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Post by dynchel on Sun Dec 23, 2012 10:24 pm

Has anyone ever adapted a later model aluminum and plastic master cylinder to a g3? When I was younger (late '90's) there was a 11 second 74 montecarlo running around ne Ohio that had this set up as well as other weight saving tricks. I remember it lookng cool and it would of course be a lot lighter than the cast original piece. When I talked to the owner he was the first person to tell me about gutting the front bumper, and the door crash braces. I remember noticing the master cylinder but didn't ask about the application or problems encountered. I was wondering if anyone has ever tried anything like this and if it worked. My only real concern is my chevelle has manual brakes which I don't believe was available in later years. Marry Christmas to all . santa
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Post by thatfnthing on Mon Dec 24, 2012 10:57 am

When I upgraded to ABS, I originally started out mating it to the original master cylinder. This worked, but yielded too much pedal travel for my taste. So this past winter I upgraded to the m/c from a 93 Caprice (to match the ABS system). It works (at least in the garage, I haven't been able to drive it yet since it's been laid up all season undergoing a Vintage Air install, and now we're back into winter again Rolling Eyes ), but here's the highlights of what you will encounter (assumes power brakes and no major differences between G3's):

o The front and rear circuits are reversed from the original.

o It will not work with the stock booster -- the bore size on the m/c is too large, so you will need the late model booster also.

o The booster & m/c rig will mount to the cast aluminum base that the car came with that mounts to the firewall, but two of the bolt holes will need to be enlarged slightly.

o The whole combo is longer than the original, so it will extend farther out and upward. The hood should just close, but it will be tight clearance-wise.

o The actuating rod will be an inch or so too short to reach the pedal. The solution is to slice off the end that connects to the pedal, then slice off the last couple inches of the original actuating rod, then use a tap & die set to add 3/8"-16 threads to both ends. Use a 3/8"-16 turnbuckle to join the two ends. This will allow for adjustment, and you will have to experiment a little to get it where you like.

o The brake warning light actuator is on the m/c itself and requires a different end connector.
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Post by dynchel on Mon Dec 24, 2012 11:13 am

Thanks for the response, i was hoping for a little more of a bolt on, however i don't have power brakes so it may be a little different. Push rod length and bore diameter being my main concerns. rendeer happy holidays.
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Post by thatfnthing on Mon Dec 24, 2012 11:27 am

FWIW, I'm expecting that it moves considerably more fluid than the original to compensate for the volume of the ABS modulator -- this would explain why I had too much pedal travel with the original. I would expect in a non-ABS setup you would have the opposite issue. I've never seen a non-power setup in a G3, so I can't speak to mounting.
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Post by dynchel on Mon Dec 24, 2012 12:34 pm

The master cylinder bolts directly to the firewall. It came with no a/c, no rear defrost, steel wheels painted body color, very minimal trim, and a 350 2bbl motor. Very low optioned, perfect hot rod material.
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Post by dynchel on Tue Mar 05, 2013 12:27 pm

thatfnthing wrote:FWIW, I'm expecting that it moves considerably more fluid than the original to compensate for the volume of the ABS modulator -- this would explain why I had too much pedal travel with the original. I would expect in a non-ABS setup you would have the opposite issue. I've never seen a non-power setup in a G3, so I can't speak to mounting.
heres what it looks like....
https://2img.net/h/i1337.photobucket.com/albums/o674/dynchel/photobucket-45537-1362489573372_zpsb8a941cd.jpg
heres a shot of the rest of the compartment.......
https://2img.net/h/i1337.photobucket.com/albums/o674/dynchel/photobucket-91136-1362489554688_zps416ddf5d.jpg
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Post by thatfnthing on Tue Mar 05, 2013 3:38 pm

Interesting.

Assuming the m/c itself is the same unit for both power- and non-power brake applications, I have to assume the only issue you would face mounting-wise would be that the bore is physically larger in diameter than the stock G3 unit. The hole in the bracket or brace will likely have to be enlarged. The two actual bolt holes that actually mount the m/c are in the exact same positions on both the G3 and the Caprice units, so you shouldn't have any trouble there.

The primary issue for me was that the actuating rod from the booster was too short compared to the old one. Since a booster is not part of your application, I would think it should just bolt to the firewall and re-use whatever the stock actuating mechanism is...

Something else occurred to me, though. The Caprice unit uses bubble flares while the G3 unit uses a double flare, so you will likely have to re-flare (or re-run) some brake lines. You may also want to consider using the Caprice combo valve instead of the G3 unit.

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