Slimy38
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| posted on 2/10/23 at 09:23 AM |
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suspension bushes and crush tube 'gap'
I was looking at my suspension yesterday, and I noticed that I could remove the shock absorber and the wishbones didn't move. It looks like the
top hat bushes are solid against the brackets. The crush tubes are the correct length for the brackets, so I think I need to give the wishbone tubes a
bit of a fettling.
The question is how much fettling do they need? The best answer I could find is that the crush tube needs to protrude 'a little bit', but I
have no idea what 'a little bit' means!
Given that I'm not looking for outright race/track car performance, would 1mm either side be ok? I appreciate that any slack translates into
unwanted movement, but my priority is more around having the wishbones able to move up and down freely than worrying about a slight caster change.
Given that I am looking at removing at least a couple of mm of material I don't want to be trimming the top hat bushes, I am 99% sure this is all
down to me being a bit over-cautious when I was cutting the wishbone tubes.
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obfripper
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| posted on 2/10/23 at 11:29 AM |
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Have you used a petroleum based grease? They can make pu bushes swell up and go sticky, which can reduce your original clearances, it may be worth
checking the top hat dimensions against the specs to rule this out.
A silicone based grease will not do this to pu bushes so is the preferred lubricant.
The locost pu bushes need a small clearance to allow free movement, I would remove the ball joint end and check for free movement at the arm, if
it's springy/creaky then either lubrication or adjustment is needed.
If you need to adjust the tube length, you will need to remove equal amounts from each side to not offset the wishbone, placing the bare wishbone in
the bracket and moving fore and aft, and checking both tubes touch the bracket at the same time should help with adjusting this if needed.
Dave
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Mr Whippy
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| posted on 2/10/23 at 12:06 PM |
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Considering how many grease points my old car has it's amazing how few we build into our homebuilts. I can understand current production cars as
they just want you to replace everything at great cost but if your building your own I would recommend at least installing greasing points so to make
topping up a lot easier.
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Slimy38
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| posted on 2/10/23 at 02:08 PM |
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quote:
Originally posted by obfripper
Have you used a petroleum based grease? They can make pu bushes swell up and go sticky, which can reduce your original clearances, it may be worth
checking the top hat dimensions against the specs to rule this out.
A silicone based grease will not do this to pu bushes so is the preferred lubricant.
The locost pu bushes need a small clearance to allow free movement, I would remove the ball joint end and check for free movement at the arm, if
it's springy/creaky then either lubrication or adjustment is needed.
If you need to adjust the tube length, you will need to remove equal amounts from each side to not offset the wishbone, placing the bare wishbone in
the bracket and moving fore and aft, and checking both tubes touch the bracket at the same time should help with adjusting this if needed.
Dave
I used LM2 lithium grease, despite a good Google session I can't tell whether it's bad or good for PU bushes... one even said that it
actually dries PU out and causes it to crack, rather than making it swell and go sticky.
As for the arms, I wouldn't call them 'squeaky/creaky', I would describe them as 'immovable'! I was going to trim away each
side of each tube, so with four each corner that's 32 times. I suspect maybe a day or so at minimum.
But coming back to the original question, you mentioned 'small clearance', what is 'small' in this context? Is 1mm of crush tube
exposed each side sufficient?
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Bluemoon
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| posted on 2/10/23 at 02:50 PM |
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The consensus here was "wishbone should just fall under its own weight" - i.e. no binding, you may need to check the crush tubes, and or
change them if they are rusted, you might also need to ream the poly bushes out in situ, depending on fit. you must avoid excessive binding as this
will stress the wishbone near the weld and has in the past resulted in failures. The above comment about the grease points is a good one - without
them, I think frequent re-builds and lubrication are required to stop squeaks and binding.
Practically this means the crush tube should protrude about 0.2mm, 1mm sounds far too much.
[Edited on 2/10/23 by Bluemoon]
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adithorp
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| posted on 2/10/23 at 03:39 PM |
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quote:
Originally posted by Bluemoon
The consensus here was "wishbone should just fall under its own weight" - i.e. no binding, you may need to check the crush tubes, and or
change them if they are rusted, you might also need to ream the poly bushes out in situ, depending on fit. you must avoid excessive binding as this
will stress the wishbone near the weld and has in the past resulted in failures. The above comment about the grease points is a good one - without
them, I think frequent re-builds and lubrication are required to stop squeaks and binding.
Practically this means the crush tube should protrude about 0.2mm, 1mm sounds far too much.
[Edited on 2/10/23 by Bluemoon]
This^
Though anywhere from, just fall under their weight, to hold but fall with slightest pressure is ok. For lube, use red rubber grease. Crush tubes
corroding can be another issue and stainless ones are a big improvement, however when trimming the length, be carefully not to work harden them.
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Slimy38
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| posted on 2/10/23 at 09:01 PM |
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Figured it out, the crush tubes were stuck inside the bushes, and the bushes were stuck in the wishbones. Even with a gap it still wouldn't have
moved.
I've opened a few of them up and there's no grease in them at all. I did manage to find a tub of rubber grease though, so using that on
reassembly got everything moving again.
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adithorp
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| posted on 2/10/23 at 10:01 PM |
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The bushes shouldn't turn in the arms.
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Slimy38
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| posted on 3/10/23 at 02:09 PM |
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quote:
Originally posted by adithorp
The bushes shouldn't turn in the arms.
yep, it was more about everything just stuck together that was the issue. I've added grease between the crush tubes and the bush but bush to arm
is dry. Now that it's back together I put the crush tube in a vice and just tested the arm 'droop', it all looks a lot healthier.
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adithorp
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| posted on 3/10/23 at 02:17 PM |
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A little bit of grease between the bush and outer can be good though as it'll reduce corrosion there that could compress the bush harder onto the
crush tube and make it stiff.
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