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Guest
Anonymous Poster
Jun 6, 2007, 10:04 PM
Post #1 of 7
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Hard brake at start up
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Hi everyone, I have a 1997 Ford Ranger, Automatic, 2WD, 4 cylinder, with anti-lock brakes.
I have noticed for two weeks now that whenever the truck sits for several hours the brake becomes very hard to press, but once I start the engine the brake becomes normal again, the brake has not been hard to stop while driving, only at start up.
What could be the problem here?
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jun 7, 2007, 4:24 AM
Post #2 of 7
(3439 views)
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Re: Hard brake at start up
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There is a reserve for power assist which is usually a vacuum booster or hydro-boost which uses PS fluid pressure for power assist. Both are designed to hold power for assist for at least one more assisted brake action even when source is not running.
Vacuum booster generally use a check valve right at the large diaphragm which has been very rare to fail in my experiance and I'm not sure where hydo-boost does the same as none have ever failed.
It does sound like that's what's happening. If you hit the brake more than once with engine off it should feel normal and about any vehicle will have a hard pedal by the third touch of brakes -- all replenished upon start up. My own will hold the reserve power for weeks.
If the vacuum boosted style the booser itself can be leaking down. It's a bad habit but I don't touch the brake until engine is running and I don't set parking brake each time as I should but will if on any incline which is rare for me.
A couple hours is too fast to loose that reserve. If vacuum check out the check valve or just replace it -- I think they are inexpense. You might get a rubber grommet also as they are real snug with a barbed hook up to booser which can break the check valve just taking it out which should get you a "whoosh" and it can be hard on that grommet to keep removing it,
T
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DanD
Veteran
/ Moderator
Jun 7, 2007, 5:02 AM
Post #3 of 7
(3438 views)
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Re: Hard brake at start up
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The vacuum power brake booster or the vacuum check valve at the booster end of the vacuum supply line may have developed a leak.
Not such a large leak that the engine cannot supply enough vacuum for the booster to operate but enough that after the engine is off the vacuum in the booster can bleed away.
If this is the case get it repaired ASAP the leak wont go away on its own but likely become larger and you could loose your power brakes at the worst possible time.
The first test you could perform is to start the engine and allow it to run for a couple of minutes, allowing it to stabilize. You could pump the pedal a few times to get a good feel of the pedal travel. Now turn the engine off without touching the brake pedal. Wait 5 or 10 minutes; then press the brake pedal with the normal amount of pressure that you would on a regular stop. It should have the same feel as if the engine were running; you should also be able to pump the pedal at least two or three times before the vacuum is used up and the pedal goes hard.
Again it depends on how big the leak is and it may take longer for the booster to leak down. But even left over night the booster should still have vacuum in reserve to do the two or three pumps.
Now to determine whether the leak is the booster or the check valve you would again run the engine. While the engine is still running clamp a pair of vicegrip pliers to the supply line; not so tight too damage the line but enough that you know that the line is pinched and will not allow the vacuum to escape.
Turn the engine off and wait for whatever time it took for the vacuum to be lost in the first test and try the pedal. If you can get your two or three pumps then replace the check valve; if the pedal has again gone hard replace the booster.
While you’re doing all this waiting have a listen for a hissing sound around the booster area, if you can hear something that’ll be the vacuum escaping.
Dan.
Canadian "EH"
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DanD
Veteran
/ Moderator
Jun 7, 2007, 5:04 AM
Post #4 of 7
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Re: Hard brake at start up
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You beat me to the punch Tom. LOL
Dan
Canadian "EH"
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Tom Greenleaf
Ultimate Carjunky
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Jun 7, 2007, 5:25 AM
Post #5 of 7
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Re: Hard brake at start up
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Yea but you had pics to really show what we are talking about. As usual I'm never sure as to vacuum or hydro as I've seen some same vehicles come with either I think for trailer towing packages or optional rear disc brakes back when .
T
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Guest
Anonymous Poster
Jun 7, 2007, 11:57 AM
Post #6 of 7
(3432 views)
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Re: Hard brake at start up
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Some great advice from both of you, thank you so much. I'll definitely do the test you mentioned Dan, and Tom thank you so much for your advice as well.
Other people have told me to go ahead and replace the check valve, because it might not necessarily be the brake booster, but that most mechanic's will replace the brake booster anyway and charge me $100-$200 without labor.
I hear that replacing the check valve is very easy, but when looking for a check valve I can't seem to find one, do you guys suggest I try this or is it easier just to take it into a shop? I'm not the most experienced when it comes to working on anything brake related, but it sounds like a 2 year old could replace a check valve, so I'm confused on what to do.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jun 7, 2007, 12:54 PM
Post #7 of 7
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Re: Hard brake at start up
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They are sticky on purpose but do pull out of that rubber grommet -- try like heck not to break it. I'm pretty sure this is available at regular parts places and make sure they have one before you try. Will be hard coming out of the hose too -- just twist a little and work it out,
T
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