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Using 5/8 bolt in place of spindle pin


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48 minutes ago, tube80z said:

The spindle-pin bolt doesn't rotate.  If it does then you have bigger problems.  In a stock car the inner bushing tubes are all compressed by the spindle pin nut against the strut.  The rotation comes from the rubber actually winding like a torsion spring.  That's why it's typically stated in the manuals that you need to torque at ride height or off jack stands.  As Jon mentions with poly the inner bushing tube is locked in place and the poly slides around the inner bush tube.  A rod end setup works exactly the same.

 

The resistance provided by either case: rubber torsional resistance for OEM & friction resistance from PU bushing riding against the steel sleeve they provide. 

 

Do you all think this resistance is necessary/important? Not arguing a point, more out of a curiosity. The resistance will act as a bit of a damper to high frequency vibration, and add a bit of static resistance to suspension travel. 

 

-Aydin 

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Since the 5/8" all thread is smaller than the original pin over time you will develop what is called fretting. The fretting is a type of wear and can create a rusty looking finish.  I personally would

The idea behind the spindle locking pin is that it is an extra safety mechanism.  If you lose one or both nuts and washers on the spindle pin it can't slide out, assuming you have one that can actuall

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1 hour ago, AydinZ71 said:

 

Do you all think this resistance is necessary/important? Not arguing a point, more out of a curiosity. The resistance will act as a bit of a damper to high frequency vibration, and add a bit of static resistance to suspension travel. 

Not only is it not necessary, it's harmful. The suspension should move with as little resistance as possible, and the resistance that you do have is provided intentionally by the shock and spring. That's why I posted that video on how properly designed PU bushings are made. You can copy some of their tricks with energy suspension stuff and improve them quite a bit.

Cary convinced me to do a lot of things on my car in the search for the least amount of friction possible. That's why I have the weird sway bar mounted on heims joints that I do among other things.

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3 hours ago, JMortensen said:

Not only is it not necessary, it's harmful. The suspension should move with as little resistance as possible, and the resistance that you do have is provided intentionally by the shock and spring. That's why I posted that video on how properly designed PU bushings are made. You can copy some of their tricks with energy suspension stuff and improve them quite a bit.

Cary convinced me to do a lot of things on my car in the search for the least amount of friction possible. That's why I have the weird sway bar mounted on heims joints that I do among other things.


This makes quite a bit of sense for a racing application. I think even worse is a big differential between the static and dynamic friction. If it takes a lot of force to “break loose” the PU bushing, it will resist suspension travel at low force inputs. Of course, I may be over analyzing this, and suspension forces may dramatically outshine bushing friction. 


For racing, why not go with bearing brass while you are at it! The surface will harden and self-polish with friction. You can use lithium or graphite lube between the steel bolt/spindle and bearing sleeve. If you really are committed to low friction, you could go with needle bearings, but you would need to watch the maximum tangential pressure. 
 

McMaster Carr anyone? 

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Again, nothing rotates around the spindle pin, so this isn't necessary. In the case of the bushings, the polyurethane or rubber is doing this. In the case of a rod end setup, they do have teflon impregnated steel races and chrome balls. Here's a shot of an aurora rod end, I've put green where the teflon lining is.

rodend.png

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On 3/17/2021 at 6:58 PM, AydinZ71 said:


This makes quite a bit of sense for a racing application. I think even worse is a big differential between the static and dynamic friction. If it takes a lot of force to “break loose” the PU bushing, it will resist suspension travel at low force inputs. Of course, I may be over analyzing this, and suspension forces may dramatically outshine bushing friction. 


For racing, why not go with bearing brass while you are at it! The surface will harden and self-polish with friction. You can use lithium or graphite lube between the steel bolt/spindle and bearing sleeve. If you really are committed to low friction, you could go with needle bearings, but you would need to watch the maximum tangential pressure. 

 

This is done time-to-time on various suspension bits, like a-arms.  The one problem is that any bending will cause bind in a setup like this.  So while it may have really low static friction when you put lateral and longitudinal loads into the bushing/bearing.  Anyone who used the old Delrin/Al replacements up put on caster or toe in the rear would see that it often lead to wear patterns on the bushings.

 

While the stock rubber bushings may not be ideal for our cars the poly versions are often upgrades.  The downside is that unless you take very good care of them they'll lead to stiction (friction  that Jon mentions) and that can lead to an abnormally harsh ride over certain sections of road in a street car or lead to weird handling irregularities.  I'm not saying all poly bushings do this as there are clearly really good one.  But unless you give them care and feeding you may run into some down sides.

 

Newer street cars still use rubber bushings, which I used to hate.  But now modelling has gotten a lot more refined and rubber bushings are designed to limit flex in one area and allow more in another axis.  Think of running into a pothole and the suspension has a little extra lateral movement that allows for the jolt that you normally feel to be reduced.  So you get a win/win.  And even sportier models often use the equivalent of spherical bearings (BMW M cars) but they have proper seals for long term use.   

 

Hope that helps, I know this is somewhat off topic to the original post.

 

Cary

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