brake servo

[iomgt6]

Hi All,  sorry if this has been asked before but I cant understand how an independent brake servo works, I understand how one can work that is linked direct to the brake pedal, secondly my GT6 mk3 is fitted with one, it looks pretty new and I know the seal is ok as I have now removed it and when I opening it a lot of air came out, the reason I removed from car was I suspected it wasn't working as I had done the simple test of starting the engine with foot on brake pedal and felt no difference, the brake pedal always feels firm and requires quite a lot of force but I can lock the wheels up at low speed, also I notice on ebay there are different specs for these units ie 2.3 to 1 etc, what would be most suitable, many thanks Paul

[glang]

Hi, Im no expert but as you havent had an answer yet thought Id try to help out. The remote servo works very similar to a direct one in that as you press the pedal the brake fluid passes through the pipe to the servo where it moves a shuttle valve/piston which allows vacuum to operate the diaphragm which then pushes on said piston to apply extra pressure to the hydraulic system and on to the brakes. If the servo fails you'll still have brakes but the pedal will need more of a push. The ratio refers to the amount of assistance the servo gives and depends on the weight of the car and also personal preference as you tend to lose a bit of sensitivity as the ratio increases.....

To test the servo you could disconnect the vacuum hose (plugging the manifold connection) and drive it on a straight, clear road to test the braking - no difference = servo not working!

[iomgt6]

thanks for reply "glang" and explanation, yes I might try the disconnect idea, Ive taken the servo off the car and noticed the outlet looked as thou the bit of fluid around the outlet was rusty colour, I now suspect that the shuttle valve you mention my be stuck so a decision will have to be made, strip but I don't know if parts are available or bite the bullet and buy new.

[glang]

Hmm rusty fluid not good as it may indicate water contamination of the system with possible damage to other components. With the servo theres a few bits that could stop it working correctly and it might be difficult to identify exactly where the problem is and then theres the spares.... Its probably easier and safer just to replace it as new units seem to be available for about 80quid.

Or another possibility is not have a servo at all - they were originally only an optional extra and I prefer the feel of my Vitesse without one.