Dual Disk Brakes: Onto a XJ650J from a XJ750RJ

I have the opportunity to get a GREAT deal on an entire front end (triple trees on down) from a 82 750 Seca, and have been wanting to put dual disks on my 82 650 Maxim.

I know the forks are significantly different, and I've done a lot of research on the site, but I can't tell if it's possible or not.

I think...all I would need is the Outer Fork Tubes to be the same size, as the Master cylinder, Brake Lines, Calipers, and Disks would fit if the outer tubes fit.

However, the outer fork tubes have different part numbers, so there is no indication that they would fit without another mod. I just got new fork springs, seals, etc, so I'm not inclined to purchase new springs again, at least not right now.

Any thoughts? Of course, for the price I could probably refurbish the items and make a profit....we're talking cheap...

 

I got an 81 650 maxim (using the stock triple clamps), seca-ish bars, 82 750 seca forks, 83 750 seca calipers/rotors, 81/82/83? 650 seca master cylinder and brake perch EDIT: clutch perch not brake perch, ss brakeline i made from stuff i got from anplumbing.com (not DOT approved; wont pass inspection).

tube diameters are the same:
http://www.dotheton.com/forum/index.php?topic=1090.0

the 750 seca's MC situation is weird. a lot of people dont like it. im sure you could make it work, but dont quote me there; i think you'll need the seca's clamps or some fab work to mount it--and i cant say if the two yoke lengths/diameters are the same.
also, make sure to use a MC from a bike that originally had dual disks.

the 750 forks on my bike seem a little stiff; i run like 2-4 psi and it still seems a little firm. (i think the book recommends 5.7). maybe your new springs would fit? id like to know too.

my excuse for doing the upgrade was that my stock rotor was way way way too warped. after the upgrade, besides the awful pulsating, i cant actually say that i notice vastly improved braking, like, hardly even noticeable, even with the ss line. however, i do use the anti-dives, i assume if i took them out of the equation, it would improve.

which reminds me. those anti dives take a lot of time. A LOT OF TIME. to get working and sealing like they should.

in my opnion, if youre in it for improved braking, your money is better spent elsewhere. if youre in it for the badas$ factor, then go for it.

and omg i cant believe its time for step 3 already! now before i know it, ill have to be surviving all over again. seems like i just got finished with today's surviving, too... o well. at least tomorrow is PAYDAY!!! WOOOOOOOOOOO!

p.s. i can upload pics if you would like to see.

 

Thanks, but that answers my question....it's not on my priority list, no matter how good of a deal they are! The springs I have aren't right for that set of forks.

It's interesting to know that the dual disks don't affect your braking significantly. I wonder if others have that same experience?

 

The XJ650 Maxim's, although having only a single front disc, have a very LARGE front disc and a very large caliper piston (which means a lot of clamping force on the rotor can be exerted by the caliper). In fact, the 650 has the same size caliper piston as the 900's, meaning it's almost 30% larger in face area than all the other models. So it's not a bad brake system, at all.....


The real benefit of the dual brakes is slightly more stable braking and especially less fade.......there is much more disc surface area to dissipate heat with dual rotors.....and "heat dissipation" is the name of the game in the braking biz.

The 750 Maxim rotors are smaller in OD (10-1/2") than the 650 Maxim, while the 750 Seca rotors are the larger 11-3/4" OD (same size as the 650 Maxim).

So the best system from a "braking physics" point of view is the 750 Seca system (well, actually, it's the 900's, due to the larger calipers).

However, the quirky anti-dive system on the 750 Seca forks makes them a less-than-ideal swap onto the XJ650 Maxim models. The XJ750 Maxim front forks/brakes make for a much easier, simpler, bolt-it-on swap, especially the forks from a 1983 model.


And yes, braided stainless brake lines WILL allow you to feel every pulse from a warped rotor, but that really just means that the rotor needed to be replaced, anyway!