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catmastertech, Technician
Category: Construction and Road Equipment
Satisfied Customers: 2334
Experience:  Field service technician for CAT 19 years.
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How to bleed rear brakes on a446b backhoe brake pedal spongy

Customer Question

How to bleed rear brakes on a446b backhoe brake pedal spongy
Submitted: 1 year ago.
Category: Construction and Road Equipment
Expert:  catmastertech replied 1 year ago.

Hello, I am sorry no one could answer your question earlier. I hope this is not too late.

Air in the brake hydraulic system escapes through the brake control valve and goes to tank.

Brake System Air Removal (bleeding the brakes)

1. Start the engine and engage the parking brake.

2. Depress and release both brake pedals ten times.

3. Check the oil level in the hydraulic tank.

This model has four serial number breaks. If this procedure does not work for your machine, please post the full machine serial number with you reply and I will look for a specific procedure.

Customer: replied 1 year ago.
5BL1018 sn. of machine
There is a metering block that looks like a resivior for brake pedals under hood next to windshield
Brake pedals very spongy
Had brakes done. 500hrs ago by cat
Expert:  catmastertech replied 1 year ago.

Thanks for the serial number. I went back and verified this brake system is self bleeding. The procedure I sent earlier is correct.

The block you are referring is the service brake valve, the oil comes from the hydraulic tank via a separate brake pump attached to the main hydraulic pump. If this pump is not working, you should have a brake pressure warning light on. (Assuming the light is working as well.)

If you have not adjusted the brakes since the rebuild, I would try that first. This problem could be the brakes have worn in and need adjusting.

If adjustment is correct, then I would test the brake cylinder supply pressure. This will determine the problem is in the hydraulic system or in the brakes.

See the attached file for more information about the brake cylinder pressure testing.

If you need further help, please let me know. I will be glad to help all I can.

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