Another rear disk conversion thread...

[DZL JIM]

So I am seriously contemplating doing a rear disk on a drag truck project I have that the drums just won't seem to hold the power. I did some reading at another site that had a few guys insist on using Super Duty calipers because they were better then the older Chevy caliper, etc. No idea how they concluded this... Anyway, from the Rock Auto website, I got the bore sizes from a 2001 F-250 front and rear caliper, and bore sizes for a 1980 Chevy front, with 2 different bore sizes listed. Not sure why there are 2 different ones. ?? Results in area of the Piston bearing on the Pad (area of the circle): 2001 Front dual Piston: 7.06 sq in of bearing. 2001 Rear dual Piston: 4.98 sq in. 1980 Chevy truck front #184124/5: 6.776 sq in. 1980 Chevy truck front #184122/3: 7.819 sq. in. It seems that the old Chevy single piston has more surface area than the '01 rears, and about as much as the fronts. Questions: 1) What are the benefits of dual Pistons over a single? Is it exclusively to spread the load over the length of the pad and this gives 'better' stopping/holding? 2) Has anyone tried the '80 #184122/3 with the larger Piston? The Chevy parts are 1/2 the cost of the Ford parts and if they work just as good it's hard not to go that route... Disclaimer: Parking/e-brake not needed for drag truck, so I'm not looking at e-brake applications this time. Thanks.

[Talyn]

Well, as for dual and single. You can really think about it simply.

Is an object easier to move with a large footprint, or a small footprint?

1 piston will apply pressure in only one spot on the pad, a dual piston will apply pressure in 2 spots on the pad, thus more surface area is applying pressure to the rotor.

Thus, even with a slightly smaller surface area, the Dual piston will have more stopping power. More pressure is distributed throughout the pad, then the larger single piston.

[DZL JIM]

I hear what you're saying. I've been thinking abotu this a lot over the last few days, never really thought about it before.

Why I measured this stuff, if the Chevy truck pad is wider to cover the larger Piston, it still has a certain surface area bearing on the rotor. If the pad for the dual Piston is narrower but longer, it has a certain surface area bearing on the rotor. Seems like no matter what, the dual Pistons just get more contact.
But at a huge cost for the DIY'er...

[Talyn]

I'd go with the duals, honestly.
I can get a set easily where i'm located though.

[DZL JIM]

The SD dual piston calipers aren't too bad from the parts store, but you still need to find the 'pad cage' or whatever it's called, and those aren't available to buy (parts store or Ford). When you replace the caliper, you use your old one. There lies the main problem.
And none of the yards anywhere around here (or elsewhere that I've checked) have the calipers, or SD axle, or won't seperate the brakes from the axle...

So I'm kind of stuck with the Chevy calipers...for now...

[c00nhunterjoe]

here is what i used from advance auto-
Wearever rotors---------YH145251 - $57.99 each
wearever silver pads- --- NAD-52 -- $14.99
Cardone calipers rt side-- 184124---- $17.99+$15.00 core
cardone calipers Lt side-- 184125----$17.99+$15.00 core
True torq ft hoses ------- H98925---$32.99 each
Caliper hose bolt(help isle) 13940----$4.28 each

so i am using the smaller ones. i can tell you that on my 33's and 35's the truck will lock the tires if you really stand on it hard. up to 100 mph it will throw you into the dash. i would not hesitate using them on a drag truck. its a dam front brake caliper workign on the rear of a truck. you cant go wrong

[crzycrazycarl]

joe, do they have emergency brakes,,,wait its a front caliper. do you have a e brake?

[Talyn]

Yes, do tell. No ebrake kinda screws it for me.

[DZL JIM]

Joe,
I used that exact list from an old thread, but at Autozone since that's what we have here. Most of the parts had to be ordered, I hope to tear into it on Monday.
I hate re-doing things which is why I looked into the SD calipers, but for the cost I can't beat the Chevy truck mod. And your input is encouraging!

As for the e-brake, this appears to be the best thing I've found so far:
http://stak4x4.com/Accessories/parking_brake.htm.
But it's for 4x4 trucks with a T-case, won't work with 2wd and slip yoke.
Don't hesitate to use a driveshaft brake. think about it, that it requires 3.55 - 4.10 less force to stop the drive shaft than the wheels, so the brake can be much smaller there.

[pjwoolw]

The loaded front calipers from Ford come with the bracket. Pre assembled with pads. They were available last fall anyways.

[tjbeggs]

Jim the chevy pads are smaller than the SD rear pads and this is compounded by the fact that you don't get full contact of the Chevy pads on the rotor. I don't have any numbers for you but I know this first hand.

The SD parts are more $$ but they also fit better if mounted well. Also the Napa parts I use all the time now come with the mounting bracket when you buy the caliper.

[c00nhunterjoe]

the chevy calipers dont have a p-brake, but the caddy calipers do, i am putting a driveline brake on mine whenever i get around to it

[DZL JIM]

Great info, thanks guys!

I was also told about the brake pressure limit valve on the master cylinder, never knew what that was. By eliminating that valve I should get full flow to the rear breaks, whereas with the valve it was limiting the drums pressure.

I love talking to idiots at the parts stores who don't know what they are talking about...

Any idea what the difference is between rear calipers for the SD "To 12/20/99" and "From 12/20/99" ???
Other than about $35 each??
Edit: Actually, the fronts look to be cheaper than the rears, might as well go with them, as long as they fit the rotors...

[Talyn]

Well, with the ford light ass end syndrome. I wouldn't want full power to the rears, atleast on the drums. I could lock my 150's rear brakes all day. Could be interesting if you wanted to power slide.
The new tires hooked up better, so they wouldn't always lock up, but I have on gravel.

[DZL JIM]

Yeah, I wouldn't do it on a driver, but to hold rears for spooling up it should help...