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rear brake upgrade

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expatmanxman

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Has anyone fitted a different caliper/rotor to the rear brake. I'm doing Moto Gymkhana on mine and have nearly set the thing alight a couple of times. I've fitted a heat sink to the caliper to dissipate some heat and stop the fluid boiling but the basic fact is the caliper is a weedy little thing and not up to the job. On the old FZS600 it's a pretty simple mod to fit the blue spot calipers but haven't ever seen an FZ6 with any modified rear brake.
 
expatmanxman said:
Has anyone fitted a different caliper/rotor to the rear brake. I'm doing Moto Gymkhana on mine and have nearly set the thing alight a couple of times. I've fitted a heat sink to the caliper to dissipate some heat and stop the fluid boiling but the basic fact is the caliper is a weedy little thing and not up to the job. On the old FZS600 it's a pretty simple mod to fit the blue spot calipers but haven't ever seen an FZ6 with any modified rear brake.
Click to expand...

Sounds like your issue is "heat soak" and how to get rid of heat at such low speeds.

Point: its very likely a bigger caliper or more pad surface area is not going to solve this problem. YOU NEED AIRFLOW and maybe fluid movement to prevent boil over!!!

The question now is how to obtain it? One option is to change out the way fluid is handled; i.e. right now the same fluid simply goes back and forth. You need it to circulate but this alone will not solve the issue but it will keep the fluid from boiling.
In the Cage world, they make calipers and valving that promote fluid circulation. That is; when you let off the brakes, special valving pushes the current caliper fluid through the lines & caliper to replace it with cool fluid from the reservoir.
I think you need fans and ducting or some means to extract heat. I don't know how to solve this one.

Good luck!
 
I don't think many members here have done a rear brake upgrade. I know the front brakes are a common upgrade with the R6 fork. But because most users here are either commuters or people who just enjoy riding and occasionally going to track days, you might not find many threads about that upgrade.

As a side note, you should be able to find a caliper that you're thinking would do the job and mount it pretty easily. I can't imagine you'll need to do more than pull the old brake caliper (maybe rotor as well), mount the new caliper (and rotor) and then bleed the brakes. You might have to do some custom work to get the caliper to mount correctly, but basic tools should allow you to do that (or some beers for a buddy with heavier metal equipment).
 
Because it's such a feeble little caliper it has to work really hard, I thought a larger caliper with maybe 4 pistons might spread the load a bit, dissipate heat better etc. Even better if I could find a bigger diameter disc to go with it, more leverage from a bigger diameter so won't need to work as hard.

Just taking a caliper off something else is not an easy job, the mounting holes will have to line up, the offset will have to be the same, all sorts of issues so can't just easily take any old caliper and fit it.

One possibility would be to have some adaptor plates made up so I can fit another caliper but ideally a bigger diameter disc that bolts straight on to the same mountings on the hub would be the first step.

Thanks for ideas
 
expatmanxman said:
Because it's such a feeble little caliper it has to work really hard, I thought a larger caliper with maybe 4 pistons might spread the load a bit, dissipate heat better etc. Even better if I could find a bigger diameter disc to go with it, more leverage from a bigger diameter so won't need to work as hard.

Just taking a caliper off something else is not an easy job, the mounting holes will have to line up, the offset will have to be the same, all sorts of issues so can't just easily take any old caliper and fit it.

One possibility would be to have some adaptor plates made up so I can fit another caliper but ideally a bigger diameter disc that bolts straight on to the same mountings on the hub would be the first step.

Thanks for ideas
Click to expand...

That said - how much are willing to spend?? Can you weld aluminum or have access to a TIG welder? Anything is possible and if you apply some basic prinicaples you can be succesful. If you're looking for a bolt on solution I don't think your going to find it.

Go to fleebay - grab the rear mounting bracket axle passes through (it holds the caliper): 5VX-25921-50-00 BRACKET, SUPPORT.

Do some measuring and start looking for a rotor that could be adapted for use in the rear. The rear is hardly ever used like your intending to do, but grab a front rotor and caliper (its about the max diameter). Here are the basics but your gonna have to do some foot work and figure out what the best option is. An S2 caliper from the front is a 4 pot and **perhaps** that front rotor could be used but the wheel is wider so you have to verify this.

I know some run dual calipers but thats more for stunts and getting an extra brake lever on the bar. Same concept could be applied here.


Rear disc brake: 2D1-2582W-00-00 DISC, REAR BRAKE
Disc outside diameter × thickness 245.0 × 5.0 mm (9.65 × 0.20 in)
Master cylinder inside diameter 12.7 mm (0.50 in)
Caliper cylinder inside diameter 38.10 mm (1.50 in)
MC is ~ 33% of Caliper bore. You need to maintain that type of ratio! Hint, may need a different MC too!
2008 FZ6 (BLACK METALLIC X) (CA ED.) - FZS6XBC Yamaha Motorcycle REAR BRAKE CALIPER Diagram and Parts

Front disc brake:
Disc outside diameter × thickness 298.0 × 5.0 mm (11.73 × 0.20 in)

Master cylinder inside diameter 16.00 mm (0.63 in)
Caliper cylinder inside diameter 30.20 mm (1.19 in)
Caliper cylinder inside diameter 27.00 mm (1.06 in)

I still think you will have the same issue but it will take longer to get hot as the pad is not that much larger but as you said, moving it out will offer more friction with less clamping force so it should reduce the heat.
 
I know you probably have taken care of it, but I have to ask if you have flushed and put fresh DOT4 brake fluid in? Just to make sure any old fluid and water are out of the lines and calipers that would reduce the boiling point.

I do a lot of commuting and highway miles, so I have no other input in this scenario :)
 
Last edited:
Are you experiencing loss of brake due to fluid boiling or are the pads overheating? What fluid and pads are you running? Upgrading to fluid with a higher boiling point and/or to pads with a higher operating temperature may get you there.

Even by moving the pad, if you're making the same amount of friction, you'll make the same amount of heat. In this case you just won't have to squeeze as hard to get it.
 
Got dot 5 fluid, braided hose, HH sintered pads, fitted a heat sink on the caliper. Doesn't take long before it's squealing like a pig, gets v v hot too, was smoking nicely after the last competition run.
Since all the changes listed I've never had it overheat but the squealing is really annoying, starts after maybe 10 minutes of abuse. Will have to do a bit of measuring etc, could really do with finding the PCD of the mounting bolts and see if there's anything bigger with the same, or if there's a caliper with mounting bolts spaced the same. I have a friendly engineering company who have NC machines that are more than capable of making an adaptor or new brake hangar. Will do some thinking. If I come up with anything I'll post it.

Thanks
 
expatmanxman said:
Got dot 5 fluid, braided hose, HH sintered pads, fitted a heat sink on the caliper. Doesn't take long before it's squealing like a pig, gets v v hot too, was smoking nicely after the last competition run.
Since all the changes listed I've never had it overheat but the squealing is really annoying, starts after maybe 10 minutes of abuse. Will have to do a bit of measuring etc, could really do with finding the PCD of the mounting bolts and see if there's anything bigger with the same, or if there's a caliper with mounting bolts spaced the same. I have a friendly engineering company who have NC machines that are more than capable of making an adaptor or new brake hangar. Will do some thinking. If I come up with anything I'll post it.

Thanks
Click to expand...

Maybe put a pad with less friction?

I imagine that you use the rear brake as a stabilizer, riding on it at slow speed continuously rather than as an actual brake, ie braking to a stop.

In that application it seems that an HH sintered pad would create a lot of friction which means heat.
I would try a different softer pad, it might wear faster, but it will create less heat too!



Saying that, i have never done Moto Gymkhana...
 
More friction = more heat = more braking force. There will always be that relationship. Braking converts kinetic energy into heat via friction. You just need the parts to take the heat. A larger brake will act as a bigger heatsink and allow for greater force, but the conversion of friction to heat remains the same.
 
How about this:

$_12.JPG



COURONNE 60 DENTS + ETRIER DE FREIN POUR STUNT YAMAHA FZ6 2007 | eBay
 
ozgurakman said:
this is so heavy and I think it's got unnecessary brake power?
Click to expand...

I've watched stunters, examined the bikes up close and spoke with several riders.

Its VERY common to have the rear brake also hooked up to a SEPARATE LEVER on the handle bars so they can control the rear as most of the times, their feet are on the rear peg set or farther back yet.

I've seen some bikes with one rear caliper and TWO lines to it (for handle bar mount) and saw one bike with two completly separate calipers on the rear.
 
Double caliper, now there's an idea.

MotoGymkhana is very heavy on the rear brake because when you're doing those tight turns you are using power to stop the bike falling in and have to use the rear brake to hold it back. You're not slowing the bike with the rear brake, you're fighting against the power of the engine.

Going to look at that double caliper idea.

Also have found a machine shop where they make rotors. I am going to ask if they have the dimensions of all the different discs and look for one with the same mounting hole dimensions, pcd etc. Could then have an adaptor made up to put a bigger or a double caliper on the larger diameter disc. Will post when (if) I come up with something.

BTW there are much better videos of moto gymkhana on youtube, watch this young lady throwing her ZRX1200 round like it's a toy https://www.youtube.com/watch?v=YVbm-cypIgg
 
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