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Vibration above 70kph - Mk2 Cortina


PHLEX

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Hey guys,  got my cortina back on the road after 2 years of rebuilding and restoring.  When I first got it I drove it a few times and it cruised at 100kph fine.  

It's now warranted and registered so I've been driving it round a few times a week and at 70kph onwards it has a vibration that shakes the whole car, feels like it's coming from the gearbox as the stick viabrates but if I turn the engine off with the clutch in at 100 and let it coast down to 70 it does it the whole time. When I have my foot on the power and it's pulling up to speed it's not as noticeable but as soon as I let off the gas it shakes the shit out of itself.

 

so far we have put in a known good spare diff, swapped to known good rear wheels and tyres, replaced front tyres with brand new ones, checked suspension is tight in front and rear, checked driveshaft universals by prying against them.

 

anybody got any ideas? Driving me mental as I just want to be able to enjoy it! 

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Obviously you've balanced the wheels. Some of the symptoms sound a bit like my wife's Laser when it dropped a couple of balance weights. Of course she didn't notice just like she didn't notice when the back shocks were fucked.

That doesn't explain the gear stick shake though.

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Hey bud, I had the exact same problem on my cortina a few weeks ago and I was worried it was gearbox too but I took my driveshaft (which looked mint and so did the universals) to a driveshaft place for a balance and universals replaced and said said it was way outta bal and the joints were screwed. Mint as now. Give that a try. I paid about $285 to get it done.

 

Cheers Cam

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angles between gearbox and diff look good, checked U bolts and they are nice and tight, Engine mounts were in good condition when installed, being a 71M in a Mk2 i had to use one long and one short mount to get the engine on the correct angle but that shouldn't make any difference. Im going to pull the driveshaft out today and check the universal joints, I have had a ute with a very worn UJ before and that caused a similar fault 

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Update:   Pulled driveshaft out, found a very small amount of side to side play in the front UJ.  put in a friend's known good (but off the road for 2+ years also) driveshaft with no play and the vibration is still there.  Also found minor up and down play in the FR wheel bearing which I adjusted but no difference there.

Yolk is 1/2-2/3 of the way in the gearbox at the current ride height and will obviously push in a bit more when its lowered so I don't think that's a factor although there is very slight up and down movement which I put down to the shaft moving slightly.

I am going to replace both universals in my original driveshaft just to be 100% sure that there wont be any future issues.

Does anybody have any other ideas of what it might be?  I do have a 1100cc flywheel on it as its lighter but I wouldn't have thought that would give me a speed related vibration. I do have the standard flywheel I can put back on if I cant work it out

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Stock cortina driveshaft, converted from column shift to floor shift, standard ride height and the driveshaft angle is almost perfectly straight. Driveshaft is far enough into the gearbox to rule out yolk wobble. There is some movement up and down on the output shaft in the box but it doesn't make any noises to suggest its blown

On a side note the only other thing I have changed since I drove it without fault (over a year ago) was I pulled out some modified rear springs (top leaf was standard and lower two were from an escort sport) out and put some stock units in, one end had new bushes the other had standards, could that make a difference?

Picked up a UJ to check for correct size and will order another tomorrow if its the correct one. Might as well do them to rule them out

Tempted to take it for a rope tow down the motorway without a driveshaft in to rule that out completely

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Front/rear shock absorbers OK?  At higher speeds the smallest of imbalance in the wheels/tyres and stuffed shocks will make the wheels almost jump up/down causing vibration.

Get someone to drive behind/beside you and observe the wheels/tyres(both sides) at the speeds the vibrations happen to eliminate this.

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Since the problem started with the change in springs I would be checking the diff angle. Use a proper gauge (I have seen people use the built in angle gauge on an iPhone) and make sure that the gearbox and diff are parallel. It is amazing how 1 or 2 degrees of miss alignment will make things vibrate.

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