Race rear disc brake options?

M

m6z

Member
Joined
Sep 15, 2005
Looking to shed a few pounds off the car this winter. Was going to go with aluminum drums, but wanting to know if anyone knows whats the weight difference between some of the aftermarket rear kits is? Like the strange or areo space kits and do they make a direct bolt on kit that doesn't require hacking the housing?

Btw will also be sticking with c-clip style axles. So how much more weight could I save by going with a strange or areo space kit?

Thanks,
Doug
 
Doug, I've got Baer's rear disc setup, I didn't weigh the parts but I don't think a 13" rotor and caliper would weigh much less than an aluminum drum, backing plate and shoes. The reason I changed was not for weight but for better stopping and the look, I went to 18" wheels and the stock brakes just didn't cut it!

Stuart
 

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I lost 15 lbs when switching from Alum drum rear brakes to Aerospace rear drag race disks.
 
Like I said I didn't weigh the parts, I did't think there would be that much of a difference, go figure.:eek:

Stuart
 
Well if your doing a "DIY" set up I have the Baer's rear disc brackets I'd sell.
 
Reviving an old thread instead of starting a new one.

I just ordered all the stuff for a rear disc conversion using the Eldorado calipers. I'll weigh everything I take off and put on and post it all here so there's a definitive answer to the question.

The parts list:

Scarebird disk brake brackets, $105 +$19 shipping ($124) - https://scarebird.com/index.php?route=product/product&path=59&product_id=129
From Summit:
AAZ-18-4138 Caliper Passenger side $51.97+$25 core = $76.97
AAZ-18-4139 Caliper Driver Side $51.97+$25 core = $76.97
AXT-AXCD154 Bendix Ceramic brake pads $18.97
BEN-PRT1261 Bendix Rotor (2) @ $17.97 = $35.94
RUS-657300 Brake Hose (2) @ $23.97 = $47.97
WIL-260-13783 2LB residual pressure valve $19.78

Grand Total = $400.57 as of today, March 3 2017.

I cross shopped the parts with Autozone and Summit was cheaper, even after a 20% off Autozone promo.

Parts should all be here early next week and I'm shooting for installation next Saturday.

This is equivalent to the Speedway Kit. It uses off-the-shelf GM parts from a 1995 El Dorado. However, the Scarebird bracket appears to be a better part. It's one piece, so you save weight on the hardware and have fewer shear points. The Speedway kit has a flange that goes on the axle, then a caliper mount that bolts to the flange. The Scarebird bracket also has a hose lock mount, which the Speedway kit doesn't have.

This kit will also require turning the axle flanges down. I'll figure that out once I know just how much has to come off the flange.
 
So, I got most of the parts yesterday, everything from Summit. The brackets from Scaredbird are supposed to be here Tuesday.

I went ahead and took the rear end apart down to the backing plates. I have the backing plate nuts, bolts, and brake line nuts soaking in oil right now, but I went ahead and weighed what I got off.

My car had OE steel drums. The drum and all the hardware (springs, brackets, shoes, etc) weighed 17.4 pounds per side.
My iron El Dorado calipers and the rotors are 22.4 pounds per side, a gain of 5 pounds per side. That didn't include lines and pads, which will likely add another pound per side.

So, a disc conversion to the GM iron calipers is heavier than an iron drum setup. If your aim is to save weight, you'll need to go to one of the high dollar aluminum caliper kits and a lightweight rotor. I still haven't got the backing plates and wheel cylinders off, but those together likely only weigh about a pound. But I will update with a total including those once I get them off.

I also use some play-doh to figure out how much to turn the axle flanges down by: 0.190"

Measurements were actually closer to 0.165", but there's plenty of meat outside of the lug studs (0.375" from stud head edge to the edge of the flange), so I'm upping it to 0.190" to make sure there's plenty of room so fitting the rotors won't be a fuss and I don't have to worry about any expansion causing interference. I'm going to drop the axles off at a machine shop tomorrow and have them turned down on a lathe instead of doing it at home with a grinder.
 
Update of the day:
IMG_0703.JPG


The brackets weighed 3 pounds each. The wheel cylinder and backing plates were right at a pound. So the net difference stands at +7lbs per side.

Turning the axle down 0.190 wasn't enough. I ended up having to take some more off with a grinder to get the discs on. Maybe shoot for 0.250" next time. Machine shop charge on the axles was $120, bringing the kit total so far to $520.

The most difficult part so far was the top bolts on the backing plates. They're stupendously tough. One side wrenched off, the other side wrenched off to a point and stopped hard. Luckily it had backed out enough for me to cut it off.

I'm about to head to Pep Boys to see if I can piece together a parking brake cable solution. The factory lines won't work with them.
 
Ok, so here's the foot-in-mouth moment.

I struck out at Pep Boys (Mine has a "speed shop" in it that usually has a smattering of stuff you'd normally have to mail order, but no brake cable kits), but there was a swap meet in town, so I went. I spoke with a gentleman from Inline Tube, and he sold me the proper e-brake cables for my setup. $100.

Here's the foot-in-mouth:

http://www.ebay.com/itm/1978-88-GM-...ash=item2eecd3f879:g:fhEAAOSwAuNW5w6D&vxp=mtr

They sell a complete kit on EBay. It has brackets, calipers, lines, cables, hardware, AND a rotor that has a hat large enough to not have to cut the axle flange down.

So, for anybody doing the El Dorado rear disc swap, save yourself a pile of trouble and just get this kit. It would have saved me $200 and a bunch of time. This setup isn't typical Ebay Chinese crap. It's all U.S. parts.
 
Turbo6inKY said:
Ok, so here's the foot-in-mouth moment.

I struck out at Pep Boys (Mine has a "speed shop" in it that usually has a smattering of stuff you'd normally have to mail order, but no brake cable kits), but there was a swap meet in town, so I went. I spoke with a gentleman from Inline Tube, and he sold me the proper e-brake cables for my setup. $100.

Here's the foot-in-mouth:

http://www.ebay.com/itm/1978-88-GM-...ash=item2eecd3f879:g:fhEAAOSwAuNW5w6D&vxp=mtr

They sell a complete kit on EBay. It has brackets, calipers, lines, cables, hardware, AND a rotor that has a hat large enough to not have to cut the axle flange down.

So, for anybody doing the El Dorado rear disc swap, save yourself a pile of trouble and just get this kit. It would have saved me $200 and a bunch of time. This setup isn't typical Ebay Chinese crap. It's all U.S. parts.
Click to expand...

It takes a BIG man to admit that there may be a better way!!

I like the way the caliper mounts on the side of the axle instead of towards the top like my SSBC kit.
 
Here's my last update on this:

The parts list I posted is still good, but the Inline Tube kit is still the best idea if you're going to do this. At the very least, their E-brake lines fit perfectly, so that reflects well on how the rest of their kit is likely to be.

Issues I had with the install that you'll probably have:
  • The parking brake ratchet system is a bear. If you don't properly adjust the ratchet before bleeding, you will have a really long pedal throw. Getting them adjusted after the system is bled is time consuming. The best instructions on adjusting these calipers I could find are in this PDF, on page 6: http://www.mpbrakes.com/docs/orig-guides/DB1792BR-INSTALLATION INSTRUCTIONS1.pdf
  • I ended up putting the 10psi residual pressure valve back in the system. It cut back on pad knockback and gave me a more consistent pedal without dragging the pads on the rotor. Wilwood says I could eliminate it completely, but I'm dubious and I don't want to crack the system open again.
  • Be mindful of clearance for the parking brake mechanism. Mine was contacting the bracket that holds on my Watts link. I had to borrow a plasma cutter and trim the bracket. Depending on the condition of your suspension, the parking brake mechanism could potentially hit the frame if your bumpstops are missing.
  • I have my proportioning valve cranked all the way open (full pressure to the rear) and still can't lock up the rears in a panic stop on asphalt. It slows down fast enough that crap in the back seat ends up bouncing off the dash, so I'll call it good for now.
In conclusion, the El Dorado rear disc kit does not save any weight, it actually add several pounds to each wheel. It does offer what the butt dyno feels is equivalent braking performance to the drums, and it'll certainly take repeated hard stops better than drums.

BUT, get the Inline Tube kit and save yourself a pile of time over piecing it together yourself. I'm not saying that as a plug for them, but as an honest assessment. Piecing this together myself was a mistake. It cost more and took what I'd hoped to be a weekend project and stretched it out over a month.

Final cost summary:

Previous parts total: $400.57

Machine work to turn down axle flanges: $120
Parking brake cable: $100 (show special)
Brake fluid $80 (ran four bottles of Motul RBF600 through it trying to bleed it @ $20/bottle)
Shop Fee $45 (gave up trying to bleed it and took it to a shop with a pressure bleeder)

Grand Total: $645.57

I hope this helps somebody.
 
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