Classic cars forum & vehicle restoration.

[rcx822]

Are they called bushes or bushings? I never know.

I've dismantled my suspension so that the parts can go off for zinc plating. The car is fitted with aftermarket poly bushes all of which are the type you see in the photo below (click photo to enlarge). Two mushrooms with a steel insert inside.



Most of the steel inserts are seriously corroded. Some are now very uneven, some are loose in the bushings and some are tight.

I was thinking of getting new inserts made up in stainless steel. How tight should the inserts be within the poly bushes?

And which is the friction surface which moves when the suspension pivots around a bush? Is it:

(a) the surface between the bolt and insert?
(b) between the insert and inside of the poly bush?
(c) between the poly bush and the metal of the suspension link it's inserted into?

[Bitumen Boy]

I always though the point of either poly bushes or the rubber bushes they replace was that there isn't any friction surface at all - movement is taken as flexion of the bush material. AFAIK the two-piece design of bushes with a separate steel insert such as the one pictured is something of a fudge to make them easier to fit - all the OE rubber bushes I've come across have been in one piece with the rubber bonded to the steel.* However, people who've bought decent quality poly bushes - which generally make a point of having stainless inserts, these you have are probably fleabay fakes - seem to be happy with them, and given the lamentable quality of rubber items in the classic marketplace these days I'll probably end up going down the same road eventually.

*However, it's worth pointing out that Triumph specified top-hat bushes with separate inserts - originally in nylon, and something else again with benefit of experience - for front and rear trunnions on the Herald (and its derivatives) right from day one. These do seem to have been intended to take friction and certainly do so in service as in example (c).

[MikeEdwards]

I think the reason for the two-piece is to make it possible to fit them - there's so little "give" in the material that it probably just wouldn't go through with any kind of lip on it.

There's one make of poly bush that doesn't use stainless steel tubes, and it looks like this is it. I'm pretty sure Superflex do use stainless, as I think it's them that point to another make using mild steel as a marketing point.

The whole way they work is different, though, because it's now pivoting. In many cases the centre bolt should be tightened up so that the inner tube section does not rotate, friction should keep the outer (whether it's sleeved by steel or not) from moving within the suspension part, and the only pivoting should be due to the "give" in the rubber. This is why when torqueing up suspension bolts, the weight should be on the car otherwise the rubber is under stress all the time. With a poly bush where the centre isn't bonded, all of a sudden the pivoting works very differently.

I am not a suspension expert (please, keep your "obviously.." to yourselves everyone) but this doesn't sound great, although I've no idea how it would affect anything. I don't drive my car in a way that it would make any significant difference, but I have tried to stick to rubber bushes where I can get them.

[badhuis]

A big negative aspect of using poly is that the damping function of rubber is gone. Which means a harsher ride, and possibly a lower life expectancy of the suspension and steering components. These components have been designed with the cushioned effect of rubber in mind. If this effect is taken away, it might gave way to fractures of other components.
While I can see the virtues, sharper steering and suspension, if proper rubber is available I use that.
_________________
a car stops being fun when it becomes an investment

[SpiggyTopes]

Certainly with the Range Rover P38 the majority stick with or come back to oem ...... the rubber ones are tough to fit but give better steering and less road wander.

[baconsdozen]