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Comeau Racing
Join Date: Dec 2004
Location: San Diego, CA
Posts: 1,777
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Booster? release brakes- engine revs up
When I take my foot of the brakes, the engine increases revs.
Brake pedal feels soft with too much travel- tho brakes are effective. Swapped out the booster with a used one. We have the booster vacuum line connected directly to the intake manifold. Check valve at booster is good. O-ring at base of Master cylinder to booster is good. Ideas?
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PCA since 1985 77 924 MARTINI Edition rescued,SOLD 88 924S Special Edition rescued,SOLD Comeau Racing Enterprises, Inc. www.comeauracing.com We do only 924S, 944's, 968's all day, every day. |
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09-21-2011, 11:35 AM
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Garage Helper
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I would be looking for a vacuum leak some place...Or the Vacuum booster Check Valve is defective...
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78-924 traded for 80-931 traded for 84-944 traded for 85.5-944 (7th one now).  UAV-M1 (Urban Assault Vehicle - Model 1) Bless the lowered, and pass the nitromethane. Pedal to the metal till you see the gates of hell then brake NLA - No longer available is a four letter word |
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09-21-2011, 11:38 AM
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Comeau Racing
Join Date: Dec 2004
Location: San Diego, CA
Posts: 1,777
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Well, no, I stated the vacuum check valve is good. A vacuum leak would cause runability problems, none of which exist. The car just won a 944 Spec race at Cal Speedway. This racecar was running a simplified vacuum for the booster.
Here's what we found: The booster vacuum line routing was the problem. We had that running directly from the check valve to the intake manifold. The stock routing splits at the vacuum amplifier and also goes to the underside of the rubber intake J-boot. One of these gets vacuum before the throttle body and the other one afterwards. We only experienced this problem at idle. That problem is gone now. BUT, the pedal is still too soft even after a pressure bleed. Maybe air in the master cylinder? Wouldn't that push thru with the pressure bleed? When ever I have a tricky problem with a 944, it's almost always 2 things wrong at the same time! We'll try a complete brake fluid flush.
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PCA since 1985 77 924 MARTINI Edition rescued,SOLD 88 924S Special Edition rescued,SOLD Comeau Racing Enterprises, Inc. www.comeauracing.com We do only 924S, 944's, 968's all day, every day. |
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09-21-2011, 02:44 PM
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Comeau Racing
Join Date: Dec 2004
Location: San Diego, CA
Posts: 1,777
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So the vacuum hose fixed the idle increase but the pedal still is soft with too much travel!
We have since tried: - flushing the brakes twice, the last time with a pressure bleeder at 15psi. -We've bled the master to make sure there was no air there. -We replaced all 4 soft brake lines. -We replaced the booster with a new one for the 924S. Still have a soft pedal with excess travel. Now we're looking at compatibilty problems. There are different master cylinders, boosters, and adapters between the booster and firewall. Both our master and booster are Ate (Teves).
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PCA since 1985 77 924 MARTINI Edition rescued,SOLD 88 924S Special Edition rescued,SOLD Comeau Racing Enterprises, Inc. www.comeauracing.com We do only 924S, 944's, 968's all day, every day. |
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10-17-2011, 09:14 AM
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Registered
Join Date: Sep 2011
Location: Florida
Posts: 1,949
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There are no compatibility issues with any of the brake components, both types are interchangeable and cars were shipped from the factory with a mixture of both. You also dont have a vacuum problem as that causes an increase in travel but not a soft pedal.
Your problem will be with bleeding, maybe you have an air pocket in one of your calipers. Try bleeding again this time tapping the calipers with a soft-faced hammer as you release the fluid. |
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10-17-2011, 10:24 AM
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ORACLE
