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Frame/Suspension/Brake... Talk & Q&A All things... Frame/Suspension/Brake

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Old 05-15-2017, 11:05 AM
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Default Hard Pedal, Poor Braking Performance - Manual Drum Brake Setup

Hi everyone, in case you didn't see my introduction post, I have a small homebuilt tractor my grandfather made in the early Ď80s. Itís cobbled together mostly from automotive parts from the 50s and 60s.



Last summer I tried fixing the brakes on it (they hadnít worked in a long time). I rebuilt the master cylinder, replaced the wheel cylinders, flushed the line, and adjusted the brake shoes. They work now, but not very well.

I have a rock hard pedal, yet there is not enough braking power to hold the tractor in place on an incline. I even tried over adjusting the shoes so they would drag- still didnít work very well (though they did work better).

Here are additional details of the setup.

MC - From an early 60s Ford sedan. Rebuild kit sourced for a 1962 Galaxie. Single pot, 1Ē bore, manual.

Wheel cylinders - From a í72 Suburban.

Shoes - I didnít replace them, not sure what theyíre from. Iíve attached a photo from when I had one of the drums off. I thought they were okay after cleaning them up. I'm certainly having doubts about that now!



Tractor in general - Weighs around 1600lbs, rear brakes only. Handbrake is mechanical and runs on a different system (it works fine).

I'm leaning towards thinking the issue is with brake shoes, but I would really appreciate a second opinion before tearing into them.

Thanks
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Old 05-15-2017, 11:21 AM
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My first thoughts for you were; I think brake drums were made to turn fast so the shoes work better on the speedy swirling of the drums, but a farm tractor does not turn the drums very fast, so the shoes don't do as much stopping.
My second thought is to ask if all four of the wheel cylinder pistons were free in the cylinders. They will probably be aluminium and the cylinder is steel. They will probably have bonded together after sitting so long. If the pistons are stuck in the cylinder, you are not squashing the shoes out into the drums at all. Your shoes should be O.K., if you can get them to move.
Good Luck.
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Old 05-15-2017, 04:04 PM
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How did they work before? Could be the master is too large, might need a 7/8" or smaller to create enough pressure.
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Old 05-15-2017, 04:19 PM
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Quote:
Originally Posted by MercuryMac View Post
My first thoughts for you were; I think brake drums were made to turn fast so the shoes work better on the speedy swirling of the drums, but a farm tractor does not turn the drums very fast, so the shoes don't do as much stopping.
Drums stop cars that are moving slow too.

The shoes alone wouldn't have anything to do with what you are describing, regardless the shoes in the pic, while old, look to have plenty of meat on them. If you have a rock hard pedal then it should be locking those wheels up no problem. If you really do have firm hydraulic pressure at the pedal, then something is making it build. If it isn't the pressure of the shoes to the drum, then there is another obstruction somewhere. The wheel cylinders in that pic don't look new. Remove them, disassemble and clean, then reinstall. May as well do the same to the M/C. While everything is off off blow some air through your lines to make sure there isn't an issue there. Brake systems aren't that complicated, especially what you have there. There are only a few things that can cause an issue like what you are describing. Get after it...
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Old 05-15-2017, 04:51 PM
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Yuppers, probably just an obstruction. The easy way to tell is leave the drums off and try pushing the brake pedal while observing the wheel cylinders. It won't take much pressure to move cylinders that aren't stuck. You'll see the shoes move. In fact if you aren't careful you'll push the ends off. If you don't see movement pretty easily, something is stopped up. I'll re-affirm that manual drum brakes work just fine.
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Old 05-15-2017, 08:24 PM
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Just my thoughts...

You have a MC designed to support 4 wheel cylinders, but only have 2... basically, the MC is delivering 4 wheel cylinder volume to 2 wheel cylinders, which will shorten the stroke and increase pedal effort, at least in my mind...

.
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Old 05-16-2017, 03:47 AM
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As was said I think a 1"bore is to large for two wheel cylinders. The photo of the rear brakes is it from the right or left side of the tractor? The short brake shoe has to be on the front side.
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Old 05-16-2017, 12:40 PM
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Thanks for your replies everyone!

I should have made it more prominent in my original post, but the wheel cylinders have been replaced.

The image of the brakes is from when I first took off the drum. The original cylinders were seized- I replaced them with new ones (which are replacements for a í72 Suburban).

Quote:
Originally Posted by Bamamav View Post
How did they work before?.
They used to work well. With all the different components, I also was thinking the system might just be out of balance. However I asked my Dad and he remembers the brakes working properly before. Certainly better than now.

Quote:
Originally Posted by Blue Eyed Devil View Post
The shoes alone wouldn't have anything to do with what you are describing, regardless the shoes in the pic, while old, look to have plenty of meat on them.
Thanks for confirming that! I had originally thought they were fine, but Iíve been second guessing myself lately.

Quote:
Originally Posted by smallfoot View Post
Yuppers, probably just an obstruction. The easy way to tell is leave the drums off and try pushing the brake pedal while observing the wheel cylinders. It won't take much pressure to move cylinders that aren't stuck. You'll see the shoes move. In fact if you aren't careful you'll push the ends off. If you don't see movement pretty easily, something is stopped up. I'll re-affirm that manual drum brakes work just fine.
I actually did exactly what you warned me to be careful of! hahaÖ I donít think I have an obstruction. The pistons move and I had a good flow of fluid when bleeding the brakes.

Quote:
Originally Posted by Dr Crankenstein View Post
Just my thoughts...

You have a MC designed to support 4 wheel cylinders, but only have 2... basically, the MC is delivering 4 wheel cylinder volume to 2 wheel cylinders, which will shorten the stroke and increase pedal effort, at least in my mind...
Iím with you 100% on this. When bleeding the brakes I got a lot of pedal travel, but normally it barely moves.

Quote:
Originally Posted by DozerII View Post
The photo of the rear brakes is it from the right or left side of the tractor? The short brake shoe has to be on the front side.
This is a photo of the right side of the tractor. The smaller shoe is on the front side.
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Old 05-16-2017, 10:14 PM
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When you replaced the wheel cyl did you keep the same bore? Thing is you want as big as you can get there and small at the master cyl ,without a booster.
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Old 05-16-2017, 10:25 PM
BlueNorther BlueNorther is offline
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just looked on RockAuto's site and the rear wheel cylinders for a 1972 Suburban are speced at 1", same as your M/C.

you would need a large brake pedal ratio to operate the system.

I would find a 3/4" bore M/C, which would give you way more leverage.
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