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1966 Fastback, 289 - C4
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Discussion Starter #1
I seem to be having a vacuum issue.
The car runs great during the first 30-45 mins then the steering starts to feel heavy and the brake pedal is hard to push down. Engine still feels strong and transmission shifts as it should.

Power brakes and Borgensen power steering with ford PS pump.
What should I look for in diagnosing this?

760106
 

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Why do you think it’s a vacuum issue, especially as the steering is unrelated to vacuum?
 
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Are you putting a vacuum gauge on it? What kind of Hg are you pulling? Is your distributor vacuum advance working properly?

Unless there is a vacuum leak, poor vacuum is a result of poor ignition timing, fuel mixture and a poorly running engine overall. Not the other way around.
 

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They seem basicly 2 seperate issues but both relate somewhat to your idle speed. What is your idle speed when the engine is hot?
It could help a little to bring idle rpms up a bit to help create more vacuum for the booster and power steering assist be better. I have the same PS pump and notice the same thing that when temps go up the assist gets weaker. I am thinking about adding a PS cooler but for now i set idle to around 800/850 rpm and that seems to be better.
 
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I’ve got a hot vacuum leak that’s been diagnosed but I haven’t yet completed the repair. Mine is due to worn hard parts and an old engine. As in the post above I increased the curb idle and tuned the idle mixture as best I could to a couple hundred over spec. The down side is the fuel can load up and it takes a blast of the accelerator to clear it.

First you need to measure the vacuum and see if it’s low. A low vacuum could cause you to stall particularly if you’re stopped, erratic idle rpm and the like. Depending on the engine there is a capped port on the back of the intake manifold where the transmission modulator and the smog system (if equipped) get vacuum. I use the extra port. Vacuum gauges are inexpensive and easy to use. On mine I can check it in the garage or bungee the hood closed so I don’t pinch the the gauge line and drive a bit with it.

At least get it up to temp, get it back in the garage and measure vacuum. Unless you have a measurement and know what it is you’re urinating into a differential pressure system.
 

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1966 Fastback, 289 - C4
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Discussion Starter #8
I'm pulling 16inHg at idle in Colorado. (high altitude).
The shop manual says with hard to press brake pedal vacuum issue is a concern.
The power steering is a separate issue, but may be related due to heat as I am experiencing both symptoms at the same time... hard to press brake pedal and hard to steer.

Here is a pic of the manifold vacuum setup... My understanding is the power brake booster shouldn't "tee" off any other line. I do not know the appropriate piece to use here.

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I'm pulling 16inHg at idle in Colorado. (high altitude).
The shop manual says with hard to press brake pedal vacuum issue is a concern.
The power steering is a separate issue, but may be related due to heat as I am experiencing both symptoms at the same time... hard to press brake pedal and hard to steer.
Do you still pull 16" at idle when it heats up and starts to give you problems? Do the RPMs drop?
This could be one of those cases where the two issues are not really related (except in time). My WAG is that you have a heat related issue (gas, vacuum, etc) that slows down the idle speed which reduces both the vacuum and power steering pressure. PCV valve maybe?
Good luck, keep us informed of your progress.
 

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I always like to set my idle mixture screws when the car is hot(preferably with vacuum gauge). Usually when you set mixture when the engine is colder you end up being rich when it heats up resulting in lower vacuum..
 
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I'd suspect the booster before anything else, but a vacuum check when hot would seem quite appropriate.
 

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1966 Fastback, 289 - C4
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Discussion Starter #12
The vacuum reading was taken while hot. I am suspecting the vacuum line being plumbed poorly is causing a lower than normal vacuum to the booster which is compounded by increased heat in the engine bay.

The power steering hoses are hot to the touch after only 10 minutes of driving. Level is fine.

I do need to get a timing light... I've been tuning with the vacuum gauge/ear. Would be beneficial for sure to have hard numbers to relay.
 

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The vacuum reading was taken while hot. I am suspecting the vacuum line being plumbed poorly is causing a lower than normal vacuum to the booster which is compounded by increased heat in the engine bay.

The power steering hoses are hot to the touch after only 10 minutes of driving. Level is fine.

I do need to get a timing light... I've been tuning with the vacuum gauge/ear. Would be beneficial for sure to have hard numbers to relay.
You could run a steel vacuum line from the intake manifold back to the trunk and up to the brake booster and so long as there are no leaks it would make little difference. A reading of 16"hg at high altitude isn't all THAT bad. Put a vacuum gauge on it when hot, pop the fitting from the booster and plug the end with your thumb.
 
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