Rear subframe bushing fit - 2nd gen

[Eagle7]

86 RX-7.

My rear subframe was rattling around with about 1/4" movement, so I tore it all apart. It has delrin bushings installed by the prior owner. The bushings have about a 23 mm hole at the top, tapering down to about 18 mm at the bottom. Problem is that the "stud" that the bushing goes over is only about 18 mm at the top, tapering down to about 14 mm at the bottom, thus the 1/4" movement.

"Gee, seems strange that these delrin bushings would wear that much", so I checked the factory bushings on the subframe that came from my '88 parts car. Same dimensions as the delrin bushings. So now it looks like the "stud" is the wrong diameter, but I can't believe that either.

This is all very strange. What am I missing? It can't be that it's supposed to be that loose a fit, can it?

Thanks,

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Marty Doane
ITS RX-7 #13
CenDiv WMR

[This message has been edited by Eagle7 (edited June 02, 2004).]

[Eagle7]

Still scratching my head on this one. MazdaSpeed doesn't seem to have any ideas either. Shouldn't be a difference in model year, as the delrin bushings are specified for 86-91.

Just to be clear, the bushings I'm talking about mount just forward of each rear wheelwell, are raised vertically into position, and are held in place by a metal plate and a nut.

Anybody know whether your rear subframe fits snugly or has this very loose fit?

Thanks,

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Marty Doane
ITS RX-7 #13
CenDiv WMR

[C. Ludwig]

I've never replaced the bushings in mine but I've had several apart. Never noticed any unwarrented slop in the factory pieces.

[paulydee]

I replaced the ones in mine with no issues.
Are these the bushings you are talking about?

http://www.iridiumracing.com/subframenew.jpg

[C. Ludwig]

How'd you post a pic showoff? http://Forum.ImprovedTouring.com/it/smile.gif

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Chris Ludwig
08 ITS RX7 CenDiv

[Eagle7]

Here's the post on the car.
http://www.i2k.com/~mdoane/RearSubframePost.jpg
And the factory and delrin bushings from the top.
http://www.i2k.com/~mdoane/RearSubframeBushingTop.jpg
And from the bottom.
http://www.i2k.com/~mdoane/RearSubframeBushingBottom.jpg

Makes no sense to me.

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Marty Doane
ITS RX-7 #13
CenDiv WMR

[paulydee]

Now who is the show off http://Forum.ImprovedTouring.com/it/smile.gif

I guess we are on the same wavelength. It has been a while since I installed my bushings but I don't recall and fitment isses or any excesive play. Maybe the bushings were installed incorrectly and caused them to "wear out:?

PMD

P.S. Chris, you have to use UBB code, and a link to a website to post pics. I have everything layed out on my website, and I just linked to it.

[Eagle7]

Wear was my first thought too, but all four bushings from two different cars with the same dimensions convinced me otherwise. Nor do the posts look worn, and they both measure the same.

I'm still hoping for some info from Mazda. If nothing else pans out, I might try to make some sleeves to fit inside the bushings.

Pauly, I'm planning Gingerman in June, BHF in July, Grattan in Aug and Mid-Ohio in Sept. Will I see you at any of those events?

Thanks guys,

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Marty Doane
ITS RX-7 #13
CenDiv WMR

[paulydee]

I don't want to go to Gingerman for a one day deal. Most likely I will be going to Mid Ohio for the rest of the season, including September. Maybe I will see you then.

Pauly D

[JeffG]

Isn't the taper there to allow the cross member to tilt, as in rear camber?

Jeff

[JeffG]

I guess I should think first!


<font face=\"Verdana, Arial\" size=\"2\">Isn't the taper there to allow the cross member to tilt, as in rear camber?</font>

The taper is there simply for manufacturing. The spacer inside the ruber wount will be torqued against the body.

However, some allowance for camber and flexing should be made if one repaces the ruber with a hard synthetic material.

Jeff

[Eagle7]

Hmmm. Hadn't been thinking about camber allowance. So might that mean that my 1/4" of rear wheel movement is normal?

BTW, I don't think the nuts under the bushings were tightened to spec. Seemed fairly loose when I took it apart. However, it doesn't seem right to expect the subframe to stay in position under accel, braking and cornering loads just because of tension on that nut.

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Marty Doane
ITS RX-7 #13
CenDiv WMR

[JeffG]

The sub frame will move some amount, to be determined by the load and the stiffness of the rubber mount. The torque on the steel spacer in the center of the mount keeps the spacer itself tied to the chassis. So any deflection of the sub frame is taken up by the mount.

I personally don't think these mounts should be replaced with a hard plastic insert. There's no sanitary way to handle motion of the sub frame, possibly inducing more bending of the mount post. I'd go back to stock on this one, IMHO.

[Eagle7]

I talked with SpeedSource this afternoon. Very willing to help. Much appreciated.

They said (as Jeff did) that the stock arrangement is good more manufacturing assembly, but not so great for performance. They also don't like the Mazda delrin bushing for the same reasons. They want to eliminate any movement at all. They sell bushings that are a very snug fit, requiring a jack and very good alignment in order to raise the subframe into position.

They suggested I make sleeves for my bushings that eliminate nearly all the slop in the fit. Sounds like a plan.

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Marty Doane
ITS RX-7 #13
CenDiv WMR

[Karl Bocchieri]

Your all on the right track, the stock bushings do alow some movement which helps in assembly, but "may" be bad for performance. The derilin are sloppy to alow for assembly, camber change and car differences. I used custom tighter ones in my old car, it was almost impossible to get the rear subframe aligned and installed. Four guys and four jacks, and if you want to change the rear, the whole subframe has to come down because there is no play or ability to tilt the subframe.
My car now has the stock bushings and I realy can't tell any difference, runs the same times as before.