Why do Americans bench-bleed master cylinders...

[NoBeardNoTopKnot]

I've done a fair bit on brakes over the years, and definitely swapped-out more than a few MCs on all sorts of vehicles, and with the MC at the top of the system, after a few pumps at the pedal, the MC always self-bleeds.

I use a combination a pressure-bleeder, and if it's a stubborn job my MityVac to reverse or vacuum. Reverse never fails.

Go on US based forums, and look to Youtube, and you'll see how to bench-bleed MCs. You can buy bench-bleed kits to do all this. It seems to be a US based thing. What are we missing, and why do we want to do this? Are there MCs out there that require this?

[Clifford Pope]

It's a useful trick to be able to replace a master cylinder without the need for any bleeding at all.
I've always done it, and I once knew a garage owner who said he had never needed to bleed any car just to replace one component.

[autorover1]

Bench bleeding a CB master cylinder on a S2 LR recommended to get the air out as its up at an angle on the pedal box , that or tip the vehicle 40 degrees or so.

[NoBeardNoTopKnot]

Bench bleeding a CB master cylinder on a S2 LR recommended to get the air out as its up at an angle on the pedal box , that or tip the vehicle 40 degrees or so.

Ohhh, I see. Thank you. Makes sense, er - nearly. Seems it's not a Yank biased thing at all.  I had it, air goes up, one or two prods and Bob's your Auntie, you're done. Your more than reasonable answer leads to the root question -  It's hardly rocketry; all the MC I've ever seen do. You could wonder why anyone would design the casting, such that the MC traps air/refuses to eject its own air?

[Noddy]

There are MCs around with their own bleed screw allowing them to be bled insitu. Land Rover did produce some models with a bleed screw on the pipe from the MC there was a topic on here about them some time ago.

Alec

[NoBeardNoTopKnot]

Thanks for that, I suppose a bleed-screw is better than an air-trap. Others do,  I wonder why all MCs can't feature an interior which funnels air to the top?

[geoff]

Where would be the fun in that 

[NoBeardNoTopKnot]

You have me there.