Snapped upper wish bone bolt

[octo0072000]

If the nuts are torqued up now are the bush inner sleeves gripped so that they spring in the rubber
If that is the case just fit the arm with the nuts slack
Put the weight on the suspension (jack under bottom arm)
Then tighten up the nuts
If you "bounce" the suspension the nuts should move with the arm

WRONG the nuts should not move at all that bar is fixed to the chassis

norm beat me to it

 

[doubleboost]

WRONG the nuts should not move at all that bar is fixed to the chassis

norm beat me to it

Well done at least you are paying attention

 

[123hotchef]

front nut NS snapped and rear nut OS keeps loosening I think it is the rear cant remember now.

I hear you about
AND A NOTE SHOULD BE IN THE PACKAGE TO STATE --- that when fitted, the arm is allowed to move the crush tubes into there 'neutral running position, so the car should be dropped into its normal running height, whilst sitting on flat ground,---- THEN and only then should the end nuts be tightened to prevent undue loading on the through shaft and associated washers and lock nuts

It does look like they have used stud lock on them because the blue don't look like a nylock nut I will look closer later when I get home.

 

[normspanners]

Well done at least you are paying attention

WE ARE !!

 

[123hotchef]

you all are and I thank you for that

 

[normspanners]

front nut NS snapped and rear nut OS keeps loosening I think it is the rear cant remember now.

sowat I said in the first place then,---- they are supplied not tight and as the wish bone tries to spread under braking the side of the arm that is moving anti clock will undo the nuts !!!argh

 

[123hotchef]

ha ha sorry mate I think I will use lock nuts on them and see what happens then

 

[normspanners]

It does look like they have used stud lock on them because the blue don't look like a nylock nut I will look closer later when I get home.

cant see that----- unless they are proper tightend they will rattle and locking them with locktite and the crush tubes are still moving means the nuts will be locked on to the shaft with locktite but not tightened up the tubes correctly, but if then/when tightening the crush tubes correctly after fitting, will break the locktite free!!"

 

[123hotchef]

cant see that----- unless they are proper tightend they will rattle and locking them with locktite and the crush tubes are still moving means the nuts will be locked on to the shaft with locktite but not tightened up the tubes correctly, but if then tightening the crush tubes correctly after will break the locktite free!!"

exactly so maybe they are nyloc nuts then

 

[PhillipM]

Well in my view it is not wrong some suspension setups use just the rubber bush as the 'spring' and use the rubber as a natural damper, rubber can be incredibly hard to twist when bonded to steel and encapsulated in a tube most polly bushes will allow the item to twist within its self quite easily, nylon especially but nylon doesn't give enough shock absorption, but can introduce rattle into the setup, well for rallying an off roading etc. poly bushed wishbones can be lifted by hand to any position and stay there whereas rubber has to be forced away from its natural at rest position and in fact to get ball joints out a large bar has to be used, that force has to be transmitted to the chassis and the fasteners at the end of the crush tube.
we are after all talking about an off road vehicle here, not a formula 1 car, and the two are TOTALLY different.

Yes, because I know nothing about off road cars, only having built a few that have won multiple british and national championships...
It doesn't matter what the use is, the physics is the same.

You cannot compare the friction from moving something by hand to that under load, by hand the preload is the dominant force, not the actual suspension loading, and as you've just said yourself, poly bushed wishbones can be moved and will hold themselves up, whereas rubber ones will not, they will return to a neutral position - how is that not a perfect example of just how much friction they introduce even under no load - they hold themselves up just from friction alone before you even start loading them!
That force from your bar to move a rubber bushed item is just spring rate, it's no different to having the spring attached, it's not friction. Friction is the enemy from a dynamics viewpoint, spring rate doesn't matter, we build suspension to introduce a soft spring rate to start with, that's it's job.
If you want to talk about off road vehicles then WRC cars used to chase so much friction reduction even the dampers had recirculating linear ball bearings supporting the shaft rather than the usual plain bush - they gave so much performance advantage over cheaper units that they banned them so the smaller teams could keep up.
Now they coat the shafts with Diamond-like-carbon instead for a similar advantage, which is still not cheap, good old regulation makers...

It's the same for the suspension links, on the longest links that have relatively low angle change they'll use a cast-in-place polyurethane that twists the same as a normal rubber bush rather than rotating on a crush tube, on the short links which have much more angular displacement - if they had the room - then they used spherical bearings which had an intermediate races of ball bearings in them for friction reduction.
Even now where they're forced to use plain spherical bearings for space/reg constraints, the liners are pumped full of PTFE/Moly to reduce friction and the top teams have the balls coated with TiN and more recently they're using DLC coatings for even more friction reduction, some are even trying Silicone Nitride/Ceramic balls the same as they use in the wheel and diff bearings.
Friction in suspension is a massive issue for suspension performance. Spring rate isn't. Low, controllable spring rates is the whole point of having suspension.

 

[normspanners]

Yes, because I know nothing about off road cars, only having built a few that have won multiple british and national championships...

Well isnt that a coincidence


All this is a bit of a mute point this is a standard road car that has a problem not a competition car

the nut itself will only loosen if there's an issue with the torque settings or a manufacturing fault, there shouldn't be anything turning against it to try to undo it so it doesn't matter if the threads are left or right or any of that

This was your first quote and it is obviously wrong, there is a force acting on the nuts from the metalastic bushes, as the arm travel through its arc, I was pointing out that there is aforce acting and it can be quite extreme I gave an example of it happening in a rally car, not an actuall wishbone pivot bush but helping form a similar situation with rubber transmitting a turning motion againt its fastener and causing it to move only on the side that that moved anticlock , nylon bushes stopped it occurring as did poly both allowed the bush to rotate and not bind, but those materials where illegal. Nylon was best but was too hard and bent the mount further on because of its solidness.
Also there is no way a metastic bush could survive on a wrc car with 300-mm wheel travel. the forces would be extreme.

 

[123hotchef]

well I am going to fit the new wishbone saturday so we will see what happens

I will keep you all posted

 

[PhillipM]

Then you'd better go have a look at the rear inboard links on the latest cars, which are using metelastic bushings in the centre joints but with cast in poly rather than rubber.

The extreme you give against it happening in a rally car would be from either the bush running out of travel or the vibration, you have the same or more force there with poly so if that was the cause you would still have the issue, the friction coefficient of a polybush even well greased is about 0.15-0.2, it gets worse and worse as they age and displaces the lubricants from the surface, it can easily double that. The torque from the rubber bush spring rate compared to the nut is tiny, and it's reacted through the arm as well as the nut.

But I also don't have to resort to pulling random quotes from some numpty on WSCC to back my point up rather than explaining the dynamics.
First you blow the explaniation off as F1 cars aren't off road cars, when I point out it's the same or worse for rally and off road cars, suddenly it's a road car vs competition car...yet your own quote is from a guy making them for competition track cars...make your mind up.
It doesn't matter, the physics don't change, that's exactly why they use metelastic bushes on road cars, they fit the travel/NVH requirements and give no friction for better ride quality.

 

[8ob]

@PhillipM and @normspanners , are you guys talking about totally different concepts? Surely the twisting forces on bushes in a rally car with relatively short control arms @300mm wheel travel would be far more extreme than in the case of a dirt buggy with purpose built long arms?

Bob

 

[colnerov]

Hi, Gents please, whilst this is all very interesting to read. We are talking here about a standard vehicle with a standard replacement part that has failed, is it a case of a error in fitting or is the part not fit for purpose?

Colin

 

[123hotchef]

not sure I hope it was error in fitting but i cant see how for a saftey point of view i will double up the nuts

oh and i just took the broken bit apart the nut was a nyloc nut m14 the stud was snapped and the threads stripped

 

[PhillipM]

@PhillipM and @normspanners , are you guys talking about totally different concepts? Surely the twisting forces on bushes in a rally car with relatively short control arms @300mm wheel travel would be far more extreme than in the case of a dirt buggy with purpose built long arms?

Bob

The displacement angles are similar because the limits are CV angles in terms of travel.


Hotchef, can you get some pictures of the break? Frankly I don't care what bush you're running it shouldn't be snapping a 14mm stud and ripping the threads off unless it's come loose and twisted/jammed.

 

[123hotchef]

i posted pics of the break back on the 1st page, I broke it with my torque wrench

 

[colnerov]

not sure I hope it was error in fitting but i cant see how for a saftey point of view i will double up the nuts

oh and i just took the broken bit apart the nut was a nyloc nut m14 the stud was snapped and the threads stripped

Hi, In that case does it bring into doubt the setting or the calibration of the torque wrench? Or is it the quality of the fulcrum pin material? Usually if parts like this are overtightened the nut strips first before breaking the bolt suggests poor quality as said back in post 25.

Colin

 

[123hotchef]

Er well I did turn the torque up after it kept coming loose! shshhh