Forum:
I have noticed that when driving my sportrak, as I engage the clutch (eg. having been coasting) and the brake pedal is partially depressed, the pressure on my braking foot feels less as the engine revs pick up. Is this to do with the brake servo getting more power from the engine? Or does the engine braking releave the brake system (although can't think this is true as there's no abs to control braking), or is it something completely different?
Thanks for filling me in 
Check your NR Valve
The engine provides more vacuum (either from the inlet manifold (petrol) or driven vac pump (diesel) and more-so at higher revs. The fact this feels different at idle to higher rpm leads me to think you may have insufficient vac at idle. There should be ample vac in reserve for braking during idle unless the non-return valve is faulty. Run the engine at idle, check you have servo assistance (longish, softish pedal as normal, huff from the servo every press). Switch the engine off. Wait one minute. You should still have servo assistance for a few pumps until the pedal feels rock hard. If it immediately feels hard your system has lost vacuum prematurely. This is usually a sign of failing / failed vacuum non-retrun valve. Find it, check it, replace if necessary
Ferg
Thank you very much for this
Thank you very much for this information, I will run this test tomorrow.
Inlet manifold vacuum
Not sure what you mean. Inlet manifold vacuum is high at idle and next to nothing when the throttle is fully open. It will be higher if you take your foot off the throttle at high revs.
YRV Tony
Well this would make sense
Well this would make sense for what I'm describing, as it happens when the revs pick up and I have my foot on the brake, therefore not the throttle.
Anyway I did the test, and there were about 5 pumps with a nice 'huff' before the pedal became much heavier. (This is having just turned the engine off)