Vibration on frame

[keithmac]

Hello all,
It seems I get one difficult problem solved and another overlaps it. Still waiting to properly drive this car after three years ! The latest mystery issue is moderate grinding/vibrating ( something is knocking against the underside near the gearbox ) . This happens in the lower gears on take off and disappears quickly as revs build.
Here is a picture of the rear engine mount. Should this washer not be hard against the mount plate ?
Could the spring be broken causing the pin to vibrate against mount plate with the torque of low gear twisting?
I will have to drop the exhaust , support the rear of the engine and drop the rear engine mount just to check it.
Or....is this the normal position of this washer ????
Keith

[mgcjag]

Hi Keith...the pin and washer should not be on the rear mount....it is just an assembly/ transit aid.....by haveing the pin in place it does not allow the gearbox the movd up/down on the spring.....Steve

[abowie]

Once you have taken the pin out check the manual to ensure you have the engine stabiliser correctly adjusted as well.

[ralphr1780]

If the pin has been there for some time, the rubber mount would have been compressed soaked in oil and should be replaced.
Getting the pin out is not easy, you will need to figure out a way to pull the gearbox further down to release it. Watch out as the spring is very strong.
Don't ask me how I know...

[keithmac]

Thanks Steve and All !
Pin and washer removed. Only took half an hour a stiff neck and some skinned knuckles. A bargain by this Jags usual fee. Test drive next.
Rubber spacer and seats were in good condition two yrs ago on engine placement but I now have new synthetic ones for a winter project.
I will be careful of the spring Ralph as I remember putting it on the gearbox. It was a bear.
That pin has been on there for decades. The mystery is why it did not cause a rattle last year. Mind you due to numerous problems I only have 700 miles since the rebuild.
Cheers All

[keithmac]

Test drive over
better but far from gone. I will remove center console , gear box cover and test/ listen and see what Ican find.
Its the rear mount spring or spacer, the speedo take off or the drive shaft universals i would guess.

[Mich7920]

Hi Keith...the pin and washer should not be on the rear mount....it is just an assembly/ transit aid.....by haveing the pin in place it does not allow the gearbox the movd up/down on the spring.....Steve

Hi Steve,
Sorry but did I understand well that there is no pin when the car is on the road ?
Thirty years ago I received the car with the same assembly as Keith and I have rebuilt it until today.
Mich

[mgcjag]

Hi Mitch...yes as in the diagram i posted above there should be no split pin fitted....by fitting a pin it does not allow full up/ down movement in the mount......Steve

[ralphr1780]

Keith, in your last pic we can clearly see the removed pin location: which means the spring is not much compressed at rest.
With a healthy spring/rubber combo you should not be able to see it.
Don't know how to express it more clearly, to me it seems that the spring/rubber combo has sagged a bit and the gearbox is still bouncing more than it should and causing still rattle.

[keithmac]

Hi Ralph ,
Do mean to say the spring rubber combo is TOO much compressed at rest ?

[ralphr1780]

Keith, no you cannot over compress at rest.
The fact that the slot of the pin is visible means that the rubber/spring combo height is less than what it should be. I doubt it is the spring that has sagged. But rather most probably, due to the long excessive compression with the pin fitted the spring has dug deep into the rubbers, helped by some softening oil of course.
Did you remove the plate and check the condition of the rubbers?

[keithmac]

So found two interesting things. A weight has fallen off the drive shaft. Found it while reaching blindly at the back of the shaft and the speedo take off has been hitting the tunnel. Tried to shift the lump 1/8" after loosening all the mounts-no dice. Was able to wedge a bit of old inner tube rubber in there . Looks like this has been a bother before as the metal has been well bashed in that area in the past.
Guess I will be dropping the rear end AGAIN !

[abowie]

It may be the photo, but the whole back of your gearbox seems to be shifted to the right. Regardless, don't take off any major bits yet.

I'd check your engine mounts to ensure they're not skewing the engine off to one side. You can loosen the main bolt, then the two small bolts that hold the mount to the pad on the engine frame and see if you can lever the back of engine over to the left. loosen off the rear engine stabiliser before you do this.

Try removing your angle drive, give it a good clean and then see if you can get it to mount any closer to the gearbox. Try rotating it to see if you can get additional clearance; there should be some slack in the cable.

Finally, just relieve the tunnel with a bit of judicious peening or a lever so it clears. You could put a huge dent in there and it'd be invisible in the cockpit.

If all of this doesn't fix it, then think about removing your tailshaft and having it rebalanced.

[keithmac]

Found "THEM"
Noise #1 : exhaust down pipes hitting each other , reverberating through whole exhaust system ( two header bolts are stripped allowing them to move into contact under load )

Noise # 2 : Left rear tire rubbing on bump stop under acceleration load making zzzz..zzz..zzz noise at the same time as the exhaust pipe rubbing.

The combination was a bit of a racket. She is quiet and smooth now
Hopefully this helps someone else

Cheers All !!

[rswaffie]

Good news, enjoy your clunk-free driving!