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Discussion Starter #1
1966 with 302ci with 268 cam, and front disc brakes with power assisted dual master cylinder with proportioning valve.

Previous owner stated he had a electric CompCam vacuum pump added due to high lift cam, because insufficient vacuum generated by the engine due to the lift of the cam. There is no vacuum reservoir.

Meanwhile, he disconnected the electric pump because it truly makes too much noise. The brakes are essentially manual brakes -- you just have to press the pedal harder.

I reconnected the vac pump (actually, I just put in the fuse) and installed a switch to to activate the pump to check it out.
Yep, that pump is loud -- just like a small one cylinder compressor, and it kicks on automatically when I depress the brakes.
But the brake pedal is halfway down to the floor now that the pump is hooked up, and in a very limited space, the power brakes kick in hard if I am not careful.

It just doesn't make sense to have power assisted brakes if they're not usable.

Here are my questions:
1) Should I really be needing a vacuum pump for a 268 cam? Is this typical?
2) Would a vacuum reservoir help?
3) Is anyone else using a vacuum pump with a mild performance engine?
4) Any other suggestions?

Thanks.

Vacuum pump.jpg


20190923_140533.jpg
 

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i would first see how much vacuum the engine is pulling with your cam, and then decide if you need the vacuum pump. you might be able to get away with just a vacuum reservoir and a one way check valve. if you really need a vacuum pump, i would suggest getting a ford spec vacuum pump from something like a 6.9 or 7.3 diesel engine. they are engine driven and very reliable, though the one on my truck crapped out after 171,000 miles.

by the way, 15 inches of vacuum should be enough to operate the brake booster.
 

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Have you checked you engine VAC? If, there are no verifiable VAC leaks, then, I would install a VAC tank. The pump will only run to replenish the tank which shouldn't be continuously. Also, tighter valve pre-load settings will reduce engine vac, unnecessarily.
 

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Hmmm… I wouldn't describe a cam that creates insufficient vacuum as "mild". The BOSS 302, BOSS 429, and 428 SuperCobraJet typically had power disc brakes, and required no vacuum pump.

Frankly, I'd ditch the whole mess. I've driven my manual disc 66 since Jimmy Carter was president, and never felt the need for power boost. Just get a 1974 Maverick manual disc master cylinder and replace all that stuff. KISS principle.
 
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Hmmm… I wouldn't describe a cam that creates insufficient vacuum as "mild". The BOSS 302, BOSS 429, and 428 SuperCobraJet typically had power disc brakes, and required no vacuum pump.

Frankly, I'd ditch the whole mess. I've driven my manual disc 66 since Jimmy Carter was president, and never felt the need for power boost. Just get a 1974 Maverick manual disc master cylinder and replace all that stuff. KISS principle.
this is probably the best advice. these cars are light enough that they really dont need power brakes.
 

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Discussion Starter #6
Have you checked you engine VAC? If, there are no verifiable VAC leaks, then, I would install a VAC tank. The pump will only run to replenish the tank which shouldn't be continuously. Also, tighter valve pre-load settings will reduce engine vac, unnecessarily.
Kenash,
I really don't know whether this is a mild cam -- "268" whatever that means in terms of performance. But, prev owner told me he wanted mild performance, but tractable in town driving, which it is -- altho it is a slightly loping idle.

1) How to check the engine vac? Vac gauge at the aperture on the manifold from which to pull the vac? Would this be at the carb, or on the mani?
2) do you have any suggestions on specs for less valve preload?

Pretty radical for me to consider downgrading the braking system to manual brakes, although it may happen. Might as well change the cam, after all, who REALLY needs performance in a street car. It's all just teenager bravado, actually. Take that last statement any way you want.

Thsnks.
 

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A Boss 302" made only like 12 in/Hg at idle, factory stock and had working power brakes. A classic 268H cam probably idles with 15 in/Hg. If the brakes don't work well with that, it's probably a badly designed power conversion kit. There's a lot of threads with people having problems getting power brakes to work well, but is always related to using an aftermarket conversion kit. Threads were people are having problems with the factory designed booster setups are rare.
 

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Discussion Starter #8
A Boss 302" made only like 12 in/Hg at idle, factory stock and had working power brakes. A classic 268H cam probably idles with 15 in/Hg. If the brakes don't work well with that, it's probably a badly designed power conversion kit. There's a lot of threads with people having problems getting power brakes to work well, but is always related to using an aftermarket conversion kit. Threads were people are having problems with the factory designed booster setups are rare.
THANK YOU! Great info.
I don't know what kit the prev owner used. No doubt it was an aftermarket conversion kit. I'll check the internet regarding problems.
 

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I'd think you'd have no issues with vacuum and power brakes with that cam.
 

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Discussion Starter #10
I'd think you'd have no issues with vacuum and power brakes with that cam.
You know, I think you're right.
UNFORTUNATELY, the previous owner was a Fxxxen idiot and did not know a thing about the engine he had someone build. When I asked him, he said I just told him I wanted something with a little get up to cruise the Hot Rod Nationals (here in Lou'vl) but that I can drive on the street.
So, I called the engine builder (Jim Mattingly). He remembered the car very well, but he did not remember specifics about the engine, as it had been over 10 years ago, He said, "I probably put in a 268 cam, with roller-tip rockers". He also said he got rid of receipts every 5 years.

So, I am going with 268 cam. It has a lope to the idle, but is very tractable in stop and go traffic.
I checked online for comments about a 268 cam, and here are several:
LUNATI - "Good cam for daily performance usage with good low end and mid range torque and HP. Good idle "
COMP CAMS: "High Energy 268H camshaft provides excellent mid-range power and is a good choice for daily driven performance vehicles with slightly lower gears. This camshaft produces a mildly rough idle. "
From a 4x4 forum: "A 268 cam isn't that radical at all, and still falls under the "CARB approveed" list "

SO, something is wrong. After reading several threads about power assisted brakes on VMF, I'm thinking I need to start with bleeding the system, as my pedal is soft. Then, I guess I need to hook the vacuum line from the booster up to a vacuum port on the engine to see what happens.
ALso, I need to check the manifold vacuum -- evidently you can rent this gauge from Autozone?

Any other ideas, before I spend another thou to revert back to ,anual brakes???
 

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Manual brakes is not a downgrade, at least on my heavier 69 M1. I have a CC 268XE cam which made a max of 13 in/hg, that wouldn't put more than 950 psi at the calipers with a Dewey's Midland booster. Swapped to manual and wouldn't go back to power for all the tea in China.
 

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Discussion Starter #12
Manual brakes is not a downgrade, at least on my heavier 69 M1. I have a CC 268XE cam which made a max of 13 in/hg, that wouldn't put more than 950 psi at the calipers with a Dewey's Midland booster. Swapped to manual and wouldn't go back to power for all the tea in China.
Yah, but from a "power assist" perspective, that booster just was not boosting at all. Afterall, power assist is supposed to exceed manual in regards to maximum braking, otherwise, why bother with needing an assist.
I gots a problem, and it just pisses me off that the P.O had not solved it in the 10 years he owned the car. Disconnecting the vacuum pump and "just using the pedal an manual brakes" was an idiot's solution -- for 10 years! Nah, I ain't gonna cut him any slack.
 

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With no vacuum to the booster, it's probably harder then if you had manual discs. I have manual disc, no issues. I ran both 1" and current 15/16" piston. The 15/16" is slightly easier but more pedal travel.
 

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With no vacuum to the booster, it's probably harder then if you had manual discs. I have manual disc, no issues.
Yep. The power pedal has a different ratio of leverage which doesn't work well as a manual pedal.
 
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