MGB & GT Forum

My latest project is restoring the transmission mount including new bushings and hardware. While removing the support brace I noticed a variety of bolts and variety of sizes/length and a couple actually missing which was why it was a little easier to remove. I have a good inventory of grade 5 & grade 8 bolts so I will typically replace most bolts with new ones. I was fighting some of the holes with the new bolts so I ended up "tapping" the holes where the support bolts into the underside as well as the holes in the transmission itself where the rubber mounts bolt on. When I test fit one of the holes in the transmission I was able to screw in a 5/16" x 24 bolt so I tapped the remaining 3 the same. I later heard that bolt was a UNC thread so I'm confused as to which is accurate? And, is it possible a previous owner tapped a fine thread into a course thread hole? My new fine thread bolts screwed in easily and seemed to have a good grip... I'm worried that I ruined the ability for that screw to hold tight...

Steve

UNC is used when screwing into soft metal like aluminium EG the 4 holes in the transmission casing for the pair of mounts. IDK what your fix is unless you go up a size.

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Mk1: CKD 11/66 first registered 8/5/67; owned since 3/77. 18GB +40 balanced. Peter Burgess BVFR head. Piper 285. 123. FidanzaFW. 4synch c/r box. Superpro. Nut and bolt rebuild 2010 - 2015. Tartan Red.

GT: 12/78. VW Golf guards, flush fit front and rear valances, frenched indicators, Mk1 rear lights - LED lights. 'Worked' Rover V8, Monsoon ECU for EFI. Commodore VSV8 GM4L60E, Lokar tiptronic shifter & Quick4 controller. Vintage Air A/C. FC IFS. CCE 4 link rear. Salisbury with Quaife. Jaguar Storm.

With a little bit of Loc-Tite or a lock washer on each one you shouldn't have a problem. May want to check them after a few hundred miles just to be sure.

Thank you for your responses... I was afraid those were my choices. If I decide to "go up a size" Barrie, have you done that before? Is it a difficult job to keep the hole straight while boring it out? I'm a bit worried about screwing it up beyond fixing...

I have only upsized the MC flanges to 3/8 UNC but they were not already threaded. Even if you used a helicoil you need a bigger hole. OTOH you should be able to feel for how tight your repair already is.

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Mk1: CKD 11/66 first registered 8/5/67; owned since 3/77. 18GB +40 balanced. Peter Burgess BVFR head. Piper 285. 123. FidanzaFW. 4synch c/r box. Superpro. Nut and bolt rebuild 2010 - 2015. Tartan Red.

GT: 12/78. VW Golf guards, flush fit front and rear valances, frenched indicators, Mk1 rear lights - LED lights. 'Worked' Rover V8, Monsoon ECU for EFI. Commodore VSV8 GM4L60E, Lokar tiptronic shifter & Quick4 controller. Vintage Air A/C. FC IFS. CCE 4 link rear. Salisbury with Quaife. Jaguar Storm.