17mm vs 19mm Brake Master Cylinder, again! |
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17mm vs 19mm Brake Master Cylinder, again! |
87m491 |
Jul 24 2023, 05:32 AM
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#1
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Member Group: Members Posts: 295 Joined: 29-July 12 From: Portland, the original! Member No.: 14,731 Region Association: North East States |
With the prospect of incoming rotten tomatoes forefront, I wade in here looking for a little BTDT.
Background, just got the 74, 2.0 back on the road after a 7 year hiatus. Over the years,, I did fuel system, brake system (19mm master(ATE) /calipers (PMB rebuilt fronts, stock rears) /rotors/hoses) engine mechanicals and cosmetics. I haven't driven the car during that time and I only had about 150 miles on it before it came off the road and memory ain't what it used to be. I did the 19mm MC many years back because it was way less expensive than the 17 and the forum feedback seemed fine. I also have a mid 80's Carrera (with turbo brakes) against which many folks relate the 19mm MC pedal feel. I like a firm pedal and the 911 is pretty easily modulated, heavy but responsive. Fast forward to this past week and some short shakedown runs. The 914 pedal is "right there" and noticeably firmer than the 911. But while being firmer, the braking is far from commensurate with pedal input. Yes, the 911 pedal is firm, but with the right effort, the car will slow/stop NOW. Been on the track with it no problem. On the 'teener, I feel like I am about to bend/break the pedal and the car seems to barely slow. No way I can lock up these brakes at any road speed, nor do I feel I could lose momentum in a hurried stop situation, even at in town speeds. I'm wondering if I have missed something or is this type of pedal feel/action is "typical" of the swap? Shamefully, I honestly can't recall if I did pads, but the rotors are spotless and look like they're getting good pad contact but would love any pad advice as well. |
VaccaRabite |
Aug 14 2023, 06:41 AM
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#2
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En Garde! Group: Admin Posts: 13,544 Joined: 15-December 03 From: Dallastown, PA Member No.: 1,435 Region Association: MidAtlantic Region |
Bleed more. Use a power bleeder to pressurize the system. Start with the caliper furthest from the reservoir and use a longish tube going from the caliper bleeder valve to our catch can. The idea is that you want to be able to watch for bubbles in the tube.
Make SURE (like 100% positive sure) that your bleeder valves are on TOP of the caliper. Calipers can be put on the wrong side, which puts the bleeder low, and will ensure you never are able to get all the air out. Tap the proportioning valve with a mallet to help free up the air trapped in it. When a 914 is set up right it STOPS. Using a 19mm cylinder does not impair that. Like many here, I'm also using the 19mm and porterfields and my car STOPS. Zach |
87m491 |
Sep 5 2023, 06:05 AM
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#3
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Member Group: Members Posts: 295 Joined: 29-July 12 From: Portland, the original! Member No.: 14,731 Region Association: North East States |
I finally got back to these over the 3 day weekend. This time I went old school 2 person style vs power bleeder last time. After 3 clean pumps and bleeds on the rears, the 4th pump, on each side oddly enough, produced a mini geyser of air bubbles! (so much so that the low fluid/low pressure warning light from the MC switch was set off!) i continued the bleed to the fronts which seemed fine.
Long story short, the pedal is right there. 1mm engagement and maybe 1.5 inches. total pedal play the brakes engage right off. Effort is high but fine for me just no linearity all all in pedal effort and stopping urgency. As of now there is no possibility of locking them up, at any pedal pressure or at any speed down to walking speed. I'll drive it a bit and see if, as PMB says any seals need to wear in etc. but that's where it is at. Bleed more. Use a power bleeder to pressurize the system. Start with the caliper furthest from the reservoir and use a longish tube going from the caliper bleeder valve to our catch can. The idea is that you want to be able to watch for bubbles in the tube. Make SURE (like 100% positive sure) that your bleeder valves are on TOP of the caliper. Calipers can be put on the wrong side, which puts the bleeder low, and will ensure you never are able to get all the air out. Tap the proportioning valve with a mallet to help free up the air trapped in it. When a 914 is set up right it STOPS. Using a 19mm cylinder does not impair that. Like many here, I'm also using the 19mm and porterfields and my car STOPS. Zach |
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