[DeTomaso] Stock rear calipers questions

Larry - Ohio Time Larry at ohiotimecorp.com
Thu Apr 24 09:31:54 EDT 2014


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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