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Strange Noise from Underneath - Tattybogle - 02-04-2019
Gentlemen,
Something to exercise your little grey cells!
My 1932 RN is fitted with late Girling axles front and rear and a 4-speed box with Hardy Spicer propshaft.
Lately I have noticed a strange noise from under the car that seems to only occur when the engine is pulling hard, say up a hill, often in 3rd gear. It sounds like a muffled dull knock, as if the floor is being struck with a hammer from underneath.
It doesn't always happen, but when it does the timing between the sounds can be one second or as much as five seconds. I usually back off when it occurs because I don't know what it is nor what damage may be caused. The car otherwise drives normally although the CWP sings at 30 - 40 mph on light throttle only, never on the overrun or accelerating.
The gearbox and rear axle have been rebuilt with all new bearings.
I think the propshaft and joints are OK, but I haven't pulled anything apart yet.
Your collective thoughts will be greatly appreciated. Thank you!
RE: Strange Noise from Underneath - John Mason - 02-04-2019
Does this happen when you accelerate hard and the torque tube is slack on the adjustment causing it to bang on its adjustable fixing.
John Mason.
RE: Strange Noise from Underneath - Chris KC - 02-04-2019
Can you feel it or only hear it?
Worn universal joints rattle, I don't think you'd mistake them.
RE: Strange Noise from Underneath - Tattybogle - 02-04-2019
Thanks for both contributions. I THINK I can feel it as well as hear it, but I have always been sensitive to mechanical irregularities and cannot be sure.
If I didn't know better, I'd suggest it was a tooth jumping in the diff, but I am sure it cannot be that as it would happen more often and not be just the one tooth. I've never heard of that happening anyway.
RE: Strange Noise from Underneath - Chris KC - 02-04-2019
Inclined to agree with John but very hard to say without hearing it.
RE: Strange Noise from Underneath - Reckless Rat - 02-04-2019
Perhaps, given that you say the rear axle has been rebuilt that perhaps the torque tube mount hasn't been correctly set up after reassembly. When you say you can feel & hear the knock, is it coming from under the floor behind the seats or from the bulkhead? The only other thing I'm thinking about is the front crossmember/radius arms ball joint, the rivets mounting the ball to the chassis can become loose. One last possibility is a road spring knocking on the underneath of the body - you'll be able to see if this is happening if you jack the car up, remove a rear wheel and look to see whether the leaf clamp has been contacting the tub - there'll be a mark. (ask me how I know that - anyone got a pair of Nobbies they don't want?)
RE: Strange Noise from Underneath - dickie65 - 02-04-2019
Take the cover from transmission tunnel by the handbrake and go for a drive with a passenger to look down at the propshaft beside the handbrake.
Its not unknown for a propshaft to tap the handbrake mechanism.
You should also be able to take the grease point cover from above the torque tube and do the same.