I can't believe that it's 2016, and there isn't a photo to be found of the firewall in a third or fourthgen showing the factory hole for the hydraulic clutch master cylinder.

I see a lot of oval shaped holes, and people mentioning using the paper gasket to mark the hole, etc. But no photos of a factory T5 or T56 firewall with the master removed.

From looking at the used gasket I've got sitting here, it sure looks to me like the factory just punched a 2" diameter hole and the master covers it. From the distant pics I can find, it looks like a round hole too.

So aside from making things harder, why use an oval shaped hole?

If anyone has a couple photos of a factory T5/T56 firewall showing the factory hole, please share.

 

https://picasaweb.google.com/1106145...52309489978290

Im missing the support braces

Other side

https://picasaweb.google.com/1106145...78907909053026

 

Take a look at this picture of the master cylinder: http://s444.photobucket.com/user/jay..._0565.jpg.html (just the first one I found on a Google search). See how it mounts on the firewall at an angle? You need an oval hole to allow a cylinder to pass through at an angle.

Here's another image that sort of shows what I'm talking about: https://upload.wikimedia.org/wikiped...ection.svg.png Image the flat plane as your firewall, and the cylinder as, well, your master cylinder.

You could cut a circular hole that's big enough to allow the master cylinder to fit through at an angle, but my understanding is that such a hole would leave very little material between your master cylinder hole and the two bolt holes.

The '90 RS I pulled apart had an oval hole. I will see if I can find a picture (I think I took some for reference).

 

Those holes are usually pop outs so you know exactly where they go.

 

Unfortunately not all of them are. My '91 didn't have the pop out; here's another that doesn't:
http://s201.photobucket.com/user/dan...esize.jpg.html

I poached that picture out of this swap thread:
https://www.thirdgen.org/forums/tran...y-t5-swap.html

Looks like that guy's car was also a '91, maybe they removed the pop outs on the later cars?

 

That photo would be exactly what I'm looking for, if it were an original T5 car.

The only knock-outs on any of these cars are the plug over the cruise/fog light harness hole (visible in the quoted image) and the pre-cut holes in the firewall pad under the carpet. Some early thirdgens may also have a blocked hole for the mechanical clutch linkage (before 1984), but they're really beyond the scope of what I'm looking for.

The hole for the clutch master doesn't need to be oval shaped unless a person is trying to make the smallest hole possible. However, cutting a roughly 2" round hole results in a large enough for the master to pass through, and the mounting flange on the master will still more than cover up the hole. As I mentioned originally, the used T56 master cylinder I've got here has the used gasket on it, and the side that faces the car has the impression of a 2" round hole. Which raises the question if the car this clutch master came from was converted from an auto and they used a 2" hole saw for convenience (possible) or if GM used a 2" round hole.

The only reason it matters is that a 2" round hole is much easier to cut than two smaller holes, with filing and connecting the dots, etc. I'd just like to see an authentic hole cut by GM for a clutch master cylinder.

 

Unfortunately I wasn't able to find a photo of the firewall from the '90 RS I pulled the T5 from on my work computer. I'll check my home computer in a bit and hopefully come up with something for you.

I've read of a few people who eventually pushed part of the pedal assembly through the firewall, which is why I was concerned about keeping as much material between the master cylinder hole and bolt holes. Not sure if that's really possible, but I know that firewall metal is pretty thin so I didn't want to take any chances!

Hopefully I'll have that picture for you soon.

 

I'll take you a couple of pictures. I part out third gens and I have I know for sure a factory 92 z28 5 speed car that I just pulled engine, trans clutch parts, pedals, brake booster, etc from.

 

Any chance yiu have a set of support rods? Im missing mine. Otgerwise i will have to fabricate something

 

I'm assuming you're after the rods from the pedal pivot to the clutch master cylinder... FWIW the year matters. Around 1987-ish they changed the clutch position switch, at the same time the support rod on the left side was changed to clear. Just one of those details that only stands out with both parts next to each other.

 

Mine is an 88 it has the big black clutch safety switch

 

Then you'll want the 87-92 braces. The later brace just jogs further to the left before dropping down, then jogs back over at the bottom. They'd be fairly easy to fab from 3/8" round steel bar, only difficulty would be getting the dimensions and angles just right, but then it shouldn't matter too much as long as they're stiff, contact both anchor points, and clear all the moving parts.

 

Cutting an accurate hole for the MC is CRITICALLY IMPORTANT !!! If these 3 holes are not correct there is very few options to correct the mistakes. Bad hole = Throw will be wrong, bent/leaking MC sure to follow ) Use the 2 support braces ( 1 on each side of the pedals from Hydraulic clutch cars ) to mark/drill the 2 MC bracket holes FIRST. BE SURE that all padding is clear of the area and BE SURE that the braces are pushed hard & are well supported TIGHT to the firewall BEFORE DRILLING.

Once those 2 bracket holes are made, the MC firewall template from the firewall pad ( found on most firewall padding ) can be used to mark the oval hole. Remove AS LITTLE metal as possible from the firewall !

There's the "easy" way and the "right" way. I'd advise drilling out the 2 bracket holes based on the brackets location when the pedals are fully installed,..... then an oval hole as small as possible for the MC to pass thru.

P.S. All the MC hole pictures I've got are from custom cuts when converting to stick !!!

 

 

Sorry, I don't have any of the 87-92 braces. I sold those with the pedals. Only ones I have right now is in a '85 z28.

 

Perfect! Thanks for the photos, they're just what I've been looking for.

Am I just seeing things or is there a round shadow around the hole? It almost looks like the firewall has a round hole, then there's a second layer of steel behind it with the smaller oval hole. The larger round shadow matches closely the round imprint on the used clutch master gasket I've got here... Interesting.

 

You are welcome. Yeah man, that's what it looks like to me as well. When I get back in the shop tomorrow, I will look and feel it and see. The inner oval could just be the rubber/board/jute backing under the carpet. I will feel and see if it's steel or not, and get a better closeup of it for you.

 

I swear there's some sort of conspiracy keeping these photos off the Internet! I couldn't find the reference photos I took of the donor car, so I spent about half an hour hunting around on Google. Nothing. Sorry OP, wish I could have been more helpful.

Curious to know your thoughts on a set of holes that are off by about .1". Will that create enough of a misalignment to cause issues with the MC down the road? I'm already prepared to have to cut and weld in a new section of firewall at some point, but I'd like to at least drive it a bit first.

 

EVERY LITTLE BIT is going to matter. Consider this; Once that MC is bolted to the firewall,.... ANY deviation from where the MC SHOULD be mounted is going to occur directly where the rod enters the top MC. ( because the top of the rod will be locked into it's proper position on the pedal. ) That's the area that you'll need to watch to be sure the upper seal remains intact.

This is true for side to side specifically,... installed too high or too low could also cause problems with the pedal engagement/release.

 

Thanks for the reply; that's about what I figured. My hole is about .1" higher than it should be, so I will do as you suggested and keep an eye on the MC.

Already been talking with a buddy about creating a plate to weld in. Guess I should see if we can speed that process up!