Wheel cylinder pistons

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PareosWC
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Wheel cylinder pistons

Post by PareosWC »

In attempting to get solid brakes on this WC52, I pulled the front drums to check for tolerance. When the brake pedal is pushed, only the rear pistons push out and move the rear shoes. All (4) wheel cylinders are new MWM products.

Should not both pistons be moving when the brake is engaged?
motto
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My garage: Harley Davidson 42WLA, Dodge WC63, Dodge WC57, Chevrolet 1-1/2 ton 4x4. Originally an Earth Borer, Pole Setter. Drilling rig gone and truck now mounts a #7 Set Lifting Frame. i.e.: Light Wrecker.
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Re: Wheel cylinder pistons

Post by motto »

Brakes are behaving as they should with the 1-1/4" pistons at the front and 1-3/8" at the rear. The reason for this is that the forward shoes are self energising, forced on due to drum rotation and the rear shoes are trailing therefore tending to be forced out of contact.
The difference in piston diameters is to try and even out the work that each shoe is doing.

David
PareosWC
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Re: Wheel cylinder pistons

Post by PareosWC »

Thanks, David.
Don
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Re: Wheel cylinder pistons

Post by Don »

I would think that because the rear shoes have the larger area piston and more force, they probably move first. Once they come in contact with the drum, the fluid would start moving the forward shoes. Without the drums on, the rear pistons could keep moving until the springs can stop them.
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Vista52
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Re: Wheel cylinder pistons

Post by Vista52 »

motto wrote:
Mon Jun 22, 2020 11:54 pm
Brakes are behaving as they should with the 1-1/4" pistons at the front and 1-3/8" at the rear. The reason for this is that the forward shoes are self energising, forced on due to drum rotation and the rear shoes are trailing therefore tending to be forced out of contact.
The difference in piston diameters is to try and even out the work that each shoe is doing.

David
Excellent explanation David.
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