Rorty
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| posted on 11/1/04 at 03:35 AM |
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I wasn't going to bother posting on this thread, as the topic has been covered in great depth on previous occasions, but certain inaccuracies in
this thread couldn't be ignored.
The crush tube lengths should be the exact internal width of the suspension bracket on the chassis.
The total assembled length of the PU bushes should be 0.5 mm longer than the crush tube.
Yes, I know that makes them wider than the bracket internal width and makes them hard to mount to the chassis, but it's the correct way of
loading the PU bushes. The PU bushes require a degree of loading in all contact areas.
Don't use WD40, Coppaslip or just any old grease to lubricate PU, use Molybdenum Disulphide grease, or silicone grease as second best.
Try searching for the other PU bush thread(s).
BTW, stainless steel is the best material for crush tubes, as there is absolutely no way it will rust and become adjoined to the bolt. Don't be
conned by pretty-looking plated mild steel crushtubes. The plating will get worn off by the moving PU within a few miles and will rust, even in that
greasy environment.
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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locoboy
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| posted on 11/1/04 at 08:52 PM |
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Rorty me old Chicken, that has thrown a right spanner in the works, im sure im not the only one but i am well confused now.
Questions! :
A) Should the wishbone and bush be one complete unit, i.e the bush will not turn in the wishbone tube, meaning that the crush tube is held fast
between the mounting brackets and the bush and wishbone will rotate about the crush tube?
B)If so how come the ends of the bush do not bind on the insides of the mounting brackets as they will be hard up againt them in order to squash them
in enough for the crush tube to be flush.
Regards
One confused suspension assembler!
ATB
Locoboy
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Dave J
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| posted on 12/1/04 at 12:04 PM |
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Now this is interesting.
I mounted my wishbones at the weekend.
My crush bushes are either flush or slightly less in length than the polybushes.
On the rear (IRS) suspension they are a tight fit in the welded brackets, needing a decent push to get them in. When alls bolted up the suspension is
very tight, so all is correct.
The front suspension is a different kettle of fish. The welded brackets are much wider than the poly bush/ wishbone assembly by almost a
centimetre.
Luego instructions are to use spacers to the internal front and rear faces of the bracket to take up the gap.
My guess is that they have done this to allow precise alignment of the front suspension wishbones and adjustment of the upper and lower wishbone
offset to the correct castor angle. ( I know this is supposed to be fixed with the position of the welded brackets, but mine are way out)
I have emailed Luego about this and hope to get an answer soon.
A couple of comments on Rorty's observations, and many thanks for taking the trouble to join our debate.
Having the poly bushes slightly wider than the mating brackets wouldn't cause everything to lock up because unless your bushes are made of
acetal, then polyethelene is quite soft and will compress sufficiently. Mine did not lock up and although very stiff, everything rotates as it
should.
My understanding is by reading various other posts on this subject, that we should be locking down on the crush tubes. You want the largest bearing
surface for the wishbones to rotate on, logically the crush tube od to polybush id.
If you didn't bolt the crush tube hard to the bracket, then the tube and bolt would rotate around the bracket bolt holes. This to my mind would
be the worst possible outcome and very poor engineering.
Curiously, Luego suggest backing off the bolts until they just turn, I have asked them about this as it seems to contradict the general consensus of
opinion. I have read somewhere however that the final tightening of the wishbones should happen when the car is on its wheels.maybe this is what they
are alluding to.
I have again asked them the question.
I'll let you know what they say Col when they reply to me.
The grease has two functions:
1) Help with assembly
2)Stop the creaking of the suspension which would eventually drive you mad.
Plastics are widely used for bearings and bushes etc in all sorts of fields where using lubrication would be a problem.
Rorty's correct about the stainless steel. In an ideal world I think we would like everything to be stainless, however sadly I will have to make
do with copious amounts of grease around my bolts and hope the sun always shines
Aplogies about the length of this post, I guess too much info is better than none, just pick out the bits that make sense.
Cheers
Dave.
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locoboy
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| posted on 12/1/04 at 01:36 PM |
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Very informative Dave, well worth the time to read it all.
I guess i will have to take a propper look at mine again and make some notes - take some measurements and see how things add up.
thanks again - i may be back for more info.
ATB
Locoboy
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Dave J
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| posted on 12/1/04 at 01:56 PM |
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You're welcome
Cheers
Dave
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flyingkiwi
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| posted on 12/1/04 at 02:02 PM |
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yip, this post has sorted out my problems, just fitted the wishbones to the car and went on a treat.
Double checked the messurements of the crush tube and the richard cranium at the shop must have buggered up as a 12mm bolt fitted perfectly.
Now just to buy the shocks! thats if teh missus will let me
cheers for everyone's help!
chris
It Runs!!!!! Bring on the SVA!
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James
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| posted on 12/1/04 at 02:19 PM |
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quote:
Originally posted by Rorty
The total assembled length of the PU bushes should be 0.5 mm longer than the crush tube.
Oh crap! Something else wrong for me to worry about then!
Cheers for the info' tho Rorty!
James
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Hornet
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| posted on 12/1/04 at 03:44 PM |
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I disagree with that. Surely the crush tube must be longer. Otherwise when you bolt everything up, you would be locking the suspension in a set
position.
The poly bushes need to rotate on the crush tube and also for lateral movement.. move on the bracket sides.
If I'm wrong.. then I'm wrong... but my crush tubes are staying longer
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Dave J
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| posted on 12/1/04 at 04:22 PM |
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Hi Hornet,
If you haven't got any sideways movement when everythings up an bolted, then I wouldn't worry too much.
Like I said in my tome above, mine are flush or slightly below the poly bushes. Its all nice and tight with everything swivelling where it should.
So thats all right then.
This really has opened a can of worms.
Cheers
Dave.
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chris.russell
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| posted on 12/1/04 at 07:40 PM |
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excuse my ignorance, but what is the material used to make the poly bushes, so I can order the correct grade of material
Chris
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Dave J
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| posted on 13/1/04 at 01:41 PM |
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Hi Chris,
They are made of polyurethane.
You might find this informative:
http://www.superflex.co.uk/
Cheers
Dave
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DaveFJ
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| posted on 13/1/04 at 01:50 PM |
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I must say that what Hornet is saying seems FAR more logical...
If the bearing surface is between the crush tube and the bush, with the crush tube effectively locked in position and the bush not rotating within the
wishbone, then surely the last thing you want is to lock the bush against the suspension mount.....
Or maybe I'm missing something as usual?
Dave
Dave
"In Support of Help the Heroes" - Always
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locoboy
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| posted on 13/1/04 at 02:37 PM |
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I agree, it kind of goes against my logic to do it the "correct" way.
ATB
Locoboy
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stephen_gusterson
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| posted on 13/1/04 at 03:50 PM |
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from a previous big argument between rorty and syd, I remember the following.
The bushes and crush tubes DONT ROTATE AT ALL.
The idea is that the 'rotation' is actually compliance within the bush. Its the bush that 'rotates' by distorting.
the crush tube stays put as does the outer circumference of the poly bush. rotational movement is within the bush material itself.
syds counter argument is that the bush rotates on the crush tube.
you are supposed to tighten the bolts that hold the crush tube at normal ride height. this allows a degree of 'bush flex' in the bump and
rebound positions.
f you look at old style bonded rubber bushes, the crush tube and bush outer are all bonded - there is no rotational movement. All movement occurs in
the rubber itself distorting.
atb
steve
ps - i have rod ends
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locoboy
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| posted on 13/1/04 at 04:23 PM |
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Stick ur rod end up ur ass! 
I have rod ends on the outer end of the rear bones but bushes at the inner end.
I can agree with this theory as the trailing arms on my F27 have the rubber bushes with the metal outer thet are presses into the tube and the crush
tube is locked up tight too so the flex is in the bush its self
Oh bleep it i shall bang it all together and see what happens!
[Edited on 13/1/04 by colmaccoll]
ATB
Locoboy
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GO
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| posted on 13/1/04 at 04:29 PM |
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Poly bushes rotate around the crush tube.
Rubber bushes dont rotate, they distort as gusters said.
Thats all I'm saying, cos anything beyond that and I've no idea!
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stephen_gusterson
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| posted on 13/1/04 at 04:30 PM |
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I think the concern is that the bolt and crush tube are not meant to be pivot surfaces, but apart from that I cant see any disasters - but im only
relaying what I heard, not what I experienced.
Apart from when you take production car suspension apart, it never flops, and seems to stay 'elastically' in place held by the bushes.
Thik I will leave my rod ends where they are thanks 
atb
steve
[Edited on 13/1/04 by stephen_gusterson]
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Peteff
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| posted on 13/1/04 at 08:12 PM |
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I used spherical bearings(rose type joints)on the axle end of my trailing arms and poly bushes on the chassis end. The bracket locks onto the crush
tube to hold it in place so the bush rotates on it. My bushes were flush with my crush tubes and they work o.k. so that's the method I'm
using next time on all the suspension.
yours, Pete.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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locoboy
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| posted on 14/1/04 at 02:19 PM |
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i have just downloaded and printed the Pdf file on GTS website for the 36 piece polybush set.
http://www.cougarracing.fsnet.co.uk/polybush.pdf
Im having trouble working a few things out, it says all dimensions are in mm unless stated, the tube side required is 1.25 (i guess thats inches) is
that ID or OD?
It also doesnt give any info on the OD of the part of the bush that goes into the tube.
Am i missing something on the drawing?
Also can anyone confirm the thickness of 18swg?
ATB
Locoboy
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flyingkiwi
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| posted on 14/1/04 at 02:21 PM |
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18 swg is 1.2mm thick, but there is a bit of doubt in that!
Nope it is 1.2mm, or so Mr Zues Table tells me
[Edited on 14/1/04 by flyingkiwi]
It Runs!!!!! Bring on the SVA!
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Rorty
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| posted on 19/1/04 at 03:58 AM |
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Appologies for not rejoining earlier to answer the questions directed at me.
PU (poly ) bushes are made from polyurethane, and come in various degrees of hardness (shore) 70 being the typical grade for wishbone bushes.
The crush tube must be a tight fit in the chassis bracket, and the assembled PU bushes must be a fraction longer than the crush tube. The PU has a
certain degree of compliance, and will squash into the bracket and still rotate in use. They will appear really tight when you try to wiggle the
fitted wishbone up and down though.
The crush tube must be tightly gripped in the chassis bracket and must not rotate on the bolt.
The PU bushes are pressed dry into the wishbone, where they should remain...motionless!
The bores and outer faces of the PU bushes should be greased with Molybdenum Disulphide grease (usually pencil-lead-black, but Redline do a red
version). Do not use Copaslip or any ordinary grease.
The PU bushes are designed to rotate on the outer surface of the crush tube, and against the inner faces of the chassis bracket, and do not have
sufficient compliance to distort with suspension movement. The earlier rubber/metal "Metalastic" bushes were designed to work in that
fashion....you just tightened up the bolt through the centre, and the rubber squished around, thereby affording the wishbone some up-and-down
movement.
If you were to use acetal (self lubricating, hard wearing plastic) for the bushes, then they would have to be an exact fit in all respects, as acetal
has zero give
Gusters, it's not like you to get the wrong end of the stick and mis-quote people! You totally cocked up that one!
Hornet, if your PU bushes aren't longer than the crush tubes, there won't be any preload on the bushes,and they'll move backwards
and forwards under normal motoring, and will give the impression of sloppy suspension, even though they may seem tight in their brackets.
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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planetester
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| posted on 25/7/04 at 10:28 PM |
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Rorty,are you there
Rorty, your argument sounds the best yet to me, tell me, my wishbones tubes have been made from a different batch of tube from my trailing arms, the
crush tubes slide easily into my trailing arms with no play but really have to be pressed into the wishbones, which is correct, should I ream out the
bushes once fitted into the wishbones to let the crush tubes slide
thanks
[Edited on 25/7/04 by planetester]
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Dave J
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| posted on 28/7/04 at 03:09 PM |
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I would suggest you don't ream out the bushes, just press them in using a vice, G clamp or similar (besides, even the sharpest of reamers tends
to chew the poly rather than cut it). use a smear of vacuum grease on the bushes etc or they will creak when in use. The bushes do need to be
tight.
Hope this helps.
Dave
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andkilde
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| posted on 29/7/04 at 10:10 AM |
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quote:
Originally posted by Syd Bridge
And you can still use Y419's rotating on a greased bolt. ie. Not tightened to compress the inner metal tube. No different to a
metal/metal rodend. SVA man I spoke to said he would prefer to see this than 'metallastic' type installations. Fewer stresses in the
wishbones and no torsional/rotational forces and stresses in the chassis/bush brackets.
Oh, and by the way, he is a chartered engineer as well!
Take your choice.
Syd Bridge.
C.Eng., M.I.Mech. Eng., MRINA, SNAME, dah dah dah.......
Syd, this is hardly the time to be playing silly buggers , someone is liable to end up with a wheel off...
Using a bolt as a bearing surface is asinine in the extreme -- FWIW, the bolt should be a good tight fit within the crush tube and a good tight fit in
the holes on your mounting points (preferably with an unthreaded shank), the crush tube length should be EXACTLY the same as the distance between the
inner faces of your mounting points. Once assembled, the crush tube should be LOCKED in position. The PU bush should swivel about the fixed crush
tube.
Steel-on-steel swivelling WILL FAIL spectacularly, dangerously and unpredictably.
If Syd and his SVA bloke are not taking the wee (which I suspect they are) they should be taken out and flogged publicly for suggesting that a bolt
can be used as a pivot. Using a bolt as a pivot is NOT NOT NOT sound engineering practice regardless of the number of letters after one's
name.
Cheers, Ted
[Edited on 29/7/04 by andkilde]
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splitrivet
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| posted on 29/7/04 at 10:26 AM |
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I would agree with Syd on that, there are bushes and bushes and all the poly bushes Ive seen from Locost parts suppliers have practically zero flex,
so the crush tube must be longer than the assembled bush.
To clamp up onto the assembled bush and not the crush tube would be a recipe for disaster, with all the load going into the thin walled chassis tube
or wishbone whichever gave way first.
Metalastic and flexible PU bushes fair enough use the flex in the PU,but even so with such thin walled tubing even then I'd think twice,it would
be interesting to know what type of bush earlier threads with bent wishbones used.
Cheers,
Bob
I used to be a Werewolf but I'm alright nowwoooooooooooooo
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