Rear suframe bolts

Technical advice Q&A

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Threadbear
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#1 Rear suframe bolts

Post by Threadbear » Mon May 11, 2026 8:03 am

Hi, I've done a stupid thing, rebuilding my rear subframe to fit new brakes etc. Ive managed to end up with 2 special bolts which I cant find a home for! They are 7/16 unf, with nuts and 2 washers each, 2 1/2" long with a 9/16 hex head. They are not the special bolts for the radius arms, those are 1/2 unf and already fitted. I have only 2 bolts for the rarb drop links, which are also 7/16 unf, so I've obviously mixed something up, but I cant figure out what I've done. Can anyone steer me in the right direction please? Note to self: always label these bolts!
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mgcjag
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#2 Re: Rear suframe bolts

Post by mgcjag » Mon May 11, 2026 9:02 am

Rear anti roll bar I think....Steve
Steve
69 S2 2+2 (sold) ..Realm C type replica, 1960 xk150fhc

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Threadbear
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#3 Re: Rear suframe bolts

Post by Threadbear » Mon May 11, 2026 9:04 am

Thanks, that would make sense because thats all I've got left to fit, but I dont understand the need for special bolts there, cant see a hex recess or anything.

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mgcjag
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#4 Re: Rear suframe bolts

Post by mgcjag » Mon May 11, 2026 9:11 am

Possibly a thinner head for clearance......without a setup in front of me I can't tell.....dont overthink it....Steve
Steve
69 S2 2+2 (sold) ..Realm C type replica, 1960 xk150fhc

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Gfhug
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#5 Re: Rear suframe bolts

Post by Gfhug » Mon May 11, 2026 9:56 am

Steve, I think you’re correct, from what I remember there is little room to pass a full size hex head beside another part.

Geoff
S2 FHC Light Blue
S2 OTS LHD - RHD full restoration

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angelw
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#6 Re: Rear suframe bolts

Post by angelw » Mon May 11, 2026 10:18 am

Steve Wrote:
Rear anti roll bar I think....Steve
Hello Steve,
No cigar I'm afraid.

That bolt with the thin head, is the bolt that secures the small rubber bush end of the Radius Arm to the Wishbone of a Series 1 car. Series 2 and 3 cars have a more conventional bolt, where the thread points towards the outside and engages with a threaded hole in the outer yoke of the wishbone that the hub carrier is attached to. To facilitate that entry direction, part of the hex head of the bolt has a flat machined down to the periphery of the bolt's shank to provide clearance so that the head of the bolt can pass by the shock absorber lower fulcrum boss. This clearance is also facilitated by a removable spacer collar.

With a Series 1 car, the bolt, which is a special bolt with a thin hex head, enters from the outside of the outside yoke, passes through a plain hole in the yoke (no thread), through the small bush end of the Radius Arm, and secured with a nut. The thin hex head of the bolt is driven into a shallow bore in the yoke, with the corners of the hex being an interference fit with the bore so as to stop the bolt from turning when the nut is being tightened. As a consequence of this system, the Radius Arm can't be detached from the wishbone without detaching the hub carrier from the wishbone.

Regards,
Bill

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tim wood
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#7 Re: Rear suframe bolts

Post by tim wood » Mon May 11, 2026 11:07 am

Spot on correct as usual Bill
Series 1 FHC purchased 50 years ago. Courted my wife in it.
Series 1 2+2 when the kids were small now sold.
Series 1.5 OTS in opalescent maroon, Californian car. My retirement present.

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#8 Re: Rear suframe bolts

Post by mgcjag » Mon May 11, 2026 11:39 am

C18296 is a special head 7/16 bolt used on the rear anti roll bar on some cars.....the original posted did say the bolts are not for the small bush on the sway bar that are larger 1/2in that he has fitted already.....what model car is this from?....Steve
Steve
69 S2 2+2 (sold) ..Realm C type replica, 1960 xk150fhc

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