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Master cylinder bore size

Hello. I have an aftermarket master cylinder on my 1955 210 that I think was bought from danchuk by the previous owner. I had my brakes fail a couple weeks ago. I bled the lines and no air came out. I removed the master cylinder and the rear resivor was a bit rusty and had some grime in it. So I pulled the master off and took it apart. The cylinder looks good except for some pitting in the very back of it and the caps inside were pitted. All the seals looked good. I have been trying to find a rebuild kit but I can't. So I was gonna buy a new one. My question is should I get a 1" bore size or a 1 1/8" bore size. It has a brake booster I believe also from you. Disks up front and drums in rear. 17149 17150 are the part numbers for the master cylinders I am looking at. The one I have now is 17149. The booster I have is part number 16645. Any info will be greatly appreciated. Thanks
 

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Hello. I have an aftermarket master cylinder on my 1955 210 that I think was bought from danchuk by the previous owner. I had my brakes fail a couple weeks ago. I bled the lines and no air came out. I removed the master cylinder and the rear resivor was a bit rusty and had some grime in it. So I pulled the master off and took it apart. The cylinder looks good except for some pitting in the very back of it and the caps inside were pitted. All the seals looked good. I have been trying to find a rebuild kit but I can't. So I was gonna buy a new one. My question is should I get a 1" bore size or a 1 1/8" bore size. It has a brake booster I believe also from danchuk. Disks up front and drums in rear. 17149 17150 are the part numbers for the master cylinders I am looking at. The one I have now is 17149. The booster I have is part number 16645. Any info will be greatly appreciated. Thanks
 

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I had problems with my brakes as well . I bought a master and booster from SSBC ( Stainless Steel Brake Company)and then used an adjustable proportioning valve. The mounting studs of the booster literally fit the stock 55 holes with alittle light rubber mallet tapping. Never had another problem...Good luck
 

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If your brakes worked consistently good befor the failure I would go with the same as you had. since you have the master off measure the bore with a ruler, then get the same size.
 

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I had always read that if you had a booster you would run a 1 1/8" booster. I did a master cylinder swap a couple of months back and was recommended to go with the 1" master cylinder. A friend and i debated and argued back and forth over it. I ended up going with the 1" bore master cylinder and am very glad i did. Now the brakes work very good. I have the disc setup on front and drums in the rear.
Terry
 

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My brakes prior to the failure were a little soft. I had to push the pedal hard to stop. That was with the 1" bore. That's why I thought the 1 1/8" bore would be better.
 

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Hyd are backwards from what you normally think

a larger master cyl is harder to push than a smaller one,
yet pushes more fluid,
so a smaller one is easier to push, and pushes less fluid,
drum brakes all around- I'd use the larger one
disc/drum - I use the smaller one,

I use 4 wheel disc and a 1 in master cyl, with booster, and can stop easily and with normal effort,
 

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My brakes prior to the failure were a little soft. I had to push the pedal hard to stop. That was with the 1" bore. That's why I thought the 1 1/8" bore would be better.
There are a lot of things that will cause a soft pedal or hard stopping. It sounds as if it was a very long time since the fluid was changed, and if there was rust, there must have been a lot of water and debris in the lines. A 1" bore will provide more line pressure but less volume than a 1-1/8". The master bore should be compatible the bores of the calipers and wheel cylinders. I would use what is recommended for the calipers and wheel cylinders.
 

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The recommendation of a smaller bore master cylinder for more line pressure is correct. The price you pay for that is that the pedal will have to move farther before the brakes activate.

In general, if you're using GM cast iron calipers, you need a 1-1/8" bore master cylinder for power brakes, and a 1" bore for manual brakes. The exception to that would be if you have one of those small 7" boosters - you usually need a 1" bore master cylinder for that.

The other related thing is that many power brake systems use a modified pedal ratio. Stock is 6:1, and when you drill a new hole 1" down from the original on the pedal arm, you get 4:1. This has the same effect as a big master cylinder. It increases the pedal effort required and decreases the stroke. In conjunction with this, the booster is mounted on an angle bracket, which helps a bigger booster clear obstacles in the engine compartment. Again, you shouldn't alter the pedal ratio with a 7" booster. That is one reason you see 7" boosters with a flat bracket, and 8" and bigger boosters with an angled bracket.
 

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The recommendation of a smaller bore master cylinder for more line pressure is correct. The price you pay for that is that the pedal will have to move farther before the brakes activate.

In general, if you're using GM cast iron calipers, you need a 1-1/8" bore master cylinder for power brakes, and a 1" bore for manual brakes. The exception to that would be if you have one of those small 7" boosters - you usually need a 1" bore master cylinder for that.

The other related thing is that many power brake systems use a modified pedal ratio. Stock is 6:1, and when you drill a new hole 1" down from the original on the pedal arm, you get 4:1. This has the same effect as a big master cylinder. It increases the pedal effort required and decreases the stroke. In conjunction with this, the booster is mounted on an angle bracket, which helps a bigger booster clear obstacles in the engine compartment. Again, you shouldn't alter the pedal ratio with a 7" booster. That is one reason you see 7" boosters with a flat bracket, and 8" and bigger boosters with an angled bracket.
I agree completely. In doing the disc conversion on my 68 firebird recently, I used what the kit came with , a 1" master and 9" booster. the pedal was good with engine off but with it runnung the pedal would go 85% of the way down then stop the car. It just felt plain unsafe. I have since changed to a 1-1/8" master and have really good brakes with much less pedal travel. about like my stock gmc 1500 pickup.
 
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