Re: 4420 Brake Problems

Posted by andy r on October 13, 2019 at 18:46:48 from (208.126.193.44):

In Reply to: 4420 Brake Problems posted by Shawn4420 on October 13, 2019 at 14:12:34:

Are you talking about a John Deere 4420 combine? If so this is what I have found over the years in running 4420's and 6620's. There is a little hole in the bottom of each side of the brake fluid reservoir which allows brake fluid to come back into the reservoir when the brake pedal is not applied. This little hole is plugged. All of the heat from the engine and all of the belts and chains, etc. warms everything up under the combine. The brake lines, master cylinder, even the wheel cylinders get warmer and the brake fluid expands pushing the brake cylinders out thereby applying the brakes. If the hole was open in the bottom of the reservoir the fluid would just expand back into it. I remember the right brake drum glowing red hot and starting chaff on fire under the combine a few years ago. Initially I thought the brake shoes were set too tight. But after it cooled the drum was free to turn. I took a small drill bit, found the little hole in the reservoir, and spun the drill bit between my thumb and index finger to "clean" or "drill" it out. Worked just fine after that. If the brake shoes (6620) or brake disks (4420) were way out of adjustment it probably would not expand enough due to heat to begin to apply the brakes. Problem occurs when you work on things - adjust shoes or disks up or install new. A little brake fluid expansion and the brakes are applied. The solution for me was to clean the little return hole in the reservoir. There are two holes. Front one supplies the piston. Back one allows for expansion. Been awhile but I think the front hole furnishes fluid for the actual brake piston. When the piston moves the back hole is covered to pressurize the system. I believe it is the back one I needed to clean. Suck all of the brake fluid out with a suction bulb so you can find that back hole.

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