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Message |
Steve Sousa
Guest
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 Posted:
Wed Dec 15, 2004 5:30 am Post subject:
e36 brake pedal resistance begins in diff points |
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Hello
Car is an 1994 e36 325tds.
If i press the brake pedal slightly then let go and imediately press it
again, the point were the resistance begins is a lot higher on the second
press than on the first.
In other words when i first press the pedal the resistance begins at about
2cm down, but if i let it go and imediately press it again the resistance
begins almost at the begining of pedal travel.
Is this normal?
Thanks
Steve
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Dave Plowman (News)
Guest
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| Posted:
Wed Dec 15, 2004 5:30 am Post subject:
Re: e36 brake pedal resistance begins in diff points |
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In article <329esrF3jc3rrU1@individual.net>,
Steve Sousa <etsteve@yahoo.com> wrote:
| Quote: | If i press the brake pedal slightly then let go and imediately press it
again, the point were the resistance begins is a lot higher on the
second press than on the first. In other words when i first press the
pedal the resistance begins at about 2cm down, but if i let it go and
imediately press it again the resistance begins almost at the begining
of pedal travel.
|
Is this when moving, or stopped?
When moving, run out on the discs/wheel bearing clearance will push the
pads back slightly, so 'pumping up' will reduce travel. If the same thing
happens when stationary, I'd say you have a leak somewhere.
--
*What happens if you get scared half to death twice? *
Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound. |
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Jim Levie
Guest
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| Posted:
Wed Dec 15, 2004 5:43 am Post subject:
Re: e36 brake pedal resistance begins in diff points |
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On Wed, 15 Dec 2004 00:30:17 +0000, Steve Sousa wrote:
| Quote: | Hello
Car is an 1994 e36 325tds.
If i press the brake pedal slightly then let go and imediately press it
again, the point were the resistance begins is a lot higher on the second
press than on the first.
In other words when i first press the pedal the resistance begins at about
2cm down, but if i let it go and imediately press it again the resistance
begins almost at the begining of pedal travel.
Some difference in the point of feeling back pressure from the brake pedal |
is normal when the car is moving. When the brakes are applied the pistons
in the calipers move toward the rotor until the pads contact. Releasing
the pedal and immediately re-applying the brakes allows the master
cylinder to refill with fluid and doesn't leave enough time for the
pistons to have retracted to any extent, resulting in a higher point of
resistance in the pedal.
I've never paid any attention to how much the difference in pressure point
is, but my gut feeling is that 2cm may be excessive. Warped rotors will
tend to cause more than a normal amount of piston retraction and could be
a cuse of this. Is there any vibration such as one might have from a
warped rotor? Even if you can't feel it it can be detected with a dial
indicator check at each wheel.
--
The instructions said to use Windows 98 or better, so I installed RedHat.
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Mike G
Guest
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| Posted:
Wed Dec 15, 2004 5:43 am Post subject:
Re: e36 brake pedal resistance begins in diff points |
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"Steve Sousa" <etsteve@yahoo.com> wrote in message
news:329esrF3jc3rrU1@individual.net...
| Quote: | Hello
Car is an 1994 e36 325tds.
If i press the brake pedal slightly then let go and imediately press it
again, the point were the resistance begins is a lot higher on the second
press than on the first.
In other words when i first press the pedal the resistance begins at about
2cm down, but if i let it go and imediately press it again the resistance
begins almost at the begining of pedal travel.
Is this normal?
|
Yes. Quite normal.
When the brake is released, the master cylinder is recharged with brake
fluid. If the brakes are not reapplied, the fluid flows back into the
reservoir through a small hole, about the diameter of a pin, just exposed
when the m/c piston is fully back.
However, if the brakes are applied before all the fluid returns to the
reservoir, and before the system can stabilize, the extra fluid in the
system, means the pedal braking point is higher than normal.
Mike. |
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Jeff Strickland
Guest
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| Posted:
Wed Dec 15, 2004 5:43 am Post subject:
Re: e36 brake pedal resistance begins in diff points |
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I'll bet that if you stop at a light and hold the pedal down as if you were
still stopping, as opposed to just enough to keep the car stationary - it
would drop slowly. If this is true, coupled with your symptom, my diagnosis
is that your master cylinder is toast.
"Steve Sousa" <etsteve@yahoo.com> wrote in message
news:329esrF3jc3rrU1@individual.net...
| Quote: | Hello
Car is an 1994 e36 325tds.
If i press the brake pedal slightly then let go and imediately press it
again, the point were the resistance begins is a lot higher on the second
press than on the first.
In other words when i first press the pedal the resistance begins at about
2cm down, but if i let it go and imediately press it again the resistance
begins almost at the begining of pedal travel.
Is this normal?
Thanks
Steve
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Guest
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| Posted:
Wed Dec 15, 2004 4:12 pm Post subject:
Re: e36 brake pedal resistance begins in diff points |
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'pumping up' will increase travel as the pistons have further to move,
surely. As someone else said, when stationary the pistons move toward
the disc then when the brakes are applied there's not as far to go. If
you really press very very hard on the brakes then you'll usually
suddenly get very immediately responsive brakes. Don't forget also the
"power" element of power brakes which is to some extent a function of
the inlet manifold vacuum. Bring a car to a stop. Swithc off the engine
& pump the brakes & the resistance at the pedal will increase. |
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Mike G
Guest
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| Posted:
Wed Dec 15, 2004 11:12 pm Post subject:
Re: e36 brake pedal resistance begins in diff points |
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"Dave Plowman (News)" <dave@davenoise.co.uk> wrote in message
news:4d1d6c9ef7dave@davenoise.co.uk...
| Quote: | In article <329esrF3jc3rrU1@individual.net>,
Steve Sousa <etsteve@yahoo.com> wrote:
If i press the brake pedal slightly then let go and imediately press it
again, the point were the resistance begins is a lot higher on the
second press than on the first. In other words when i first press the
pedal the resistance begins at about 2cm down, but if i let it go and
imediately press it again the resistance begins almost at the begining
of pedal travel.
Is this when moving, or stopped?
When moving, run out on the discs/wheel bearing clearance will push the
pads back slightly, so 'pumping up' will reduce travel. If the same thing
happens when stationary, I'd say you have a leak somewhere.
|
IME all hydraulic brakes can be pumped up to a greater or lesser degree,
stationary or rolling. Their design virtually makes it obligatory. But, if
under sustained pressure, the pedal gradually sinks, that would certainly
indicate a leak.
On it's own, being able to pump the pedal up, means very little. If
accompanied by sponginess it could mean the brakes need bleeding. If
excessive with drum brakes it could mean the brakes need adjusting.
According to the OP the difference is only 1cm. If the brakes are OK apart
from that, I'd say he has nothing to worry about. IMO his brakes are
behaving normally.
Mike. |
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