How do bushes work?!

[macdonald.dm]

Ok, I know what they do...

I'm referring to the type used, for example, at the inner ends of suspension arms etc; the cylindrical type which have a steel inner sleeve.

What I've never been sure off is how they allow full suspension movement - the steel sleeve is bonded to the rubber, and is usually 'pinched' tightly when the bolt is tightened up I'm assuming the sleeve cannot rotate, and therefore neither can the rubber part?

So, does the rubber absorb all the movement by twisting, or does it partly turn in the outer tube where it's fitted (surely not - the wear would be huge!)?

I've been curious about this since I restored a Triumph GT6 - and that was 25 years ago! I know you are meant to have the suspension at normal ride height before final tightening, so this suggests the rubber (or whatever is used) handles the movement by twisting.

Can anyone confirm, please?! Ta.

[amalgamated users from prior forum]

Re: How do bushes work?!

Message originally posted by: Don
Yes It is the rubber that takes the movement in shear. Neither of the metal bits should move.

[macdonald.dm]

Re: How do bushes work?!

Cool! Thanks Don - as I suspected. Quite a bit of movement needs to be absorbed over full travel then - do polyurethane bushes have as much flex as rubber?

Cheers.

[b_caswell]

Re: How do bushes work?!

Thats why you should fully settle the car on its wheels with the bush bolts loose and then tighten up with it all in a neutral position. If you do up all the suspension with the wheels hanging the bushes are in tension when you put the car down.So when the car depresses in use it rips the heart out of the bush.

[macdonald.dm]

Re: How do bushes work?!

Thanks to you both, I can sleep better now

[gaddbrose]

Re: How do bushes work?!

Hi Donnie, there's a bit more to it than so far mentioned. Everything said above is perfectly correct in that the rubber is elastic and when the steel arms and bushes turn , then the elasticity in the rubber sandwich causes the whole lot to return to the original position, but at a price, because the rubber did'nt last long, it sheared off either the sleeve or outer bush and had to be replaced at regular intervals. however science pervailed and the alternative initially was a 'nylatron' bush designed to do the same job .Nylatron is a form of nylon with a graphite additive. However, there's no elasticity as in the rubber version, so what happened is that the nylatron bush rotated around the fixed central bush. No wear took place because of the lubrication properties of the graphite and these bushes lasted for years longer. The absence of the elasticity of the rubber did'nt make much difference to the suspension, and probably made it a touch more sensitive, but putting more load on the shockers. The current version seems to a yellow bush and I don't know its properties , but I suspect they would be similar. Be aware of the trap some members have fallen into, if you fit these bushes , do not fit any to the front end of the arms ,i.e which couple to the chasis, because there would be nothing to stop the axle and road vibration travelling up into the car. All of a sudden the driver is complaining that the car/axle is falling apart.. regards Brian

[Dane_Rescueman]

Re: How do bushes work?!

Hi all,
I fitted Deflex/Superflex nylon bushes to all rear joints and the steering rack on my Berli in 1998! I do not experience any extra vibration from the rear axle.
I have just dug out the fitting instructions for them. It is suggested that the nylon and steel bushes are lubricated prior to fitting. this makes them easier to fit and prevents wear in use. Brian is correct in that the nylon bushes are not welded to their [stainless] steel bushes which are thus free to rotate. I have torqued the bolts to the Cortina book setting with no ill effects so far.

[macdonald.dm]

Re: How do bushes work?!

Thanks Brian and Dane for the extra info. Interesting stuff.

Aren't Superflex bushes made from Polyurethane rather than Nylon, or do they make both?

I've just bought some Superflex bushes for my rack and was trying to figure out if they felt 'firmer' than the rubber ones - if they were, would that mean they'd have to operate in a different way when used as suspension bushes as mentioned above (ie: they wouldn't have enough flex to accommodate the rotational movement)?

[Dane_Rescueman]

Re: How do bushes work?!

Donnie,
I am not an expert on this but the material in the suspension bushes felt more compliant (easier to squeeze/manipulate) than that for the rack mounting.

[macdonald.dm]

Re: How do bushes work?!

Cheers, Dane - that makes sense.

[b_caswell]

Re: How do bushes work?!

Superflex bushes are made from a waxy polyurethane with a microscopic lubricating polymer impregnated at manufacture.Designed to work like a bearing by running on a stainless steel sleeve. They come in four grades 70 80 90 95 shore, depending on application and car use.

[macdonald.dm]

Re: How do bushes work?!

Ah! Interesting! So they work in a different way to the original rubbers? In theory, this would be a significant improvement.

I have come across occasional disgruntled comments from users (usually on various classic car sites) claiming their replacement Superflex bushes have worn out after only 3k miles. I obviously don't know the circumstances, and I guess the odd user will experience problems due to all sorts of factors.

Dane, I guess you are happy with your bushes fitted in 1998! What sort of mileage have you done since then?

[Dane_Rescueman]

Re: How do bushes work?!

Only about 3500 miles so far(I'm always "improving" some bit of the car). I drive mostly on "B" roads or lesser, which gives the suspension a good work out. (and the brakes too!)
The manufacturer says that the bushes will last much longer than the old rubber types, but, I suppose they would wouldn't they.
Are there any racing people viewing the site who could say how long the bushes last in a track car?

[macdonald.dm]

Re: How do bushes work?!

Cheers Dane.

Was it a case of you HAD to replace (some of) your bushes as the originals were worn, or you just wanted to try an 'upgrade'? Did you notice any difference? (I guess if the former, you would have, but not necessarily with the later situation?)

[Dane_Rescueman]

Re: How do bushes work?!

Hi Donnie

Probably due to my slightly warm 2 litre engine I had ground my light [1600] diff to a pulp that even krause could not improve. I purchased a heavy Atlas axle and mounted it with the superflex bushes. On the old axle the old rubber ones had not parted company but were becoming ragged and I sensed that the axle wasn't as secure as I thought it should be. I was very impressed with the handling after the refit and as I have said, didn't notice a big change in body noise or vibration.

( Note: my job at the time was flying a vintage helicopter so I am definitely not in any way a reliable judge of good or bad vibration !! My judgement of really bad vibration was when everything appeared blurred and I could feel my kidneys rattling against my ribs ! Anything else is OK.)