THROBBING/PULSING

[CHRISYD]

thanks Andy. it does look like mine so as ive got nowt else to do I might as well get one and fit it.

[TrevorK]

Why does the length of the hose make any difference?

Pete

Having thought about this I wonder if it's because the vacuum supply is pulsing, as it's from one runner only, Lotus didn't want this to excite a resonant frequency of the valve's spring and mass combination and the different hose lengths are to suit different valves.

[CHRISYD]

so you mean the shorter the pipe, the quicker the vacuum builds and valve will close quicker?

[TrevorK]

No, not really. The vacuum will build in one engine cycle at closed throttle as long as the pipe's volume is less than that of the cylinder.

What I meant is that the pipe acts a bit like an organ pipe so will have a resonant frequency which amplifies the pulsing. If this were to coincide with the frequency of the valve, which, being a weight on a spring, is a bit like a pendulum, then it would be likely to shake the valve to bits.

[CHRISYD]

aaahhhhhhhhhh I see. makes sense. I must have been off school that day!

[DavidOliver]

In my opinion the servo hose length is irrevelant to pulsing and in no way is related to valve spring resonance.
For Richard, the ticking I get behind the dash is the Voltage Control unit, which in my 85MY I still have failed to locate having dismantled
the dash a couple of times. I still think a new Voltage Control would also tick, but i will try again to locate.
In my opinion pulsing may come from leaks from hose, clips, non-return valve or servo, and will correspond with engine speed.
As previously posted, if you have a leak there is no brake pedal assistance a few seconds after switching the engine off.

Dave the cog.

[CHRISYD]

Fitted the new valve. brakes dont feel any different but ticking has gone. old valve spring seems still firm so have kept old valve just in case.

[AndyD]

Good news

My brakes felt the same too but just happy to get rid of the ticking.

Cheers

Andy