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Brake Servo bore size effects


ThePog

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The remote servo in the humber is leaking so needs to be fixed or replaced...

 

The bore of this is 5/8th of an inch = 15.875mm

 

I have a remote servo out of an MGB that looks ok with a bit of loving, this has a bore of what looks like 0.7" = 17.78mm.

 

Clearly this difference will have some effect on the brake feel and power, what will this be?

 

In my head the bigger size will mean more applied pressure at the brakes themselves cos the servo will supply more pressure, but there will probably be a harder pedal feel..... maybe.

 

Anyone got an opinion?

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With a normal M/C larger bore means less brake system psi for the same pedal pressure - since the piston is larger (more square inches).

The basic physics will be the same for a remote, which means you will get less 'boost' for the same pedal effort.

The bigger bore of the MGB one is 25% less area, so the same drop in boost.

If it's easy to swap you could stick it in and see how it goes.

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As Nominal said, use the MGB one and see how you get one, it should be an easy swap.

 

Going by the photos of the Humber, it looks like you have a Girling 'Powerstop' Mk IIB, which apparently are a bit of a prick to repair (and the kits aren't that cheap really). 

 

I had the same servo in my crab and it gave up the ghost around 2 years ago. I used a new Lockheed one as a replacement and has done the trick nicely so far. 

 

Best of luck _b

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