Spindle Pin Rubber Washers

[Captain Obvious]

I'm having the issue that when I tighten up the spindle pin nuts, the control arm locks down so tightly to the strut assembly that the only articulation between the parts is what's allowed by the rubber bushing deflecting.

What you are describing is exactly how the rubber bushings are supposed to work. The only movement in the bushings comes from torqueing the rubber portion vulcanized between the inner and outer sleeves. Essentially, the inner sleeve rotates and the outer sleeve does not. That twists the rubber between the two. So, the spindle pin DOES act like a hinge, but the relative motion is not right at the surface of the pin. It's at the rubber.

That's why (with the stock style bushings) it's so important to put it on the ground before you tighten up for the final time. You want the rubber to be "at rest" in it's unstressed natural position when the car is sitting neutral. That way, the rubber can twist one way when the suspension is extended and twist the opposite when the suspension is compressed.

All the rubber bushings are like this too. Inner front, inner rear, outer rear. They all operate the same way.

Interesting to note that the poly bushings do NOT operate this way. They rotate the inner sleeve inside the poly bushing and because of that, you can tighten them with the suspension hanging.

And no... Mine isn't back together yet. Projects spiraling out control!

Fridge died. Garage door opener died. Battery in one of the other cars died.

[Captain Obvious]

And I know it seems like it takes a lot of force to twist the rubber bushings, but to the springs and the weight of the car? Easy. Those bushings will twist alright! They'll twist, or they'll tear!

And one more thing... The most common issue I can remember seeing with this type of bushing is that the mounting bolt or nut was not installed tight enough and the inner sleeve was allowed to rotate on the bolt. Galling, clicking, and mysterious hard to find odd knocking sounds usually result.

PS - I'm not at all a suspension guy. I had an epiphany about this stuff a little while ago and it suddenly all made sense.

[bacarl]

Awesome, thanks for the feedback Captain!

They'll twist, or they'll tear!

Tearing is exactly what I was worried about. It's counterintuitive to think that the full range of suspension travel could be taken up by the deflection of the bushing. No wonder they wear out.

...Projects spiraling out control!

I know we can all relate to that. Good luck with all of them!

[Captain Obvious]

It's counterintuitive to think that the full range of suspension travel could be taken up by the deflection of the bushing.

Agreed, but that's exactly what happens! The hard to believe-edness why it took me so long to catch on too. If you really study it though, there really isn't that much rotation. Especially if you start unstressed at the middle of travel. If you were to measure it plus-n-minus from there in degrees, it's really not that bad.

You doing inner rears too? Note the teeth on the inner sleeve of the inner rear bushings. Those teeth are intended to bite into the control arm and washer surfaces as extra insurance to prevent the inner sleeves from slipping.

Fridge is fixed. Garage door opener is fixed. Battery is still dead.

[jcb]

Agreed, but that's exactly what happens! The hard to believe-edness why it took me so long to catch on too. If you really study it though, there really isn't that much rotation. Especially if you start unstressed at the middle of travel. If you were to measure it plus-n-minus from there in degrees, it's really not that bad.

You doing inner rears too? Note the teeth on the inner sleeve of the inner rear bushings. Those teeth are intended to bite into the control arm and washer surfaces as extra insurance to prevent the inner sleeves from slipping.

Fridge is fixed. Garage door opener is fixed. Battery is still dead.

Captain, Thanks from me too. I have tried to figure out why it was so important to have the car on the ground before tightening those nuts. After your explanation it became, I hate to say it but I will, OBVIOUS. I could not resist. Thanks again for the lesson John

[Captain Obvious]

I hate to say it but I will, OBVIOUS. I could not resist.

Haha!! Glad to help!

Here I was thinking that I was the last person on the planet to realize what was really going on. Feels better to know that I'm in good company! Thanks!!

[EuroDat]

I read in a Holden HT Monaro workshop manual (very long time ago) that the bushes are designed to rotate a maximum of 22degrees in both directions (up and down).

I can't remember the figures on the car itself, but the suspension travelled a less than that, so I believe there is a certain amount of safety margin built in to compensate for differences in vehicle road height. The Monaro had more travel down than up and in a lowered car the effect would increase the downward amount.

Therefore if you had a suspension with say 30degrees movement and the road height at the rest position was at 18degrees (18 down and 12 up). Tightening the bushes in the down position (suspension hanging) would mean they are under a lot of tension when the car is at rest on the ground. Not good for the bushes.

Driving over bumps, causing small amouts of movement upwards, would send the tension over 22 degrees and damage the bushes. If the suspension reached the bump stops it would have then 30degrees on the bushes, way over the limit.

If the bushes had been tightened at rest position, they would only reach a maximum of 18 degrees downward movement.

I don't know what the figures are for the Datsun S30, but the bushes would probably have similar figures. I think the inner and outer diameter of the bush would also be a determining factor. A larger distance between the inner and outer ring means more rubber to flex and a greater rotation radius.

Chas

Edited April 6, 2014 by EuroDat