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Vibration issues


Doof

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I have had my GBS Zero (Ford) dyno tuned by Northampton Motorsport today and they alerted me to a bad vibration in the car which may point to drive train issues - possible gearbox/prop/diff/drive shafts alignment or balance problems.

Apparently, it behaved pretty badly at the top end (clearly, speeds greater than I have taken it on the road thus far since my late Nov. 2020 IVA pass and thanks to Covid, weather etc.)  

Has anyone any experience at where I might start my investigation first?

I know my engine is a few mm off centre in the chassis (checked this out with GBS during the build) and I feeI I have been really spot on with everything, believing (perhaps naively), that the prop shaft Universal Joints would deal with minor angle/phasing differences between the gearbox and the diff.

Would appreciate any wisdom please as I am just feeling a little frustrated when my hopes were that I could finally get to drive the flipping thing rather than have to take it all apart again!!!

Thanks in advance.

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If the car has been standing for a year have you had the tyres off the ground they could have flat spotted with standing, get wheel balance checked could have just lost a weight, do a nut and bolt check from the bellhousing through to the back wheels, check prop-shaft u.j.s, get the prop rebalanced. I would check one thing at a time and then try the car to eliminate as you go. Hope that helps you find the problem.

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I had a similar problem years ago.  My diagnostic route was chock the front wheels and put the back of the car up on axle stands.  Spin up the wheels and see if you still get the vibration.  If you do, take the wheels off.  If it's still there, take the half shafts off to the diff.  If its still there, take the prop off.  If it's still there are that, then the only spinning components left are the gearbox and engine.  I would guess at a problem with the clutch / flywheel at the point as the heaviest rotating mass.  One change at a time and you'll be able to figure out what the route cause is.

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I had a vibrating steering wheel at+70. I lifted reach wheel of the ground so it clears the floor by a few mm and spun each wheel. I've of the front tyres would still before a full Revolution. It's was the dreaded over winter flat spot on the tyre.

Hope yours is as simple Andi

 

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Many thanks Alan

I had planned a nut and bolt check, with the car having now covered just over 100 miles, but will also work through the other checks you have suggested (not sure how easy it will be to get the prop out - MT75).

Fingers crossed something will reveal itself via a process of elimination!

Kind regards

Geoff

 

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Cheers Andi

Yes, wheel get wheels/tyres checked first as most of you have suggested including Troy at Northampton Motorsport, however, he qualified this by saying in his experience of many 100's of tests, he did feel it was likely to be conflicting gearbox/prop/diff planes/angles that were likely to be causing it!

Regards

Geoff 

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Cheers Andy

I wondered about flywheel (as I have changed it to the lightened kit from GBS), however, Troy at Northampton Motorsport said he would have also expected to experience issues with the clutch if this was the case, yet that all behaved fine.

Regards

Geoff

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I think that the off center is not a problem.

The Exmo and series 3 ( and probably more RH cars) had the engine offset a couple of degrees from straight to give more foot room in the drivers foot tunnel giving more room round the pedals.

the front of the engine is nearly central but the gearbox mount and transmission tunnel is displaced left so the engine/gearbox is not strait. This does not cause vibration problems.

A lot of production cars did not have a straight power line and did not have problems with vibration.

I have had problems in the past with out of round tyres, easy to check, jack the wheel up and spin it whilst observing the tread of the tyre for even rotation.

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