cb125 disc brake conversion to hydraulic - was this ever resolved?

R

revengineering

New Member
Hello. Im new here. I bought a cheapo cb125 with a front disc and the swinging cable caliper. I managed to disassemble and rebuild the internals (i dont know if the adjuster is gonna work right but atleast the brake works) however i see there have been numerous posts about mounting a hydraulic caliper.

has anyone come up with a caliper thats a good fit? my plan is to design a swing arm that allows the hydraulic caliper to float like the original cable caliper did.

i chose a random cheapo chinese hydraulic caliper for my first go round:

http://www.amazon.com/gp/product/B008II133E/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1

stupidly its a left side lever pull so i'll probably be using this:

http://www.ebay.com/itm/Honda-CR-Brake-Master-Cylinder-CR80-CR125-CR250-CR500-NEW-/271074097504

I CADed up a swing arm to mount it. i ran FEA on it, based on a 200lb total brake force (100lbs per pad) with a .33 coefficient of friction, and it should last 500,000 braking cycles if make from 6061. I 3d printed it and confirmed fit.... and I could cast one out of aluminum, or order a bunch from china in cast iron, but before I do all that... is there a consensus on what a better caliper choice would be? Something thats actually properly oriented and can be more readily mounted?

https://31.media.tumblr.com/f73da953c36a7597827831d66d54cb67/tumblr_nd9eikjkFk1sqxoxko3_500.jpg


https://38.media.tumblr.com/b4b7e381614dc6c80b4f530a26b22056/tumblr_nd9eikjkFk1sqxoxko1_500.jpg
 

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Hell yeah! I wanted to do this for the longest time!

I'd check over with Wilwood calipers to see if anything fits the bill. Please, please, please keep me posted on this!
 
Wilwood is expensive. Check out Ducati Monster rear caliper. Below is a mount I designed for the Ducati Monster caliper. Unfortunately that is for a Harley Wheel and a 3/4" axle. I'm actually building a CB125 and if I had a disc brake front end I could redesign it to work on a CB125.
 
I swapped out the entire front end from a Rebel 250 into my CB125,they have the same steering bearings & steerer tube so that part fits well.The braking is now 100% better than the old drum I had.
 
grcamna5 said:
I swapped out the entire front end from a Rebel 250 into my CB125,they have the same steering bearings & steerer tube so that part fits well.The braking is now 100% better than the old drum I had.
Click to expand...

Good to know!

Looks like all years of Rebel 250 should work according to All Balls' fork conversion utility when I put in 1980 CB125S.

How much did it cost when it was all said and done?

I've been looking at the Honda MB-5 forks/wheel to get a disc brake onto my CB125S. 27mm forks and 12mm axle diameter so it might work. Have the parts on order right now.
 
Cost me between $2-300 all said and done w/ all new everything;I found a pr. of 86' forks on Ebay in exc. cond. which is tough to do considering that most all of them have small rust 'pits' along the tubes.The fork assemblies are about 31" overall length compared to the oem 81' CB125S forks that're 27"... so I'm planning on lifting the tubes above the top triple and installing 33mm clip-on's.I already had a CB350 headlight bucket w/ H4 Candlepower bulb and then all I did was buy some aftermarket fork brackets.I had to drill 2) 6mm holes into the Rebel lower triple to install new steering stop 'bolts' after cutting off the Rebel headlight mount/steering stop casting.The steering is a bit quicker because the Rebel triples are less offset which is good because the Rebel front rim is a 1.85 x 18" compared to the 1.40 x 18" of the oem CB125S.
The Rebel 250 triples are much wider than my CB125's and it makes it respond quicker,kind'a like power steering w/ less input required to countersteer.

That MB5 set-up you're getting will probably be lighter than my set-up and that should be good also.
 
The MB5 parts more or less fit! The caliper bracket needs to be extended about 10 mm to fit the disc but other than that everything is gravy.
 
Stock CB125S disc wheel. The MB5 wheel would fit without any modification. The MB5 has a ~220mm disc and the CB125S ~240MM. Tire and wheel dimensions (diameter, axle diameter, width) are the exact same otherwise. I already had a spare disc wheel so I figured I wouldn't buy the MB5 wheel, but that is definitely the easier path.
 
Hey,

I'm new here and just got a 78 cb125s with the swinging caliper front brake and the internals are completely disintegrated. I've contacted a bunch of online parts suppliers but no one has these parts in stock. I would be interested in buying the stock setup from anyone who has converted to the hydraulic instead of converting mine at this point. Thanks
 
Dude. It would be cheaper, easier, and a significant braking improvement to use MB5 forks/wheel/caliper than to use the bicycle brake. The only downside is it's "not stock".
 
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