[DeTomaso] Stock rear calipers questions

[Asa Jay Laughton]

If you look closely at the innards of the piston assembly, you'll see
it's a set of ratcheting teeth, allowing it to expand and lock but not
compress.

The back of the piston assembly is bolted to the upright.
The large frame slides on the caliber.
When pressure is applied, one piston presses on the brake pad and then
against the rotor; while the other presses against the sliding frame
which then transmits the force to the -other- side of the caliber
against the other brake pad and then against the rotor.

The parking brake simply does the same thing mechanically.

I thought someone at some point built a moving illustration of this
somewhere but I don't know where it is now.

Asa  Jay

Asa Jay Laughton, MSgt, USAFR, Retired
& Shelley Marie
Spokane, WA
******************************     
http://www.racingagainstautism.com
http://www.teampanteraracing.com
http://facebook.com/racingagainstautism


On 4/24/2014 6:31 AM, Larry - Ohio Time wrote:
> 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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