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Author Topic: Help with Brakes  (Read 1411 times)
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« on: October 13, 2006, 06:40:43 PM »

I have moved this post from the board help area to this board where it should get mre attention.


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    Help Welcome > Brake Lockup

Hi  I own an older GMC PD4108A         Its up here in Maine Where I am afraid last Winter & Spring , the Humidity has caused the Back brakes to Lock up and , Unlike Years past where I could rock or shake it loose then drive it---its no go

Have tried bleeding all air resevoirs of air while engine running    air pressure good at 120 pounds but no release

Have pulled tires and jacked & cribbed rear end and despite beating on rear drums with sledge hammers ( what a local truck garage suggested ) they are still locked up.

Depressing brakes does cause brake actuator do extend the threaded rod !

Any suggestions on how to release them would be welcome !   Thanks Ed Hammond WN1I
                                                                                                    Buckfield Maine ( pushing for Fla)

Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body. But rather to skid in sideways, chocolate in one hand, a good Reisling in the other, body thoroughly used up, totally worn out and screaming:  WOO HOO, what a ride
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1988 Neoplan AN 340, 6V-92 TA DDEC II, HT 748 ATEC

« Reply #1 on: October 13, 2006, 07:30:06 PM »

   I would try heat, not a lot of it, but something like a small electric heater to dry out the brake shoes applied over a day or two.  Also being of dissimilar materials the shoes and drums expand at different amounts, and that might break them loose.

Or, on the expansion contraction theme, you might pack the outside of the drums with dry ice.


location: South central Ohio

I'm very conservative, " I started life with nothing and still have most of it left".
Orange Blossom Special II
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73' MC-8 8V71/HT740 Southwest Florida

« Reply #2 on: October 14, 2006, 06:27:03 AM »

Sounds like the DD3 parking brakes are locked up. Air up bus to full pressure, push parking brake knob, then make a hard service brake application and hold for 5-8 seconds.  You may have to try this several times. You can also try spraying PB Blaster around the shaft and into the DD3. If the locking balls are rusted the shafts in the DD3s, they will have to be removed from the bus if they cannot be broke loose by above method.  Hope this helps, Jack

Growing Older Is Mandatory, Growing Up Is Optional
Arcadia, Florida, When we are home
Buffalo SpaceShip
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« Reply #3 on: October 14, 2006, 08:13:56 AM »

I also have a 4108, and they are indeed DD3 chambers. It could also be a leaky aux. diaphram in one of the cans, a bad inversion valve, or even the push-pull valve. If you've previously had issues getting them to release, I would look into these possibilities first.

Find a schematic and start going through the troubleshooting. Just removing the individual air hoses from the cans should give you some idea on where the air is (or is not) going.

But don't bang on the brakes or apply heat. You can try backing the brake shoes off the drum with the slack adjusters to insure that the shoes aren't rusted to the drums. But I suspect that you have issues in the parking brake system.

Let us know what you find out and good luck!
Brian B.

Brian Brown
4108-216 w/ V730
Longmont, CO
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