[DeTomaso] Stock rear calipers questions

Thu Apr 24 10:06:18 EDT 2014

 Here is my attempt to describe how the stock rear brakes work.

There are "teeth" on the rod connected to the piston that engage a mating surface inside the pot that the piston slides in and out of.  The teeth allow the piston to move out as the pads wear but do not let it move back.  This keeps the pads within the same distance of the rotor as they wear so there is not as much pedal movement when you apply the brakes and to automatically adjust the parking brake.  The pot is mechanically connected to the lever that is actuated by the parking brake so that when the handle is pulled up the whole pot is forced against the rotor so the locked piston can apply pressure to the pads.

The teeth and mating surface are only present on the middle of the quadrants of the piston rod.  Hard to describe but think of it as the rod having teeth at the 1 to 2 o'clock, 4 to 5 o'clock, 7 to 8 o'clock and 10 to 11 o'clock positions.  The other positions do not have teeth.  This is why when you turn the piston 45 degrees the teeth unmesh from the mating surface and the piston can be moved in and out freely.   If the piston is not rotated back to the locked position, the parking brake won't work.

Tom
5186

-----Original Message-----
From: Larry - Ohio Time <Larry at ohiotimecorp.com>
To: MikeLDrew <MikeLDrew at aol.com>; detomaso <detomaso at POCA.com>
Sent: Thu, Apr 24, 2014 8:33 am
Subject: Re: [DeTomaso] Stock rear calipers questions

Mike,

I am no expert on the stock brakes, but this is how it works in general on
cars with this type of parking brake. 

Yes it all has to do with the parking brake. 

What all this is doing is keeping the parking brake adjusted as the pads
wear. When the piston is in the "normal" mode it can come out, but can not
go back into the caliper. As the pads wear down the piston stays out more
and more. This way when you set the parking brake it does not have to move
much to be applied. This action can be looked at as automatic parking brake
adjustment.

I have had some vehicle, at one time, that the top of the parking brake
handle would turn to shorten the cable to make adjustments as needed. Simple
and EZ, but one has to think to use it, so it will never be seen again.

Larry (uses a brick) - Cleveland

-----Original Message-----
From: DeTomaso [mailto:detomaso-bounces at poca.com] On Behalf Of
MikeLDrew at aol.com
Sent: Thursday, April 24, 2014 4:11 AM
To: detomaso at POCA.com
Subject: [DeTomaso] Stock rear calipers questions

Guys,

I've been trying to figure out how the stock rear calipers work.   I 
haven't touched a set in years and I confess I've just given up trying to
figure 
out their mechanics.

I understand that the piston must be rotated 45 degrees to unlock it before 
it is compressed to fit new pads; it is then rotated back into position.

But as to how the caliper actually works, I'm at a loss.

AJ has terrific photos here:

http://www.teampanteraracing.com/gallery2/v/asajay/pantera/brakes/rearbrakes
/

I'm used to the idea of a caliper that is open on the rotor side, and 
closed on the back side; I can wrap my brain around the idea of hydraulic 
pressure being applied to the back side of the piston, and being forced out
of the 
caliper housing and thus acting on the back of the brake pad.

But the stock rear calipers are open on both sides.   I know there is a 
heavy steel housing that wraps around the calipers, so it's safe to assume
that 
the side facing away from the rotor presses against this housing, which 
wraps around to the inside and acts on the back side of the inside pad.

I take it that brake pressure is introduced into the center of this 
chamber, and the two halves of the piston arrangement are forced outwards,
away 
from one another?   One works directly against the back of the outer pad
while 
the other works on the metal surrounding housing and transmits force to the 
other pad?

What I don't understand is the function of the parking brake system.   It 
appears that when the caliper is in the normal orientation, with the slot 
facing straight up-and-down, the two halves are locked together, and by 
rotating the piston 45 degrees, the threads unlock and the piston can be 
compressed.

What I don't get is how the piston then extends out of the caliper, if it 
is locked to the other side and pressure is trying to force them apart?
How 
does the piston move and compensate for pad wear?

Because I've never had a set of rear calipers apart in my hands, I'm just 
not getting it.   Anybody care to do some 'splainin'?

Mike (loves the simplicity of non-sliding four-piston fixed calipers!)

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-------------- next part --------------
   Here is my attempt to describe how the stock rear brakes work.
   There are "teeth" on the rod connected to the piston that engage a
   mating surface inside the pot that the piston slides in and out of.
   The teeth allow the piston to move out as the pads wear but do not let
   it move back.  This keeps the pads within the same distance of the
   rotor as they wear so there is not as much pedal movement when you
   apply the brakes and to automatically adjust the parking brake.  The
   pot is mechanically connected to the lever that is actuated by the
   parking brake so that when the handle is pulled up the whole pot is
   forced against the rotor so the locked piston can apply pressure to the
   pads.
   The teeth and mating surface are only present on the middle of the
   quadrants of the piston rod.  Hard to describe but think of it as the
   rod having teeth at the 1 to 2 o'clock, 4 to 5 o'clock, 7 to 8 o'clock
   and 10 to 11 o'clock positions.  The other positions do not have
   teeth.  This is why when you turn the piston 45 degrees the teeth
   unmesh from the mating surface and the piston can be moved in and out
   freely.   If the piston is not rotated back to the locked position, the
   parking brake won't work.
   Tom
   5186

   -----Original Message-----
   From: Larry - Ohio Time <Larry at ohiotimecorp.com>
   To: MikeLDrew <MikeLDrew at aol.com>; detomaso <detomaso at POCA.com>
   Sent: Thu, Apr 24, 2014 8:33 am
   Subject: Re: [DeTomaso] Stock rear calipers questions
Mike,

I am no expert on the stock brakes, but this is how it works in general on
cars with this type of parking brake.

Yes it all has to do with the parking brake.

What all this is doing is keeping the parking brake adjusted as the pads
wear. When the piston is in the "normal" mode it can come out, but can not
go back into the caliper. As the pads wear down the piston stays out more
and more. This way when you set the parking brake it does not have to move
much to be applied. This action can be looked at as automatic parking brake
adjustment.

I have had some vehicle, at one time, that the top of the parking brake
handle would turn to shorten the cable to make adjustments as needed. Simple
and EZ, but one has to think to use it, so it will never be seen again.

Larry (uses a brick) - Cleveland

-----Original Message-----
From: DeTomaso [[1]mailto:detomaso-bounces at poca.com] On Behalf Of
[2]MikeLDrew at aol.com
Sent: Thursday, April 24, 2014 4:11 AM
To: [3]detomaso at POCA.com
Subject: [DeTomaso] Stock rear calipers questions

Guys,

I've been trying to figure out how the stock rear calipers work.   I
haven't touched a set in years and I confess I've just given up trying to
figure
out their mechanics.

I understand that the piston must be rotated 45 degrees to unlock it before
it is compressed to fit new pads; it is then rotated back into position.

But as to how the caliper actually works, I'm at a loss.

AJ has terrific photos here:

[4]http://www.teampanteraracing.com/gallery2/v/asajay/pantera/brakes/rearbrakes
/

I'm used to the idea of a caliper that is open on the rotor side, and
closed on the back side; I can wrap my brain around the idea of hydraulic
pressure being applied to the back side of the piston, and being forced out
of the
caliper housing and thus acting on the back of the brake pad.

But the stock rear calipers are open on both sides.   I know there is a
heavy steel housing that wraps around the calipers, so it's safe to assume
that
the side facing away from the rotor presses against this housing, which
wraps around to the inside and acts on the back side of the inside pad.

I take it that brake pressure is introduced into the center of this
chamber, and the two halves of the piston arrangement are forced outwards,
away
from one another?   One works directly against the back of the outer pad
while
the other works on the metal surrounding housing and transmits force to the
other pad?

What I don't understand is the function of the parking brake system.   It
appears that when the caliper is in the normal orientation, with the slot
facing straight up-and-down, the two halves are locked together, and by
rotating the piston 45 degrees, the threads unlock and the piston can be
compressed.

What I don't get is how the piston then extends out of the caliper, if it
is locked to the other side and pressure is trying to force them apart?
How
does the piston move and compensate for pad wear?

Because I've never had a set of rear calipers apart in my hands, I'm just
not getting it.   Anybody care to do some 'splainin'?

Mike (loves the simplicity of non-sliding four-piston fixed calipers!)

_______________________________________________

Detomaso Forum Managed by POCA

DeTomaso mailing list
[5]DeTomaso at poca.com
[6]http://poca.com/mailman/listinfo/detomaso_poca.com

References

   1. mailto:detomaso-bounces at poca.com?
   2. mailto:MikeLDrew at aol.com
   3. mailto:detomaso at POCA.com
   4. http://www.teampanteraracing.com/gallery2/v/asajay/pantera/brakes/rearbrakes
   5. mailto:DeTomaso at poca.com
   6. http://poca.com/mailman/listinfo/detomaso_poca.com