Topic: Anyone shim out their second rotor instead of the caliper?

[mrrch]

I'm going with dual disks up front on my 750 and I understand that the second caliper mount needs to be shimmed out to line up properly. I was going to shim out the disk instead (I'm using an electronic speedo so there will be no cable fitment problems.
Anyone one else done it this way? any tips?
Thanks
Ray

[Shenanigans]

I have only done one dual disk conversion but if I remember right the shimming was not to bring the disk in the right spot, but to even out the second caliper mounts because they were not flush with each other from the factory. I also think there is also very little room between the disk and the fork leg and the disk when you add that second disk.

I think anyways...

[scottly]

If any shims are needed, shim the caliper. What year 750 forks are you adding the right-side brake to, Ray? The earlier forks have different caliper mounts.

[seaweb11]

I filed off what was to high on the fork itself.

[scottly]

I filed off what was to high on the fork itself.

What year forks, seaweb? Got any pics?

[seaweb11]

My 78k no photos.

[scottly]

My 78k no photos.

So with 78k forks, and "T" caliper mounts, you had to file the fork bosses off? Was this to center the caliper over the disk, or to make the pads parallel with the disc? Was more material removed from one boss more than the others?

[scunny]

My 78k no photos.

So with 78k forks, and "T" caliper mounts, you had to file the fork bosses off? Was this to center the caliper over the disk, or to make the pads parallel with the disc? Was more material removed from one boss more than the others?

I think MC Rider mentions this in his build

[scottly]

Well, I guess it's a bit of a moot point for now, as I have been unsuccessful locating a later caliper with a bracket. Also, I'm not planning on running a speedo, so that may affect the spacing.

[seaweb11]

My 78k no photos.

So with 78k forks, and "T" caliper mounts, you had to file the fork bosses off? Was this to center the caliper over the disk, or to make the pads parallel with the disc? Was more material removed from one boss more than the others?

One of the mounting areas on the top is high, so it's to make it parallel.

[mrrch]

My bike is a 77 CB750K. The speedo drive side disk sits closer to the centerline of wheel because of the speedo cable. The tabs look the same on both fork legs but I will double check and make sure all the tabs are parallel. I've seen the caliper mounts shimmed up with washers but I want a cleaner look.

[kos]

Shimming out the rotor is the proper way to do this and in fact was they way Honda did this on kit bikes. Part #44642.300-970 spacer plate was offered in kit parts listing.


KOS

[Gamma]

Although I don't have the parts to look at here, I am reading from my notes.  I did this last year and made a 2mm spacer which put both fork legs at 4.15mm from the discs, CB750F1 1976.
http://i192.photobucket.com/albums/z293/galaxy8155/spacer.jpg[/img]]

This meant I only ended up filing about 2.5mm off one of the mounts on the fork leg to make the caliper line up and run parallel.  be very careful, I nearly took too much off!

I also intend to run an electric speedo, so one side of the axel has the normal 17mm wide spacer and the other side I have had made a 28mm wide spacer, which has a large flange incorporated to protect the wheel bearings.  Sorry no photo of this.
http://i192.photobucket.com/albums/z293/galaxy8155/DSC02498.jpg[/img]]
http://i192.photobucket.com/albums/z293/galaxy8155/DSC02499.jpg[/img]]

Note that the adjuster has to have the lock nut on the inside of the added caliper!

[SKTP]

This is the first I have heard of this...don't most people file their forks? Adding this 2mm spacer sounds like a much more elegant solution

I pray to HONDAMAN for spacer confirmation  

edit* I just read Gamma's post more thoroughly and you still have to file with the spacer...so the fork-mounts are about 4.5mm too tall generally? That seems like a lot...

[mrrch]

I looked at my fork tubes last night and one of the 8mm lugs is too long and would require filing to let the T bracket sit properly. I'll try to remember to take a picture and post tonight showing the lugs.

[mrrch]

Here is the picture of the lugs on the fork legs. The lug that the 8mm bolt goes into is slightly longer on the leg ion the right in the picture.

[scottly]

I couldn't see it in the picture, until I held a ruler up to the screen: the boss on the right is definitely longer. I haven't had a chance to look at mine yet. 

[mrrch]

I take lots of pictures when I do the conversion (hopefully this week) and post.

[scottly]

Thanks. I will be watching...

[Tintop]

I take lots of pictures when I do the conversion (hopefully this week) and post.

will also be watching with interest.

I am finishing a dual disk on my 550, but with the calipers on the back.  My leg with the longer boss is now on the left.  From this thread it looks like I can either put spacers behind the upper bolts, and then shim the disk / or just file the boss to get the proper alignment.

[bwaller]

You can also thin the flanged section of the pivot bolt instead of the forkleg boss. See picture (this is a 550). Remember the caliper bracket can become close to the leg. Everything becomes clear what needs to be shimmed or machined when the parts are mock mounted.

I just made a 1.5mm rotor shim to make both equidistant from the forklegs for another project but am using different calipers. Two other bikes I didn't bother.

 

[754]

Been off this thread a bit..
 On my 73, I have shimmed (and maybe even reversed) the top mount for the 2nd caliper, then shim the the other one..end of problem.. I would rather do that than file the fork.

 Would I move the disc out.. no way.. Reason try changing a tire or fixing a flat on side of the road,, I could do mine with fender and calipers on.. Id hard enough to get a dual disc wheel off, let alone start removing fender or caliper, to fix a flat..

 The adjusters.. after the first time removing the wheel with dual disc, I took them out forever.. and never looked back. Yeah some folks feel there is a need for them, but I never missed them... just too big a PITA for a ridden road bike...

 Scottly..if you still need a calper and bracket PM me, I will start looking..

[Tintop]

You can also thin the flanged section of the pivot bolt instead of the forkleg boss. See picture (this is a 550). Remember the caliper bracket can become close to the leg. Everything becomes clear what needs to be shimmed or machined when the parts are mock mounted.

I just made a 1.5mm rotor shim to make both equidistant from the forklegs for another project but am using different calipers. Two other bikes I didn't bother.

 

thanks bwaller - great suggestion, will check this out tomorrow.  everything is mocked up, just need to get correct measurement of the change required.  Removing a couple of mm's from the lower mount makes more sense than filing the boss.  If I still feel a shim is needed, I can get it cut by the waterjet guys quickly.

Tintop

[MRieck]

You can also thin the flanged section of the pivot bolt instead of the forkleg boss. See picture (this is a 550). Remember the caliper bracket can become close to the leg. Everything becomes clear what needs to be shimmed or machined when the parts are mock mounted.

I just made a 1.5mm rotor shim to make both equidistant from the forklegs for another project but am using different calipers. Two other bikes I didn't bother.

 

Boy that assembly looks tight and clean Brent. You rule.

[754]

Geez, I weighed the calipers yesterday. Both halves, bolts, no piston, non moving pad..

Finned was 802 grams

77/78 was 625 grams..