires and had left rear wheel on blocks.
    Backed the adjusters off and it still wouldn't turn. Heated drum with oxy-acetylene, put truck in reverse and it broke loose. Then put it in 1st, then 2d, then 3d, then 4th, then 5th and kept running it. Took pressure washer and blew brake dust out, and began cooling drum. Kept running it. Did this till it was totally loose and not dragging.

    - - - Updated - - -

    I am amazed at how much help I get from this forum. Thanks.
  3. waynebrv

    waynebrv New Member

    As I re-read my own post, I left out a key step in getting those brakes on the left rear to loosen. Before I applied heat, I pulled the axle shaft out of the left rear, pulled the outer bearings and THEN applied heat. I used a 2lb hammer to rap the flange of the bearing hub, not the drum and applied heat. By doing this, I broke the shoe loose from the drum. Then I installed the shaft without the bearing and spun the drum rearward and forward. Pulled shaft again. Then packed the outer wheel bearing, since the hub is dry and reinstalled shaft. Then I ran her thru the gears and kept the drum hot but not too hot, by cooling with water and blowing out brake dust thru backing plate holes.
    My point in this post is clarity and to emphasize that at no time would I recommend rapping a drum with a hammer. Additionally, I hope I drew a word picture how just a thousands of an inch makes the difference in brakes. I can now pull this drum, and believe all I will need is wheel cylinder springs and new rubber rebuild kits with a little hone out. Kits are available, as well are new wheel cylinders.
    This is the first vehicle I have worked on with 2 wheel cylinders, one at top and one at bottom of shoes. I would not be surprised I have to replace a little damage hardware. Already, I know I need the bearing nut washer with alighnment tooth and bend tabs. Inside lock alighnment tooth is missing. Small stuff.
  4. tbplus10

    tbplus10 Super Moderator Staff Member Platinum Contributor 1000 Posts 100 Posts

    Good tips for anyone that may have this issue in the future on a TopKick.
    Unfortunately theres only a very small number of TopKick owner/users on the site.
    We have a dozen TopKicks at my work and even though were not supposed to do maintenance and repairs on them normally if its something simple Ill do the work instead of sending them to the shop.
    All our trucks have frt/rr disc brakes which have locked a couple times, Ive been able to open the bleeder every time and get the pucks to release. More often our brake problems are leaks which almost always soaks the pads.
  5. waynebrv

    waynebrv New Member

    The country, especially in the south & west is full of topkicks. I am amazed at the quantity of Gen 1 topkicks on farms here in VA. I use several NAPA stores around, and they all know how to look up Topkick parts. While there may not be many Topkick owners using this site, there are many Topkick owners.
    Not that I owe money on any of my topkicks, but I found the blue-book and loan value on them is high. My 91 BB (bank loan value)was 19.5K as is pristine. My 81 still has value as a truck, not a collectors item. Point is other than in the rust belt, these topkicks and kodiack will be ran till they drop.
    I am a little turned off by this site. The level of technical detail in discussion is below elementary. The emphasis is on posting quantity, with little value on quality. Far too many posting by interlopers from the other vehicles sites, and one by one those who own topkicks or kodiaks may just quit posting. Ironically, this site is the only game in town, but apparently, you can keep a topkick or kodiak running without the advice found here.
    I have raise several topics and almost in every one answered my own question in the end. I had questions about filters. Did my research off this site and solved he problem. Posted about air-ride, finally gave up because the posting was hijacked. Posted about brakes, with silence on responses.
    I use many forums, because I have a large varied fleet on my farm, but on most forums my posting quantity is small. Many forums provide valuable informative responses and most are usefull. This one I post to inform, in the end, and seek my information elsewhere.
    I have many topics I would like to bring up and discuss, gearing, transmission regearing choices, clutch details, turing up CAT 3116, but after the simple topic of air ride suspension, and simple topic of brakes and the most basic topic of filters....seriously, what would my expectations be?

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