Fuel Vapor in brake booster??

[kcolas]

Got a note with my rebuilt servo that there was fuel vapor present in the booster. Has anyone experienced this? As far as I can tell, the only vacuum input is from the manifold, but fuel should not be going "upstream" against full manifold vacuum. I hope I'm not scratching at something big here... /ubbthreads/images/graemlins/confused.gif

 

[Dave Russell]

Some of the older cars had a "vapor trap" in the line from manifold to brake booster. Modern cars use the charcoal canister to do the same thing. The inlet of the booster has a one way valve which normally only allows flow from the booster to the manifold. In theory, vapors could leak back into the booster via the open valve when no vacuum is present. The vapor could cause deterioration of the booster, or very unlikely, the vapor in the booster could get ignited.

The rebuilder might be concerned that vapor was present. It might be of more concern where the booster is mounted below the manifold level, such as on the Healeys. There might be some gravity flow of vapor or liquid into the brake booster.

I don't think it was much of a worry when the Healeys were designed. If you are concerned, there are "vapor traps" available to be installed in line, to intercept any fuel vapor that could get into the booster.

You can see a vapor trap here:
https://www.ecihotrodbrakes.com/brake_system_accessories.html
D

 

[kcolas]

Thanks Dave, I just checked the site and I think it might be worthwhile to protect the new booster. Not sure how long the vapors had been getting to the booster, there was some rocker trouble a couple of years ago, and a period of reduced vacuum until I got it fixed, but maybe that was enough... k