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Old 12-03-2021, 06:40 PM   #1
Mr. V
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Default 740: vibration at 2200 RPM

My 1986 740 Turbo with manual transmission vibrates / shudders slightly between about 2200 and 2600 RPM to where I can feel a slight vibration / shaking from both the steering wheel and the shifter.

Thoughts as to possible cause?
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Old 12-03-2021, 07:22 PM   #2
Kjets On a Plane
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Resonance from collapsed hydro motor mounts, or does yours still have 'solids' (simply rubber, not goo filled) in '86 like most do?

There's the updated bracket/trans mount that works way better in those?
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Old 12-03-2021, 10:10 PM   #3
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Solid mounts, seem OK.

What updated bracket?

Source?

Thanks.
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Old 12-03-2021, 10:17 PM   #4
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Search brickboard IDK?

It allows you to use the same 'sunken' trans mount the (later) 7/9 AW cars use with the M46, works well with the solid mounts, the M46 doesn't flop around like a fish in the trans tunnel anymore.

I think I sold my last NOS one, may no longer be available.

Or PM sbabbs? He's local & I think has said bracket that's only used on some late M46 700s.
But he might not want to break any of his 7/9 manual trans specific stuff up?

The late 7/9 auto crossmember and mount is obviously abundant.

If it's RPM based and does it neutral revving it, IDK tho? Sometimes it's a resonance thru the exhaust/messed up mount or someone installed an aftermarket cat or muffler that doesn't fit or work right or didn't get it on the hangers right or the rubber vibe-isolating exhaust hangers are dried out &/or partially or 1 of the many is compromised &/or broken?
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Old 12-04-2021, 06:16 AM   #5
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Could be the driveshaft support bearing / bushing too.

Could also be something easy as wheels or tires out of balance.
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Old 12-04-2021, 07:07 PM   #6
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I’ve had a driveshaft center support cause vibrations at 30mph but it seems like the op has an issue with engine speed not wheel speed. The accessory bushings are known to degrade and cause sagging accessories. It’s possible that a resonant frequency at those rpms is putting a strain on things.
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