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

 

anyone..

 

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.....

 

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

 

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.

 

75 bucks for the booster.

 

62 at autozone

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

part number 54-73189

 

lol, i need to see if its the booster first...

Thanks for the #'s

 

Buy it from autozone and install it if it don't work take it back

 

Yeah i checked the vacuum hose again a little while ago and the fittings are tight...Looks like i'll be getting the booster.

 

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?

 

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.

 

I see, so IF i had a leak the pedal would never depress upon startup?

 

To replace the booster, is the master cylinder going to have to be removed as well?