Vibration- Ideas please

[Errol62]

Prolly best finish assembling and bed in the new suspension first I reckon Drew


FB ute fixer upper, EK van on rotisserie

[ardiesse]

I'm making this up as I go, but -

instead of installing wedges, would it not also be possible to get the rear springs reset in such a way that the front part of the spring has less curve, and the rear part of the spring has more curve? This would have the effect of rotating the spring pack where the rear axle attaches.

But I'm trying to imagine explaining the idea to a spring-maker . . .

Rob

[fraze]

Hi Harv, interesting concept to reset the springs to achieve correct drive line angle. Doable of course but wow, the calculations to get the correct angle, then getting the spring guy to work to those dimensions does my head in. I will stick to wedges. Putting packers under the lower spring plates was a short term fix to prove a concept. With the weight of the diff, resilience of the rubber insulators etc I think the diff would quickly fall back out of alignment. I have ordered wedges for both cars, 70 x 110mm for the ute and 60 x 110 for the sedan . The bloke at Steel Wedges was very helpful and worked out that wedges tapering from 6mm to 0.7mm would give me my required 3deg angle. These wedges will be installed on top of the springs between the pad on the axle and the insulater. Once I get them installed and aligned correctly I will tack weld them to the axle spring pad, so that we don’t get any for and aft movement of the axle. Interesting that both cars had the diff angle 3 deg down, compared to the gearbox shaft. I am wondering if it is to do with the Rare Spares engine mounts which I have in both cars because that is the only thing changed from original.

[EK283]

The engine mounts could be different heights, smaller, taller etc.

The other thing that can have an affect is soft rubbers around the spring that let the diff increase in angle as you drive.

Also the springs do sag over time and what may look normal is actually lower in stance, especially the rears.

If you measure your tailshaft from one side to another you will also notice that its not in the centre so there is already offset in the unis so any deviation from the original heights and angles start to take affect.

Its really good to hear that that issue has been resolved Fraze, there's nothing worse than chasing a problem only to come to a dead end.

Greg

[Blacky]

As I mentioned in Clays post , I am setting up a Torana diff for my mate, we ground
all the brackets off yesterday and set it up in a diff jig we knocked up - put the stock diff in it first and measured the pinion angle - it’s 5 degrees up on a standard diff with the spring saddles level





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[FbSTDwagon]

Fraze if you are still casing the weird vibration I have another suggestion.

It’s a far shot but it may be worth checking the fron hub and rear axle faces to see if they are running true.

Set up a dial indicator and spin them, the reading should be too far out but if something is bent it should show up.

[fraze]

Thanks for the suggestions Drew. However i have solved the vibe problems on both my FC sedan and FB ute by lifting the nose of the diff on both cars to closely align the diff pinion shaft angle with the gearbox output shaft angle. Very satisfied. I did along the way check the axle mounting flanges and found that one of my axles was out a bit so I removed the wheel studs and machined the flange flat again. i have two spare axles and with both of these the flanges are distorted also. Wonder how? Cheers Fraze

[Harv]

I have two spare axles and with both of these the flanges are distorted also. Wonder how? Cheers Fraze

Silent coppers. Hitting one of those at speed will lift the front of the car off the ground. Don’t ask how I know

Cheers,
Harv