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PostPosted: April 16, 2013, 11:00 am 
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Mid-Engined Maniac

Joined: April 23, 2006, 8:26 pm
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Location: SoCal
I built a mid-engine car using Miata uprights, with the rubber bushing in the top of the rear uprights. I've been driving the car for about a month and noticed that the steel bushings in the rubber bushings have shifted, and now the uprights are grinding on my upper A-arms :?

Anyone else have this happening?

I'll add a picture later.

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PostPosted: April 16, 2013, 11:54 am 
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Sounds like the steel sleeve isn't bonded to the rubber anymore? If you cycle the suspension up and down does the sleeve rotate in the rubber?

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PostPosted: April 16, 2013, 12:17 pm 
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Mid-Engined Maniac

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Maybe... I'll check. Both sides are doing it though so it seems odd I'd end up with two "broken units", but who knows.

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PostPosted: April 16, 2013, 2:33 pm 
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Joined: July 7, 2011, 12:17 am
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They should be 'relaxed' at roughly ride height. If they get tightened down at full droop, for example, they can be asked to rotate through more angular degrees than they can handle. This will tear them of course. Just a shot in the dark.

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PostPosted: April 16, 2013, 6:46 pm 
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Turn some plastic top hats, flanged two piece arrangement that fit very tight to the inner, loose to the outer for longer lasting bushings, due to much greater area to rub on the od. A hand torch can eventually ignite the rubber and the entire mess will slide out clean, leaving the steel shell. Best to do in an industrial park rather than a subdivision in CA.

UHMW is very tough and long lasting but also difficult to keep greased. Make some grease retaining grooves and add zerks.


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PostPosted: April 24, 2013, 3:19 am 
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Location: Portland, OR
I think rtz hit the nail on the head - all of those stock rubber mounts need to be tightened up at ride height - even being off a bit will cause extra stress. it's all too common to see them be tightened down at full droop and then twisted up when set back down on the ground.

Miatav8,MstrASE,A&P,F wrote:
Turn some plastic top hats, flanged two piece arrangement that fit very tight to the inner, loose to the outer for longer lasting bushings, due to much greater area to rub on the od. A hand torch can eventually ignite the rubber and the entire mess will slide out clean, leaving the steel shell. Best to do in an industrial park rather than a subdivision in CA.

UHMW is very tough and long lasting but also difficult to keep greased. Make some grease retaining grooves and add zerks.


could also buy some off the shelf poly bushings as a replacement. I've got some poly bushings I used before I replaced them with heims (also a good option, see [url]=http://locostusa.com/forums/viewtopic.php?f=5&t=14096]here[/url]) I'd be happy to ship you the bushings for the cost of shipping if you'd like an easy replacement option.

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PostPosted: April 24, 2013, 9:40 am 
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Mid-Engined Maniac

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Thanks for the input, picture below of how it was. I realized that the stock rubber bushings see higher force in my car due to: more horsepower, more weight, more traction, and the thing that likely caused them to shift, higher braking forces attempting to rotate the uprights forward (both were shifted toward the front of the car.) FWIW there was no evidence of the rubber being damaged in any way. It's fairly soft; I stuck a screwdriver through the bushing and was easily able to move it around.

I got the old ones out by using a 1/8" drill and drilling multiple holes down between the upright and steel sleeve (the rubber thing has two steel parts, an outer sleeve and an inner bushing that the bolt runs through, and therefore two areas of rubber.) After drilling a bunch of holes I grabbed the end of the steel bushing with ViceGrips and spun the assembly out.

Tongboy, thanks for the offer of the bushings. However, since I'd been meaning to replace the rubber with spherical bearings anyway, having this happen just sped up the process. Interestingly, the ID of the bore is 1.500", so a 1.500" bearing can be driven into place unmodified. The parts I used came from http://www.iscracing.net/miatasuspension.html and were bought mostly to save time but also to see how they designed it. The bearing is held in place by two press-in bushings which go on either side of the bearing. They're tack-welded in place and realisticly aren't ever coming out, making the upright a throw-away assembly if the bearing wears out. Since the bearing has a 0.75" bore it's way overbuilt and should last the life of the car. Adaptor bushings reduce that bore down to whatever you want; I drilled and reamed mine to 0.500"


Image

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PostPosted: April 24, 2013, 12:51 pm 
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KB58 wrote:
Tongboy, thanks for the offer of the bushings. However, since I'd been meaning to replace the rubber with spherical bearings anyway, having this happen just sped up the process. Interestingly, the ID of the bore is 1.500", so a 1.500" bearing can be driven into place unmodified. The parts I used came from http://www.iscracing.net/miatasuspension.html and were bought mostly to save time but also to see how they designed it. The bearing is held in place by two press-in bushings which go on either side of the bearing. They're tack-welded in place and realisticly aren't ever coming out, making the upright a throw-away assembly if the bearing wears out. Since the bearing has a 0.75" bore it's way overbuilt and should last the life of the car. Adaptor bushings reduce that bore down to whatever you want; I drilled and reamed mine to 0.500"

http://www.midlana.com/Diaries/Current/offset_bushing.JPG


Haha, I literally did *exactly* the same thing down to drilling the bushings to .5" (okay, fine, I did a 1st undersize to .498") the thread I linked about the sphericals was talking about those very parts.

From a locost perspective I think the total cost of the DOM tube (which is all the outer spacers that get tacked in were) and the heim joints could be done for a lot less than ISC charges but their value add (and it really isn't that costly for so much of an improvement in suspension control) is the smaller bushings that would be difficult/impossible to make without a lathe

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