The Brakes Of The D-Series Backhoe Loader Caterpillar

Problem:

Caterpillar has received a number of communications from dealers showing concern about the amount of brake pedal travel on the D-Series Backhoe Loaders.

Solution:

The mechanical advantage of the brake pedal system was changed on the D- Series Backhoe Loader in order to reduce the brake effort required to stop the machine. The D-Series pedals have a mechanical advantage of 11.8 to 1 verses the C-Series, which had a mechanical advantage of 7 to 1. Due to the increases mechanical advantage of the D-series, the force necessary to achieve the same braking is less.

One of the side affects of this change is that the brake pedal must travel farther on the D-Series than on the C-Series in order to achieve the same braking. For example, on the C-Series the brake pedal may go hard after an inch or so of pedal movement, the D-series pedal must travel much farther in order to achieve the same braking. In some cases, the brake pedal of a D-series backhoe loader will only be an inch or so from the firewall of the cab.

Reference: RENR3576 Axles, Differentials & Brakes Specifications for the D-series Backhoe Loader and RENR3577 Axles, Differentials & Brakes System Operation, Testing and Adjusting for the D-series Backhoe Loader Checking the Brake System of the D-series Backhoe Loader

1. Raise the tractor off of the ground using the stabilizers and front loader bucket.

2. Perform a torque converter stall test in 2nd gear and at high idle.

3. Check the brakes (both pedals applied) should be able to stop or prevent the wheels from turning without the brake pedal touching the firewall.

If the wheels turn during this test or if it is necessary to touch the firewall to stop the wheels from turning, please perform the following checks or procedures:

Check the "free play" in the pedals

Brake "free play" must be between 5 to 10 mm (approximately 1/4 inch) measured at the pedal. Measure "free play" of each brake pedal individually. Depress each pedal by hand until resistance is encountered. Because of the large mechanical advantage of the pedal system, this dimensions is critical. Too much free play may allow the pedals to touch the firewall.

If the "free play" is found to be out of specification, and adjustments have been made, the pedals must be stroked individually approximately 6 times, and "free play" rechecked to assure some clearance does exist.

Make sure there is some distance between the push rod and the master cylinder piston.

Bleed brake system to remove any trapped air.

If the "free play" is correct and the pedals still contact the firewall during the 2nd gear stall test, the brakes will have to be bled (purged) in order to remove any air that may remain in the brake system.

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