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I'm trying to make a decision about converting my brakes to manual (if it is even possible) or installing a vacuum pump to operate the booster. The car is an '83 porsche 911 SC.

It looks like there is an unboosted master cylinder listed for my car on Pelican Parts. The bore is a few mm smaller. I don't know if pedal travel would increase enough that other parts would have to be replaced or modified (longer piston, pedal pivot). I also don't know how much more effort would be required to stop the car. I think only the front calipers are boosted now. The car weighs 2700 lbs pre-conversion and might be 3000 lbs after. I don't think that vacuum is used on any other system that will remain after conversion (like heating duct doors on some cars). I love the feel of manual steering, and don't mind a stiff pedal. I would love to avoid the power draw, noise, and extra parts that represent a reliability risk. But I don't want an unsafe car, and the brakes must be solid.
 

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You will need to find some Porsche specialist who can tell you, or parts lists for the power and manual brakes, or a visit to wrecker that has a manual brake car. If the manual brake version of the car uses a smaller master cylinder bore then the parts difference could be as simple as the master cylinder and push rod. There may be other changes like the brake pedal, or caliper sizes, or ???

It sounds like converting to manual is a viable option for you. Step 2 is figuring out the brake system differences.
 

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Hi Joey

I like manual brakes, in your shoes I would get the manual cylinder and try it out

Tests required
(1) - before you drive it
Your car will have a split brake circuit, after bleeding the brakes open a bleed valve on the front and ensure that the other brakes still work,
repeat for the back

(2) - test drive - are the brakes too heavy
Most modern cars are set up so a frail 80 year old woman can drive them, you may have stronger legs

(3) - test drive - ensure the fronts lock up first

(4) - take it to a track day
 

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you also need to see if the manual cylinder uses 2 or 4 attach points. generally, the booster has a large central hole with 4 mounts while the master has only 2. the master will not mount directly to the opening in the fire wall.
 

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You are right about the 2 and 4 bolt mounting. I don't feel comfortable just bolting parts together. My service manual only covers models with the booster. The suggestion to find a specialist is a good one, if I can't find more info online.
If you aren't already a member rennlist.com is a great resource for anything Porsche related. I don't visit the 911 sections, but the guys in the 944 section were invaluable for certain questions I had early on.
 

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Discussion Starter #7
If you aren't already a member rennlist.com is a great resource for anything Porsche related. I don't visit the 911 sections, but the guys in the 944 section were invaluable for certain questions I had early on.
I'm not yet a member, but I was looking through their forum this afternoon. Did you tell them you were converting the car to electric? Some people at work have stopped talking to me. It seems that when you mess with something someone has admired since boyhood, they take it as a personal affront. It is like I am rejecting their ideals or messing with their personal property. I can image some of the people on a Porsche forum would not be happy with me.
 
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