Strange noise

[timclarke]

Hi

I wonder if any one can help help with a strange noise my cat is making!

Its a 4.2 series 2 roadster 1970. On pulling away with around 1000rpm in first, there is a scraping noise at about 2 times a second as I accelerate that disappears once revs rise to about 2000rpm. It does not always occur, seems to be more prevalent when hot, and usually once it has occured, i cant get it to do it again till i have driven a mile or two then come to rest again. The best discription is it sounds like a brake disc rubbing on the brake disc dust cover (but its definitely not that!!) - metallic, fairly high pitch. Positioning wise, it seems to probably be coming from the rear of the engine or gearbox area, as far as I can tell when driving. It does not make the noise when stationary in nuetral with the clutch in or out, nor when coasting.

I thought maybe drive shaft catching as engine shifts on mountings, or rear axle but cant see anything obvious, wheels/brakes/bearings seem OK.

Any suggestions welcome, as I am reluctant to drag the engine out and find its something simple later.

Thanks for any help

[vee12eman]

Hi Tim,

I had a similar noise after rebuilding my car, which turned out to be the cover plate at the lower front of the gearbox. This plate closes the open area at the bottom of the bell housing, forward of the flywheel and in my case was a case of using a home made plate as I have a non-standard gearbox (Getrag). Replacement with a better plate made the problem go away.

I'm not sure that normal, manual e Types have this plate, but most cars do, to protect the forward face of the flywheel and stop foreign objects getting into the bell housing. Anyway, if you do have one, perhaps something has hit it and deformed it, or maybe it has come loose and is fouling on the flywheel.

Might be wildly off the mark here, but it's a thought.

Regards,

[kingzetts]

If the noise vanishes on coasting, I'd agree with your diagnosis of mountings flexing under torque and allowing something to foul slightly. At the frequency you describe it has to be post-gearbox drivetrain related, as anything before the gearbox output flange would be rotating much faster than 2 cycles per second.

You could try checking the state of the gearbox mounting, if it is weak it could allow the tail to droop enough to allow a bit of contact. Its pretty hard to inspect the area around the tail of the gearbox as the exhaust, mounting plate, and prop tunnel floor are all in the way. You could try removing the console and gearbox cover for a good look around and maybe drive the car like that to see if it helps locate the noise.

I assume you have a standard gearbox. If by chance you have a T5 conversion, or any other 5-speed with a shortened propshaft, this moves the front propshaft flange and UJ a bit further back into the tunnel where it can foul the internal metalwork. I have a minor problem with this where the UJ ears knock on the side of the tunnel under certain conditions, but the noise is a much harder, deeper knocking than the one you describe.

The bellhousing closure plate mentioned by v12eman should be present on all models, I believe. Certainly my S1 3.8 has it.

Good luck tracking the noise down!

[christopher storey]

The first thing I would look at is the dustcovers on the rear drive shafts . This is (approximately) the right frequency, and the noise telegraphs itself over an amazingly wide area , and can be strangely sensitive to load . You can usually see witness marks on the edges of the dustcovers where they have touched the hub carrier

[Heuer]

And while you are there (rear suspension) check the water throwers on the hubs. If one is loose it will ring like a bell.

[timclarke]

Thanks for the thoughts. Have checked the halfshafts and no catching covers. I checked the flywheel closure cover and by pushing on it, it seemed to touch something with less than 1mm movement, so decided to remove it. There is a small drag mark on it but its odd as the flywheel must be at least 20mm in from the edge. One of the set screws was missing so maybe it was the plate vibrating against the bellhousing. Anyway, a test drive today and no noise so will leave it off a while and see if the noise is definitely gone. Will let you know if its cured and what happens when I put the plate back on.