Mazda MX-5 Miata banner
1 - 20 of 25 Posts

·
Charged but not Prosecuted
Joined
·
1,640 Posts
Discussion Starter · #1 ·
Becuase I'm still vibrating from the horrific ride home.

A friend has told me I should have torqued the bushes up with the wheels on the ground, as they will twist and deform if I do it in the air and lower the car onto them - anyone been told this?

Just in general, the arms are now very stiff to move by hand (need 2 hand) - is this normal?

I used crap loads of grease.
 

·
Registered
Joined
·
760 Posts
You should tighten everything up with the weight of the car against the suspension. I just used my jack on the bottom arm, but be careful as it can slip. Keep your axle stands in place.
 

·
Charged but not Prosecuted
Joined
·
1,640 Posts
Discussion Starter · #5 ·
Google got me this

"Poly bushes can be bolted straight up (same torque settings) without any requirement to load the car or settle the suspension. This is because the central tube actually rotates in the bush as the wishbone pivots. With a conventional bush this movement is achieved by the rubber twisting so it was important to ensure that no strain was on the rubber in the "normal" settled position.
Logged "
 

·
Charged but not Prosecuted
Joined
·
1,640 Posts
Discussion Starter · #7 ·
I used every drop provided in the red tub.

I put it on the outer edge that mates with the wishbone, the inside of the bush and outside of the crush tube.

I'm wondering if I've done the bushes in the arms up to tight? That said the car was at WIM last week so all the lower arms will be correctly done up.
 

·
My boys in an Atom 300!
Joined
·
1,389 Posts
Just in general, the arms are now very stiff to move by hand (need 2 hand) - is this normal?
Here's your problem, not the amount of grease used or at what position the arms were when you torqued the alignment bolts up (if you can move them by hand eventually, then a few hundred kgs certainly will).

The problem is stiction and that's because the bush is too long so when it's all torqued up you're squashing the ends of the bush onto the subframe. In essence you need x amount of force applied to the bush before they break the static friction and move. This results in you bobbing up and down on the tyre sidewalls until you hit a bump big enough to move the suspension.

The only answer is to remove the arms again and inspect each bush. You'll find that the crush tube is slightly under the top surface of the bush. You want them to be flush both sides (you really should have them machined so each end of the 'cotton reel' is the same height).

These sorts of problems give properly engineered PU a bad name.....

HTH
Phil
 

·
Charged but not Prosecuted
Joined
·
1,640 Posts
Discussion Starter · #10 ·
Of course Phil is correct, Whipped a rear wheel of today and my arms are ridiculously stiff.

This is my first polybush experience so this rang alarm bells before.

Indeed the middle insert is not taking the force, instead the bush is.





Didn't expect this from Energy suspension...
 

·
Registered
Joined
·
289 Posts
I tried
haha

So just need to make sure the crush tube is exactly in the middle of each bush?
And that the end of the crush tube is flush with the face of the bush - you want the crush tube to take the clamping load rather than the face of the bush. If the tube is proud the suspension arm could waggle from side to side causing interesting geometry changes. If it's below then the clamping forces stop the arm from rotating as it should, and as you found.
 

·
Registered
Joined
·
1,925 Posts
I tried
haha

So just need to make sure the crush tube is exactly in the middle of each bush?
And that the end of the crush tube is flush with the face of the bush - you want the crush tube to take the clamping load rather than the face of the bush. If the tube is proud the suspension arm could waggle from side to side causing interesting geometry changes. If it's below then the clamping forces stop the arm from rotating as it should, and as you found.
[/quote]

One fundamental problem here is the variability, the wishbone eye width could easily be say 60mm +- 3mm in the OE application and not cause an issue, with a polybush it becomes a critical dimension, especially when as a lot of aftermarket parts are, the original pattern is made from the measurement of a set of customers arms rather than based on the OEM nominal figure.
 

·
Premium Member
Joined
·
19,520 Posts
so how far out do we think the crush tube should protude either side of the bush? 1/2mm?
0mm

And that the end of the crush tube is flush with the face of the bush - you want the crush tube to take the clamping load rather than the face of the bush. If the tube is proud the suspension arm could waggle from side to side causing interesting geometry changes. If it's below then the clamping forces stop the arm from rotating as it should, and as you found.
 

·
Registered
Joined
·
289 Posts
I tried
haha

So just need to make sure the crush tube is exactly in the middle of each bush?
And that the end of the crush tube is flush with the face of the bush - you want the crush tube to take the clamping load rather than the face of the bush. If the tube is proud the suspension arm could waggle from side to side causing interesting geometry changes. If it's below then the clamping forces stop the arm from rotating as it should, and as you found.
[/quote]

One fundamental problem here is the variability, the wishbone eye width could easily be say 60mm +- 3mm in the OE application and not cause an issue, with a polybush it becomes a critical dimension, especially when as a lot of aftermarket parts are, the original pattern is made from the measurement of a set of customers arms rather than based on the OEM nominal figure.
[/quote]

My view is that it is inordinately simple to get the crush tube to be the same width as the finished bush and allow the thin tabs on the suspension arm to deflect to take up any slack present. Producing an oversize bush in relation to the crush tube is pretty unforgiveable given when you know what the end result will be.
 

·
Registered
Joined
·
1,925 Posts
If you're using the two top hat construction for the bush then you're at the mercy of the wishbone eye width for your crush tube required width was the point I was trying to make. (if that makes sense)
 

·
Registered
Joined
·
289 Posts
If you're using the two top hat construction for the bush then you're at the mercy of the wishbone eye width for your crush tube required width was the point I was trying to make. (if that makes sense)
It makes sense but I can't see how this would ever occur. If the eye width is undersize then you'd get unacceptable end float in the connection irrespective of whether you got the crush tube the right length or not. I'd be stunned if a maunfacturer works to more than +/-0.2mm on something like a pressed steel wishbone with computer welded eyes.
 

·
Charged but not Prosecuted
Joined
·
1,640 Posts
Discussion Starter · #20 ·
Well ive got the rear up in the air.

The upper arms seem to be the issue here, as the hub and lower arms seem okay (lower arms are a little stuff but so I don't effect my allignment too much I'll leave those be for now.

The Upper arms are close, ie less than 1.5 mm between both sides, but you should beable to see from the pics the poly sticks out past the metal.



 
1 - 20 of 25 Posts
Top