Loud vibration/humming/resonance at 40mph

[hugh_jenjin]

Hi there, hope someone can help or give some guidance on this.

Basically, as the title suggests, at 40mph, I'm getting a very loud (I mean very LOUD) humming or resonance coming from the diff area, and you can feel the vibration. If you drive through 40, it is very brief, but when slowing down, or if you get stuck in traffic it can be so bad it makes you wince!

I'm planning to go to the local meet tomorrow and hope to get someone who knows what they are talking about to come down the road with me for an expert opinion.

I've been told it could be the front extension, although this hasbeenreplaced this year.

Thanks in anticipation!

[stustag]

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Hi

To check the diff extension just look at the front of the diff and check for cracks, if it has gone the rear wheels will be at an angle and very obivous by eye. See mag number 309 Aug addition.

If not cracked have check the diff oil level recently?

One other thing it might not be the diff, it could be the rear gearbox mounting these sometimes go. The rubber cracks and then the gearbox sits on the cross member causing hugh vibrations which sound like there coming from the rear of the car.

Stuart

[mad cyclist]

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stu is the current diff expert, but check your uj.s are sound.

[John]

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Propshaft UJs were the source of an horrendous vibration and intermittent rattle (where the shaft was tapping the exhaust) on mine - worth a check.

[hugh_jenjin]

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Thanks for the advice. A couple of local members diagnosed either UJs or the front extension, so will have a look at the former first. Fingers crossed :?

I've been recommended agarage as well that's local to me to inspect the latter as well.

[Guest]

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I had an annoying resonance/vibration at 35 to 45 mph range, though your problem sounds worse. I had a new propshaft fitted, new driveshaft UJ's fitted, then recondition driveshafts, new rear hub bearings, new diff mountings, new diff nose bearing, new outer subframe mountings fitted, new rear springs, shocks, changed gearbox mountings etc etc, to no avail, and at considerable cost.

I ended up getting the vibration source analysed with sophisticated vibration measuring equipment ( £100 for the firsthour, £55 per hour afterwards ). Turns out, the wheelbase of my Stag is 102 inches instead of 100 inches. This combined with the standard prop angles induced a very very slight propshaft whip ( propshaft is balanced ok ). Then this whip induced a bigger vibration in the drive-shafts because 30 year old splines are worn, even on reconditioned shafts.

Cure: Brand new custom driveshafts and the working angle of the propshaft adjusted. ( Pity I spent more getting myvibration cured then the carcost)

[hugh_jenjin]

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Thanks for the ideas, car now in the garage so hopefully will have an answer soon (and not too big a bill!)

[hugh_jenjin]

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Took the Stag over to the garage last week, couldn't pinpoint the problem, so they started a process of elimination from the diff outwards (sounded like it was coming from the diff area (i.e. not from one side).

They have nowtraced it to one of the wheel bearings! I've had wheel bearings go before and never heard a noise like it nor any vibration.

The chap at thegarageand his son (both Stag experts) had never heard a noise like it either.

Also found the rear brakes need relining and one cylinder is leaking, which could explain the brake fade.

More expense, but glad it's sorted at last and can use it again!