mk7matt
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| posted on 10/2/16 at 08:05 PM |
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Tight suspension bushes
The suspension bushes on my MK are very tight. I've read through numerous posts trying to come up with a solution but have not found a
definitive answer.
I've done about 2000 miles on them and they creaked from day 1.
I'm in the process of rebuilding the car currently and cannot get the crush tubes to rotate freely enough.
Here's what I have done so far -
Ground down the weld on the inside of the wishbone tube.
Sanded off all the powder coating.
Removed any burrs from the bushes and crush tubes.
Installed using lithium ep2 grease.
The crush tubes rotate freely in the bush when they are out of the wishbone, so the bush is getting crushed too much.
Should I purchase a 3/4" reamer to open up the bushes once fitted?
Cheers
Matt.
2.0 Pinto powered Mk Indy.
10 years in the making.
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rusty nuts
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| posted on 10/2/16 at 08:14 PM |
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Common problem is the crush tube is too short , easy to test assemble the bushes and crush tube then nip the crush tube in a vice, the wishbone should
rotate around the crush tube under its own weight . Skimming the outside of the larger diameter of the bush worked for me .
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Bluemoon
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| posted on 10/2/16 at 08:34 PM |
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quote:
Originally posted by rusty nuts
Common problem is the crush tube is too short , easy to test assemble the bushes and crush tube then nip the crush tube in a vice, the wishbone should
rotate around the crush tube under its own weight . Skimming the outside of the larger diameter of the bush worked for me .
Diito and "just about fall under own wishbone weight"== pass 
Some have fitted 0.2mm PTFE washers between bracket and bush (if there is clearance) to stop binding under load on the brackets. Some have reamed them
as you suggest, but they don't want to be loose either so there is a compromise..
But first off the crush tubes need to be the correct length for the brackets, and slightly longer than the bush assembly.
Dan
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Slimy38
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| posted on 10/2/16 at 08:51 PM |
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quote:
Originally posted by mk7matt
Ground down the weld on the inside of the wishbone tube.
Just to pick this out on it's own, the bushes should rotate 'with' the wishbone tube. It should only rotate around the crush tube.
Some builders actually roughen the inner surface of the wishbone tube (I think Talon's wishbone tubes are rough cut inside?) to allow the bush
to move only against the crush tube.
But I think you're on the right track with the crush tubes being too short. If necessary you could file down the wishbone outer tube which would
allow the crush tubes to be slightly longer in relation to it.
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mk7matt
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| posted on 10/2/16 at 08:54 PM |
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The crush tubes are slightly longer than the bush.
The problem I've got is its too tight when pushed into the bush, without it even fitted on the car.
There is no way it would drop under its own weight when bolted up.
Would it be a better idea to reduce the diameter of the crush tube rather than ream the bush?
This way each crush tube would be custom fitted to the bush.
2.0 Pinto powered Mk Indy.
10 years in the making.
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mk7matt
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| posted on 10/2/16 at 08:58 PM |
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quote:
Originally posted by Slimy38
Just to pick this out on it's own, the bushes should rotate 'with' the wishbone tube. It should only rotate around the crush tube.
Some builders actually roughen the inner surface of the wishbone tube (I think Talon's wishbone tubes are rough cut inside?) to allow the bush
to move only against the crush tube.
But I think you're on the right track with the crush tubes being too short. If necessary you could file down the wishbone outer tube which would
allow the crush tubes to be slightly longer in relation to it.
I ground down the seam weld as I thought it was causing the bush to be crushed too much.
I've not fitted the wishbones yet so crush tube length is not the main issue. The issue is how tight the crush tube is inside the bush. 
2.0 Pinto powered Mk Indy.
10 years in the making.
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rusty nuts
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| posted on 10/2/16 at 09:13 PM |
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Have you tried nipping the assembled wishbone as I suggested to be absolutely sure ?
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Slimy38
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| posted on 10/2/16 at 09:13 PM |
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Ah, now I get you.
You've only done 2000 miles so I might be wrong, but have the bushes swelled up? I'm nowhere near the same place with my build so
I'm working with 'fresh' bushes, I'm sure someone on here suggested that cheaper bushes swell over time.
(Or is it perhaps a reaction to some lubricants? Not sure, I'm working off my bad memory here... )
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mk7matt
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| posted on 10/2/16 at 09:33 PM |
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quote:
Originally posted by Slimy38
Ah, now I get you.
You've only done 2000 miles so I might be wrong, but have the bushes swelled up? I'm nowhere near the same place with my build so
I'm working with 'fresh' bushes, I'm sure someone on here suggested that cheaper bushes swell over time.
(Or is it perhaps a reaction to some lubricants? Not sure, I'm working off my bad memory here... )
Swelling is not something I'd thought of...................it's possible.
I may have used normal grease when I first assembled the car many many years ago.
The bushes themselves look in good health - what does a swollen bush look like? (I daren't google it )
2.0 Pinto powered Mk Indy.
10 years in the making.
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Slimy38
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| posted on 10/2/16 at 09:38 PM |
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If you can get hold of the original measurements for the bush, then a few minutes with a vernier caliper might reveal something?
Or even measuring them against the wishbone tube and crush tube to see exactly how much of the quart you're squeezing into a pint pot?
[Edited on 10/2/16 by Slimy38]
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perksy
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| posted on 10/2/16 at 10:01 PM |
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Just curious
Are you lads tightening the wishbones up with the car on its wheels and on the ground ?
Or up in the air with the weight of the car off the ground ?
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mk7matt
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| posted on 10/2/16 at 10:14 PM |
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Ok, been out to the garage to have a measure.
Unfitted bush
OD is 28.7mm ish
ID is 19.1mm ish
Fitted bush
ID is 18.9mm ish
Crush tube is 19.0mm
Wishbone is 28.6mm ish
To me these measurements seem ok. I did notice that the bushes were out of round though, possibly caused by the seam weld in the wishbone tube.
Should I bite the bullet and buy new bushes?
Are the ones on eBay any good?
2.0 Pinto powered Mk Indy.
10 years in the making.
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mk7matt
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| posted on 10/2/16 at 10:17 PM |
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quote:
Originally posted by perksy
Just curious
Are you lads tightening the wishbones up with the car on its wheels and on the ground ?
Or up in the air with the weight of the car off the ground ?
I didn't think it mattered due to the design of the bush?
We're talking about the two part polyurethane bush with crush tube not the triumph style rubber bush.
2.0 Pinto powered Mk Indy.
10 years in the making.
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CosKev3
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| posted on 11/2/16 at 07:30 AM |
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quote:
Originally posted by mk7matt
quote:
Originally posted by perksy
Just curious
Are you lads tightening the wishbones up with the car on its wheels and on the ground ?
Or up in the air with the weight of the car off the ground ?
I didn't think it mattered due to the design of the bush?
We're talking about the two part polyurethane bush with crush tube not the triumph style rubber bush.
Yeah your correct,no need to tighten these with the car loaded.they work more like a bearing than a bush.
One thing I would be careful of,grinding down the ERW weld inside the tube,fingers crossed on yours it's between the welds onto the wishbone
tube?
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CosKev3
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| posted on 11/2/16 at 07:34 AM |
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I wouldn't recommend Duraflex bushes off E-Bay,returned mine as sizes and quality were awful.
Got some now off Danny at MK,much better bush.
I have read you should not use petroleum based greases with polyurethane,lithium based grease is ok
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mk7matt
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| posted on 11/2/16 at 10:46 AM |
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quote:
Originally posted by CosKev3
One thing I would be careful of,grinding down the ERW weld inside the tube,fingers crossed on yours it's between the welds onto the wishbone
tube?
Yes. The ERW weld was between the wishbone welds.
Thanks for the info re duraflex bushes too.
I might try reaming first, before shelling out for a whole new set.
2.0 Pinto powered Mk Indy.
10 years in the making.
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rusty nuts
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| posted on 11/2/16 at 06:39 PM |
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quote:
Originally posted by perksy
Just curious
Are you lads tightening the wishbones up with the car on its wheels and on the ground ?
Or up in the air with the weight of the car off the ground ?
If the bushes and crush tubes are assembled correctly then it shouldnt make any difference unlike metalastic bushes
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907
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| posted on 11/2/16 at 08:55 PM |
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I won't go over the same ground that's already covered in this thread (and others) but instead would like to
mention a couple of other points.
When the wishbone is welded the outer bush tube will shrink and become out of round. The bushes may have
been a perfect fit before welding but they won't be afterwards.
If the bushes are then forced into the now shrunken and misshapen tube the bush will be compressed, and
therefore the i/d will be less, resulting in the binding of the crush tube inside it.
The answer is to ream AFTER the insertion of the bushes. I did mine on the lathe to ensure perfect alignment.
Hope this helps,
Paul G
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mk7matt
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| posted on 11/2/16 at 09:04 PM |
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Thanks Paul G.
I'll be ordering a reamer then.
2.0 Pinto powered Mk Indy.
10 years in the making.
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rusty nuts
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| posted on 11/2/16 at 10:07 PM |
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Good point Paul.
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907
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| posted on 11/2/16 at 10:27 PM |
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Perhaps I should also add a quote from post 3 from Bluemoon.
quote
"But first off the crush tubes need to be the correct length for the brackets, and slightly longer than the bush assembly.
Dan"
end quote
A combination of reaming and compatible component lengths result in the "free fall" of the wishbone under it's own weight.
IMHO, the binding of polybushes is THE major cause of failures in wishbones.
Cheers
Paul G
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nick205
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| posted on 12/2/16 at 08:57 AM |
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My understanding is that the crush tube needs to be slightly longer than the distance between the outer faces of the bush halves. This prevents the
suspension bracket from squashing and trapping the bush preventing it rotating freely around the crush tube. I believe the bush halves should be a
relatively tight fit in the wishbone as you don't want them to rotate in the wishbone, but rotate around the crush tube without squeaking. On
my MK Indy I used to remove the bushes annually and re-grease them to ensure free movement without squeaks.
Some people seem to fit grease nipple in the wishbone tubes. Myself I feel this could weaken the wishbone tube and is best avoided.
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DIY Si
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| posted on 13/2/16 at 10:55 PM |
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quote:
Originally posted by 907
IMHO, the binding of polybushes is THE major cause of failures in wishbones.
Cheers
Paul G
It definitely did mine in! Along with not appreciating the level of attention I should have been paying to the bushes. Of course, if they didn't
bind then they would have needed much less attention in the first place.....
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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steve m
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| posted on 14/2/16 at 08:20 AM |
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" From Nick,
My understanding is that the crush tube needs to be slightly longer than the distance between the outer faces of the bush halves. This prevents the
suspension bracket from squashing and trapping the bush preventing it rotating freely around the crush tube. I believe the bush halves should be a
relatively tight fit in the wishbone as you don't want them to rotate in the wishbone, but rotate around the crush tube without squeaking. On my
MK Indy I used to remove the bushes annually and re-grease them to ensure free movement without squeaks. "
The above is exactly how ive done mine, the poly bush needs to be a firm fit, and still needed to be pressed in
I cleaned up the inside wall with a small grinding wheel on the drill, so you do not need a reamer, unless a lot of metal needs to removed, and that
would cause a failure in itself, too much metal was removed
The centre crush tube needs to be slightly longer than the overall length of the two bushes and suspension tube
In my application, the crush tube was 42mm long, and the bushes plus suspension tube came to 41.5mm
and even that was a nice tight fit when greased,
My suspension arms do not fall naturally, but will do very easily when moved by hand, and rest in the "left" position
steve
Thats was probably spelt wrong, or had some grammer, that the "grammer police have to have a moan at
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mk7matt
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| posted on 14/2/16 at 08:13 PM |
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quote:
Originally posted by steve m
The above is exactly how ive done mine, the poly bush needs to be a firm fit, and still needed to be pressed in
I cleaned up the inside wall with a small grinding wheel on the drill, so you do not need a reamer, unless a lot of metal needs to removed, and that
would cause a failure in itself, too much metal was removed
steve
I think there may be a bit of misunderstanding here.
I'm planning on reaming the bush once it's fitted inside the wishbone tube so that the crush tube fits nicely.
I'll report back on Wednesday when the reamer turns up.
2.0 Pinto powered Mk Indy.
10 years in the making.
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