My loader won’t stay up?

[GreensvilleJay]

Master cylinder was professionally rebuilt by the best shop in town, well respected,contracts with most major players in Steeltown
After the incident, I went to local auto parts place, guy grabs NEW master cylinder which I paid LESS for than having the original 'professionally' rebuilt.
Installed it and 20 minutes later went for road test...ZERO issues,drove it on and off road (real off road ) for 2 decades, never had any brake issues.

 

[DustyRusty]

Master cylinder was professionally rebuilt by the best shop in town, well respected,contracts with most major players in Steeltown
After the incident, I went to local auto parts place, guy grabs NEW master cylinder which I paid LESS for than having the original 'professionally' rebuilt.
Installed it and 20 minutes later went for road test...ZERO issues,drove it on and off road (real off road ) for 2 decades, never had any brake issues.

Even well-respected professionals screw up more often than people will ever know. They might be considered the best shop in town, but your experience proves that a new master cylinder was superior to their professionally rebuilt master cylinder. If it had been done correctly the first time, it would be as good as your replacement master cylinder.
Would you agree that a lift cylinder that was professionally rebuilt by a local shop that has a track record of quality work should perform as well as a new lift cylinder that is purchased through a Kubota dealership parts department? The answer should be yes, however, if they screw up this one time, then the answer is no. Even the new cylinder from Kubota can be defective, but the chances of that are less than the chances that the rebuilder screws up.

 

[GreensvilleJay]

yup, 'should be' !!!
FWIW, Went to local hydraulic shop years ago to have price for one lift cylinder repaired (it was with me ) , but kept going and ordered TWO for less than their estimate from another company,they were custom built. Have no idea why the shop was so pricey.

 

[whitetiger]

It'd be interesting if someone would remove their seals from their cylinders and see what happens.

It has been done in the hydraulics 101 class at the Technical College where I took some classes.
The cylinder extends just as it did with the seals on the piston.
Now retracting or down pressure is another story.

 

[TheOldHokie]

It has been done in the hydraulics 101 class at the Technical College where I took some classes.
The cylinder extends just as it did with the seals on the piston.
Now retracting or down pressure is another story.

I think you left something important out.

With the seals removed it will only extend with one of the two ports plugged. And even then with reduced force.

It basically becomes a displacement type single acting cylinder with reduced piston area.

Dan

 

[6869704x4]

I think you left something important out.

With the seals removed it will only extend with one of the two ports plugged. And even then with reduced force.

It basically becomes a displacement type single acting cylinder with reduced piston area.

Dan
View attachment 132390

Reminds me. That was a question on my promotion test in the USAF. Paraphrasing here. With equal pressure on both sides which way will it move? Why?

 

[GreensvilleJay]

In the case of the master cylinder on my Willys (same as forklifts and a zillion other vehicles...), in the right drawing the upper left black port actually goes to the reservoir,or so I was told. 'somehow' the oil went 'round and round and no brakes.constant pressure on pedal.it went to the floor yet NO leaks. This was back in '75 or '76, so ,yeesh, 1/2 a century ago.....when i was 21,sigh

 

[TheOldHokie]

Reminds me. That was a question on my promotion test in the USAF. Paraphrasing here. With equal pressure on both sides which way will it move? Why?

For me that was AP physics in my freshman year of college. I could have learned a lot more if the partying had not gotten in the way.

 

[TheOldHokie]

In the case of the master cylinder on my Willys (same as forklifts and a zillion other vehicles...), in the right drawing the upper left black port actually goes to the reservoir,or so I was told. 'somehow' the oil went 'round and round and no brakes.constant pressure on pedal.it went to the floor yet NO leaks. This was back in '75 or '76, so ,yeesh, 1/2 a century ago.....when i was 21,sigh

On your Willys the master cylinder is a pump that operates just like a bicycle tire pump. On that vintage they typically have a cup seal on the brake rod that pushes oil out to the brake cylinders creating the pressure needed to actuate and maintain the brakes. Just like the bicycle pump pushes air into a tire.

In your case the cup seal was probably defective and not capable of holding the pressure built up on inward stroke. So oil leaks backwards past the seal into the intake port (reservoir).bleedimg off tje pressure. By rapidly pumping the brake pedal you repeatedly build enough pressure to actuate the brakes but it bleeds off quickly.

I just had a similar failure on my 2004 Ram truck two weeks ago. One of the steel lines had developed a pinhole leak that allowed pressurized oil to leak onto the ground. Same technique and a quart of brake fluid for mid trip replenishment got me to the repair shop. Then $625 got me the truck back with three new hoses and two new brake lines

Dan

 

[DustyRusty]

If automobile manufacturers were to use stainless steel brake lines and fuel lines, they would never deteriorate and leak. We had a 1988 Ford Taurus that came with a stainless steel exhaust system and the exhaust system never failed while we owned that car, however, the transmission was replaced probably 10 times until it was out of warranty. The car made it to 100,000 miles and then it died with a bad cylinder. The transmission problem was cured by an independent shop rebuilding the transmission instead of Ford's factory rebuilding service that used parts from other transmissions to replace defective parts.

 

[whitetiger]

With the seals removed it will only extend with one of the two ports plugged. And even then with reduced force

You are correct, I forgot to add the plugged port.

 

[6869704x4]

For me that was AP physics in my freshman year of college. I could have learned a lot more if the partying had not gotten in the way.

Force comes from pressure x area? Or something like that.