 914/4 914/6 brake master cylinder, Difference? |
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| Driver174 |
 Feb 24 2025, 03:42 PM
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#1
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Member  Group: Members Posts: 113 Joined: 2-February 17 From: Nevada Member No.: 20,806 Region Association: None 
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I’m looking at a FTE master cylinder for my 1974 -4, and website says it’s for a 70-70 six, and is not compatible with my car.
I’m curious as hat the difference is between the -6 and -4. I rebuilt my complete brake system including an ATe master cylinder two years ago, and now needing to replace the it already. Was told the FTE unit had silicon seals and would withstand the heat better than seals in the ATe. Your thoughts are appreciated |
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| brant |
Feb 24 2025, 03:55 PM
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#2
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914 Wizard Group: Members Posts: 11,884 Joined: 30-December 02 From: Colorado Member No.: 47 Region Association: Rocky Mountains 
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The stock 4 was a 17mm
They are nla The 911 unit is a 19mm Works fine And the only choice available |
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| rgalla9146 |
Feb 25 2025, 07:52 AM
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#3
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Advanced Member Group: Members Posts: 4,711 Joined: 23-November 05 From: Paramus NJ Member No.: 5,176 Region Association: None
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In some cases a 23 mm MB master cyl is adapted.
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| BENBRO02 |
Feb 25 2025, 04:25 PM
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#4
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Member Group: Members Posts: 485 Joined: 6-March 15 From: Nokesville, Virginia Member No.: 18,493 Region Association: MidAtlantic Region
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I believe the larger the master cylinder requires more force to brake but would need less travel.
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| zoomCat |
Feb 25 2025, 04:39 PM
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#5
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Member Group: Members Posts: 189 Joined: 13-August 04 From: Cincinnati, OH Member No.: 2,526 Region Association: None
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QUOTE(BENBRO02 @ Feb 25 2025, 05:25 PM)  I believe the larger the master cylinder requires more force to brake but would need less travel. The 19 would be about 25% stiffer, but the 23 would require about 85% more force. I’m not that strong anymore. |
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| flxzcat |
Feb 25 2025, 05:12 PM
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#6
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Newbie Group: Members Posts: 15 Joined: 13-June 11 From: lake forest socal Member No.: 13,188 Region Association: None |
I use the 23 but I like a stiff pedal, oh, and I use Brembo Alfa front and Mercedes rear calipers.
I have a new uninstalled Ate 19mm that I purchased late last year before I found the 23mm----$200 +shipping? |
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| bdstone914 |
Feb 26 2025, 04:35 AM
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#7
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bdstone914 Group: Members Posts: 4,776 Joined: 8-November 03 From: Riverside CA Member No.: 1,319 |
@flxzcat
I have a new uninstalled Ate 19mm that I purchased late last year before I found the 23mm----$200 +shipping? [/quote] .Would you trade it for a pedal set restoration that normally costs $275? |
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| flyer86d |
Feb 26 2025, 06:49 AM
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#8
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Member Group: Members Posts: 458 Joined: 12-January 11 From: Corea, Maine Member No.: 12,585 Region Association: North East States |
QUOTE(rgalla9146 @ Feb 25 2025, 09:52 AM) In some cases a 23 mm MB master cyl is adapted. I had a 23mm Mercedes master cylinder on my 911SC track car with turbo brakes. It was very firm but confidence inspiring. I was standing on the inside of the 90 at Watkins Glen watching my wife. On one lap, I heard a pop as she applied the brakes and then a scraping noise. She continued on and finished the session without any change in lap time. When she got back to the paddock, she mentioned having to pump the brakes once. I inspected the brake pads and one had separated from its backing plate and was gone. Sue said the brakes worked fine! Charlie |
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| zoomCat |
Feb 26 2025, 09:40 AM
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#9
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Member Group: Members Posts: 189 Joined: 13-August 04 From: Cincinnati, OH Member No.: 2,526 Region Association: None
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QUOTE(flxzcat @ Feb 25 2025, 06:12 PM) I use the 23 but I like a stiff pedal, oh, and I use Brembo Alfa front and Mercedes rear calipers. The force at the pedal required for a given clamping force is a function of the ratio of the caliper and master cylinder pistons. If you balance things out then brake pedal effort will change little. The factory brakes /6 have both larger calipers and master cylinder, but the ratio is little very close to the same. Interestingly the hydraulic line pressure does change, largely based on caliper piston area, which is why the six has a different pressure regulator and why racing applications often replace the it. |
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