I'm currently starting on the suspension tubes, and the first is chopping up the 33.7mm tube to go round the bushes. The first one was cut to the
35mm measurement from the book, I then clamped it in the u bracket with the nylon bush and crush tube in place. And the blasted thing would not move
at all!! I could actually see the bush edges deforming round the bracket.
So the next one was cut to 34mm, built up and still felt a bit tight. Gut feel with a pair of pliers suggests around 20lbft of torque required to turn
it. Liberal amounts of grease and it got down to about 5lbft of torque (probably loose enough for the fully welded wishbone to drop under it's
own weight), but I'm aware that the bush may spend more time without grease than with.
Should I drop down to 33mm to make sure everything is really loose, or does a 34mm tube sound about right? I'm aware that if I reduce the tube
too much I then introduce fore and aft travel which isn't going to be good.
Is there anything else I need to consider?
I may be corrected on this but in my experience the whole point of this arrangement is that it is the flex in the bush that permits rotation. The bolt and crush tube are fixed. No grease necessary.
Mmm, not considered it that way. I know that most production cars use bonded bushes, but those bushes are quite thick, several times thicker than what
is used on a locost. Although the bushes I'm using are quite soft, they're not that thick compared to a typical tintop.
The one thing I want to avoid is undue stress on the wishbone welded joints, along the lines of several failure threads on here. But it does sound
like 34mm should be fine.
You need to tighten the suspension bushes when the car is finished and settled on the road, they will not then be in tension standing still so should
not rip in use as the overall movement is within the design parameters of the bush.
Tighten with it jacked up and they will rip very quickly when in use, even standing still !
From your description I assume your using poly type bushes?
If so then you need to make sure they're greased between the crush tube and the bushes. The crush tube should be clamped in the suspension
bracket and the bush free to rotate around the crush tube. The bush led should also be a tight fit in the wishbone tube.
I.e. the crush tube should be slightly longer than the outer faces of the bushes when pressed into the wishbone. The outer faces of the bushes sold
also be greased to prevent stiction between the bushes and chassis brackets.
OEM type bonded suspension bushes are very different and rely on torsional flex in the rubber material. They will have a service life far higher than
poly type bushes, but inherently more movement and damping quality.
Hi Nick, yes I am aiming for what you're describing. As I'm trialling the wishbone tube, I have the crush tube clamped still in the U
bracket, and the bushes move with the outer tube.
So when you say 'the bush free to rotate around the crush tube', what is regarded as 'free'? I don't expect to be able to
rotate them with finger pressure, at the moment it feels like I'm tightening a nyloc nut, IE it's stiff but it is moving smoothly.
I want to get this stage sorted first before I use the tubes on the wishbones, that way I'll know when it all goes together that the wishbones
will work well.
Difficult to quantify in words how tight they should be, but I'd suggest the wishbone should fall slowly under it's own weight if that makes
sense. That way, when loaded with the weight of the car on it's wheels it should move smoothly with no squeaks or undue load on the
wishbones.
When assembling my MK Indy with all MK supplied parts, I had to take some time to match and adjust the crush tubes to the wishbones and bushes to get
the best fit. I also packed the small void between the bush halves very well with grease, then filled with grease before pressing the crush tubes
into the bushes, then a smear of grease on the outer faces of the bushes before the wishbone is fitted into the suspension brackets.
quote:
Originally posted by nick205
Difficult to quantify in words how tight they should be, but I'd suggest the wishbone should fall slowly under it's own weight if that makes sense. That way, when loaded with the weight of the car on it's wheels it should move smoothly with no squeaks or undue load on the wishbones.
When assembling my MK Indy with all MK supplied parts, I had to take some time to match and adjust the crush tubes to the wishbones and bushes to get the best fit. I also packed the small void between the bush halves very well with grease, then filled with grease before pressing the crush tubes into the bushes, then a smear of grease on the outer faces of the bushes before the wishbone is fitted into the suspension brackets.
Having taken a similar approach myself, I wonder how do Caterham and Westfield manage to amke theirs work?
Presumably they work to much closer tolerances for the tumes, bushes and spindleas and it just does?
Having taken a similar approach myself, I wonder how do Caterham and Westfield manage to amke theirs work?
Presumably they work to much closer tolerances for the tumes, bushes and spindleas and it just does?
Took me a while to figure out that the rotation should be around the crush tube and not the 34mm outer tube. I think if you get this wrong it could lead to the outer tube fracturing and failing. This is a critical part so somebody correct me if I'm wrong.
quote:
Originally posted by ReMan
Having taken a similar approach myself, I wonder how do Caterham and Westfield manage to amke theirs work?
Presumably they work to much closer tolerances for the tumes, bushes and spindleas and it just does?
quote:
Originally posted by Smoking Frog
Took me a while to figure out that the rotation should be around the crush tube and not the 34mm outer tube. I think if you get this wrong it could lead to the outer tube fracturing and failing. This is a critical part so somebody correct me if I'm wrong.
quote:
Originally posted by Slimy38
quote:
Originally posted by ReMan
Having taken a similar approach myself, I wonder how do Caterham and Westfield manage to amke theirs work?
Presumably they work to much closer tolerances for the tumes, bushes and spindleas and it just does?
Exactly, they make all their own parts that match up with correct tolerances, and they've had years to get it right. I'm working with a length of outer tube that I'm cutting to fit, and crush tubes bought from Ebay. So I have to be more flexible with my measurements.
I didn't take it as a criticism, more an entirely valid comparison of the resources available. As you say, some things do work out cheaper as pre-cut parts. I looked at buying steel tube to make up the crush tubes, but to get either the right sized metal (or the tooling required to make it the right size) would have cost me more than buying them from an engineer. In comparison, the outer tubes averaged around £3 a pop as pre-cut parts, and for 22 (ish) it was cheaper for me to buy a tube and cut it myself.
The old crush tube problem again! A few years ago there was a number of wishbone failures being reported on this site, from my own experience I suspect a lot of them were due to the crush tubes being too short or the wishbone eyes too long causing severe binding of the polybushes. Sorting the problem out makes the car so much more pleasant to drive and the suspension actually does what it's supposed to. Been covered several times
Yep, that's the one, but thankfully I'm at a place where an ounce of prevention will work better than a pound of cure.