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‘60 NSS hissy fit

Started by David Greenburg, June 16, 2021, 07:26:28 PM

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David Greenburg

The NSS on my '60 hisses at startup. The hissing subsides after 20-30 seconds, and the car does not exhibit any other vacuum issues; vacuum door locks work fine, as does the automatic brake release. I might not even notice that this is not normal, except that my '61 does not do it.  Is this the beginning of NSS failure, or is it ok to live with it?
David Greenburg
'60 Eldorado Seville
'61 Fleetwood Sixty Special

savemy67

Hello David,

I love these sorts of conundrums.

Is there a correlation at start-up between fast idle and choke unloading,and the hiss?

At start-up (fast idle), I would suspect highest vacuum level.  Half a minute later, maybe a drop in RPM, and less vacuum.

I don't think the '60 NSS has a diaphragm (someone correct me if I am wrong), but maybe it is slightly out of alignment so that the internal passages are not spot-on.

Can you connect a vacuum gauge somewhere and observe the state of engine vacuum at start-up and shortly thereafter?

Respectfully submitted,

Christopher Winter
Christopher Winter
1967 Sedan DeVille hardtop

The Tassie Devil(le)

Quote from: savemy67 on June 16, 2021, 09:13:22 PM
....I don't think the '60 NSS has a diaphragm (someone correct me if I am wrong), but maybe it is slightly out of alignment so that the internal passages are not spot-on.....   
The NSS has a sliding "valve" that simply moves sideways, covering and uncovering the vacuum port.

If they are leaking, then the surfaces are not completely smooth, and have lost their "slipicity".

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

cadillactim

David

Sounds like the vacuum valve is going bad. There are two rubber seals in that valve, and likely the lower seal is sticking open, thus the hissing sound. It finally seals all the way and the hissing stops. The problem will likely worsen until the hissing doesn't go away.

I've rebuilt many of these switches, and most of these valves leak after 50 years.

Tim
Tim Groves

David Greenburg

Thanks, guys.  That's what I was afraid of.
David Greenburg
'60 Eldorado Seville
'61 Fleetwood Sixty Special