Wishbone Bushes

[Chris_Mi 6]

Hi all,

 

This is basically a post out of curiosity (and also an argument I'm having with the ol' man!)

 

I don't know how to place a link to another post, so apologies.

 

On Jul 2 2008, maturin23 (as have many others) wrote (about changing wishbone bushes):

 

"When refitting the wishbones it's VITAL to ensure the car is on the ground or the suspension is compressed until the wishbones are parallel with the ground before tightening the wishbone bolts. I forgot, tightened them up with the hub/suspension hanging in mid-air and needed new bushes within a few hundred miles."

 

Now my logic would be that when tightening the wishbone bolts, the wishbone bush becomes 'locked' against the subframe (if thats what it is), and as such maturin23 is correct - the wishbones should be horizontal to stop stress on the bushes (twisting) them when the car is lowered off the jack. However, when changing my bushes the other day, and refitting the wishbone, I noticed that no matter how tight I did the bolt, the bush wasn't 'locked' against the subframe too tightly, and once done up the wishbone could be moved up and down without twisting the rubber in the bush i.e. the rotational load was mostly on the bolt.

 

My ol' man reckons that this is correct, and that the rubber in the bushes are not meant to 'twist' (i.e. they should not be firmly locked against the subframe), merely that that rubber is there to absorb knocks and vibration, and the wishbone should move freely.

 

Who is correct (because there are a few beers, and plenty of pride, at stake) ?

 

Chris

Edited March 12, 2009 by Chris_Mi

[hengti 2]

was thinking about this yesterday whilst replacing a damper on something else - same thing applies. i'd guess that it depends upon whether or not the rubber in the bush is bonded to the arm and the ferrule through which the bolt passes.

 

if you consider the weight that they have to support when you lift the front end of the car, you'd not be doing them any good by that either

[Chris_Mi 6]

was thinking about this yesterday whilst replacing a damper on something else - same thing applies. i'd guess that it depends upon whether or not the rubber in the bush is bonded to the arm and the ferrule through which the bolt passes.

 

if you consider the weight that they have to support when you lift the front end of the car, you'd not be doing them any good by that either

 

The rubber is definately bonded to both the metal outer, and the ferrule. But is it the bolt that take the rotational load of the wishbone moving up and down, or the bush? My ol' man is definately convinced that bushes of this type should not take any rotational stress within the rubber.

 

I'm not liking the idea of getting the beers in!

[Rippthrough 98]

The bush absorbs the rotational twist, otherwise the bolt would wear, it'd knock like bugger as bolts are always undersized, and the load it could take would be limited by the shear strength of the bolt.

Damned near every mass-production suspension bush for the last 30 years has been of this design.

Edited March 12, 2009 by Rippthrough

[hengti 2]

i think it's the ferrule that should be clamped between the mounting points so, if the rubber's bonded on both surfaces, it's going to be load bearing. that said, not sure why yours is still moving (freely?) - perhaps the bolts aren't pulling the brackets on the subframe up to the ferrule? shouldn't they? (may well stand corrected)

 

the aftermarket poly bushes aren't bonded to either and will behave as your old man describes

 

ed. typing whilst you got another

Edited March 12, 2009 by hengti

[Chris_Mi 6]

The bush absorbs the rotational twist, otherwise the bolt would wear, it'd knock like bugger as bolts are always undersized, and the load it could take would be limited by the shear strength of the bolt.

Damned near every mass-production suspension bush for the last 30 years has been of this design.

 

Lol. Looks like the ol' man is getting the beers in then! That's the problem, mine is knocking like buggery. Especially over potholes!

[GLPoomobile 958]

I don't have a great deal of experience in this area, but on the couple of occassions that I have fitted new bushes and re-fitted the wishbones I have found they are an extremely tight fit in to the subframe, to the point of being a positive pain in the ass lining up the holes to get the bolts through. Once bolted up, there is a little bit of movement but essentially the wishbones should spring back in to the position it was clamped in if moved up or down.

 

So I suspect that this is correct, and that the bush is not supposed to be able to move, and therefore it is taking rotational forces as the wishbones moves up/down. And therefore, if the bush is clamped with the wishbone not in it's natural state, it is going to be put under undue stress (pre-loaded?) and is likely to fail sooner.

[Chris_Mi 6]

I don't have a great deal of experience in this area, but on the couple of occassions that I have fitted new bushes and re-fitted the wishbones I have found they are an extremely tight fit in to the subframe, to the point of being a positive pain in the ass lining up the holes to get the bolts through. Once bolted up, there is a little bit of movement but essentially the wishbones should spring back in to the position it was clamped in if moved up or down.

 

So I suspect that this is correct, and that the bush is not supposed to be able to move, and therefore it is taking rotational forces as the wishbones moves up/down. And therefore, if the bush is clamped with the wishbone not in it's natural state, it is going to be put under undue stress (pre-loaded?) and is likely to fail sooner.

 

The ol' blighter is not giving up. He recons that if the bush is designed to be locked it would not have a simple flat face on each end of ferrule (ie relying on compression alone to lock using the bolt), and would have some sort of keyed mechanism to lock it against the subframe. His reasoning is that you would not be able to 'lock' the ferrule indefinately using a tight bolt i.e through compression, the ferrule face would eventually become loose, negating any rotational absorbtion capacity of the rubber. He is also stating that the fact that the rubber compound is bonded to the metal faces of the bush indicates that it is not designed for rotational stress.

 

Shall I buy him the beers or not ?

[hengti 2]

think he owes you beers - your problem will either be bolt tightness or ferrule length (and who doesn't have ferrule length issues?)

[Rippthrough 98]

His reasoning is that you would not be able to 'lock' the ferrule indefinately using a tight bolt i.e through compression.

 

 

Tell him it's worked pretty well ever since the first bolt was invented, that's how they work...

[AndyJ 1]

On all the ones ive ever done the ferrule has been clamped in place by the bolt. I think your old man needs to admit defeat at the hands of the almighty internet

Edited March 12, 2009 by AndyJ

[Rippthrough 98]

Show him this from a 306:

 

 

And demand beer.

 

 

Centre is pressed on the wishbone, the outer casing is 'P' shaped and bolted to the chassis....

Edited March 12, 2009 by Rippthrough

[Chris_Mi 6]

Show him this from a 306:

 

 

And demand beer.

 

 

Centre is pressed on the wishbone, the outer casing is 'P' shaped and bolted to the chassis....

 

Thanks people. Just out of interest Rippthrough, does centre piece try to rotate under stress?

Cheers

[kyepan 291]

just to add spice to the sauce,

 

the poly replacement bushes do not have an inteference fit outer metal jacket, so they float in the wishbone, as such these might be more free to move up and down.

 

Although that being said, they were tight as a bugger to fit and I jacked the hub up to tighten them anyway.

[marksorrento205 80]

Dont you just love the father son arguments. It brings back memories

[platty 1]

The Poly bushes are an absolute b@stard to fit. I had to chamfer the edge a little to get the wishbone onto the subframe. It took increasingly larger hammers and leaver bars to eventually get the holes to line up. Even with a little lubrication, and the bolts loose, the wishbone is tight to move. I'd rather pull my teeth out than have to go through that again.

[Rippthrough 98]

Thanks people. Just out of interest Rippthrough, does centre piece try to rotate under stress?

Cheers

 

It'd try, but given it takes 2 tons to press them on the wishbone, it's not going anywhere...

[Anthony 1,000]

I'd rather pull my teeth out than have to go through that again.

Given that the other wishbone is still sat in my garage and thus not yet fitted to your car, shall I dig the pliers and laughing gas out Sir?

[Baz 421]

I was also thinking about this last night as i fitted some poly-bushed bones to one of my cars, i was thinking about how i hardly ever remember to do them up oince the car is down on it's wheels etc, and have never had any problems. But did these up at roughly where they'd be once on the ground, before i slotted the ball joint back into the hub, this is when i noticed as mentionned, that the wishbones rotate easily! i was starting to think like your dad too Chris, that the bushes are there to limit lateral force, and that any rotation, as it will be minimal anyway, is fine if the bushes move, but the more i thought about it the more i thought of course the bushes would then wear prematurely?

 

Confusing!

[platty 1]

Nope, a deadblow and molegrips will suffice Anthony

 

As soon as I clicked Add Reply, I thought the nearside's not done yet.

 

Edit: Baz, what bushes are you using? My wishones are stiffer than a Vicar at choir practice!

Edited March 13, 2009 by platty

[Baz 421]

The rally design red ones iirc.

 

'PolyRace'?

[C_W 3 1 Cars]

For the OE bushes you need to tighten them up on the ground so the bush isn't stressed at the cars resting positon. Any suspension compression or rebound twists the bush from it's resting position so it's best to preset that by tightening them up on the ground. You can bolt them up with the suspension off the ground but they will be twisted when the car is back on the ground; they'll probably last a while but their life is reduced as compression twists them even further.

 

The polybush ones are usually not bonded to the centre steel pin/tube (whatever it's called! ) so it's probably not critical (plus sometimes they are greased anyway)

[Baz 421]

For the OE bushes you need to tighten them up on the ground so the bush isn't stressed at the cars resting positon. Any suspension compression or rebound twists the bush from it's resting position so it's best to preset that by tightening them up on the ground. You can bolt them up with the suspension off the ground but they will be twisted when the car is back on the ground; they'll probably last a while but their life is reduced as compression twists them even further.

 

The polybush ones are usually not bonded to the centre steel pin/tube (whatever it's called! ) so it's probably not critical (plus sometimes they are greased anyway)

 

That's pretty much what i was going to post after the conversion with my father just helped...

 

I suppose it pays to be sure, but as usual i just over-worry about things!!

[Chris_Mi 6]

For the OE bushes you need to tighten them up on the ground so the bush isn't stressed at the cars resting positon. Any suspension compression or rebound twists the bush from it's resting position so it's best to preset that by tightening them up on the ground. You can bolt them up with the suspension off the ground but they will be twisted when the car is back on the ground; they'll probably last a while but their life is reduced as compression twists them even further.

 

But that's the whole point. My bushes don't seem to be tight enough when bolted up as to put rotational load on the bush. Once on the wishbone can be moved easily without 'twisting' the rubber in the bush i.e. the bolt is taking the slight rotational load.

 

Anyway, thanks fellas, cause I am now utterly confused (I think I might just give it to the ol' man a) because he's not gonna leave it, he's got 35 years of engineering experience designing parts on big Rolls airplane engines (about 34.98 years more engineering experience than me), and c) he is the ol' man)

 

Gotta love the response a fatherly son argument produces tho!

 

Cheers

[Baz 421]

So you're using OE bushes/bones and still getting this rotational ovement in the subframe?

 

Gotta love the response a fatherly son argument produces tho!

 

Cheers

 

Fun isn't it, mine's the same, usually i walk away red faced from the old git!! There's barely much he's wrong about after 45yrs in engineering...