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1976 single axle dump truck, one rear wheel locks up?

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Cariboo4x4

05-17-2019 08:07:43




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We recently put new dual wheel cylinders on this 1976 gmc dump truck. 2 wheel cyinders per backing plate. We cleaned the shoes and drums. We bled the brakes and then realized master cylinder was leaking. We put in a new master cylinder on firewall. I bench bled it and told buddy we need to bleed brakes again yet he needed truck on his property to move some soil this week.

The truck stops well if you pump the pedal a couple times yet the drivers rear wheel locks up once in a while when braking in the forward motion. I told buddy that its most likely there is no air in that one brake line. It unlocks if you back up. I'll have to confirm if it unlocks if you continue forward. Its odd its the drivers rear wheel that was locking up before we put new cylinders in both rear wheels. It is not locking up as bad as before brakes were serviced. This brake system has that dual vacuum type booster located under the rear part of the cab too. The master cylinder is just a single reservoir type. I read online that when a rear wheel bearing starts to go it can cause the brakes on that side to lock up yet never heard of that. How would you diagnose a bad wheel bearing on a big truck like this? I think the brakes just need bleeding. We are not using any fancy setup to bleed brakes. Just one guy in cab pumping brakes with 2nd guy cracking bleeder at wheel.

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Cariboo4x4

05-18-2019 08:23:55




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 Re: 1976 single axle dump truck, one rear wheel locks up? in reply to Cariboo4x4, 05-17-2019 08:07:43  
Thank you!



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cole in mo

05-17-2019 17:44:34




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 Re: 1976 single axle dump truck, one rear wheel locks up? in reply to Cariboo4x4, 05-17-2019 08:07:43  
Needing to pump the petal to get a good petal, means air in the system, or the shoes need adjusted, or both. A wheel locking up when stopping could mean, there is still oil or brake fluid still on the shoes or drum. IF a wheel bearing is going out it puts weight on the seal causing it to leak. Jack that side up enough for the tires to clear, then put a long bar under the tire and see how much movement you can get up and down.

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