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Vibration Again
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Trevor



Joined: 04 Feb 2009
Posts: 8

PostPosted: Sat Apr 04, 2009 8:58 am    Post subject: Vibration Again Reply with quote

Hello all
Morris 1934 10/6
A couple of months ago I put it into my restorer/mechanic and asked them to tune the car and have a look at the engine, which seemed not to have a great deal of power. At the same time they were to fit a pair of gearbox mounts as, they said, the old ones had started to de-laminate.

This was all duly done and I received a call asking if I knew about “the vibration” – it turns out that the car when under load suffers from vibration through the steering.

They suggested that it could be a prop shaft problem – consequently they replaced one of the fabric couplings – but it made no difference.

They then took off the prop shaft and discovered that the “nose” which sticks out at the front was partly broken off – they managed to find me a replacement prop shaft, which was duly fitted –the vibration still occurred.

They now feel that the problem must be with the gearbox and it is only when in 4th gear. Vibration disappears when car declutched or freewheeling and does not occur at the same speed when in 3rd gear.

They say that the issue has been made more noticeable because the gearbox has now been firmly mounted to the chassis with the new mounts – the vibration may have been dampened out by the rotten old gearbox mounts.

If the problem lies in the gearbox the gearbox will have to be removed – that will probably lead to work having to be done on the clutch – and if that is being done why not take the engine out and re build that at the same time, as it is knackered.

Not surprisingly I am concerned about the cost of all of this and wonder if anything strikes any chords with any of you and your experiences.

As always any comments gratefully received.

Best wishes

Trevor
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peter scott



Joined: 18 Dec 2007
Posts: 6201
Location: Edinburgh

PostPosted: Sat Apr 04, 2009 10:07 am    Post subject: Reply with quote

Hi Trevor,

If the vibration is altered by changing down to third then I would doubt that it has anything to do with the gearbox or transmission. I think it's much more likely to
be an engine vibration. If you gradually increase the engine revs with the car at rest and out of gear does the vibration appear at certain revs?

Peter
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1939 SS Jaguar 2˝ litre saloon
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victor 101



Joined: 03 Apr 2009
Posts: 449
Location: East Yorkshire

PostPosted: Sat Apr 04, 2009 2:47 pm    Post subject: Reply with quote

I'm not conversant with the Morris 10/6, so this is a stab in the dark. If the engine and transmission are close to the steering coloum/box/links etc, if the engine mounts are a bit weak, then under power it might just rock the engine enough to touch, giving a vibration through the steering.
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Keith D



Joined: 16 Oct 2008
Posts: 966
Location: Upper Swan, Western Australia

PostPosted: Sat Apr 04, 2009 4:01 pm    Post subject: Reply with quote

Trevor,

Being a cynic, it seems to me that your restorer/mechanic is playing the old "let's built this up into a major reconditioning job" game. It would seem pretty obvious that he really doesn't have a clue what is wrong with your car.

I'm not a mechanic, but like Peter I don't think it is anything to do with the gearbox. Perhaps with the new gearbox mountings, the gearbox is fractionally higher and is touching the chassis or similar and causing a sympathetic vibration. Perhaps your harmonic balancer is breaking up. (Being a 6 cylinder engine, I presume it has one) This would cause a vibration that varied according to the engine speed. It could even be a missing fan blade.

Check out the new fabric coupling. If it is a home made one, they are notoriously difficult to install accurately .i.e. with everything in line and balanced. Maybe you need to securely block the rear axle on secure stands and run the motor slowly in gear. DON'T get under the car, but check it out from the side, WELL CLEAR! That way you can see how true the tailshaft is turning.

I think that you are just going to have to persevere and spend a weekend trying everything you can think of and what is suggested on this forum.

Good luck! - Keith
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baconsdozen



Joined: 03 Dec 2007
Posts: 1116
Location: Under the car.

PostPosted: Thu Apr 09, 2009 8:53 am    Post subject: Reply with quote

As free wheeling or running at the same speed in third gear doesn't cause the car to vibrate I wonder if this is 'sympathetic' vibration.
Sometimes fitting new,harder gearbox or engine mounts causes the normal vibration of the engine to be transmitted through to the chassis at certain frequencies.Sometimes this causes a part of the body or some other fitting to vibrate in sympathy,if the revs stay fairly constant the two vibrating assemblies 'excite' one another and the vibration increases in amplitude.
If,this is the case you have to try breaking this cycle.
On my old transit a 35mph the whole floor vibrated,I'd had the prop balanced but by putting a jubile clip on it and turning it round I was able to damp out the vibration.
Altering the angle of the engine /box assembly,harder or softer mounts,turning the prop through 180 degrees are all things that can cause vibration and all things that can be tried to cure it.
Best of luck.
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