[DeTomaso] Wilwood Brakes WTF????

Pantdino pantdino at aol.com
Sat Apr 20 00:29:02 EDT 2013


I suppose there are many kinds of calipers, masters, and seals out there
But I know for a fact that when I recently installed new calipers on the front of my TR6 you could see the caliper pistons retract as the pedal came up.  So much so that there was a visible gap between the pads and disc and the first bit of pedal motion didn't do anything.
After a while this went away, presumably because the dust seals stretched a bit.

IIRC Wilwood brakes don't have any dust seals, so there would be less retraction effect.




-----Original Message-----
From: Tomas Gunnarsson <guson at home.se>
To: pantdino <pantdino at aol.com>
Cc: theemonkey <theemonkey at yahoo.com>; detomaso <detomaso at poca.com>
Sent: Fri, Apr 19, 2013 1:46 am
Subject: Re: [DeTomaso] Wilwood Brakes WTF????


Not in the cylinders I've seen. Take the following scenario: You're bleeding the brakes two-person-style. Towards the end you have a basically air free system. Open bleeder on caliper -> push pedal -> pedal goes "low" as fluid leaves caliper bleeder -> close bleeder -> release pedal. The system is now free from pressure and the mc is close to the bottom of the bore. The mc piston returns from internal spring pressure but it does not retract the caliper pistons. The mc seals are often of the lip type, this type of seal is in practice one-way as the lip un-seals when subject to reverse pressure.
 
Tomas

<-----Ursprungligt Meddelande----->
From: Pantdino [pantdino at aol.com]

Sent: 19/4/2013 6:48:28 AM

To: theemonkey at yahoo.com; detomaso at poca.com

Subject: Re: [DeTomaso] Wilwood Brakes WTF????



But the sealing function is lost only when the pedal is at the full up position. At that point the fluid in the master cylinder reservoir is in continuity with the fluid in the master cylinder., but as soon as you step on the pedal at all the master piston moves past that little hole and the bore is a closed space which decreases in size as the pedal is depressed. As the master cylinder piston retracts from "on hard" to "lightly on" positions, a slight "suction" will be produced which will tend to pull the caliper piston back a bit. 

But what I was told is that it is the deformation of the seals that does most of the caliper piston retracting.

-----Original Message-----
From: richard bosch <theemonkey at yahoo.com>
To: detomaso <detomaso at poca.com>
Sent: Thu, Apr 18, 2013 7:17 pm
Subject: Re: [DeTomaso] Wilwood Brakes WTF????


The master cylinder piston and seals are designed so that the sealing
function is lost when the piston travels back from the "brakes on"
position. Also, the seals allow fluid to run past them as long as the
brakes are not applied. 

Tomas

Maybe that is the difference.Maybe the "race" brakes and some American designs 
do not have the "one way" seals and that is why they require the residual 
pressure valves.
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