Brake issue

[sujitroy]

Can a brake booster intermittently fail? Most of the time I have assist but other time no assist. I'm not suspecting a vacuum leak. Everything in the circuit was rebuilt within the last couple of years, but I have not touched the booster. I have a spare unit which I can swap, but would swapping out the valve on the side be the first thing to do or will that break while trying to remove it? Since the problem is intermittent is there any way to test it for sure?
Sujit

[richardthestag]

Oh good Lord, take it to a specialist Sujit

Your personal liability insurance will thank you

[KOY 23]

…. and the cars infront of you.

[stagwingnut]

Think I would first change the valve and see if that solves your problem as it’s a simple changeover, if it doesn’t cure the problem, swap out the booster unit .Graham

[Phil S]

With the engine off pump the brake pedal a couple of times, with your foot on the brake start the engine, you should feel the pedal drop a little. Try this a few times if on occasion there is no drop then the servo is at fault, try the valve as a simple option.