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#1
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Hard Brake Pedal when cold
'91 Mazda 626 2.2 not turbo.
On especially cold mornings, when I first start out, the brake pedal is hard as a brick and very high, like the vacuum assist isn't working. It stays that way for 100 - 200 yards and two or three uses of the brake, then it goes to normal. Vacuum connection from the manifold seems secure. Am I gonna have to replace that whole stinking vacuum assist unit? I hope this is not a dealer item. They will bend me over the sink while some kid plays dueling banjoes. Thanks for any help, Hamish |
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#2
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On Sun, 30 Jan 2005 11:48:44 -0500, Hamish WAUGH >
wrote: >'91 Mazda 626 2.2 not turbo. > >On especially cold mornings, when I first start out, the brake pedal >is hard as a brick and very high, like the vacuum assist isn't >working. It stays that way for 100 - 200 yards and two or three uses >of the brake, then it goes to normal. Vacuum connection from the >manifold seems secure. Am I gonna have to replace that whole stinking >vacuum assist unit? I hope this is not a dealer item. They will bend >me over the sink while some kid plays dueling banjoes. > >Thanks for any help, > >Hamish > The first thing to try is having the brake fluid replaced. You may have enough water condensed in the cylinder and lines to form a plug of ice. That makes for the hard pedal when cold. |
#3
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In article >,
the fly > wrote: > On Sun, 30 Jan 2005 11:48:44 -0500, Hamish WAUGH > > wrote: > > >'91 Mazda 626 2.2 not turbo. > > > >On especially cold mornings, when I first start out, the brake pedal > >is hard as a brick and very high, like the vacuum assist isn't > >working. It stays that way for 100 - 200 yards and two or three uses > >of the brake, then it goes to normal. Vacuum connection from the > >manifold seems secure. Am I gonna have to replace that whole stinking > >vacuum assist unit? I hope this is not a dealer item. They will bend > >me over the sink while some kid plays dueling banjoes. > > > >Thanks for any help, > > > >Hamish > > > > The first thing to try is having the brake fluid replaced. > You may have enough water condensed in the cylinder and lines to form > a plug of ice. That makes for the hard pedal when cold. Actually, with the other post about bad idle Hamish made, I'd have to come to the conclusion that the vac. assist is the culprit for both problems. (I'm also reading his use of the word "cold" to mean "engine not hot/freshly started", as opposed to "temperature below freezing") Hamish - Try this test at a stoplight (or wherever you usually get the idle problem: Stop, set the parking brake, GET OFF THE SERVICE BRAKE, and try to duplicate the "screwy idle" - I think your other post said it happens when you take the car out of gear. Can you duplicate it when your foot isn't on the service brake? If not, that REALLY strongly points to the vac. assist unit being your source of vac. leak. Supposedly, the vac. assist is always under some level of vacuum (unless the brakes have been applied often enough after engine shutdown to equalize the pressure) but if you've got a pinhole or leaking check valve, it could very well be "leaking down" overnight/while parked, giving you the brake misbehavior you're seeing. Similarly, the "delay" I think your other post mentioned between stopping and the onset of the "weird idle" at a light could be caused by the same thing - At first, vac. is normal, but as the brake is held, it leaks down to the point where it needs to rebuild vaccuum, opens the valve needed to do that, and effectively opens up a vacuum leak to the manifold, causing your weird idle. I *REALLY* think both problems are related to the same cause, and expect that in the end, that cause will be found to be the brake vac. assist unit. A new vac. assist unit should be relatively cheap. "Should be" and "relatively" being the worrisome concepts... -- Don Bruder - - New Email policy in effect as of Feb. 21, 2004. Short form: I'm trashing EVERY E-mail that doesn't contain a password in the subject unless it comes from a "whitelisted" (pre-approved by me) address. See <http://www.sonic.net/~dakidd/main/contact.html> for full details. |
#4
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In article >, Don Bruder wrote:
> Actually, with the other post about bad idle Hamish made, I'd have to > come to the conclusion that the vac. assist is the culprit for both > problems. (I'm also reading his use of the word "cold" to mean "engine > not hot/freshly started", as opposed to "temperature below freezing") My beater car, an '86 mazda had the same issue without screwy idle. Brake pedal hard brakes less effective for the first few yards before going away. I cannot offer a solution as the problem went away on it's own and only happened on very cold mornings. |
#5
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Hi,
Thanks to all for responses. Brake fluid was recently (less than six months ago) replaced. I will clarify as to "cold." The brake problem only happens on espectially cold mornings, under 20 F," And only first thing in the morning, so the engine is cold when this happens. The idle problem (see recap below) only happens when the car is warmed up, and doesn't seem to be affected by outside temperature. It only happens in gear, not in neutral, not in park, and, get this, NOT EVEN IN REVERSE. The idle problem is the same whether or not I am using the parking brake or the service brake. This car has the dreaded "all-electric" transmission, which was rebuilt about 6 months ago. I haven't dug around sufficiently to see whether any vacuum lines go to it, but I have been given the impression that none do. If I am wrong, and the trans. has some vacuum input, is there any way that vacuum could leak only when the car is in gear? ====== Idle recap.: '91 Mazda 626 2.2 without turbo has a rolling miss at idle when in gear. It runs and idles smoothly at all other times, but if the car is fully warmed up and I stop at a traffic light, it will idle smoothly for about four or five seconds, then the idle will drop and surge, drop and surge, from almost stalled to normal. If I put it back into gear it will go right to normal (about 750 - 800 rpm) and stay there. ===== Thanks for any help, Hamish ================================== On Sun, 30 Jan 2005 19:40:19 GMT, Don Bruder > wrote: >In article >, > the fly > wrote: > >> On Sun, 30 Jan 2005 11:48:44 -0500, Hamish WAUGH > >> wrote: >> >> >'91 Mazda 626 2.2 not turbo. >> > >> >On especially cold mornings, when I first start out, the brake pedal >> >is hard as a brick and very high, like the vacuum assist isn't >> >working. It stays that way for 100 - 200 yards and two or three uses >> >of the brake, then it goes to normal. Vacuum connection from the >> >manifold seems secure. Am I gonna have to replace that whole stinking >> >vacuum assist unit? I hope this is not a dealer item. They will bend >> >me over the sink while some kid plays dueling banjoes. >> > >> >Thanks for any help, >> > >> >Hamish >> > >> >> The first thing to try is having the brake fluid replaced. >> You may have enough water condensed in the cylinder and lines to form >> a plug of ice. That makes for the hard pedal when cold. > >Actually, with the other post about bad idle Hamish made, I'd have to >come to the conclusion that the vac. assist is the culprit for both >problems. (I'm also reading his use of the word "cold" to mean "engine >not hot/freshly started", as opposed to "temperature below freezing") > >Hamish - >Try this test at a stoplight (or wherever you usually get the idle >problem: Stop, set the parking brake, GET OFF THE SERVICE BRAKE, and try >to duplicate the "screwy idle" - I think your other post said it happens >when you take the car out of gear. Can you duplicate it when your foot >isn't on the service brake? If not, that REALLY strongly points to the >vac. assist unit being your source of vac. leak. > >Supposedly, the vac. assist is always under some level of vacuum (unless >the brakes have been applied often enough after engine shutdown to >equalize the pressure) but if you've got a pinhole or leaking check >valve, it could very well be "leaking down" overnight/while parked, >giving you the brake misbehavior you're seeing. Similarly, the "delay" I >think your other post mentioned between stopping and the onset of the >"weird idle" at a light could be caused by the same thing - At first, >vac. is normal, but as the brake is held, it leaks down to the point >where it needs to rebuild vaccuum, opens the valve needed to do that, >and effectively opens up a vacuum leak to the manifold, causing your >weird idle. > >I *REALLY* think both problems are related to the same cause, and expect >that in the end, that cause will be found to be the brake vac. assist >unit. > >A new vac. assist unit should be relatively cheap. "Should be" and >"relatively" being the worrisome concepts... |
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