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4.0L OHV & SOHC V6 Tech General discussion of 4.0L OHV and SOHC V6 Ford Ranger engines.

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Old 01-22-2007
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Vacuum Leak?

When i first start my truck up and go down the road, my brake pressure is crap. If i "get on it" (upon acceleration - 4-5grand), then come to a stop, my brake pressure is much better. If i drive on the expressway for 15+ miles, the brake pressure also gets alot better - even better than accelerating like crazy.....Any ideas? Im probably going to have to check my vacuum lines..



Im thinking this *might* have something to do with that HUMM noise i ONLY have had in the summer as well...
https://www.ranger-forums.com/forum2...ht=vaccum+leak

Last edited by 01xltranger4x4; 01-22-2007 at 08:00 PM.
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Old 01-23-2007
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anyone..
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Old 01-23-2007
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check the main vaccum line going to the brake booster from the intake manafold.......there is a vaccum line diagram on the header panel that shows were the vaccum lines go.....


could also be that you have air in your brake lines.....try bleeding your front brakes.....
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Old 01-23-2007
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To summarize:

poor brake assist after an engine start;
improves after a high vacuum decel:
improves after a medium vacuum cruise.

How about a leak in your brake booster? It has a fairly large volume that has to be "pulled down" by engine vacuum. In a healthy truck, you can feel that happen through the brake pedal right after the engine starts. If there is a leak in the booster diaphragm or a leak/restriction in its supply hose, it will take longer to build the vacuum necessary for power assist.
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Old 01-23-2007
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Quote:
Originally Posted by rwenzing
To summarize:

poor brake assist after an engine start;
improves after a high vacuum decel:
improves after a medium vacuum cruise.

How about a leak in your brake booster? It has a fairly large volume that has to be "pulled down" by engine vacuum. In a healthy truck, you can feel that happen through the brake pedal right after the engine starts. If there is a leak in the booster diaphragm or a leak/restriction in its supply hose, it will take longer to build the vacuum necessary for power assist.
Yes, exactly what i was saying, or trying to say.

I did check this vacuum line a few days ago and everything appeared to be fine - plugged in, etc. So how could i tell if there was a leak in the booster or a restriction in the supply hose?

Thanks for the help
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Old 01-23-2007
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replace it.

he said you would notice something funny in the pedal at start up, check yours and compare to your dads 250 or something.
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Old 01-23-2007
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75 bucks for the booster.
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Old 01-23-2007
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62 at autozone

http://www.autozone.com/servlet/UiBr...%7ENONE%7C%7EW

part number 54-73189
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Old 01-23-2007
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lol, i need to see if its the booster first...

Thanks for the #'s
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Old 01-24-2007
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Buy it from autozone and install it if it don't work take it back
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Old 01-24-2007
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Yeah i checked the vacuum hose again a little while ago and the fittings are tight...Looks like i'll be getting the booster.
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Old 01-24-2007
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Quote:
Originally Posted by rwenzing
To summarize:

poor brake assist after an engine start;
improves after a high vacuum decel:
improves after a medium vacuum cruise.

How about a leak in your brake booster? It has a fairly large volume that has to be "pulled down" by engine vacuum. In a healthy truck, you can feel that happen through the brake pedal right after the engine starts. If there is a leak in the booster diaphragm or a leak/restriction in its supply hose, it will take longer to build the vacuum necessary for power assist.
I just tried this my my truck and my moms 04 4.6 explorer.

Before i started the explorer, i put my foot on the brake pedal and fully depressed it. I then started it and the pedal felt like it depressed even more, even felt a little squishy as this happened.

Tried it in the ranger and the first time i started it with the brake pedal fully depressed, nothing happened - pedal didnt depress more or feel squishy. But the second time i tried it, the pedal did depress down a little but not like my moms explorer. The pedal did feel a bit squishy as it depressed but only depressed 1/2 as much as the explorer.

I guess i could still have a vacuum leak in the booster, just a minor or 'unpredictable' one?
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Old 01-24-2007
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There is a check valve in the booster that tries to maintain full vacuum in the booster even though the vacuum varies in the intake manifold. Maybe a small amount of vacuum was trapped in the reservoir on the first start and didn't have time to leak out before the second start. Just guessing though.
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Old 01-24-2007
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I see, so IF i had a leak the pedal would never depress upon startup?
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Old 01-29-2007
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To replace the booster, is the master cylinder going to have to be removed as well?
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