Rear brakes. Drum to disk conversion?

Has anyone ever modified the rear brakes from a drum to a disk?

I have noticed that there were several years of XJ750's that had rear disk brakes. Any ideas on doing this mod?
Anyone have any factory drawings? Parts lists?

Looks like it might be a fun project.

Peter

 

It is an XJ, and it is a 750, but it's really a 900 chassis.
To put the 900 swingarm into a 750 chassis, something needs to be cut-to fit, and the driveshaft alignment needs to be about perfect when done.
Someone put a rear disc on a turbo 650, a little welding, no swingarm swap, and ran the 900 rims.

Are you thinking of adding a disc to a 750 spiral rim??

 

Would the problem come in with finding a rear wheel that would fit? I've thought of it as well but with the issues that others have mentioned in this website plus the fact that I rarely use my rear brake, I don't think it is worth the trouble...at least in my little pea-brain!

 

I would love to do this to my max X but I fear it would at least mean a rim swap and I just had mine custom painted to match the rest of the bike when it got painted last summer

 

I was toying around with the idea of doing this to my 82 750 max. I think it's do-able. i could remove the drum from the wheel and bolt up a disc to it using spacers. Then would come the mounting of the caliper. I figure it would be fairly simple to create a mount on the swingarm for the caliper. Then just mount up a little master cylinder to your brake pedal and run the lines. Could be a good weekend project.

 

so here i am, diggin up anothe thread how far has anyone gotten with the disc swap? ive actually got a complete rear brake setup off my 99 YZF600R in my garage, and i was lookin at the bike and thinkin of a way to do it. ive also got the complete front brakes off the same bike, and was thinkin of doin a swap, puttin my 4 piston calipers on the maxim.

 

Since most of the Yam 79-83 XS series bikes used a simple rear disc brake that varies little from model to model why not take a look at the oem hardware (very adaptable).
Disc bolts onto rear cast wheel (either style), caliper attaches on a vertical carrier plate, axle bolt slips thru its center. Carrier's torque 'stay arm' rotates forward & clips onto a male stud welded thru the swing arm about 8"-9" toward the pivot.

It looks like XS axle bolts are a common size throughout the model lineup.

This is a relatively ez project and the parts are dirt cheap.

An idea ....

 

Im currently in the process of making this swap reality on my 81 xj750,I had a complete 78 xs 750 for a doner,But when I switched front ends I used the rear brake rotor from the xs on my front brake assembly do to the kawasaki caliper differances.I kept the master cylinder,brake arm and the lines and axle but gave my rear caliper away to someone who needed it more.So now my bike is sitting waiting on the caliper and rotor to be finished.If anyone needs some xj front rotors calipers master etc,I would be happy to trade you.I cheated and used the whole rear wheel and the differential,The drive spline looks to be the same as the stock xj but does anyone know if the 78 uses the ratio differential as my xj?

 

The XJ has 4.129 gearing. The XS 750 is 2.90. The XS-11 had shorter gears than the 750/850, so it could be numerically HIGHER.
It's going to feel like a 40 % overdrive, even your fourth gear will be taller than fifth used to be.

I didn't think these parts went together anyway. You bolted the XS pumkin to the XJ swingarm, used the XJ axle and driveshaft, the XS rim and brake bracket?? I'd like to hear if this works or not, keep us posted, thanks.

I've read where this mod doesn't work, but I don't remember where.

 

I'd like to say its working but right now its just mocked up.Thanks for answering my gearing question TimetoRide, Only time will tell exactly how the project will end I havent turned the pumpkin up yet to measure the holes to make sure they will be the same but they did appear to be a match made in hog heaven at a glance.I did slide the xs wheel into the xj pumpkin and its a perfect fit without mods.Keep in mind I havent got a rear caliper to install for now so I'm sure I'll be fabbing a new spacer or creating and welding a bracket to the stock xj axle spacer when I do get one.I will keep you posted in the meantime if you hear of any solid numbers let me know.

Thanks Steve,

 

I went to XS-11.com and got some numbers.
It looks like the XS-11 uses 3.33 gears and the V-Max uses 3.67

These would work better than the 2.90 gears.
You will feel like youre setting off from a light in 2nd gear.

 

Hi All
Long time no post but some info that might help,Had a donor 750,
XJ750 swing arm would'nt fit into my turbos frame, had to use the Turbo swingarm (750 too wide at the bearing end),fitted the 750 final drive case to the swingarm,used the 650 Turbo driveshaft,used the 750 rear wheel,wheel spacer,caliper carrier,and disc,and the 750 caliper,now its all bolted up and there is ample clearence for the tyre in relation to the swingarm,and the clearence between the caliper and the wheel is the same as it was when fitted to the 750 so its basicly a straight swap, but i haven't ridden it yet ( bike aint finished yet too much other stuff going on)(( oh sorry no pics)) sooo,
you pays your money and takes your choice
stay safe
c ya
ferret

 

Bump, almost a year old but wonder if anything has happened with this.

 

I've been look to do this swap with all of the rear brake parts coming off of a 82 XJ 1100 Maxim.
I know this is a older post, but I hope someone has successfully accomplished this swap??

 

I am in the process of doing this now. I have the xj 1100 wheel and the axle diameter is bigger. Also the dust/dirt shield that goes into the pumpkin has more offset. So, the 1100 wheel WILL NOT just go on and swap onto a 750, positivley. I bought an 1100 swing arm going to cut the axle mount and diff mount off and graft to my swinger. I will be updating all pics as soon as I get some work done.

 

Thats a lot of work but will be nice in the end. Are you going to try to match the front wheel to the back when your done

 

At first I was looking to do a complete xj 1100 rear swap swing arm, diff, 16" wheel and so forth. Too many problems I would run into.

My thought are to use my rear 19" wheel remove the drum rotor will bolt up to it. Use spacers to make up the difference between the caliper bracket to wheel on the axle shaft and use a collar/spacer where the axle shaft goes into the caliper brackets. Last would be to weld that guide(locating) stud onto the right side of my swing arm as well as a bracket for the master cyl. Swap out the sensor, brake linkage & lever.

It sounds good in theory and if it didn't work I could still go back to the drum set up with the only thing changed is mounts/tabs being welded on the the frame.

 

worth a try just don't brake any of the old parts. I don't remember the drums unbolting that's all but if they do that's great

 

It comes off, I remember because I painted my wheels last year.

 

The drum cover comes off with the pads, BUT the only way you would be able to put a disc on it is to machine a large complicated spacer. The spline for the drive, bolts through to the other side. So when you look into the brake cavity you will see the end of the bolt not the head. If you are looking to go with a seca type rear wheel anyway, do a search, I talked with a guy that said he swapped a 900 and all he did was make the mounts for the caliper.