someotherguy
Truly Awesome
The cab already had a smaller clutch master cylinder hole because it was a standard trans truck to begin with. For the older trucks they had a single smaller hole and a diagonal bolt pattern as the m/c bolted directly to the firewall, instead of locking into that bracket that bolts into the cab on the interior side of the firewall.What technique did you use to enlarge the second hole? Did you have the clutch pedal installed while you made it bigger?
I'd say it's practically impossible to copy what the factory did, after the fact, or at least extremely difficult. So what I did was simply make one single large hole. I used a die grinder and just kept going a little bit at a time until the m/c would fit. Made a template from the newer cab and marked the firewall then went after it with a variety of bits, and it wasn't fun.
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However without the stepped hole the newer style cab has, the m/c will clock into the bracket, but will be loose on the firewall. That's why I had to use the "gasket" made from whatever that piece was I found in the bolt bin. It sounds like a hack but it worked perfectly, it was a slightly flexible piece of rubbery plastic (possibly an old antenna bezel/grommet) that took up the slack and kept the m/c firmly in place so it couldn't twist and come out of the bracket.
No worries at all. Was just pointing it out so you'd know when I replied that I knew what I was talking about because I'd been there and suffered that whole mess, LOLAnd sorry that I stole your picture. It was the best one that I could find!
I'm sorry I don't have any better pictures of that part of the project. I had painted the firewall of the cab in POR-15 (it was a former diesel truck and those have an insulating pad on the firewall so it had slight surface rust; I was already doing the cab floor so I said why not do the firewall, too) so it's glossy and made for bad flash pictures. You can see the old m/c diagonal bolt pattern and small hole; as I said I just kept enlarging it a little bit at a time with the die grinder and test-fitting along the way. (Obviously with the interior bracket's square hole you can't have the bracket in the way while you're grinding.)
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Can't see the grommet I used but it's in there now.
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Richard