How not to: Propshaft balance weight replacement

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thetim

Well-Known Member
Posts
379
So...
I'm swapping my Discovery 300Tdi's 3-bolt rear propshaft for a 4-bolt. However, on arrival, the balance weight on the 4-bolt prop looked like this:

Propshaft before.jpg
Not great. Rust had got to it such that part of it was missing and the rest was flaky. I didn't want it coming away and causing a vibration that would trash my differential pinion seal and possibly bearings. If it needs it, I'll send it away for balancing, but I figured that I could probably achieve an acceptable level of out-of-balance simply by replacing what was there with good metal. So I marked and measured the old weight, and then prised and chiseled it away, catching it all in a plastic bag. No power tools - I didn't want to lose any of the rusty weight in the process.

Bag of rust, on scales:
Propshaft rust.jpg Propshaft weight.jpg

I guestimated that that weight represented perhaps 90% of the original balance weight. Mild steel has a density of about 7800kg/m3. 1.5mm thick steel sheet delivered the required weight at close to the original 50mm x 40mm size of the old balance weight:

Propshaft new weight.jpg

Then I needed a means of welding it to the shaft. I didn't want to add extra metal in the process, so I drilled some holes in it to plug weld through, before bending it to match the curvature of the shaft:

Propshaft new weight drilled and shaped.jpg

Then I welded it in and ground off any excess metal:

Propshaft weight welded and ground.jpg

Finally it all got a coat of paint ready for fitting.

Propshaft sprayed.jpg

It won't be as well-balanced as a new shaft, but it should be as well-balanced as when it came into my possession, with the added benefit of being balanced with steel rather than rust and hence standing half a chance of holding together for a while without further deterioration.
 
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Good thinking and nice work.

I'm going to search YouTube for clips of over-spun balance weights flying off now. I wonder what damage they'll do :rolleyes:
 
Good thinking and nice work.

In the 'old days' when transmissions weren't as refined as now, some degree of balance could be achieved by clamping jubilee clips around the shaft with the 'worm' in the appropriate position.
Just showing my age ;)
 
Yes - I guess that's coming at the problem from the other side, i.e. adjusting the correction until balanced. As I know where the old balance weight was, I could add and remove jubilee clips until the shaft was acceptable, then apply the required correction more permanently as a welded on weight. I'm hoping that my approach will deliver acceptable results on a "right first time" basis but haven't run it yet...
 
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Took it out for a run (the rest of the propshaft swap was a mission, in summary, if Bearmach or Britpart can make it wrong, they will - but you knew that) - seems fine, no vibrations. Hopefully this is happily ever after, until the next thing breaks.
 
Six month update - seems to be behaving itself; the vehicle's hardly quiet and refined in any case but there are no obvious signs of the drive line bearings dying. At least, not yet!
 
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