Another cheap rear disc conversion idea

broncosbybart · Nov 8, 2011

First off- I recommend this for something other than your pristine mall crawler.
A fair amount of fab work is needed.

I used a set of 4 door 91' Sidekick rotors. They are vented (unlike the 2 door ones) and are 5x5.5. They fit right over the 9" axle shafts and there is no need for grinding or fooling with lug studs. I did plasma a semi-circle in each to allow for access to the retainer plate nuts.

I used a set of $10 Speedway Motors weld on caliper mounts and the big (non-metric) GM calipers. I did have to weld a 1/4" thick 'shim' on the piston side of the one pad in order to make the big caliper work with the thinner rotor. I didn't want the piston extending too far. In all, I did it for under $100 with a cheat code on the Advance Auto site and some already had stainless flex hoses. Works great! I am using a cutting brake on the rig as well and it really likes these discs over the stock drums!

Broncobowsher · Nov 8, 2011

Did that to several years ago as surge trailer brakes in the 9" in my pickup bed trailer. They fit under stock 15" wheels

I used the original Tracker calipers and fabbed up my own brackets. No need to weld shims to the pads. Speedway offeres caliper shims if you want to use the GM calipers on thin rotors without welding shims on as well, it is a machined puck that fits on the piston.

The rotors are now lugcentric, but they fit so increadibly well that it isn't an issue. If the rotor doesn't fit, you probably have a bent stud. The rotor fits that tight.

broncosbybart · Nov 9, 2011

Good info. Didn't know about the piston shims. Makes sense and is a good idea! Yeah, the rotors fit very nicely on the studs.

br0nc0xrapt0r · Nov 9, 2011

Looks fantastic, I think I will use this route as the rear on my 69. Are the side kick rotors from the front or the rear? Also do you think this would work with the caddy calipers that have the Mech E-brake?

Thanks

Broncobowsher · Nov 9, 2011

I used front rotors and calipers. I don't think they have rear rotors, I think they are drums in back. The little front brakes are will sized for the rear.

I suspect that mechanical park brake calipers can work. I don't wee why not.
Found the GM spacers I mentioned before http://www.speedwaymotors.com/Speedway-Brake-Pad-Spacer,2147.html
I forget how thing the Tracker rotors are, they may not be thick enough.

broncosbybart · Nov 10, 2011

what he said. rotors are from the front. caddy calipers would work fine as well. i think they are actually a little narrower, so no shims should be required. caddy pistons don't have a hollow section in them, so the spacer idea wouldn't work on those. i liked the idea of being able to swap axles w/out having to screw around with an affixed brake rotor, in case of axle breakage on the race rig.

408Bronco · Nov 10, 2011

What year would you be looking for on the caddy calipers?

bmc69 · Nov 11, 2011

broncosbybart said:
I used a set of $10 Speedway Motors weld on caliper mounts and the big (non-metric) GM calipers. !

Would you happen to have the PN for those mounts? I found some in the Speedway catalog for 10 bucks but they say the caliper pin spacing is 7 1/6" ..the ones I have only measure 5 1/2" pin to pin, but were advertised as being "Caddy calipers with e-brake". I'm cornfused...

stupidboy · Nov 11, 2011

No e-brake?

Apogee · Nov 11, 2011

408Bronco said:
What year would you be looking for on the caddy calipers?

The 1976-1977 Cadillac Eldorado rear calipers used the larger D52 caliper body and 7+ inch pin spacing. To the best of my knowledge, 1978 was a transition year to the 5.47" [139mm] pin spacing metric calipers.

Aside from the parking brake, these calipers also have smaller piston diameters than the front calipers, 2.5" versus 2-15/16", making them much better suited for a short wheelbase rig with either Ford truck (2-7/8"), T-bird/LTD (3-1/8") or GM front D52 calipers (2-15/16"), albeit still somewhat oversized IMHO. The smaller metric calipers used on the 1978-1985 Eldorado's have even smaller pistons, 2-1/32", making them an even better choice strictly from a brake balance perspective.

bmc69 · Nov 11, 2011

Apogee said:
The 1976-1977 Cadillac Eldorado rear calipers used the larger D52 caliper body and 7+ inch pin spacing. To the best of my knowledge, 1978 was a transition year to the 5.47" [139mm] pin spacing metric calipers.

Aside from the parking brake, these calipers also have smaller piston diameters than the front calipers, 2.5" versus 2-15/16", making them much better suited for a short wheelbase rig with either Ford truck (2-7/8"), T-bird/LTD (3-1/8") or GM front D52 calipers (2-15/16"), albeit still somewhat oversized IMHO. The smaller metric calipers used on the 1978-1985 Eldorado's have even smaller pistons, 2-1/32", making them an even better choice strictly from a brake balance perspective.

Awesome!...thanks! Went back to the Speedway catalog and sure enough..the metric brackets are correct for my calipers and still only 10 bucks each. One disk-braked BB 9" going together....

Sorry for hijack.

broncosbybart · Nov 13, 2011

thanks for posting. was gone for the weekend. i will say that the weld on brackets require a fair bit of 'fitting' to get them set up. my application is on a race rig, no e-brake.

SpareParts · Nov 14, 2011

The easiest way I have found to "fit" them was to install the calipers and lines. Then mount the rotor on the axle and mock everything up. Have someone hold the brakes on while you weld them in place. This makes sure they centered and in the correct position. Of coarse the rotors have to be secured with lug the lug nuts first.

The Lincoln continental studs from a 79' work well with the 70's and 80's truck rotors too, it doesn't use any thing extra to hold the axle in either. In a race application I would think a thinner rotor would warp?

Another cheap rear disc conversion idea

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