Old Ford with disc conversion, doing something weird, help please
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Laughing Gas
Joined: Apr 2006
Posts: 1,121
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From: Middle Georgia
Old Ford with disc conversion, doing something weird, help please
I have a '68 F-100 4x4, that has a front disc conversion done using a mix of Chevy and later F-150 parts. The conversion is well tested by various people in the Early Bronco, and possibly F-100, community. My issue is with the booster and master cylinder side of things. I'm running a dual reservior master cylinder and dual diaphragm brake booster from a later F-series, mid 70s F-250 or F-350 IIRC.
Under normal light braking everything feels normal. If I get on the pedal to stop hard it gradually goes hard and gets to the point of feeling like I've got a bad booster. Never really delt with a dual diaphragm brake booster so I don't know how they feel when they are going out. My only experience with a bad single diaphragm booster being bad, it was just bad, hard pedal from the start nothing gradual to it.
Also have noticed that times if I'm on the brake pedal hard the engine starts popping through the exhaust. I guess its kinds like lite backfiring, but I usually think of backfiring as through the can and intake rather than through the exhaust. It only does it if I'm on the brake pedal hard, as soon as I let off it goes away.
Engine is an old FE running on a Holley Sniper EFI and it seems to run great other than this.
Under normal light braking everything feels normal. If I get on the pedal to stop hard it gradually goes hard and gets to the point of feeling like I've got a bad booster. Never really delt with a dual diaphragm brake booster so I don't know how they feel when they are going out. My only experience with a bad single diaphragm booster being bad, it was just bad, hard pedal from the start nothing gradual to it.
Also have noticed that times if I'm on the brake pedal hard the engine starts popping through the exhaust. I guess its kinds like lite backfiring, but I usually think of backfiring as through the can and intake rather than through the exhaust. It only does it if I'm on the brake pedal hard, as soon as I let off it goes away.
Engine is an old FE running on a Holley Sniper EFI and it seems to run great other than this.
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Joined: Apr 2004
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Sounds like a leak. You are running out of vaccum and thus lose the power assist. As that happens, the vacuum demand on the engine becomes a vacuum leak, causing a lean condition, which causes a lean miss and extra fuel in the exhaust with the resultant popping as it lights off in the manifolds or pipes.
That's my theory.
That's my theory.
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Laughing Gas
Joined: Apr 2006
Posts: 1,121
Likes: 267
From: Middle Georgia
That's kinda whats been bouncing around in my mind since posting this. It's been storming regularly here, so once I get a clear day, I'll do some poking around for anything obvious. Have a feeling I'm going to be replacing the booster.
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