The V8 Owners Forum -

Has anyone ever had a gearbox (LT 77)vibrate at a given speed.

My Cobra has developed an unusual vibration, but only at 55 mph, no other speed.
Wheel bearings are ok. Feels like it's coming from under my bottom when sat in seat.
I have greased the UJ'S on the prop. But not taken out to physically check if stiff.
Box works fine,changes gear easily, I have just refilled with correct oil.
May gland get rear wheels balanced just to rule it out.

I guess I just need to rule one thing out after another which will hopefully leave the culprit.

Thanks Mark.

Does it happen at the same speed in any gear? If so it pretty much rules out the gearbox, sounds like a prop shaft UJ or maybe a balance weight has come off of the prop shaft.

Thanks for the advice.
Happens in 4th or 5th at 55 mph.
Will drop the prop off to check UJ's.
Will also see if there is a local place that can check balance.
Has only just happened.

Mark.

If you put the car in neutral and coast does it still happen?

Are your UJ's set up correctly.

If in phase they can cause this problem.
Have a read on threads like this
http://www.locostbuilders.co.uk/viewthr ... tid=186232

Or
You could have a tyre out of round, flat spot from sitting for a long period or delaminating after hitting a curb / pothole etc.

Ian

Half Shaft UJ on jag axle could cause this.

Check the phasing of the jag rear u/j's to. I've done enough burnouts to put mine 90o out

Update.

It was a faulty rear wheel bearing in the Jag hub. Sent to Wards for refurb.

Mark