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Discussion Starter #1
Hello everyone,

I recently bought a 1979 Silver Shadow, serial #SRK35541. It's in good shape overall but has a few issues I will address as I have time. The most significant, I think, is that suddenly at around 55-60 MPH, it will begin making a medium-pitched mechanical squealing or grinding noise from under the dash or possibly under the hood (bonnet). Once it begins, the pitch does not seem to vary, and it goes away again as speed drops down around 35 MPH. My first thought is a speedometer cable needing lubrication, but I am not too familiar with these cars yet. My intent is to do as many of the repairs as I can myself on this car, so I'm hoping to at least diagnose this and have a good idea what the problem is before I commit to tearing into it, or to taking it to a repair shop. Any suggestions about what components might be acting up here are welcome. Thanks!

Best,

Geoff K.
Sunnyvale, CA, USA
 

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Possibility that power assisted steering fluid level is low, power steering pump can make a squealing sound (like a grass strimmer) if air gets sucked in due to low fluid level.
 

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I would check the viscous fan clutch, based on your speed factor. The speedo for this year may very have the electric sender and not the traditional cable.
P/Steering issues are most evident when the wheel is turned because that opens your valving to permit hi-pressure into either side of the rack.
Does the fan wobble by hand?
Google viscous fan clutch symptoms
 

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Discussion Starter #6
Hi Geoff K, Did you find the cause of the strange noise yet?
Hi, no, I haven't had a chance to investigate it other than confirming the PS fluid level looks OK. Being in shelter-in-place mode I haven't driven it much yet. Sometime in the next few weekends I will get it up on jackstands and poke around underneath to begin familiarizing myself with the layout of everything, and try to identify the hydraulic lines that have been suggested elsewhere as a possible vibration culprit.
 

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Another thing to look for is worn engine mounts, the engine naturally tilts on acceleration but if the mounts are perished and it tilts too much the cooling fan can rub against the radiator shroud.
 

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Hi i have had a similar problem with my brooklands found it to be bonnet catch no quite holding bonnet down .Just needed adjustment kind regards Martin.
 
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