Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) diff noise

Hi,4/4 Sport 2009 strange noise at speed.I suspect a problem with the diff which I have been led to believe is a lsd.On throttle(drivetrain under load)there is no noise,let the throttle off(again drivetrain under load)no noise,on a very light throttle(cruising at 65/70)the noise from the diff is a loud wailing sound,sounds like metal on metal or tractor tyres at speed on a tarmac road!Apply a little throttle and it immediately goes,as does completely lifting off.Any journey at motorway speeds is a real pain.This is my sixth Morgan and the only one to sound like this.Mrs Anderson is not impressed.Your thoughts would be greatly appreciated.I have tried new diff oil with a friction modifier but this has made no difference.

When did you last change / check the oil level. LSDs need oil with a special friction modifier. I would change the oil as a first step.

Some advice here in GoMog and in Dave's how to section under Roadster servicing

If it happens in a straight line I doubt the LSD is to blame (if you jack up rear of car and one wheel turns the other you have a LSD). As oil change has made no difference a strip down is maybe needed which should reveal issue. Thoughts are poor pinion support/mesh with crown wheel.

Without listening to the noise it is difficult to diagnose. Richard is probably correct if that is indeed the source.

Just to throw in a curved ball, is it possible that does not come from inside the diff at all, and is could be due to other issues .The fact that the noise is different power on/power off makes me wonder if the diff (or some other part of the rear axle) is hitting the transmission tunnel (or the top "shelf"?) under power. This will result in a very metallic whirr which will probably be speed dependent. However this theory does not fit the fact that the noise is prevalent on a light throttle.

Have you checked that the exhaust system does not contact the chassis , or bodywork at any point ? Clutching at straws here I admit .

The 4/4 Sport is a wonderful car, in many ways truer to historic Morgan DNA than any post 2000 model, and I am sure this can be sorted.

To give some consolation, should it be a problem with the diff, and assuming you are a spirited sporty driver, then it would be an opportunity to upgrade to a 4.1 final drive if you had to pay for the repair anyway. I would love to do it, but my BTR diff won't allow a change. Your 2009 Salisbury axle does though.

Have you checked for play in the wheel bearings ?

Check the rear suspension where the brackets fit onto the wheel drum. They can shear off

4/4's don't have an LSD as standard, unless the Sport spec was different ?

Sounds like the drivetrain rubbing on something, check for play in the UJ's, is the handbrake outer catching on a propshaft flange, also look at the engine mounts if the rubbers gone off in one side it will shift as described with power on / off

No the Sport was conventional diff - I had one from new in 2009.

This one could have been interfered with of course..

Some pinions have a preload with a collapsible spacer behind the drive flange. I'm not sure if the BTR axle is like this, but I would drop the rear of the propshaft, and check the tightness of the pinion nut. Don't Tarzan it. Just a gentle nip with a ring spanner so you can see if it turns. If it has loosened, a blob of loctite should hold it.

Before doing that, the Sport doesn't usually have a tool tray, and the ply cover may be glued down, but I would remove the cover, and go for a drive with the roof up, and a passenger who can lean over and do a visual on the rear end.