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Power brake question

Also posted on 944 n/a forum.

My turbo has the brakes rebuilt, new lines and new master cylinder. I've flushed the system and bled it numerous times but even when I stand on it, the brakes won't lock up. It will stop after it slows down but I'm not sure if it's the booster or not. I'm asking the forum if they can tell me how much the brake pedal goes down when you start the engine? Mine doesn't seem to move noticeability when the engine is started. I've put 10 inches of vacuum on the booster line and it holds it until I push the brake pedal which I determined as normal. I did install the Lindsey Racing venturi elimination hose package and I'm generating about 12 inches of vacuum on the booster 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 10-17-2020, 10:29 AM
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Normal vacuum reading at idle should be 18-22inhg. Check for a vacuum leak, check vacuum hose routing and connections. Remember KIS Theory, if it was ok before you did the Venturi delete, check that everything is connected and that you donít have a leak.
Iím assuming the base hydraulic system is absolutely air free, pedal is firm and travel is consistent.
Old 10-17-2020, 11:12 PM
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The hydraulic part of the system is solid but I'll check the vacuum supply again. I thought I was meticulous about the install of the venturi delete but I'll pull the intake manifold (again) and see what I find after I recheck the vacuum readings.
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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 10-18-2020, 06:31 AM
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Bought a quality vacuum gauge today and after hooking it up, I found just over 18 inches of vacuum at idle and 21 inches at about 2000 RPM. Looks more like I'm replacing a brake booster after all. Really looking forward to this.....not.


IDLE



2000 RPM
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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 10-18-2020, 10:40 AM
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Found a defective vacuum reservoir in the system. Replaced it with a good one and, like another forum poster suggested, it wouldn't have any effect on the system. He was right and now I'm back to square one, trying to figure out why the power brakes don't work. At least I have a new vacuum reservoir.
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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, 06:23 PM
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Out of ideas

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.
Old 11-19-2020, 05:26 PM
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Okay here's one more for you: The shop manual says to match the booster brand to the master cylinder brand (ATE/ATE, Girling/Girling).

Are yours matched?

I am not sure if is just for NA's, or also turbo cars.
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Old 11-20-2020, 05:42 PM
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could there be a block in the hydraulic brake line somewhere? have you tried pumping the pedal when bleeding the brakes to see how much brake fluid squirts out at each caliper?
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Old 11-20-2020, 07:46 PM
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Quote:
Originally Posted by kdjones2000 View Post
Okay here's one more for you: The shop manual says to match the booster brand to the master cylinder brand (ATE/ATE, Girling/Girling).

Are yours matched?

I am not sure if is just for NA's, or also turbo cars.
I was careful to match per the book. the master cylinder and booster are both ATE.
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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, 09:30 AM
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Quote:
Originally Posted by nize View Post
could there be a block in the hydraulic brake line somewhere? have you tried pumping the pedal when bleeding the brakes to see how much brake fluid squirts out at each caliper?
I manually bled the brakes (two man method) and then used the power bleeder to final bleed the calipers. I also added a couple of drops of compatible blue dye in the system to ensure I was getting a full purge of the lines. I've used that method for years on 944's since they prevented the US from selling tinted brake fluid. I use it in every OTHER brake fluid change.
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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, 09:38 AM
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Quote:
Originally Posted by mytrplseven View Post
I was careful to match per the book. the master cylinder and booster are both ATE.
I am out of ideas, other than to change pad compounds.
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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 11-22-2020, 07:02 PM
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I noticed a small leak where the proportioning valve screws into the master cylinder. Ordered a new one just to be sure. Not cheap for new and I don't trust used. There is a difference between 944 na, S2, and turbo models. The ratios are different, I found. Every time I lift the hood it's another learning experience.
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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, 07:33 PM
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do you have really sticky tires? good tires are harder to lock up.
do you have ceramic pads? typically they are garbage and barely have any bite at all.
rotors have even wear patterns (all brakes working?)
cracked firewall deflecting under pedal load?
Old 11-23-2020, 12:13 PM
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Quote:
Originally Posted by v2rocket_aka944 View Post
do you have really sticky tires? Good tires are harder to lock up.
Do you have ceramic pads? Typically they are garbage and barely have any bite at all.
Rotors have even wear patterns (all brakes working?)
cracked firewall deflecting under pedal load?
no
no
yes
no
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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 11-23-2020, 03:34 PM
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Quote:
Originally Posted by mytrplseven View Post
My turbo has the brakes rebuilt, new lines and new master cylinder.
do you trust the rebuild?
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Old 11-26-2020, 12:26 PM
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Yes, I'm a mechanic, armed with the proper manuals and the forum. I was meticulous about the rebuild. My new proportioning valve gets in on Monday and then a new round of rear brake bleeds. We'll see if that makes the difference. Also replaced the aux water pump relay. I noticed the pump wasn't working while I was under the hood.
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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 11-26-2020, 03:52 PM
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Also replaced the aux water pump relay. I noticed the pump wasn't working while I was under the hood.
I don't think I've ever worked on my car without having to go down some sidetrack after discovering another 'issue'. Good thing I enjoy it...
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Old 11-26-2020, 05:27 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, 01:08 PM
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I sound like a broken record. But I likes to stick with all stock parts, expecially on forign jobs like these cars. good luck triple, hope your ride works for you..
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Keep cool man..
Old 12-06-2020, 03:50 PM
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Quote:
Originally Posted by Fast Freddy 944 View Post
I sound like a broken record. But I likes to stick with all stock parts, expecially on forign jobs like these cars. good luck triple, hope your ride works for you..
These are all stock parts. Because of that the little proportioning valve cost $300. The only thing on my car that's not are the shocks/struts, brake pads and rotors and wheels. This car is really fast, fun and now, finally, stops like it should.

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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 12-06-2020, 06:15 PM
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