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THROBBING/PULSING

Posted: Sat Apr 18, 2020 17:12
by CHRISYD
While I was tinkering with the excel today I noticed the hose between the servo and engine was throbbing or pulsing when you held it with engine running. It felt like you were hitting it with a hammer. Is this normal? cant say ive noticed it before.

Re: THROBBING/PULSING

Posted: Sat Apr 18, 2020 17:47
by AndyD
Hi,

Yes it certainly is normal. It's the suction of the 4 stroke cycle amplified through a small hose.

The reason I know is that if the non-return spring on the servo vacuum connection (white connector from this hose at the servo) goes weak the sealing ball rattles with each pulse and sounds like a serious top end issue. I thought I had bought a pup...

Fortunately a new non-return is only a tenner on eBay and sorted it.

Andy

Re: THROBBING/PULSING

Posted: Sat Apr 18, 2020 20:23
by RED BARON
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Re: THROBBING/PULSING

Posted: Sat Apr 18, 2020 21:10
by AndyD
Hi Ian

Mine is Girling (86 SE), but oddly enough and just to confuse matters the original nrv was white as you correctly identify it is on the Bendix.

The new one is black, eBay item no 392068577346 but I note it's now £15, not the 10 I paid.

The hose lengths are really useful thanks - I suspect mine has been shortened as it was so sensitive that tightening the clips made a difference too. I will check it now I have the dimensions ☺️

Much appreciated,

Andy

Re: THROBBING/PULSING

Posted: Sun Apr 19, 2020 10:14
by RED BARON
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Re: THROBBING/PULSING

Posted: Sun Apr 19, 2020 12:24
by richardw
As the engine is fed through four separate intake runners, the servo vacuum take off only takes its vacuum from the one it is attached to, thus creating the 'throbbing' sound you have noticed. I believe it can also be heard as a speed related 'ticking' sound behind the dash.

Good info about the non return valve and hose length - thanks AndyD and Red Baron.

Cheers, Richard

Re: THROBBING/PULSING

Posted: Sun Apr 19, 2020 12:44
by CHRISYD
Thanks for the info. I thought it might have been sucktion from the engine (honest!) but wasent 100% sure. going out to check the length of my hose now!!

Re: THROBBING/PULSING

Posted: Sun Apr 19, 2020 18:33
by Pete Boole
Why does the length of the hose make any difference?

Pete

Re: THROBBING/PULSING

Posted: Sun Apr 19, 2020 19:32
by CHRISYD
Dont know but mines only 630mm long.

Re: THROBBING/PULSING

Posted: Sun Apr 19, 2020 20:08
by Lotus-e-Clan
Mines only 150 mm :(

Re: THROBBING/PULSING

Posted: Sun Apr 19, 2020 20:41
by RED BARON
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Re: THROBBING/PULSING

Posted: Mon Apr 20, 2020 11:48
by CHRISYD
Lotus-e-Clan wrote:
Sun Apr 19, 2020 20:08
Mines only 150 mm :(
:wink:

Is it cold in Gods own county today?

Re: THROBBING/PULSING

Posted: Mon Apr 20, 2020 12:26
by Pete Boole
CHRISYD wrote:
Mon Apr 20, 2020 11:48
Lotus-e-Clan wrote:
Sun Apr 19, 2020 20:08
Mines only 150 mm :(
:wink:

Is it cold in Gods own county today?
:lol: :lol:

Pete

Re: THROBBING/PULSING

Posted: Mon Apr 20, 2020 19:25
by MetBlue
Hi RB. I saw your earlier post. It was far from clear to me where the frustration had arisen from.
I've come and gone from the forum over the last couple of years, and find the contributions from many regular and senior posters invaluable in my persuit to return another of our cars to the road.
A bit of light hearted banter, especially in these challenging times can't be a bad think as long as it doesn't turn personal and I'm sure nothing in this thread has been posted with such intent.
Hopefully you'll soon be back

Re: THROBBING/PULSING

Posted: Mon Apr 20, 2020 20:56
by RED BARON
MetBlue
Just look at the two comments above yours.
It was said on another site that so many have left this site.
The type of some posters left on here now, means I do not want to lower to that level.
I left before because of the "P" taking I just think if you can't say something good then keep your gob shut.
Since Angus left the reason is probably the same.
I don't need this site as I get all my technical info direct elsewhere, and just thought I could help others.
I am gone for the last time now, as I don't need it so hope you people are now satisfied.

RED BARON.