[DeTomaso] Gotta love professionals!

[MikeLDrew at aol.com]

In a message dated 7/28/08 12 25 11, asajay at asajay.com writes:


> What tab?  And how does it affect the parking brake function?
> 
> Photos would help.
> 

Dude!   Where you been?

The piston on the rear calipers has a slot in it.   This slot engages a tab 
protruding from the backing plate on the pad.   There is some sort of magic 
going on inside the caliper, whereby the tab on the pad keeps the piston in a 
certain orientation, and it can not be compressed.   If the tab isn't there, the 
piston is free to rotate as the brakes are used; if you're unlucky, it will 
rotate the requisite 45 degrees, which then disengages it from the parking brake 
ratcheting system and allows the piston to be fully compressed, and the 
parking brake doesn't work properly.   Hydraulic pressure will let the rear brakes 
continue to function with the pedal, but the piston will be disconnected from 
the mechanical parking brake mechanism inside the caliper.

I admit I'm a bit fuzzy on the specifics; the shop manual does a good job of 
describing what you have to do when you install new pads (insert screwdriver 
into slot in piston, rotate 45 degrees, fully compress piston, then rotate back 
to original position), and of overhauling the calipers, but it doesn't 
sufficiently explain *why* you have to do this.   I do know that if you just try to 
compress the piston using a C-clamp, without first rotating it to unlock it, 
you *will* break the mechanism, and parts are not available.

I (of course) have a spare set of rear calipers, and I really should take one 
apart to gain a better understanding of how the system works.   Someday...but 
in the meantime, RTFM (of which you have plenty!) and you'll be fine.

Here's a photo of the stock, original (and worn-out) rear brake pads mounted 
on one of my calipers.   Both pads are made with the tab on the backing plate; 
the non-functional outer pad is shown in this photo for clarity of the very 
slightly raised, rectangular tab directly in the center of the backing plate:

http://members.aol.com/mikeldrew/RearBrakePad.jpg

And here's a shot of the caliper (complete with primer overspray, a legacy of 
when my car was painted 12-13 years ago), which shows the vertically oriented 
slot in the piston that the corresponding tab on the inner pad engages:

http://members.aol.com/mikeldrew/RearCaliper.jpg

If your aftermarket pads are lacking this apparently important tab, several 
people on this forum have made their own by drilling a hole in the backing 
plate, installing a screw, then filing the top and bottom edge of the screw head 
so that it forms the shape of a square-ish tab.

Mike


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