Rear Inner Fulcrum Shaft Bearing Tubes - Material ?

[angelw]

Dave wrote:

I was really highlighting that even these tiny items cannot be supplied with a better surface finish as I for one would be be prepared to pay a higher price to get a better quality item - especially on such small items - than settle for a poorer quality item even though I know they will do the job. It just hurts me to fit parts I personally don’t like the look of.

Hello Dave,
Its not the surface finish per se that is the issue, but surface finish in unison with the hardness of the surface; a soft bush, irrespective of how good the surface finish is, won't last long with needle rollers running on it. Even with a hard bush, because the arc of rotation of the bearing is relatively small, you will note that the brinelling is at the 4:0 o'clock to 8:0 o'clock area of the bush (provided that it's been prevented from rotating as it should). A soft bush would pound itself to death quick smart.

In an earlier Post, Steve wrote that he was able to source a bush of the correct ID/OD, but longer than required. If these bushes are of a suitable material, heat treated to provide a hard surface for the rollers to run on, they could be cut to length by either turning, or rough cut to length then finished using a surface grinder. Even if the surface hardness is in the 60's RC, some Carbide, and all CBN turning inserts will cut it.

Regards,

Bill

[44DHR]

Bill,
I understand.
It was not so much the physical appearance of the bush finish that concerned me, but also realising this finish had no treatment to provide a hard surface to interface with a needle bearing. Just wish such a small component could be supplied correctly and not just “near enough” to function.

[Series1 Stu]

Hi Dave

I think Bill has given an excellent analysis of the fulcrum bearings with insightful comment on brinelling and fretting damage.

Traditionally, these parts would have been turned to an oversize dimension, heat treated to required hardness and then ground to size on a cylindrical grinder. This would have produced a near mirror finish, whether it was required or not. This is what you are seeing on the original bearing sleeves, not chrome plating.

Modern hard turning techniques, as described by Bill, negate the need for finish grinding and can produce a surface finish of 1.6 microns or better, which is good enough for this application.

Whether the aftermarket parts are of the correct hardness can only be determined by testing them. As mentioned previously, running a file over them is an indicator but not a definitive one. For that you need to use the correct hardness testing equipment to suit the specification. First though, you need to know what that specification is.

Regards

[mgcjag]

Hi All.....the reason i resurected this old post was two fold...mainly the size difference of the replacement parts being smaller and looser in the needle rollers.....and i mentioned the chrome like finish on the old parts.....not sugesting they were chrome plated.....compared to the far rougher new part.......ideally was looking for a good supplier of quality replacements...Steve

[PeterCrespin]

At the risk of going off on a tangent to this thread, the idea of eccentric bushes for altering the rear camber angle would presumably need some form of locking mechanism to maintain the bushes in their rotated position to move the wishbone pivots outward, if the fulcrum shafts are maintained in their original positions in the rear mounting cage holes ?

If anyone objects to our tangent Dave, you can sine a rebuttal and I'll cosine.

As for chains, I can't break the habit of a lifetime and just turn the sprockets round for one extra chain's-worth. Off-road riding just grinds them to dust and sandracing measures their lifetime in hours, not months.

I've never used wishbone fulcrum bushes but Dick Maury won the JCNA slalom championship a few times with them. Some kind of industrial adhesive maybe, and/or medium interference fit?

[johnetype]

The rear subframe already has eccentric bushes and they are held in place by welds. The bushes that the inner fulcrum shaft passes through on the frame itself are eccentric, no doubt to allow manufacturing tolerances to be zeroed out on a jig before welding them in place.
Remove the welds and you could adjust both toe and camber - in theory. In practice it wouldn't be easy but you could engineer an arrangement that allows you to rotate and lock these bushes in any position.
...and you'd also have to take into account the influence of the dog-bones so not easy.

[angelw]

John Wrote:

The rear subframe already has eccentric bushes and they are held in place by welds. The bushes that the inner fulcrum shaft passes through on the frame itself are eccentric, no doubt to allow manufacturing tolerances to be zeroed out on a jig before welding them in place.
Remove the welds and you could adjust both toe and camber - in theory. In practice it wouldn't be easy but you could engineer an arrangement that allows you to rotate and lock these bushes in any position.

Hello John,
No way is that going to work. What influences the Camber is the relationship between the Half Shaft where it attaches to the Diff via the Brake Rotor, and the axis of the Inner Fulcrum. The bores in the Rear Cradle through which the Inner Fulcrum Shaft passes must be aligned with the bores of the Inner Fulcrum Bracket that attaches to the Differential Housing, hence the shims used between the Fulcrum Bracket and the Differential Housing. Accordingly, whatever you might do with the bores in the Rear Suspension Cradle, at the end of the day they must be made to align with the bores of the Inner Fulcrum Brackets. So to move the position of the bores in the Cradle, you would also have to add, or subtract shims between the Inner Fulcrum Bracket and the Diff Housing. Clearly its going to be easier to add, or subtract shims between the Half Shafts and the Brake Rotors.

Regards,

Bill