Addo - too late! I'd already got the arm off and back on. As you say, I may regret not thinking of this valuable tip for myself (and I've even got a spare new dog-bone somewhere amongst the bags of stuff salvaged from the Green Lady).
As of last night: Arm off, bush replaced, and arm re-fitted but not bolted-up; no problems with removing or re-fitting the arm, the trick is to move the ARB up out of the way with suspension fully compressed on the other side.
My successful technique was (in summary):
Removing radius arm
Depressurise
Support the front on axle stands.
Wheels off
N.B. Keep all nuts with their bolts, chances are the drop link nuts are coarse thread while those for the radius arm should be fine thread.
Undo one end of both drop links
(If you've got standard (6-sphere) suspension, unclip front dog-bone as Addo suggests - other wise be very careful of the electrovalves!)
Unbolt radius arm N.B. Keep all nuts with their bolts, chances are the drop link nuts are coarse thread while those for the radius arm should be fine thread.
Prop ARB up so that the 'P' bush can we carefully wiggled out forwards and under it. Do not push the ARB further up than it will easily go
Remove radius arm
Removing old bush
Note the alignment of the old bush
Capillary action inevitably draws some moisture into the joint between bush and arm so rust acts like loc-tite!
If you don't have access to an air chisel or similar, cut out the centre of the bush by cutting the rubber with a dry-wall saw or even a deep hole-saw in an electric drill (use plenty of soapy water as lubricant). There's really no way to press-out the bush unless you make a mandrel exactly the right size as the out sleeve of the bush is probably less than 1mm thick.
Collapse the outer steel sleeve with a small cold chisel being careful not to damage the bore of the 'eye' in the arm
Fitting the new bush looked like a complete PITA as there's no space to get the jaw of a vice on top of the bush. To use a press would require a special mandrel shaped like a question mark to go right around the 'P' bush. There is another way that's not difficult:-
Fitting bush
'Tools':
A large ½” drive bi-hex socket into which the un-flanged end of the new bush fits (32mm (IIRC).
If I had access to a lathe
it would have been worth quickly turning up a mandrel like a very thick domed washer: OD same as the machined recess in the radius arm, slight under-cut to hold the bush flange, then a deeper recess the rubber and the sleeve. In the real world:-
- A selection of thick M10 'penny' washers. A couple of Big thick washers with an ID larger than the central sleeve of the bush and an OD no smaller than the OD of the bush outer sleeve. The idea is to assemble a stack that will apply the compression from tightening the bolt to the outer flange of the bush rather than trying rip out the inner sleeve. The problem is the very limited space on the 'inside' of the arm.
A pair of M10 bolts, the longer of the two being socket length, plus twice the bush length, plus about about 25mm nut and the collection of washers. The thread of the shorter must overlap that of the longer by rather more than the thickness of the nut. And its plain (non-threaded) length no longer than the bush plus socket. If the threads are short you might have to use more bolts. Alternatively a length of M10 studding from a builder's merchants or DIY super-store
It's essential to use M10 bolts and a ½” socket to keep the bush aligned.
Procedure
A smear of oil or grease in the 'eye' and on the outside of the bush sleeve will help fitting (and hopefully stop it rusting in place!)
Thick washer under bolt head, then bolt down though ½” square; bolt through eye from 'outside'; bush onto bolt followed by the large diameter washers then a stack of M10 washers and finally the nut.
The next problem is that the outer, un-machined, face of the eye is not at right angles to the bore so it's necessary to pack the rim of the socket at two places with washers of suitable thickness so that the socket is supported at 3 points on precisely the same axis as the eye. You turn the nut only, keeping the bolt head still to avoid moving the socket out of alignment.
Once I'd got it all assembled and got a little pressure on the bush, I found it easiest to then clamp the arm in the vice so that the bush was on top with its axis vertical. This made it easier to make sure the bush was at a perfect right angle to the machine face of the eye. One I'd got it started, I put one drop of engine oil (don't get any on the rubber) in the shallow ring formed by the chamfer on the eye so that the bush sleeve was lubricated as it was drawn down. Then its just a matter of slowly and carefully tightening the nut, constantly checking that the bush is dead square to the eye - the packing washers will distort under load and will need re-adjusting. The secret to success is to not rush it – if the bush tilts, the sleeve will get marked and the job will become a whole lot more difficult.
When the bush has only a few mm to go, make sure that as the bush sleeve emerges from the eye, it won't be damaged by either the packing washers or the socket rim – by this stage, the risk of misalignment is negligible but you don't want to chew up the bush sleeve.
Re-fitting the radius arm
P-bracket bolts: longer one through the ARB clamp with shorter (19mm) nut and thick washer, shorter one with through other hole with taller (18mm) nut and washer.
It's essential that the bush bolts are only tightened when the radius arm is in the correct position see
this post for an alignment diagram. I used a short (330mm) cheapo laser level and a tape measure with a magnetic end to do the measuring with the brake disc(hand-brake on) supported on the jack. Not difficult at all.
I wish I'd ordered some new nyloc nuts - I'll look up part numbers and specifications when I have a bit more time.
