The Miata Bushing MEGAthread: Heirarchy, DIY delrin dimensions, info and discussion - Page 13 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 03-16-2017, 04:54 PM   #241
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Originally Posted by Godless Commie View Post
Spacer thing, good idea. I just make the flange width wide enough to take up the gap, but with about a 0.010" relief. So there is enough slop so it doesn't bind, but not enough to be even close to noticeable in use. And its worked well so far.

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Originally Posted by PAdutch View Post
Very clear, thank you.

I am coming from a Macpherson strut car, where I used to run alot of caster 6deg+. Having alot of caster allows you to run less static camber because of camber gain. This, in-turn, has better contact patch under braking and can increase your ultimate turning grip.

I guess I need to do more research on set-ups but I was thinking getting camber is easier than caster. I will be running a extended lower ball joint already and if I needed more static camber I could always make offset FUCA bushings (I may have to run a spacer for wheel clearance, no biggy).

I guess I curious about a setup like this:
Offset FUCA (adds camber)
Extended Lower balljoint (adds Camber)
Offset FLCA-R (adds caster, slightly decreases camber)
Poly FLCA-F

I'm not sure where that would leave you as far as alignment specs but Ill be doing some more research. Seems like to much caster can lead to corner jacking and bump steer issues possibly.
Most cars cant get the camber needed for autoX and track duty in stock form. So you usually need some form of camber correction, and tire wear seems to be more important than caster to most people, especially when you can get caster to an acceptable range. Having said that, you do either the ELBJ or offset bushing, you should never need to do both.

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Originally Posted by Godless Commie View Post
Given the amount of suspension travel, bushing ends obviously rotate just a couple degrees.
Wouldn't that require at least 10 or more "grooves" to properly clean the rotating sleeves in there?
Yup, another reason I wont do it. Especially on that offset pictured, the thin side is already kinda thin, grooving that could possibly make the bushing collapse. It was one of those, 3 is better than nothing things.
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Old 03-17-2017, 06:01 PM   #242
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FUCA-
1.There is no inner thrust face period. The bolt passed through a tube in the subframe, which is around the same diameter as the steel sleeve. So you would have to add a washer to make a thrust face for the flanges that would face each other.
2.. There is little relative load on this arm, 1 thrust face is fine.
3. Assuming you did #1, you would have to machine the sleeve length specific to each car. Alternatively, you could make sure that the sleeve bore lengths are within a few thou of each other, and that the gap between them is the same, minus flange thickness, as the mounting point width. And that whole stack-up cant exceed a few thou. Delrin is not squishy, so in order for the rear facing or front facing thrust surfaces to both take a their full load, you would have to fit them to each arm so there is probably around a 0.002" gap. There is too much variation in arms and subframes, and they are definitely not within 0.002" in any dimension. If not, one thrust surface will makes contact first, and the arm will have to bend the amount of the difference between sleeve length and flange gap on the other bushing before it make contact, and even then they are very unequally loaded. Never mind the fact that would make things kind of tight and a pita to install for the end user, for almost no benefit. This is true of all locations, and one of the benefits of running poly in each lower is that it mitigate this on the arms that carry the majority of the loads on the car (the LCAs).
Please bear with me on this, I am really having hard time wrapping my head around the FUCA bushings.
Pertinent statements are highlighted in bold above.

Regardless of design, ideally there should be no gap in the stack. (Stack: FUCA front bushing sleeve + tube in subframe + FUCA rear bushing sleeve)
Also, sleeves should not protrude from either end of the delrin bushings. Otherwise, the entire FUCA would slide fore and aft on the sleeves, and the sliding distance would be equal to the total sleeve protrusion from the delrin bushings.
Let's suppose sleeves are protruding 0.5 mm on either side on both bushings. This would mean a total travel distance of 1 mm.
Given the spindle height, a 1 mm travel will alter caster angle by 2.69 degrees - a 2 mm travel distance creates 5.38 degree caster variance.

So, there has to be a very precise fit for the FUCA bushings on either side of the subframe tube.

I really can not figure out what difference a 1 piece or 2 piece design makes in the light of the facts I tried to explain above.

If there is any gap in the stack at all, one surface will make contact first, like you said.
It's not like you can pull your one piece bushings into place by torquing the big bolt nut, because both bushings have lips on them. Can't move.
Bolt ends/washers etc make sure sleeves can not move in beyond flush with delrin surface.

All of these add up to one inevitable fact: Sleeves must have very precise dimensions.
And, once you have very precise sleeves, it really makes no difference whether you have 1 or 2 piece bushings, or if you are using washers on both ends of the subframe tubing.
All you need to do is subtract the thickness of the washers from the sleeve length and make them exactly that long.

Like I said, I am having the worst time comprehending your approach.
What the hell am I missing here?

-----------

Completely unrelated:

I am chrome plating my sleeves for the smoothest possible articulation, so there.

Thank you, and sorry for dragging this thing this far.

Last edited by Godless Commie; 03-17-2017 at 06:16 PM.
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Old 03-17-2017, 08:27 PM   #243
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Originally Posted by Godless Commie View Post
Now, if one were to move the FUCA towards the front by splitting that 11 mm difference like, say, 8 mm front and 3 mm rear, that would angle the upright towards the front at the top, yielding more caster.

I can never get the prescribed 5.5 degrees, best I can get is around 3 degrees or so.
Would such a modification be helpful, or am I missing something here?
Other way around?
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Old 03-17-2017, 08:29 PM   #244
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Other way around?
No.
Think shopping cart wheels.
The top moves forward to increase caster angle.
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Old 03-17-2017, 08:35 PM   #245
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No.
Think shopping cart wheels.
The top moves forward to increase caster angle.
AFAIK actual casters have zero caster angle
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Old 03-17-2017, 08:45 PM   #246
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Originally Posted by afm View Post
AFAIK actual casters have zero caster angle
They actually have quite a bit:


Red line is imaginary spindle/knuckle/upright, arrow points to the direction of travel (front)
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Old 03-17-2017, 08:55 PM   #247
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Caster is the angle between the steering axis and the vertical axis. In a caster, they are parallel, ergo zero caster.

What you're describing is trail (usually measured as a distance between intersection points with the ground), not caster. Also, moving the FUCA forward would potentially decrease trail, not necessarily increase it.
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Old 03-17-2017, 08:57 PM   #248
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Old 03-17-2017, 09:16 PM   #249
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Damn you.
I was so blissfully contended and happy till about 15 minutes ago.
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Old 03-17-2017, 09:18 PM   #250
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Lol
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Old 03-17-2017, 09:21 PM   #251
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Originally Posted by Godless Commie View Post
Damn you.
I was so blissfully contended and happy till about 15 minutes ago.
Just move the FUCAs back? Is there something that interferes if you do?
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Old 03-17-2017, 09:28 PM   #252
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Just move the FUCAs back? Is there something that interferes if you do?
Of course not.
I'm just angry at myself for getting it wrong and insisting on it.
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Old 09-10-2017, 04:28 PM   #253
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Default 65-75 ShD PU Bushes

Just read this thread with great interest.
Have you considered a 65-75 Shore D PU for the bushings instead of the Delrin ?
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Old 09-12-2017, 03:56 PM   #254
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Originally Posted by PKB222 View Post
Just read this thread with great interest.
Have you considered a 65-75 Shore D PU for the bushings instead of the Delrin ?
I'm really not sure how to respond.

So ill just go with: No, we have not.
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Old 09-12-2017, 04:49 PM   #255
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Might be worth considering it.
In general, polyurethanes have a better abrasion resistance, due to the elastomeric properties, that plastics do not have.
Polyurethanes are not brittle and even in the highest durometer ranges, remain elastomeric.
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Old 09-12-2017, 05:36 PM   #256
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Good to know. Thanks.
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Old 09-12-2017, 05:37 PM   #257
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Have you considered oem rubber bushings?
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Old 09-12-2017, 06:38 PM   #258
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Could not find a supplier "concealer404". If only there was like, 3, huge multinational corporations selling them that we could buy from....
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Old 09-12-2017, 06:43 PM   #259
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Originally Posted by PKB222 View Post
Just read this thread with great interest.
Have you considered a 65-75 Shore D PU for the bushings instead of the Delrin ?
So you state that you read the thread, then make a statement that makes it sound like you didn't.

You gon' earn some neg cats today...
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Old 09-12-2017, 08:30 PM   #260
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The bigger question is why they dont have a billet aluminum options for the front and rear uppers for the hard core amoung us. I already have billet front upper bushings, just now realized that they'd work fine in the rear too.
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