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Here is a brake booster test routine. Maybe the check valve is backwards? https://www.knowyourparts.com/technical-resources/brakes-and-brake-components/vacuum-booster-diagnostics/

Old 11-06-2020, 01:22 PM
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Quote:
Originally Posted by djnolan View Post
Here is a brake booster test routine. Maybe the check valve is backwards? https://www.knowyourparts.com/technical-resources/brakes-and-brake-components/vacuum-booster-diagnostics/
Thanks for the link. I'll see if this bears fruit. I plan to put the car up on stands and do a thorough bleed on the Brembo calipers one more time.
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3 944's, 2 Boxsters and one Caman S, and now one 951 turbo. Really miss the Cayman.

Some people try to turn back their "odometers." Not me. I want people to know 'why' I look this way. I've traveled a long way and some of the roads weren't paved.
Old 11-08-2020, 07:53 AM
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Have you checked that your vacuum reservoir is good, and the vacuum line is connected properly?
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Old 11-11-2020, 05:17 AM
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Just did a complete (again) bleed of all the calipers, inside and out. No bubbles, solid brake pedal.
I'll go check the vacuum reservoir for function and vacuum to it as we speak.
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3 944's, 2 Boxsters and one Caman S, and now one 951 turbo. Really miss the Cayman.

Some people try to turn back their "odometers." Not me. I want people to know 'why' I look this way. I've traveled a long way and some of the roads weren't paved.
Old 11-11-2020, 10:58 AM
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Quote:
Originally Posted by mytrplseven View Post
Just did a complete (again) bleed of all the calipers, inside and out. No bubbles, solid brake pedal.
I'll go check the vacuum reservoir for function and vacuum to it as we speak.
The fitting on the vacuum reservoir was broken off. Looks like the PO had tried to fix it and it didn't stay. I ordered a replacement. Thanks KD.
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3 944's, 2 Boxsters and one Caman S, and now one 951 turbo. Really miss the Cayman.

Some people try to turn back their "odometers." Not me. I want people to know 'why' I look this way. I've traveled a long way and some of the roads weren't paved.
Old 11-11-2020, 12:00 PM
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Quote:
Originally Posted by mytrplseven View Post
The fitting on the vacuum reservoir was broken off. Looks like the PO had tried to fix it and it didn't stay. I ordered a replacement. Thanks KD.
The new reservoir had no effect on the system. I still am chasing why I don't have power brakes. At least the battery box is cleaned and sorted.
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3 944's, 2 Boxsters and one Caman S, and now one 951 turbo. Really miss the Cayman.

Some people try to turn back their "odometers." Not me. I want people to know 'why' I look this way. I've traveled a long way and some of the roads weren't paved.
Old 11-18-2020, 06:28 PM
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Have you measured your vacuum at the booster? That should narrow it down pretty quickly.
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1987 924S 944 SPEC racecar - '88 pistons/DME, short 5th
1987 944S - Restored salvage title, ready to live again
I can fix your late 944 Cruise Control module - PM for details
Old 11-18-2020, 08:16 PM
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Here's the list: I've replaced the rotors, pads, booster, check valve, master cylinder, vacuum reservoir, booster input hoses, vacuum hoses throughout, installed the Lindsey venturi delete kit and rebuilt the calipers. Brake booster line vacuum is as shown at 2000 RPM. At idle it's 18 inches hg. STILL NO POWER BRAKES. I simply have run out of ideas.

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3 944's, 2 Boxsters and one Caman S, and now one 951 turbo. Really miss the Cayman.

Some people try to turn back their "odometers." Not me. I want people to know 'why' I look this way. I've traveled a long way and some of the roads weren't paved.

Last edited by mytrplseven; 11-19-2020 at 05:28 PM..
Old 11-19-2020, 05:10 PM
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Well at least you know the issue is downstream from the hose going into your booster.
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NASA/PCA Instructor: '88 951S - with LBE, Guru chips, 3Bar FPR, 1.3mm shimmed WG, 3120 lbs, 256 RWHP, 15 psig boost
1987 924S 944 SPEC racecar - '88 pistons/DME, short 5th
1987 944S - Restored salvage title, ready to live again
I can fix your late 944 Cruise Control module - PM for details
Old 11-20-2020, 05:39 PM
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When observing the vacuum when applying the brakes, does it maintain the same level? Also is it possible the linkage is binding? Or the line is pinched and not delivering full volume? How about going back to the original venturi setup?
Old 11-21-2020, 03:29 AM
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Quote:
Originally Posted by djnolan View Post
When observing the vacuum when applying the brakes, does it maintain the same level? Also is it possible the linkage is binding? Or the line is pinched and not delivering full volume? How about going back to the original venturi setup?
I was careful about installation that all linkage was smooth and didn't over-extend the pedal to booster linkage. I wasn't concerned about low vacuum capacity since I ran the numbers on the supply line to the booster. I assume you are talking about a vacuum indication on the boost gauge or at a fitting on the boost supply line with the booster attached? I have to wait as I noticed the aux water pump had stopped working and after running electrical checks, looks like a bad relay. After the replacement arrives I'll check per your recommendation if you can verify the configuration in my question above.

I'd hate to have to go back to stock venturi setup since I'm reading proper levels on the booster supply line.
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3 944's, 2 Boxsters and one Caman S, and now one 951 turbo. Really miss the Cayman.

Some people try to turn back their "odometers." Not me. I want people to know 'why' I look this way. I've traveled a long way and some of the roads weren't paved.
Old 11-22-2020, 09:24 AM
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On my N/A there is a plastic fitting on the booster with a large line to the venturi and a small line to the recirculate flap actuator. I was thinking putting the vacuum gauge on the small nipple and checking to see what the vacuum level is when you depress the brake pedal.
Old 11-22-2020, 10:03 AM
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Quote:
Originally Posted by djnolan View Post
On my N/A there is a plastic fitting on the booster with a large line to the venturi and a small line to the recirculate flap actuator. I was thinking putting the vacuum gauge on the small nipple and checking to see what the vacuum level is when you depress the brake pedal.
The same on the turbo. I'll check that after the aux water pump (turbo) arrives. I also noted a little leak from where the brake proportioning valve meets the master cylinder. I decided to order a new one just for security sake. Darn things new aren't cheap.
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3 944's, 2 Boxsters and one Caman S, and now one 951 turbo. Really miss the Cayman.

Some people try to turn back their "odometers." Not me. I want people to know 'why' I look this way. I've traveled a long way and some of the roads weren't paved.
Old 11-22-2020, 07:28 PM
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UPDATE: Replaced the proportioning valve, put the vacuum gauge on the T off the supply line to check the vacuum with the system connected to the booster. Vacuum was right on spec with engine running and brakes applied. Re-bled the brakes with power bleeder (again) and road tested the car. Brakes are much improved. I'm hoping the pads will settle in and get even better. If not I'll replace them with generic semi-metallic pads.
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3 944's, 2 Boxsters and one Caman S, and now one 951 turbo. Really miss the Cayman.

Some people try to turn back their "odometers." Not me. I want people to know 'why' I look this way. I've traveled a long way and some of the roads weren't paved.
Old 12-02-2020, 01:06 PM
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So a bad proportioning valve? That's a new one for me.

Great to hear you figured it out.
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NASA/PCA Instructor: '88 951S - with LBE, Guru chips, 3Bar FPR, 1.3mm shimmed WG, 3120 lbs, 256 RWHP, 15 psig boost
1987 924S 944 SPEC racecar - '88 pistons/DME, short 5th
1987 944S - Restored salvage title, ready to live again
I can fix your late 944 Cruise Control module - PM for details
Old 12-02-2020, 02:50 PM
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Quote:
Originally Posted by kdjones2000 View Post
So a bad proportioning valve? That's a new one for me.

Great to hear you figured it out.
Yeah, it seems the rear brakes weren't getting the juice.

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3 944's, 2 Boxsters and one Caman S, and now one 951 turbo. Really miss the Cayman.

Some people try to turn back their "odometers." Not me. I want people to know 'why' I look this way. I've traveled a long way and some of the roads weren't paved.
Old 12-02-2020, 07:20 PM
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