Help - John Deere 6620 brake problems - dragging/heating up

andy r

Member
I can't quite figure this out. The right hand brake slave cylinder was leaking brake fluid. Honed the cylinder and put in new cups. Cleaned everything up well and reassembled. Dry brakes shoes. Bled the lines and cylinder. Brake peddle had maybe 2 inches of travel before the brake shoes hit the brake drum. Everything seemed just right. The brake drum was free (you could rock it) when the pedal was not pushed and the brake drum was solid when the brake pedal was pushed. I probably had ran close to 10 acres of beans when I thought I smelled a hot brake. Sure enought the right brake was hot and would sizzle when you touched it with water on your fingers. Also, I noticed the brake pedal wouldn't move any. It was clear to the top and you couldn't move it any with your foot.

I let it cool for a couple of hours. Now the brake pedal had the same 2 inches of free travel like it did when I reassembled it and the brake drum was now loose from the brake shoes as you could wobble it slightly.

In 2012 the brake got hot once just like it did today. I let it cool, never used it during harvest, and never had a problem the rest of the season.

Didn't use the brake in 2013.

It is interesting to note that when I bought the combine in 2012, the previous owner had the brake drum wired over the brake shoes. The center splines of the brake drum were gone. Wonder if it got hot and broke out?????

The brake is assembled right. I didn't even use the brake today when it got hot. Never even touched the pedal. I haven't even adjusted the brake shoes up against the brake drum.

It is almost like heat expanded the slave cylinder pushing the shoes out causing more heat. Then 3 hours later everything cools and the slave cylinder retracts allowing the shoes to return, also allowing the brake pedal to move again.

What do I need to do????? Maybe I will depressurize the brake lines by cracking the brake line coupler underneath. Maybe that will let me run tomorrow without it heating up.

Thanks for any ideas.
 
There's a tiny hole in the bottom of the master cylinder reservoir that passes through into the bore and yours is clogged with debris/rusted shut.

When the pedal is fully UP, that little hole is supposed to release any pressure trapped in the slave cylinder or lines bask into the reservoir.

With it clogged, you get the pressure buildup you are seeing.

Can also happen if the pedal does not come fully "up" or the linkage between the master cylinder and pedal is set too long so the master cylinder piston can not fully retract.
 
I bet that is exactly it - the hole is plugged which allows brake fluid to return to the master cylinder when it expands. Question??? Can I clean the hole out from the top of the master cylinder reservoir? Maybe take a drill bit in my fingers and spin it in the hole. I assume there would be a hole for this on each side - left and right brake - left and right sides of the shared reservoir. Would the hole be towards the the brake pedal side or towards the back of the reservoir where the brake lines come out??? Thanks alot. I will check back to see if you have left any answers to my questions.
 
There may be two holes, both visible looking into the reservoir through the fill hole. The one you are looking for is TINY, and if there are two, it will be the one more towards the end of the cylinder where the line connects.

A cutting torch tip cleaning bit works well, maybe .015" or .020"???

The rubber cup inside the bore passes the tiny hole on each stroke, so if the hole is enlarged, or sharp, it will cut the cup.
 
That was exactly the problem. Took the cover off of the reservoir and soaked up the brake fluid with shop towels. Two holes on each side. Front hole was open and I could see the movement of a shaft from the top. Second hole back towards where the lines come out was plugged. Worked pushing a torch cleaner through the hole and some brake fluid came back at my hand and into the reservoir as I opened the hole. Brakes worked fine all day. The pedal resumed having 2 inches of free travel and didn't change. Certainly was the problem. Amazing how such a small and probably weak plug could cause such serious and complicated problems. Thanks
 

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