Baby Got Brakes!

[ericfreeman]

I finally finished a project that involved adapting a pair of 4-piston calipers to my '79 CBX. About a year ago I replaced my sub-standard stock Harley calipers on my '78 Sportster with a pair of GMA 4-piston calipers and found the difference to be astonishing. Gone was the wooden feel of the lever and the lack of stopping power. It was shortly after that I got a good deal on another pair of new GMA calipers designed for late model Harleys. A shop had ordered them for a customer who bailed on the project so I got them for about half price.

A little work with some aluminum and I made adapter brackets, along with new stainless brake hoses. Initially, I wasn't happy with the feel of the stock '79 master cylinder and fitted a new Nissin M/C that was original equipment on Kawasaki ZXR's around 2000. Bled the system today and went for a nice ride.

Huge difference in braking! Lever is much firmer than before and it's very easy to modulate the stopping power. The old girl really pulls down now from highway speeds whereas before you prayed for lots of room. I'd prefer if all the components were black but for now I'm going to leave them as is. Riding season is fast approaching and I'd rather ride than scuff/paint parts.

Eric

[steve murdoch icoa #5322]

Looks good, Eric.
Are those EBC rotors? Same diameter as stock?

[ericfreeman]

Yes, EBC rotors in stock diameter.

[NobleHops]

Yes, EBC rotors in stock diameter.

Eric, that kicks ass. Would you mind writing it up with more detail? eg what model are those calipers, what pads do they use, any fitment issues, price, etc. Do you have a pattern for those brackets? A drawing?

Very cool upgrade.

N.

[ericfreeman]

The GMA calipers are for a 2000-2007 HD Twin front disc application, and they actually do come in black along with a chrome finish (mine are satin anodized). Retail price is around $680/black or $940/chrome. I'm not sure where my satin finish come in price wise since they don't seem to be listed in the catalogs. I paid $340 for mine which is why I bought them originally. I had already compared my very similar GMA 400 Series calipers from my '78 Sportster and they looked like they'd work on the CBX with adapter plates so I went ahead and bought the other pair.

Fitment required fabricating the adapter plates and since I had a spare front end, I simply removed the wheel and hung the entire front end from a beam over my workbench to allow for easy access to the fork/rotor area. I applied layers of tape evenly over the rotor in the area where the caliper would fit until the caliper was snuggly held into place by the layers of tape. I figured this would keep the caliper nicely centered over the rotor with even spacing side to side and radially from the rotor.

Then it was just a matter of making a plywood template that bolted to the CBX forks and also to the calipers. I lathed some small spacers (about .18") to fill the gap between the caliper mounting bosses and the adapter plates. I cut the adapter plates from some 3/8 thick 6061 aluminum flat plate using a bandsaw to rough the shape and then a combination disc/belt sander to get the curved shape. I used the plywood template to transfer the hole centers to the aluminum. Drilled the holes, checked for a good fit and then machined some shallow reliefs in the plates to break up the flat surface. A little satin black paint and they were done. Test fitted all the parts and measured to ensure the calipers were evenly spaced around the rotors. Since the calipers are rigidly fixed, it's necessary to have as even a gap as possible for proper pad wear and braking.

Fitted the brackets to the CBX forks with Grade 10.9 metric bolts and nuts using Loctite. The calipers easily fit onto the adapter plates and can be removed in seconds.

The GMA calipers use a 3/8-24 inlet thread so a normal banjo bolt will fit. I fabricated and ran 2 stainless steel brake lines directly to the Nissin master cylinder (will take some pics of that next time I'm at the garage) to avoid the air-trapping manifold setup of the CBX.

I don't have a drawing for the adapter plates since I used an easy to make template. There are a variety different calipers available so it all depends on what you're trying to adapt. I found the layer of tape method to hold the caliper in position on the rotor to be very easy to work with.

Hope this helps answer some of the questions.

Eric