Mounting the rear caliper under...need opinions!

Sn34ky

Sn34ky

Farmer's can build bike 2
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Here's my ''problem'' : I want to mount my stock rear caliper under the swingarm, for achieving this I need to find a good spot on it to bolt a brake stay. Which one of a pulled or pushed caliper have the greatest energy transfered to the brake stay?

Here's the 2 options, just tell me if you think it can be safe and what you think about that!

#1: Mount a 1/8 thick bar to the 8mm bolt that keep the caliper on the bracket and then mount it to the swingarm with a swivel of fix mounting point??:shrug: Do you think this bolt is strong enough? I'm not planning on racing, it's a cruiser, but in case of emergency braking I still need to have a bolt that will not snap

img0137ow.jpg


No dimension but here's a quick plan of the plate, I know you'll understand what I mean

brakestay.jpg




Option#2: Drill a hole (#1) thru side to side for an 8mm (~5/16'') bolt and 2 others (#2) maybe 1/2'' deep in the bracket, tap them and put an 8mm bolts, make a custom bracket that will mount there and have a swivel mounting point at both ends of a stay rod or plate, whatever... something that will work like the oem configuration imho!!

img0139pyt.jpg



I think #1 could be the cleaness, but #2 the more safe? What you think?

Thanks alot!
 
Sn34ky, interesting challenge. I see from your sketches that you have a sound concept of brake stay geometry. From other previous posts, we've established that max viable stopping torque would be around 500 ft-lbs, and with a 100% safety factor, design for 1000 ft- lbs torque. In your 1st pic, looks like 3" torque arm, 1/4 ft, requiring 4000 lbs. Doing a google search of "bolt shear strength" yields several good hits with 'pdf' tables. A grade 8 bolt of 5/16 (8mm) shows nearly 10,000 lbs, within this design criteria.

The real problem here is the load paths. In your pic #1, you have a rod in your hand, the tip of which is touching the contact area of the caliper and mount yoke. It is this zone where brake forces from the caliper transfer to the yoke, in compression. As this load wraps around to the proposed mount point(s), the load would try to spread open the yoke. Visualize the yoke as an aluminum 'C' clamp, see it trying to open up?

The challenge here then is to figure how to get that load path to solidly wrap around the caliper to an adjustable brake stay link.

Angus's point about brake bleeding is very valid and startling:doh:. Could design this so caliper is removeable, with flex line, so that it could be removed and rotated, bled rightside up, with a rotor-thick spacer fitted between the pucks. Bleed, then remount.

Gotta think about this awhile.
My 2 cents...
 
ya, wasn't me. But I wouldn't mount it to the bolt with the float like in design #1. and as angus....er...unfocused says, air will get trapped inside.
 
Thanks guys! already knew about the bleeding issue, but here's 2 other options i have in mind ...

option #3:

Make a little bracket that will act like a '' double articulated stay'' to mount it at the oem location

img0141bk.jpg



or

option #4

make an ''attachment'' to the existing caliper bracket that will be the ''hidden brake stay'' something that can be found with other bike model... in steel an bolted or in aluminum and welded?

brakestay2.jpg

img0142go.jpg


what you guys think? Can I find a kit or a ''transplant'' that fit directly or with a minimum of custom work that can goes Under the SA??
 
I know a lot of flat track bikes run the brake underneath. Maybe you could try and check out some photos online and get an idea on how they run there setups.
 
option #3 is discarded... the bracket will need to be welded on the stock stay bar, or the caliper will rotate on tension and hit the bracket.
 
If it were me i'd make a new bracket with 3/8 steel plate and have it cut with waterjet. Costs like $30 not including metal cost. Worst case cut it with a bans saw and drill it where needed. Not a fan of the cast aluminum stuff.

I like option 3 but not the prettiest. Think about cutting out a new mount plate. Good luck on the path!
 
number 3 will not wrk. no matter how tight that short piece is bolted to the long, as soon as you tap that brake, the two will straighten, and cause serious bodily harm. not even sure if weldin the two together would work. Maybe the one piece water jet cut one would do, but, If this is just to help hide the caliper, show a little more wheel, its not worth the trouble.
Some guys go for test rides, and not have a cheap cotter pin in the brake stay, just bolted on, in original design, .Somehow the arm comes off the brake plate(I know you have disk, no different) and wraps around the axle and locks up. Bad day all around
 
I was thinking you we're showing where the 2 would both together in 3, you were proposing a two piece linkage though. Definitely not as mentioned. But is there no room for the arm to mount from behind it directly using just 1 arm for 3?
 
Your option #3, using a single/thick stay will work, but adds to the ugly factor you're trying to avoid.

BobbedSled's idea (in post #11) is intriguing. You could replace that cast aluminum bracket entirely. Make up a new caliper bracket from steel, with option #4 built-in. Would need to weld-in a bung to inside of swingarm. Not much room in there, though, between rotor and swingarm. But, if this is a new one-piece bracket, could have that option #4 arm located under swingarm.
 
TwoManyXS1Bs said:
Your option #3, using a single/thick stay will work, but adds to the ugly factor you're trying to avoid.

BobbedSled's idea (in post #11) is intriguing. You could replace that cast aluminum bracket entirely. Make up a new caliper bracket from steel, with option #4 built-in. Would need to weld-in a bung to inside of swingarm. Not much room in there, though, between rotor and swingarm. But, if this is a new one-piece bracket, could have that option #4 arm located under swingarm.
Click to expand...

Ugly is the word!

Making a new hanger is something that I'll look at... but OMAR'S already making one, but you need a brembo caliper and maybe a thinner rotor... I can live with the brembo, but I want to keep the stock rotor, I kinda like the look of it! If I change the rear rotor i'll change the front setup too... or it's gonna look stupid imho... I've e-mail him about that to know if he can trick me something!

I'll put an option#5

''Floating brake jack'' , Bore and shave a little of the inner spacer of the oem hanger to fit a bronze bushing on the axel as the ''spacer'' , put a grease nipple, then make a stay with heim joints at each ends and instead of mounting it to the swing, go in a parallel line with the SA and mount it directly to the frame... 100% floating rear brake... What about that?

img0146so.jpg
 
That's a clean setup man! Thanks for sharing me that! That's something I can do myself and this is what I like!


I'll do a search but if someone can answer this before i'll find it: Which model use a brembo caliper that fit on the stock rotor? 7mm I think?
 
You can use the stock rotor (7 mm) with a Brembo Goldline caliper. You do have to grind the throat area of the caliper. You have to widen the throat because the cailper was designed for 4 mm rotors as used on Ducati bikes. Its not difficult to grind the extra clearance needed for our stock rotors.
 

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