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Discussion Starter #1
I got a great set of recovered Mustang GT seats that came from an 87 and I’m putting them in my 84 Bronco.

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My seat had low back buckets already so the mounts are mostly compatible. Here is a photo of the bottom of the passenger seat after I removed the original Mustang rails and installed the flip-forward seat mount.

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The passenger seat is a direct fit. There or 8 holes drilled on the bottom of the seat at the rear for the mount and 2 in the front (4 + 1 on each side, respectively). The front two holes are used regardless of the application. In the rear the Mustang seat rails use the holes 2nd closest to the back, but the Bronco seat mount uses the holes that are 3rd closest to the back. Easy-peasy-Japanesey.

Not quite as easy with the drivers seat. It has the depression for where the holes should be drilled for the Bronco mounts, but it isn’t actually drilled out! See the picture below of the bottom of the drivers seat and you will notice that the 3rd “holes” from the back are just depressions and not holes.


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So it looks like I will be drilling those out myself. Anybody know what size and type of drill bit I will need to use? I’m assuming that the bolts that go into the bottom of the seats are self-threading and I just need to drill the appropriate size hole for the standard seat bolt. Correct?

Thanks
 

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85 Bronco, 309ci I6 w/4bbl, np435, 4" lift, 37" Irok NDs, 4.56 w/ Detroit Locker and tru trac
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I did the same with 03 mach1 seats in my 85. Passenger side went in just the same as yours. Driver side requires the two rear holes drilled. My driver seat was powered, so it didnt have those two series of 4 holes drilled at the back. The bolts from the factory are metric. I drilled all my holes out to 5/16 and tapped them for 3/8-16 bolts. This way I could raise the seat on spacers and longer bolts for offroad visibility.

Neither the 85 or 03 seat bolts were self tapping, especially in that super steel the bases are made of.
 

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Discussion Starter #3
Thanks again BigBlue. I saw your earlier post but wasn't sure if the seats were the same. In retrospect was it worth the extra effort to tap it or do you think a flanged nut would've been sufficient?
 

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85 Bronco, 309ci I6 w/4bbl, np435, 4" lift, 37" Irok NDs, 4.56 w/ Detroit Locker and tru trac
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Definitely worth it imo, but drilling and tapping is no issue for me. I'm a trained machinist. I hate having to fight nuts in an odd or hard to get to area. So it was a no brainer. Plus, since I was adding length to the fastener, going to a larger bolt keeps some strength in the mount.

A flanged nut, or nut and washer would definitely be sufficient without spacers.
 

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Well I’m an engineer and the only machines I use regularly are a computer and a mechanical pencil, but I’m not going to let my complete lack of skills or equipment stop me. Isn’t that what YouTube is for?

Seriously though, if I want to use the existing bolts which are 5/16”-18, do you know what size carbon drill bit and hand tap I would need? I’ve got time on my hands while I shelter in place...
 

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An F drill is correct for 5/16-18 tap. It measures .257, so I've used a 1/4" bit many times when I didn't have an F drill handy.
 

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85 Bronco, 309ci I6 w/4bbl, np435, 4" lift, 37" Irok NDs, 4.56 w/ Detroit Locker and tru trac
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Seriously though, if I want to use the existing bolts which are 5/16”-18, do you know what size carbon drill bit and hand tap I would need? I’ve got time on my hands while I shelter in place..
I would guess the factory bolts are a metric, since they used a metric head on em. Some imperial threads match up close with some metrics.

And yeah, an F drill is right, but 1/4 works in a pinch. Just break your chips off a bit more often.
 
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