Hydraulic drum brake woes....

Absent Minded Farmer · Sep 17, 2014

This is a new one on me. I have one brake on the (SP) chopper that sets up by itself. You don't have to push on the pedal, it will lock itself up tight in about an hours time. Have to take a rubber mallet to either side of the drum to get it loose. I checked the bleeder & there was no undue pressure in the line. 'Bout all the info I have to play with at the moment. The drums are in place between the final drives & the frame.... so they are anything but easy to access. Also, I don't have a clue as to how that all comes apart, yet. I'm still on the hunt for service bulletins.

I'd elaborate here on the brakes, but it's a fairly basic setup, both left & right pedals have their own master & wheel cylinder, with their own dedicated line connecting them.

With all those facts in place, I'm going to guess the inside of the drum hasn't seen the light of day in a very looooong time..... or a good servicing. So, I can understand why it sticks, I just can't understand where this phantom pressure is coming from to make it stick in the first place.

Thanks in advance!
Mike

JD Seller · Sep 17, 2014

What brand and model of SP chopper???

Absent Minded Farmer · Sep 17, 2014

Ooops, sorry, it's a Gehl SP 188. The drivetrain appears to be all Rockwell, brakes included.

Mike

John B. · Sep 18, 2014

I would say you have a broken brake shoe return spring inside or a leaky seal allowing the brake shoes and drum to become coated with gear oil which can cause this also. The parts become sticky once soaked in oil and become heated.
Most drum brakes are self energizing once they are applied. Meaning that once the shoe touches the drum it is drawn into the drum just by the drum's rotation. That's why the cars/trucks with drum brakes had better braking power in forward direction than in reverse. On cars & trucks one shoe has longer lining on it than the other which causes this self energization. They have to be put in the right location though so make sure to look at and measure the shoes before you remove them so you can put them back they way they came off.

glennster · Sep 18, 2014

check if you have a rubber brake line in there somewhere. if the line rots, it gets a flap inside the line and will hold pressure. see it occassionally in cars and trucks here at the shop.

Absent Minded Farmer · Sep 18, 2014

I double checked, it's just a steel line. Your idea makes me wonder if it's possible to have a o-ring or seal, of some type, that could have broken down & got lodged in the wheel cylinder.

Mike

Absent Minded Farmer · Sep 18, 2014

"They have to be put in the right location though so make sure to look at and measure the shoes before you remove them so you can put them back they way they came off." - John B.

Will do. As a matter of fact, I think pictures are in order. I find myself doing that a lot, lately. Quite helpful!

I always wondered why the brakes on my Galaxie were weaker in reverse. I also remember you would have to back up every great once & a while & give the brake pedal a heavy tap to reset the brakes. Always got a kick out of that & thought it was an excellent idea.

Mike

Bob · Sep 18, 2014

Besides the possibility of a brake hose failed internally, master cylinders have a tiny port in the top of the bore into the bottom of the reservoir.

When the brakes are released, the rubber cup in the master cylinder moves back behind the port, opening a passage from the cylinder to the reservoir.

That tiny port often clogs/rusts shut, causing what you are seeing.

Also, the linkage rod from the pedal to the master cylinder must be set up to allow the cylinder to fully retract when the pedal is released.

The linkage rod should actually be loose/have a little play/wiggle to be SURE the cylinder can fully retract.

Absent Minded Farmer · Sep 18, 2014

Yep, you may be right. The reservoir was dry & rusty when I opened it initially. I used a Dremel to clean out the rust & wiped it out good. The port in the bottom was rusted, too. Wasn't much I could do there.

If your wondering why I put fluid in, in the first place, I was hoping to find the leak in the system. Well, dang it all, it doesn't leak. Anything but!! Lol! That's Murphy's Law for ya! Guess I'll have to Band-Aid this project for a few days. Being a shade tree mechanic has a few drawbacks when it rains.

Mike

Steve@Advance · Sep 18, 2014

If the reservoir was dry and rusty, that means there is likely rust in the wheel cylinder. It probably made just enough pressure to push the pistons out and they stuck there.

At minimum both master cylinder and wheel cylinder will need to be honed and kits put in. Even that will be a temporary fix, replacing both new will be the safest and easiest fix. Probably want to replace the steel line too.

Hydraulic drum brake woes....

Absent Minded Farmer

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JD Seller

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Absent Minded Farmer

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John B.

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glennster

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Absent Minded Farmer

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Absent Minded Farmer

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Bob

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Absent Minded Farmer

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Steve@Advance

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