master cylinder update - JeepForum.com
 
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post #1 of 9 Old 09-27-2021, 08:49 PM Thread Starter
fibersport
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master cylinder update

Since the master cylinder on the CJ7's is a GM unit, has anyone ever replaced it with a newer style GM unit? It would sure make things look a little updated with a plastic reservoir rather than that old style cast iron unit. I have to believe that there really isn't that many style master cylinders, that they pretty much are all the same but I'm hoping that someone has gone down that road before ...


1984 CJ7 Renegade
4.2 with 4 speed
researching other details!
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post #2 of 9 Old 09-28-2021, 10:34 AM
bob4703
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The last master cylinder I bought with a plastic reservoir I had to reuse the reservoir. Can you interchange plastic and cast reservoirs?

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post #3 of 9 Old 09-28-2021, 12:00 PM
Fourtrail
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Check the mounting flange, the depth for the pedal pushrod and the piston sizes. make sure that you are looking at disc/drum master cylinders. should be no issue to move to a newer style master as long as those things match up.

80 CJ-5, 74 CJ-6, 56 CJ-5
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post #4 of 9 Old 09-28-2021, 03:56 PM Thread Starter
fibersport
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Was hoping someone had already done the research, those dimensions aren't something that is easily found.

As for the reservoirs, the cast iron one doesn't come apart like the plastic one does so no they themselves don't interchange.

1984 CJ7 Renegade
4.2 with 4 speed
researching other details!
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post #5 of 9 Old 09-28-2021, 04:57 PM
Fourtrail
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piston and fitting size is listed for most all. I would assume that all GM have the same spacing. Might be a try and return for a few. Here are a pair that seem to be matched well, you will likely need an adjustable pushrod.


1984 Jeep CJ-7 https://www.rockauto.com/en/moreinfo...t=1836&jsn=922


1988 GMC S-15 Jimmy https://www.rockauto.com/en/moreinfo...=1836&jsn=1147

80 CJ-5, 74 CJ-6, 56 CJ-5
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post #6 of 9 Old 09-28-2021, 05:52 PM Thread Starter
fibersport
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Wow, that's some great information - thank you. I'm a frequent buyer at Rockauto but never gave it any thought to look there.

1984 CJ7 Renegade
4.2 with 4 speed
researching other details!
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post #7 of 9 Old 09-29-2021, 08:23 AM
Axhammer
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Years ago I swapped out the power brakes on my Firebird race car, for manual brakes, for weight reduction.

Initially I used one like in the link above from a late model Grand Prix, that I pulled in a wrecking yard. Several years later I replaced it with a new one from Summit and if I remember correctly it cost less than $20, and it came with the plastic reservoir. I should have bought a new one to begin with.

I recall opening up the mount bolt pattern a little, filing by hand, adding a PV and modified the brake pedal push rod, but that’s all easy stuff. I don’t see any reason why you couldn’t install the same MC on a CJ-7.

I’ve been running this system for years, and it works well.
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post #8 of 9 Old 09-29-2021, 06:23 PM Thread Starter
fibersport
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Thanks. As weird as it may seem, I just think it updates things under the hood a tiny bit.

1984 CJ7 Renegade
4.2 with 4 speed
researching other details!
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post #9 of 9 Old 09-29-2021, 06:38 PM
PrincessJ
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I put a 69 model Corvette small bore manual brake master cylinder in mine. Just had to get a brake pedal rod kit. The factory lines (at least mine did) have the same thread pitch and size. I replaced all my lines at the same time. Stops great for a manual brake setup


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