Clutch Master Cylinder

[Chevyho]

Can anyone tell me how big of a hole needs to be drilled in firewall for the hydraulic clutch master cylinder? I am not near the truck and need to pick up a hole saw. Or does anyone have a template or blue print? Thanks in advance!

 

[SquareRoot]

Cant recall BUT you need to measure the the flange on the master cylinder and use that as your guide. It needs to be almost exact as there are two mounting studs on each side of it. You only have like an1/8th inch in diameter to play with. What year truck is this? The OEM hydraulic clutch trucks (85-87) have dimples in the firewall where the holes for the M/C and support rods go.

 

[Chevyho]

Thanks for the reply. It is a 84, its a race truck that is being converted from auto to manual with hydraulic clutch. Peddle assembly is already in just need to mount cylinder with rods, there are no dimples as most the firewall has been smoothed previously. Was hoping someone had the measurement so I could grab the correct or even one size smaller hole saw then dremel out when Im back in town on days off. If I was near the truck to measure this would be a non issue

 

[Chevyho]

I will drill the center hole first, then mark the 2 rod support holes with the cylinder set in place

 

[nvrenuf]

Here's a templete.

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[Chevyho]

Thanks, I have seen that but doesnt mention diameter of center hole

 

[AyWoSch Motors]

Too bad you hadn't mentioned that a day earlier, I just had mine out, could've measured it.
Heres a pic if that helps at all.

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I'd guess about an inch, inch and an eighth..

 

[Chevyho]

Thank you! I was thinking roughly 1-1/8 too if I wasnt such a dumb a** I woulda measured before I headed out of town hah

 

[nvrenuf]

Thanks, I have seen that but doesnt mention diameter of center hole

Right but you said you were drilling other holes so...

Worst case just go to a parts place and have them pull the m/c to look at.

 

[CRM]

Taking a tape to the previous drawing it looks like it's somewhere between 1 1/4" to 1 3/8".

 

[Chevyho]

Thank you! At least I can make sure I buy a couple in that range

 

[Elliot W]

There is an existing hole in the firewall on my 74 that was close enough to use for the clutch M/C, just to the right of the brake M/C, so you may not have to drill a hole. I think it had the speedo cable going through it, which, depending on your transmission choice, may not be needed anymore or possibly relocated if still needed. What transmission are you going with?

 

[Chevyho]

Would you happen to have a picture of the hole? I am using a saginaw 3 speed (its a hobby stock truck). No speedo

 

[Elliot W]

Truck looks awesome! I'll get some photos this evening with the MC attached. The hole I'm talking about is the one to the right of the brake MC with the cable coming out of it.

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[Elliot W]

Here are some other photos from using the existing hole for the clutch MC