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Ok, so my rear disc conversion deal fell through...for now...so I decided to put new shoes on the back of the car in preperation for Summit Point this weekend. At the same time, I slapped on a set of new front rotors and some new Mintex A/F pads I had sitting around. The only thing original in the wear item list of brake parts is the rear drums with about 70k miles on them.

The pedal now feels like it was when the car was new. Nice and firm. Shorter travel. Like it should be. Can anybody explain this?

I'm sure just about everybody in this forum has been at a track event where either they or someone else was complaining about either a soft and/or longer travel pedal. No ammount of bleeding would cure it.

The shoes were definately much thicker than what I took off there. Also, and I think Sean has experienced this, shoe friction material thickness definately varyies from shoe to shoe and from manufacturer to manufacturer. I put some el cheapo Napa shoes on today that I think were probably thicker than the OEM pads. Could that have helped?

Lastly, I haven't run a full thickness rotor in quite some time. All the rotors I have(three sets) have some pretty significant wear on them. These new ones are obviously full thickness(whatever the actuall number is). But even just putting full thickness (new) pads alone on those rotors and bedding them in properly, it didn't seem to cure the problem.

What I'm getting at is, in the way the braking system works, does the 'extension' of the pistons have somethign to do with pedal feel and pedal travel? Does the rear have more effect on this?
 

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Maybe...

With the new shoes, you're moving less brake fluid volume, so your pedal travel is shorter.

The auto adjusters take up slack, yes, but don't move the wheel cyl pistons back where they were when the linings were fresh.

 

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I think it could do with the springs in the drum system? The springs retract the shoes, which pushes the cylinders in. The amount the cylinder has to move to push the shoes plays into the long pedal.

As the shoes wear, they move out more, stretching the springs more. Stretched springs have more force, and so retract the shoes further off the drum, requiring more fluid to engage them, thus a longer pedal.

That's my guess.

But I dunno... I hate drums. Sean's term "Byzantine" is about right. They're rediculous.

I remember a couple years ago, my Father In Law was shopping for a new pickup. He's a GM guy. He told me the new GM pickups (that was then... we're talking about the current generation) were going back to 4 wheel drums, and he was happy, because drums are better than disks, because...

I wanted to tell him he's a moron, and there's no way... But I didn't.
 

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the new pads , discs, and shoes ABSOLUTLY created the change. the new stuff is thicker than the worn bits, hydraulic fluid is effectivly solid (uncompressable)so when you move the pistons back on the calipers you shorten the pedal travel. i would assume the same is true of drums but i have limited experience with them (none until now). as for the stiffer pedal im not certain how it works but i have noticed the same effect many times on all my cars and race cars, even go karts i think it has to do with less play but im not sure. all that extra mass should go a long way towards preventing you from overheating the system as well. more mass equals more heat absorbtion just like a BBK.
 

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the new pads , discs, and shoes ABSOLUTLY created the change. the new stuff is thicker than the worn bits, hydraulic fluid is effectivly solid (uncompressable)so when you move the pistons back on the calipers you shorten the pedal travel.
Not quite true since modern car brakes are open systems that allow for fluid expansion and pad and shoe wear.

My personal hypothesis, is that with 70k + you have some wear in the calipers which in turn allows some slop. That slop turns into squish at the pedal. I think it was beaverun last year that I had Eric's dad help me bleed the brakes. We bled the fronts and when the car was still the pedal was nice and firm. When the car was moving the pedal tended towards the soft side. Changed pads and rotors and the pedal was nice and firm all the time with no further bleeding. The further the piston is extended, the more room for slop. With new pads and new rotors the piston is fully compressed so more overlap from the piston and the sleeve of the caliper which takes away some of the slop.

I hope that all makes sense, if not, I can probably explain it better in person.
 

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Discussion Starter #6
My personal hypothesis, is that with 70k + you have some wear in the calipers which in turn allows some slop...
Makes sense but for the record, I have less than 20k miles on the calipers. I noticed a leaking caliper at the end of that same BeaveRun weekend last year so I replaced both with new ones from Ford.
 

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Oh, one other things: Pads flex when you use them hard, single pistons sliders are the worst, two piston sliders a little better, 4 and 6 piston fixed are the best.

So, they flex, and as you use them, they get tapered wear, or even curved wear. When you release the breaks, they straighten out and move the piston in further than if they were flat.

That hurts too.
 
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