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No, not the beach boys and no they aren't good good good good vibrations either.

I swapped motors into the old girl last weekend. Bolted the exhaust back up and the engine pipe had broken around the flange. So I got a whole new system made up and went to put it on and of course it fits like crap. Its currently held on with welding wire and coat hangers. So this morning I drove it down to the exhaust place to have it sorted out.
And you guessed it, at 55mph the car was shaking like Dolly partons boobies in a running race.
I'm hoping its the exhaust causing the vibrations but the new motor has a different harmonic balancer on it too.So maybe that too I suppose???
Bloody cars!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

John, when I first bought mine it had a hideous vibration (plus noise) at roughly 40-50mph , though mine was more rev based as it did it at slower speeds too depending on what gear I was in .

it turned out I was missing the rubber on the exhaust mount that sits about halfway along the car.

Hi John,
not discounting the different/new harmonic balancer as an issue but I would check to see that ne muffler is consistent in design/dimension to the old one it replaced. I have seen resonate harmonics induced in the drive shaft by a muffler that was located to close to the shaft. The muffler and system was also larger than the standard one it replaced. This used to be somewhat negated by hanging sacrificial floating rubber blocks on the exhaust system at the required points. These blocks would vibrate and absorb transient vibrations but I think they were about as effective as Brocky's Polariser's!

Thanks all for the advice.

Ok, new system on, standard, all the way through.
At 55 MPH it vibrates bad, and go faster the worst it gets.
I push the clutch in and its still there, so that means it HAS to be from the gearbox back?? (Considering I replaced the motor and took the box out at the same time) I'm thinking maybe the rear uni /tailshaft issue??

Check the rear uni is seated properly, I had that problem with a HX van once ......

As Blacky said, check the unis.

John wrote:Thanks all for the advice.

Ok, new system on, standard, all the way through.
At 55 MPH it vibrates bad, and go faster the worst it gets.
I push the clutch in and its still there, so that means it HAS to be from the gearbox back?? (Considering I replaced the motor and took the box out at the same time) I'm thinking maybe the rear uni /tailshaft issue??

Ok that helps a lot more knowing it vibrates when not under power.
If you cant find an issue with the uni's, get your drive shaft checked for balance. You may have had a weight that has come off (rare).
While its off check your pinion for radial play. These diffs were noted for pinions coming loose after the wore a bit. Usually as they lost the preload on the pinion bearings overtime (solid bearing spacer) they would start to wear the bearing shims down till they disappeared into the oil! After that the bearings would start to go and you'd end up with some radial paly and a lot of backlash. Get a tension wrench on the pinion nut and if you find it loose or it tightens up substantially you may need to look at doing the bearings in the diff centre. Don't forget wheel balance and weights that might have come off too!

Spot on guys. When you tighten the nuts on the uni make sure you do all 4. Not 3.
65 miles per hour and not a vibration in sight

That's a win