Radius arm shims

[Macker2]

I have just changed the bushes and pins on the rear radius arms, but I am not sure what the small round shims in the repair kit are for
There wasn't any on the bits that came off.

[Lord Croker]

I've never seen any such shims, but I did once make some because for some reason, after fitting a new shaft, the arm locked up when the nuts were tightened. Maybe there have been issues with similar problems & the shims are now included.

[Macker2]

Cheers, I thought they might be but wasn't sure if they were to keep a grease gap under the dust seal.

[Spider]

Can't say that I've seen any shims either.

Could you post up a pic? this does have me rather curious.

[Macker2]

No doubt all will become clear when I fit the arms to the car

[ianh1968]

I think that Lord Croker is correct...

Surely these are just to allow for production tolerances?

There are two sets of dimensions which need to be considered here:
1) The overall width of the trailing arm at the thrust washer location.
2) The comparative length of the shaft.

If a new replacement shaft is machined a bit too short, it will pinch up the arm on assembly and it will be not free to operate correctly. The shaft will rotate with the arm and will probably end up undoing the nuts "automatically"... These shims will allow you to set a nominal amount of end-float.

In reality, with an old arm at least, the thrust faces on the arm will have worn sufficiently such that this would not be a problem. In fact, the reverse can happen: the shaft can effectively end up being too long in comparison to the arm. If this is the case, the end-float will be excessive. I have had this problem myself and the cure was to put the new shaft in a lathe and carefully turn a small amount off the length of the main part of the shaft. I think that I aimed for just a couple of thou for the end-float...

Measuring how much to take off is simply a case of assembling the shaft into the arm with the thrust washers and the nuts just nipped up a sensible amount. (If you do them up too tight, you will need to put the shaft in a soft jaw vice to get the second nut off the shaft again). NB, there is no need to actually assemble this onto the car, you can do it on the bench. Use a feeler gauge to determine how much adjustment is required. You will probably find that the end of the arm has not worn all that square either, especially on the outside which is under constant attack from road dirt from the tyre. I simply used a file on the arm face to make sure that the gap was the same all round before I took a final measurement. The alternative would have been to get the machine shop to machine finish the ends which would cost much more in workshop time, whereas the shaft machining is both easy and quick and therefore cheap.

Ian

[Spider]

Yes, I think that the good Lord is correct.

I have had to machine some steps in the thrusts, mainly to compensate for wear rather than machining from the factory.

Were did that kit come from?

[Macker2]

Thanks for explaining. The shims would certainly be handy if the pin was a bit short.
I have nipped the thrust washers up without any shims,while the arms are off the car. Filled up the grease tube and the arms can be moved relatively easily using a double nut on one end. So the fit seems pretty good.
I didn't buy the repair kits off eBay as I have checked my purchase history so I must have got them from one of the online shops.

Thanks again.

[Lord Croker]

What your photos shows is exactly what I had to make on the one & only occasion I ever had a radius arm lock up when tightened, but I'm wondering if they now reduce the effective length of the shaft by a few thou, because I've had plenty of them which have had end float after re-bushing & fitting a new shaft, & to be able to set this up with shims is a lot easier than taking a few thou of the shoulder of the shaft.
Oh yes! Thanks, Spider for referring to me as the good Lord, it's the best anyone's said to me all week

[ianh1968]

& to be able to set this up with shims is a lot easier than taking a few thou of the shoulder of the shaft.

The shims are for if there is no/not enough endfloat, so you effectively increase the length of the
shaft to create some.

Machining the shaft shorter is what you do if you have the opposite problem, ie too much endfloat...
NB: Putting the shaft in a lathe and turning off a few thou is much easier than trying to machine a
recess in the thrust washers. These are both ways of achieving the same thing, but the former is
so much easier/cheaper if you are paying someone to do it for you.


It may well be that the manufacturers now deliberately make the shafts too short and supply shims
for adjustment purposes. That way, if there is EITHER too much or not enough endfloat, the shims
can be removed/added to adjust this out.

[Spider]

& to be able to set this up with shims is a lot easier than taking a few thou of the shoulder of the shaft.

Machining the shaft shorter is what you do if you have the opposite problem, ie too much endfloat...
NB: Putting the shaft in a lathe and turning off a few thou is much easier than trying to machine a
recess in the thrust washers.

I only machine the thrusts (if needed) as I make my own pins - fronts and rears - and they are properly hardened and ground to size, like the originals. All the pins available these days are soft and can be filed. Try that with an original pin. The thrusts are hard but softer then the pins and so machine easy

shimming would be easier again