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mystery moan

uplander

Newbie
Joined
Nov 25, 2007
Messages
36
for some time now i have been trying to diagnose a periodic moaning sound from my 76 302 auto. i even replaced my old saginaw with a new pump but the sound still occasionally comes back. when i first noticed in it was while braking on a curve, but it also happens after i bring the truck to a stop and the key is out of the ignition. sound is in the front, possibly by the brake booster/master cylinder. it is not my wheel bearings. thanks for your ideas.
 
OP
OP
uplander

uplander

Newbie
Joined
Nov 25, 2007
Messages
36
that would never have crossed my mind. my speedo needle does jump around a bit once in a while. not that i know that means anything.
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,353
Yes it does, or could, in the case of your sound. A moan doesn't sound like a speedo cable, but the jumping needle is usually a dried out or failing drive cable.
Best thing to do is to remove it from the back of the speedo and either drip some liquid or powdered graphite lube down the tube. Supposedly you can just yank the inner cable out of the jacket to clean and lube things more easily, but I've never been able to get the cables out of the jackets past any kinks or binding. So I've just sprayed liquid lubricants down the whole thing with good results.

Bottom line though is, even if it doesn't fix your moaning, it'll hopefully fix the speedo and keep the cable from self-destructing some time in the not-too-distant future.

Good luck.

Paul
 
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uplander

uplander

Newbie
Joined
Nov 25, 2007
Messages
36
thanks. sounds like something else is the source of the loud/deep moan. could it be a vaccuum leak in some part of the vehicle? other ideas? again, it happens sporatically--both when wheels are turning and at full stop immediately after braking. thx.
 

akafrankcastle

Sr. Member
Joined
Dec 8, 2002
Messages
876
Loc.
Kansas City
Long shot, but have you checked your coolant/water level lately?

Low levels of coolant/water at operating temperature could be turning into steam inside the coolant passages and radiator. Coming to a stop would cause the liquid to slosh about, exposing it to other warmer metal parts, and then causing a continued transfer to steam. If you are older enough to remember the old steam radiators in homes would moan as the system turned on and liquid flooded the pipes.

It could also explain the continued moaning after you turn the engine off.
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,353
From your first post, are you saying that it even makes the sound with not only the vehicle stopped, but the engine off too?

Paul
 

70_Steve

Old Guy
Joined
Dec 13, 2002
Messages
8,317
I'm thinkin' it could be the brake booster. It does have vacuum in it even after the engine stops. If there's a wierd leak, or the check valve is bad, it could make all kinds of noises.
 
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uplander

uplander

Newbie
Joined
Nov 25, 2007
Messages
36
yep. the moan even happens with the engine off. but it is unpredictable and only about 10% of the time. usually stops by the time i get the hood open but does sound to be in the vicinity of the brake booster. then again, that's where i'm sitting when i'm running to open the hood.
 
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