[DeTomaso] Poor brakes
Thomas Tornblom
Thomas.Tornblom at hax.se
Sat Jul 11 05:48:31 EDT 2009
Amen.
MikeLDrew at aol.com skrev:
> In a message dated 7/10/09 11 05 11, JDeRyke at aol.com writes:
>
>
>> To clarify: if a pad wears, more fluid is used in that part of a caliper
>> during braking which moves the shuttle, indicating pad wear, as well as
>> what
>> you describe.
>>
>>>> Again, you aren't getting how this thing works--not even close. The
> shuttle valve is not displaced because more fluid has flowed into the chambers
> of the calipers whose pads have worn. It is a differential pressure
> valve, plain and simple. When you step on the brakes, you generate some rather
> high pressure (1000 psi? I don't actually know). If you suffer a
> rupture, you will have that high pressure on one side of the valve and zero psi on
> the other, and that differential pressure is what displaces the valve. The
> valve actuates a switch which illuminates the light on the dash.
>
> The brake wear indicators are metal tangs on the backing plate of the
> original brake pads, which contact the rotor and illuminate the same light on the
> dash.
>
> Although they happen to use the same light, the two warnings are totally
> unrelated to one another.
>
>
>> I know you like this infernal device,
>>
>>>> Actually, I very much *don't* like it. I advocate its removal, and in
> fact my car hasn't had it since forever. But I advocate its removal in a
> proper manner, keeping the front and rear brake systems totally isolated from
> one another.
>
>
>> but it really needs the
>> modification that AMC and others did- adding a spring on both ends of the
>> bore to help return the shuttle from the ends of the bore.
>>
>>>> Yes, that would be very helpful if you chose to keep it--but I think
> it's far more trouble than it's worth.
>
>
>> The trouble often
>> starts when one bleeds the brakes and the motion of the fluid bled out
>> drives
>> the shuttle far to one side where varnish sticks it in its bore.
>>
>>>> Again, you are confusing fluid flow with pressure differential. When
> you open a brake bleeder nipple, you all but eliminate the ability for that
> caliper to sustain any brake pressure at all; the pressure that is generated
> is consumed by pumping fluid overboard--which is exactly what happens in the
> event of a line failure too. During brake bleeding (assuming you are
> bleeding one caliper at a time) the pressure differential is causing the fluid
> to flow on only one side of the valve, but it isn't the actual flow that is
> creating the movement of the valve--it's the difference in line pressure.
> Gradual fluid flow (as when the brakes are applied, or when the pads wear
> over a long period of time) when the pressure remains constant will have no
> effect on the valve.
>
>
>>> I've
>> cleared several shuttles that were stuck solid, Larry Stock has done the
>> same in
>> his shop, and Roger Sharp has found at last one during Nor-Cal Tech
>> sessions.
>> I believe its an endemic problem to the Pantera best fixed by eliminating
>> the thing entirely. My 2¢- J Deryke
>>
>>>> And on that we are in complete agreement! :>)
>
> Mike
>
>
>
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--
Real life: Thomas Törnblom Email: Thomas.Tornblom at Hax.SE
Snail mail: Banvallsvägen 14 Phone: +46 18 444 33 21
S - 754 40 Uppsala, Sweden Cellular: +46 70 261 1372
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