Topic: 1978 cb750 dual front disc brake conversion.

[thelowmax]

I tried to address this in the FAQ section but for some reason couldn't reply. If this needs to be moved to another forum, please do. I appreciate it.

I have seen the conversion of single front to dual disc brakes in the Brakes FAQ section. It seems pretty straight forward and I have all the parts on hand to do it except for the CB500/550 speedo drive unit which I just purchased on eBay. After I made the purchase, I read that the cb500/550 speedo will NOT work in this conversion, even though the pictures tell a different story. Can anybody confirm the ability to use this particular unit and if not, is there an alternative? If it doesn't fit, can't I just bore out the hole a little?

I realize I can wait and simply try it but it's a daily rider and I don't want to disassemble my front end if it's a futile effort. Once again, I appreciate any info to spare me the torture of a Japanese puzzle made up of the wrong pieces.

[the technological J]

im in the middle of trying this i'll let u know.... anybody else have input?
here is the site im using for instruction..
http://www.salocal.com/sohc/tech/dual_disks/dual_disks.htm

[MCRider]

There have been several threads on this, FYI. I contacted ben directly and he admitted to the error about the 500 speedo drive plate. It will not work without modification. Just modify the 750 one. I have had several pictures of my modified drive plate in prior threads. I did it with a bench grinder and vice grips, and a later version more neatly done by a machinist.

Essentially you must reduce the diameter of the plate and establish two nubbins to engage the cut outs of the hub. Either by bending over metal of the plate or welding nubbins on.

Clear as mud?

[Old75_ratafe]

ok so just to be clear if I were doing this I would modify a 750 speedo not a 550.

[MCRider]

ok so just to be clear if I were doing this I would modify a 750 speedo not a 550.

In my opinion, yes. I did 2 conversions, but on a K1 and a K2. So I don't know first hand on a 1978.

[Tintop]

I posted this in Tips & Tricks awhile ago.  Process is the same for 550 or 750 conversion.

http://forums.sohc4.net/index.php?topic=70195.0

I'm pretty sure the parts are the same, as my 78 550 drive assembly fits on my extra 750 hub (has flats).

[Flying J]

If anybody needs a 77/78 750 caliper i have a spare i was sold as a 550 but its not, its for a 750....

[lordmoonpie]

Speedo? What you want a speedo for...? 

[Old75_ratafe]

ok so just to be clear if I were doing this I would modify a 750 speedo not a 550.

In my opinion, yes. I did 2 conversions, but on a K1 and a K2. So I don't know first hand on a 1978.

I got a 75 750 with spoke rims MC so I'm 99% sure its all the same stuff as the k1 and k2. 

I actually bought a set of air forks for a 78 that have the spoke type wheel mounting and a dual disc setup for the same year with the bigger calipers.  I was considering just doing the easy route and making my current forks work with another caliper and changing the air caps over.  Or go the full harder route and making the dual disc 78 setup work.

[Tintop]

I posted this in my build, it describes how I did my dual disk conversion on my 550.  The process is the same for a 750.  This is much easier than the 'filing the boss down' method.

Don't have any pictures, but a quick explanation of how I aligned the 2nd caliper.  My calipers are reversed, but this should work either way.

Install just the caliper arm on the 'out of alignment' side.  Lightly tightened the pivot bolt, and only finger tightened the 2 upper mounting bolts.  At this point there is a gap beween the upper fork bosses and the upper mount.  Alternately tighten / loosen these bolts until the gap is equal at both ends of the top mount.  Now take a straight edge and place it against the disk; move the arm against the straight edge.  Adjust using the upper bolts until the caliper mounting face is true to the straight egde.  Double check that gap is still equal at both ends of the mount.  Measure gap / record.  Now measure the space between the arm at the pivot & the fork.  If the gap at the top is smaller than the space at the bottom, machine the top amount off one side of the pivot pin.  If it is greater (shouldn't be) you can only remove the smaller bottom amount less some for 'swing clearence'.  In my case the top amount was 2.4mm, and the bottom was 2.6mm+.  Removed the 2.4 and fitted everything back together.  Got perfect pad alignment, and the adjuster lock nut is on the outside.

Again, many thanks to bwaller for this method.

[speeddemon]

I did a dual front brake conversion on my '75 F. I purchased a complete (rim, hub, speedo drive, axle and discs) '75 GL1000 dual disc front wheel for $40 on ebay, and already had two front brakes. I removed the GL1000 discs and installed 750 discs (6 bolt). I installed the left brake first, slid the wheel assembly into place and bolted it up. I installed the right brake next, adjusted the calipers, attached the speedo cable to the drive. This works with the early style sliders with brakes mounted on the front. 

[Ira]

I've read a few posts on this topic, but I'm missing a (possibly obvious) piece of information.  Are the 77/78 calipers/mounts side specific (left and right, respectively), or can any caliper from those models go on either side?

Thanks!

[cben750f0]

no the 550 drive plate doesnt work, the only reason i said it was a 550 plate, was because i bought one it off ebay and it was miss labeled there, the plate i acutally used was a '69 Ko drive plate, that i happened to A55 getting lol.

need to modify the 750 one.

peace
(Ben)

[scottly]

I've read a few posts on this topic, but I'm missing a (possibly obvious) piece of information.  Are the 77/78 calipers/mounts side specific (left and right, respectively), or can any caliper from those models go on either side?

Thanks!

The K7/K8 calipers and mounts will fit on either side.

[Eydugstr]

If anybody needs a 77/78 750 caliper i have a spare i was sold as a 550 but its not, its for a 750....

I would, ffjMoore!  If you still have it, please PM me with a price.

[scottly]

If anybody needs a 77/78 750 caliper i have a spare i was sold as a 550 but its not, its for a 750....

I would, ffjMoore!  If you still have it, please PM me with a price.

One of the late calipers came up recently on the "for sale" forum..