Club 80-90 Forums

Food for thought....

I could make that...no maybe not... what's that bar off.. Looks very familiar.

Little bit of layman's applied maths/practical physics, brace yourselves...

ARB's generally work best with the links working at 90 degrees, viewed in side elevation i.e at kerb weight, moderately loaded. Small variations due to load (at the front of the vehicle) don't make a big change to the working angles, so the effective leverage (or apparent stiffness of the bar) stays much the same.

So far so good.

But this only truly applies if the links are also working at 90 deg. when viewed in plan. If the ARB's arms splay out and a vehicle is lowered or raised beyond the manufacturers design limits, the geometry start to go awry. The links may also be working at compound angles and also subjecting the working lever end of the ARB to torsional forces as well as leverage (there is a transition from torsion to bending throughout the bends at each end)

Now as the angle of droop increases (pos. or neg.) the effective lever arm length starts to become shortened, making the bar seem stiffer than it really is (think what it would be like if the bar ends were hanging straight down: Lever arm length = zero, with the bar only subject to bending of the unsupported ends, from link to clamp. Stiff as hell, but no torsion at all!)

This is how adjustable ARB's work, they have rotating "blade" ends that vary in stiffness from horizontal (full soft) to vertical (full stiff)

Suspension forces are massive and are quite capable of bending the apparently unbendable. Any rubber components will get deformed quite dramatically but since rubber is inherently rising-rate (more force for a given deflection) it can also transmit a lot more force. That's why Polybushes are great for some racing applications i.e. where a small amount of deflection is desirable/tolerable i.e. to improve component life and give a degree of occupant comfort.

Then again, it could just be metal fatigue or a manufacturing fault in an end-of-run component. Quality control does tend to fall off at the end of a production run, so that might be a contributing factor too

v-lux wrote:Food for thought....

was it the pink bushes that cauht your eye Al ? Ye big gayer

Red and blue! How patriotic...

Something else occurred to me that might be a contributing factor to the ARB failure:

Halfshafts that have been used on one side of a vehicle (and this applies to torsion bars too) do NOT like being subject to reversed stresses. They often fail soon after fitting to the opposite side, loss of drive not being uncommon just after reversing out of a parking space.

Could it be that ARB's that have been conditioned to being stressed at particular angles (i.e. standard ride height) could fail due to the increased/different forces being put upon them as a result of a lift?

Lowered vans probably don't suffer this failure since they are so much stiffer sprung and have far less suspension travel.

I do like pink.....

better than brown

I like a bit of both myself...

max and caddy wrote:I like a bit of both myself...

Same here but they must be very close!

Ian, have you a degree in the bleedin obvious?

syncropaddy wrote:
Ian, have you a degree in the bleedin obvious?

No, but not everyone has had the benefit of a classical education, old chap. It's good to share