A little more stopping power,please?

CP

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#1
Wanting a little more stopping power on a 97 K1500 Chevy pickup 5.7. I know there are a lot of things involved to make this happen, but see there were 2 different bore size master cylinders used. 1-1/8 and 1-1/4. Am I thinking right about the physics here, the smaller the bore the more power to the wheel cylinders? But farther the travel? And will semi metallic have better grip than ceramic? Thanks
 

kev2

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#2
I would be hesitant to mess with this factory combo.

The larger MC - did you check to see if it had a corresponding increase it caliper or wheel cylinder piston sizes ?
From Air craft days I believe The theory FAP (force = area X pressure) the larger bore is an increase in area (π r2) the foot pressure being the same would result in greater force on the caliper piston and the resulting increase in force on pads.
GTG
 

billr

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#3
"the smaller the bore the more power to the wheel cylinders? But farther the travel?"

Yes, that is correct. And you may run out of travel at the pedal/MC. I gotta ask... what are the symptoms, what makes you feel you need more braking? I have a '97 Express van that mus have similar brakes, and those will start to lock-up just before the ABS takes over. There isn't much I can think that would make braking better.
 
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#4
A few answers to "Why won't my old truck stop?"
Because the rear wheel cylinders are seized up.
Because the front caliper guide pins are seized up.
Because your old pads/shoes are thin and glazed.
Because your new truck stops better.
 
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#5
Chevy uses the larger bore wheel cylinders in the rear with the bigger bore master cylinders on the trucks and vans. I can tell lots of stories where homeowners did rear wheel brake jobs and brakes do not stop as well. Tear it apart and they put the smaller WC in place of the larger bore ones
 

CP

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Thanks for all the replies
Been new rotors and calipers with pads put on the front recently. Also new rear drums I see but haven't pulled them to see if there are new wheel cylinders and shoes. Pedal height is good and things are firm. No pulling or grabbing or leaks. This pickup gets used for pulling farm wagons with corn or beans. I would think the wagons have brakes too, but you get 6-8 tons behind you, it is good to go, but even better to stop! Even with no load behind, I noticed she just didn't want to "whoa " like was expected. So it just seemed like there should be something we could do to improve a little.
 

billr

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#8
Does it have ABS, can you get the ABS pulsing by braking hard on a good, dry road?
 

oddone1975

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#9
Make sure of the obvious in that your rear brakes are adjusted properly as well if it feels you have excess pedal travel have experienced this first hand
 

CP

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#10
Billr
I haven't tried the abs like you said. Doing some other things to it and can't drive it for a day or two yet
 

CP

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#11
Letting you in on what I did to this pickup to make it ' a little better'? Even tho it had new front hoses, front calipers and pads, new drums,shoes ,wheel cylinders and hardware in the rear, I noticed the rear shoes were only making contact with the drums 50 maybe 60 percent of their surface. This is after 5000 miles of use. I measured the drums and they were right. When placing the shoes loosely in the drums they contacted the center of the shoe and would rock. Went to 3 part stores and tried three different sets of shoes, and they were all the same. Some were better on primary but not the secondary or vice versa. So I just did light cuts on resurfacing rotors and drums and but in new 'ultra premium' Napa brakes. Adjusted the rears up good, bled the brakes, road tested to carefully wear them in, and they seem to have a little better bite. Wonder if anyone else has had this where the shoes don't have good contact? I like to see a little more perfection in contact, with new parts. It seems that for these rear brakes to have full contact with the drums, it would take 30-40 thousand miles. And thus not full braking till then.
 
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#12
I believe the rotating 'applied torque' will pull the shoes into (or close) to full contact -
 

billr

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#13
Crap, I had a nice reply typed up and then it got lost with one key-stroke. Thanks, Win8/Firefox/Yahoo!

Bottom line is that it doesn't matter if the shoes have full contact, braking force is the same. And, they will eventually (quickly?) wear-in to match the drums. If you want them to match perfect right at the beginning, they have to be "arced" (sanded-to-fit), a common practice in the olden-days.
 
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#14
I agree with Billr. We used to arc all shoes to match the drums. That was when all 4 corners had drums. That was long before we even knew what disc brakes were.

Today most shops simply let the shoes seat in by letting the customer wear them in, which does happen fairly fast and works OK. Especially since they are usually only on the rear that does not do but aprx. 40% of the braking anyway. Of course, most vehicles have discs at all four corners today.
 

jd

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#15
I remember The Drill: Turn Drums, New Shoes, ARC the Shoes.

Remember Velvetouch Metallic? I put them on a '69 LeMans with those tiny drums GM used on midsize back then. Arc'd and all. The hotter they got the better they worked. Really hot and they worked about like disc. If you didn't run into a neighborhood tree at low speed during warmup. They're still available.