Vibration from drive train somewhere over 100 MPH+

[620Rapid]

Hi all

Took My 620R to Snetterton Thursday just gone, which is the first time I've driven it hard and at all really since purchasing it back in November where she's sat on trickle charge in garage until this trackday. 

First problem I noticed was engine miss firing at higher revs which seemed to clear and sort itself out as day went on.

But more worryingly was the vibration coming from somewhere near my backside when approaching 100 MPH and above.

Did jack rear end up to have look around, only thing I could see was small weep of Diff oil coming from near side drive shaft entry point and LSD Aluminum casing was very hot but guess/hope this is fairly normal?

Oil leak from Diff never got worse throughout the day or even made mark/drip on tarmac where it was parked while not on track.

Anyone have ideas on what could be cause of vibration would be much appreciated.

My own theories are out of balance propshaft or problem with LSD?

Thanks

Steve

 

 

 

[Tony Whitley]

Check the propshaft UJ's for play.

[mic]

Check the diff mounting bolts, especially the lower right one.

 

[Drakman]

Check also the alignment of the prop/tailshaft in relationship to the gearbox and diff.  The shaft should be in line with the diff pinion gear shaft and the gearbox output shaft.  The pinion shaft and gearbox output shaft should be parallel with each other.  I think they make a spacer plate to go under the rear gearbox mount if the gearbox is tilted down.

 

[ScottR400D]

#4 That would be true in an ideal world but unlikely to be the case in fact. 

Duratecs in 7s normally tilt forward to get the engine to clear the hood so the gearbox tail is upward relative to the prop. I assume the 620 isn't an exception. 

My diff also tilts downwards towards the front (possibly to achieve the parallel situation you quite rightly say is desirable) but it tilts at a slightly bigger angle then the engine/box! 

When the Great LSD Thread was alive this was discussed at length and several of us found the same thing, though the variance from parallel was well within the point that would cause an issue. 

So, certainly worth a check but don't expect to find all is exactly parallel. 

[blueyedbiker]

I'd check the rear wheel balance weights first.

[7 wonders of the world]

also check for missing balance weights on the prop shaft (plates spot welded on) that may have come adrift