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Chassis Brace and trans brace necessary?

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Old Aug 9, 2022 | 08:16 PM
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Chassis Brace and trans brace necessary?

So, I finally got my FD off of the ground with a pair of quick jacks and got a good look at the undercarriage and just realized that there is no chassis brace (4121D 2H7-1378) or A tunnel brace, I’m sorry if I have these names wrong. Should I get these and put them on? If so are there any aftermarket ones that make a noticeable difference or is stock just fine. Thanks!! Parts missing circled in pic.
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Old Aug 9, 2022 | 08:36 PM
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There are 3 aluminum tunnel braces.
1. Front (under trans)
2. Middle
3. Rear (under diff)
I have 1 & 3...$25 each shipped
You circled 1 & 2
Jim T
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Old Aug 10, 2022 | 05:28 AM
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No technical background… you could drive the car (easy) without them. However… I think those braces are there for chassis torsional loads. The engineers felt they were necessary and probably should be replaced asap.
No connection to tomsn16, but that doesn’t sound like a bad price for two of them.
I’m only aware of Banzai’s transmission brace as a substitute for the front (#1) brace and I think some of the aftermarket differential braces would take the place of the rear (#3) brace.

Last edited by Sgtblue; Aug 10, 2022 at 05:32 AM.
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Old Aug 10, 2022 | 05:45 AM
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Originally Posted by Sgtblue
No technical background… you could drive the car (easy) without them. However… I think those braces are there for chassis torsional loads. The engineers felt they were necessary and probably should be replaced asap.
No connection to tomsn16, but that doesn’t sound like a bad price for two of them.
I’m only aware of Banzai’s transmission brace as a substitute for the front (#1) brace and I think some of the aftermarket differential braces would take the place of the rear (#3) brace.
Those were kind of my thoughts as well. I’ve owned it for the last 4 years and just now found out about it. I saw the banzai ones and I think sake bomb makes one as well but they seem very expensive lol well if anyone has the second one, I’m looking for that one as well! Lol
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Old Aug 10, 2022 | 06:10 AM
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You’ll also need some of the standard 12mm flanged-head bolts. I think the stock ones are galvanized but since they go into factory nut-serts I still use a bit of silver anti-seize.
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Old Aug 10, 2022 | 09:52 AM
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Originally Posted by tomsn16
There are 3 aluminum tunnel braces.
1. Front (under trans)
2. Middle
3. Rear (under diff)
I have 1 & 3...$25 each shipped
You circled 1 & 2
Jim T
pm’d
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Old Aug 10, 2022 | 09:52 AM
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Originally Posted by Sgtblue
You’ll also need some of the standard 12mm flanged-head bolts. I think the stock ones are galvanized but since they go into factory nut-serts I still use a bit of silver anti-seize.
that’s good to know, saved me from trying to fold bolt size lol thank you!
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Old Aug 10, 2022 | 10:17 AM
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Check out the AutoEXE braces. Chances are your car had them in the past, and they were stripped off before the car was sold. Best explanation as to why the OEM braces are missing.

https://www.rhdjapan.com/autoexe-mem...rx-7-fd3s.html
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Old Aug 11, 2022 | 04:32 AM
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They may have some pole vault safety function if the tailshaft gets crazy and starts ripping up the tunnel, breaking the ppf - and your lower limbs.

I wouldn't necessarily expect a brace to have been removed, a lot more common, the captive nuts are often loose between skins......or stripped! The bolts are M8. speccing by head size if trying to buy at a fastener shop rather than oem, might result in another trip....and unless they deal in jap standard, it would be a 13mm hex.
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Old Aug 11, 2022 | 05:35 AM
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Originally Posted by billyboy
They may have some pole vault safety function if the tailshaft gets crazy and starts ripping up the tunnel, breaking the ppf - and your lower limbs.

I wouldn't necessarily expect a brace to have been removed, a lot more common, the captive nuts are often loose between skins......or stripped! The bolts are M8. speccing by head size if trying to buy at a fastener shop rather than oem, might result in another trip....and unless they deal in jap standard, it would be a 13mm hex.
I do like my lower limbs where they are…lol that’s good information though thanks man! i hope they aren’t stripped. I haven’t even messed with it yet. I have sourced the necessary parts though, thanks guys!!
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Old Aug 11, 2022 | 06:27 PM
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I'd like to suggest considering the aftermarket tranny and diff braces. The FD was fantastic when it came out, but has a fair amount of chassis flex compared to what is available today. The very much improved bracing from Banzai do help stiffen the chassis a bit if for nothing other than eliminating the effects of the transmission tail movement. There may be others like these, but these are what I've been using.

Transmission Crossmember

Differential Brace
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Old Aug 11, 2022 | 06:41 PM
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THE BRACE
https://www.rx7club.com/market/11535...ght=hpp%202in1
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Old Aug 12, 2022 | 08:14 AM
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Originally Posted by gmonsen
I'd like to suggest considering the aftermarket tranny bracing from Banzai do help stiffen the chassis a bit if for nothing other than eliminating the effects of the transmission tail movement…
@gmonsen Almost pulled the trigger on that a couple times. Has it been as advertised? Any NVH increase from it?

Last edited by Sgtblue; Aug 12, 2022 at 05:39 PM.
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Old Aug 20, 2022 | 10:16 PM
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@Sgtblue I am very happy with them. It feels stiffer. More solid. No added NVH.
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Old Aug 23, 2022 | 12:01 PM
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Originally Posted by tomsn16
I’m gonna keep that in mind, I got the sake bomb garage trans brace and put that on. Near future I’ll be putting a 20b in her, so I’m not sure what kind of rear end I’ll be running just yet.
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