Topic: My other last question about twindiscs

[timtune]

Ok so I have the speedo drive turned down and pinned. I understand the need to shim the mounts to get the pads parallel with the disc.

I've read most of the twin disc posts and nobody mentions the problem I have which is the mounting surfaces for the discs are not symmetrical about the centerline of the spokes on the hub. In other words the outer face of the disc is about 3mm from the fork tube on one side and about 7mm on the other. Because the caliper, fork tube and brake arm are either mirror image or identical both calipers are the same distance from the fork tube. One article mentioned removing material from the fork tube mount but that was more of the shimming operation I thought - he talks about removing some material from one mount to reduce the shimming on the others.

Also I want to flip the forks (calipers behind forks) does present special problems??

[MauiK3]

First, a few photos might help, are you saying the disc is not equidistant from the fork top and bottom? The casting of the fork lowers is not conducive to such a measurement, it wouldn't be the same.
The measurement you need to check is how the caliper drops over the disc, you can use feeler gauges to help check for irregularities, try to duplicate what you have on the other side. Some simple washers can often adjust the alignment. Mine were off a bit and I had some bad squealing until I re-did the washer spacing. I imagine the sizes may vary by bike and I don't remember the thicknesses I used. Others here may be able to provide that.
Swapping the forks around can be done with some benefits in weight swing but there is the matter of when brakes are applied it can cause some fork stiction due to the flexing from behind. I'm not smart enough to describe how it is different from the stock arrangement other than that the force comes from the opposite side and has a different effect on how the forks work. Our forks are marginal by today's standards so I always like to keep things as gentle as I can on the forks.

[timtune]

No the disc is closer to the fork tube on one side than it is on the other. The discs are not equally centered between the fork tubes. The calipers are equally centered. To make it right one caliper needs to move closer to the fork tube. No one has mentioned this (that I've read)
If you look closely at the front hub you can see one face is pretty much flush with the spokes at the hub and on the other side that face is about 3mm beyond the spokes.

Sorry no smart phone so pics are a pain.

[scottly]

The right side disc mounting surface on the hub is 3mm further from the fork. If you want the discs to be symmetrical, you need to add a 3mm spacer between the disc and the hub, have no spacers on the top two mounts on the right side fork, and machine 3mm off the lower mount on the fork leg (You could also machine 3mm off one side of the head of the mounting pin instead of the fork leg). Note: this may cause problems with the speedo drive.
If you want to flip the calipers to the rear, the right side fork gets moved to the left side, so the 3mm difference in the fork leg will need to be addressed to align the caliper with the left disc.

[Kaze]

I would very much like to see photos.

The brakes weren't symmetrical when I did mine either, and I rode all over Washington State for a couple years like that. It was great. I never experienced any sort of uneven handling, or strange weight issues or leaning. Bike was awesome at freeway speeds and beyond.

Also, I didn't shim anything, so I'm not sure why anybody thinks that's necessary. I had to grind my speedo drive plate, but that was the extend of my suffering. I wish I knew what bike I got the longer hub bolts from. GL1000?

If you haven't bought your brake lines yet, I recommend looking for the type of braided lines that go from your (double) banjo bolt at the in-line brake switch, directly to the calipers. Don't faff around with those stupid bent metal tubes. That part can at least be symmetrical if you go with those sort of lines. I'll put a pic to illustrate what I mean. Good luck. Pics please?

[scottly]

Also, I didn't shim anything, so I'm not sure why anybody thinks that's necessary.

The stock fender brace acts as a spacer for the top two mounts on the right side. (I tend to forget that since I don't use a stock fender. )

[Kaze]

OOOoooooh. Glad you brought that up Scottly. I'm into those double front fender bracers.

[scottly]

OOOoooooh. Glad you brought that up Scottly. I'm into those double front fender bracers.

Looking at your pic, it doesn't look like the fender brace is between the fork leg and the caliper bracket like it should be?

[timtune]

The right side disc mounting surface on the hub is 3mm further from the fork. If you want the discs to be symmetrical, you need to add a 3mm spacer between the disc and the hub, have no spacers on the top two mounts on the right side fork, and machine 3mm off the lower mount on the fork leg (You could also machine 3mm off one side of the head of the mounting pin instead of the fork leg). Note: this may cause problems with the speedo drive.
If you want to flip the calipers to the rear, the right side fork gets moved to the left side, so the 3mm difference in the fork leg will need to be addressed to align the caliper with the left disc.

Scotty,
Those mounts in your pic, are they stock or did you grind one down?

[scottly]

Those are the stock mounts. The ruler is sitting on the upper mounts, which are the same on both sides. The taller lower mount boss is the right side fork leg.

[timtune]

Thanks. I must check mine. I thought those forks were identical.

[Kaze]

Scottly: Where the heck were you in 2001? I needed your help!

[Gamma]

The right side disc mounting surface on the hub is 3mm further from the fork. If you want the discs to be symmetrical, you need to add a 3mm spacer between the disc and the hub, have no spacers on the top two mounts on the right side fork, and machine 3mm off the lower mount on the fork leg (You could also machine 3mm off one side of the head of the mounting pin instead of the fork leg). Note: this may cause problems with the speedo drive.
If you want to flip the calipers to the rear, the right side fork gets moved to the left side, so the 3mm difference in the fork leg will need to be addressed to align the caliper with the left disc.

Agreed, very similar to my notes. I made a 2mm spacer for the extra disc (my wheel rim has been re-laced putting the hub in the centre, not sure if it was originally central) this put both fork legs 4.15mm from the discs,  then I very carefully filed approximately 2.5mm off of one of the fork lugs to get things lined up and symmetrical.  I am not using a cable drive for the Speedo (KOSO electric), so I just made new spacers for the wheel hub.

[Don R]

  It sounds like the K0 front hub may make a symmetrical situation since it is wider on the speedometer side. I just purchased the last one I need, so it won't matter to me if I create a run on them on ebay. L0L!
   My double disc project will use F1-K7 type calipers and either an F0 or late A hub, I need to pump out a couple pistons for inspection since compressed air didn't do it this morning. 
  This was allegedly my other last answer. 

[pekingduck]

Did any of the CB500, CB550, CB750 SOHC (except F2s) ever come standard with dual discs?  If not, doesn't it seem weird Honda would offer a right side fork leg for that purpose?  Maybe a different market?

I remember the early CB500 fours didn't have that provision, but a French or German company sold a clamp-around bracket that you could add a right side caliper bracket.  (Thank you Racecrafters).

[timtune]

OK so I checked mine and of course their identical to Scottys. Tempest in a teapot..

As well as adding a second disc I'm flipping them back behind the forks. Is there any way to do this and retain the speedo on the right side?
I couldn't figure out how to do that so I ground ( Very carefully) material away from both fork and speedo drive and I now have the speedo drive fitting above the axle on the left with the cable drive exitting to rear.

I thought this would be mostly a bolt on affair.......

[scottly]

As well as adding a second disc I'm flipping them back behind the forks. Is there any way to do this and retain the speedo on the right side?

The speedo drive stays on the right side!!! You don't flip the wheel, only the forks!

[Don R]

 Won't the speedometer turn backwards? Will it cause you to time travel? Will the bike be new after it zeroes out again?

[Mark1976]

Won't the speedometer turn backwards? Will it cause you to time travel? Will the bike be new after it zeroes out again?

   And I thought you could only do it with a Delorean.... who knew!!!

[HondaMan]

Won't the speedometer turn backwards? Will it cause you to time travel? Will the bike be new after it zeroes out again?

Yes! It's much easier than rebuilding everything.

A comment about the brake: the dual-disc mod fits well except on the K0 bikes made before 4/69 (and a few later than that). Those don't have the right-side of the hub machined off to accept a disc.

My other comment about flipping the calipers to the rear: I discovered, during a [quite rapid] descent from Mt. Evans, 14,259 feet high, that if it sleets and rains together while you're doing this, the pucks don't grab well until for 3 times longer than when the pucks are up over the top of the discs, in the rain. The following weekend found me in the garage, flipping them back to the top.

...just thought I'd mention it, just in case...

[timtune]

Scottly, how can I flip the forks w/o flippin the wheel? The discs are not centered and they need to meet up with the appropriate offset of the forks.

[Don R]

 Remove the fork tubes, swap them side to side, roll to face the brake brackets to the rear and install the wheel as always.
  I guess the bottom fork caps need the gap reversed (see your manual) Voila! Or Bob's your uncle, or you got this, or any other form of encouragement.   

  Or just face them to the front. I even cut up a pair of rotor fenders and made duals. Do not ask how, it is highly technical and a patented process. And I don't remember.
  I still contend it was the worlds only triple drilled disc F1 with dual rotor fenders. 

[scottly]

I thought this would be mostly a bolt on affair.......

It would be if you didn't try to flip the calipers to the rear. The off-set in the forks matches the off-set in the hub. It's like Honda planned a second disc from the start!!?? 

[Kaze]

PekingDuck: From what I have gathered, a customer could indeed buy that second disc all set up as an option.
http://forums.sohc4.net/index.php?topic=86255.0

[Kaze]

Is there a particular reason that someone would go against convention and face the calipers the opposite direction?

[robvangulik]

I tried it for a while, long time ago, and didn't notice any real advantages. I went back to the normal spot in front of the forklegs because of the easier accessability, easier to work on...

[timtune]

The reason for flipping them is to lower the weight - that and it looks way cooler.
No doubt the effect is most minimal that it's hardly worth the effort but I'm retired with time to fritter.

[timtune]

Won't the speedometer turn backwards? Will it cause you to time travel? Will the bike be new after it zeroes out again?

Yes! It's much easier than rebuilding everything.

A comment about the brake: the dual-disc mod fits well except on the K0 bikes made before 4/69 (and a few later than that). Those don't have the right-side of the hub machined off to accept a disc.

My other comment about flipping the calipers to the rear: I discovered, during a [quite rapid] descent from Mt. Evans, 14,259 feet high, that if it sleets and rains together while you're doing this, the pucks don't grab well until for 3 times longer than when the pucks are up over the top of the discs, in the rain. The following weekend found me in the garage, flipping them back to the top.

...just thought I'd mention it, just in case...

HM : Why do you think the rear position would be worse at shedding water? I find that surprising.

[bryanj]

So when i did an early 500 with one in front and one behind what did that do

[Tracksnblades1]

So when i did an early 500 with one in front and one behind what did that do

Twice the braking power on a single disc. ??

[bryanj]

Nope twin disc but had to use 2 lh sliders as the rh one had no mountings

[HondaMan]

Won't the speedometer turn backwards? Will it cause you to time travel? Will the bike be new after it zeroes out again?

Yes! It's much easier than rebuilding everything.

A comment about the brake: the dual-disc mod fits well except on the K0 bikes made before 4/69 (and a few later than that). Those don't have the right-side of the hub machined off to accept a disc.

My other comment about flipping the calipers to the rear: I discovered, during a [quite rapid] descent from Mt. Evans, 14,259 feet high, that if it sleets and rains together while you're doing this, the pucks don't grab well until for 3 times longer than when the pucks are up over the top of the discs, in the rain. The following weekend found me in the garage, flipping them back to the top.

...just thought I'd mention it, just in case...

HM : Why do you think the rear position would be worse at shedding water? I find that surprising.

When riding in heavy rain, the water flings off the disc straight at the oil filer's finned housing (I've watched in on many a friend's bike during tours in the wet). This meant that the water was about 1/4 of the way up into the brake pucks: when I went to flip mine back over to the top I found lots of sand and grit already packed in around the (then front) of the pucks. I had flipped them on a weekend and rode it 2 days before rain (commuting to work, about 24 freeway miles/day then) and then 2 days in the rain, followed by 1 day with no rain. In just that much time it had collected quite a bit of debris in the front side of the pucks. That made me pretty wary of it, so I flipped them back the next weekend.

Something to notice: whenever bikes have the calipers behind the fork legs, the calipers are way up on the back of the leg. The calipers on these bikes are on a longish arm, so it puts the pucks quite a bit further back and down by comparison. Honda was concerned enough about wet-riding that they put it on the top, and in the K3 and later 750 they added a little water umbrella to keep the water from flinging off the disc and up in the ignition coils: I can attest that is EXACTLY where the water goes when it is deep on the pavement and you are running 70+ MPH. That's a longish story, but it ended up causing me to be frequently shocked in the left leg when riding in very heavy rain (which the Vetter lets you do, probably not that wise, really) with over-aged sparkplug cap rubber booties!   

[newday777]

Won't the speedometer turn backwards? Will it cause you to time travel? Will the bike be new after it zeroes out again?

Yes! It's much easier than rebuilding everything.

A comment about the brake: the dual-disc mod fits well except on the K0 bikes made before 4/69 (and a few later than that). Those don't have the right-side of the hub machined off to accept a disc.

My other comment about flipping the calipers to the rear: I discovered, during a [quite rapid] descent from Mt. Evans, 14,259 feet high, that if it sleets and rains together while you're doing this, the pucks don't grab well until for 3 times longer than when the pucks are up over the top of the discs, in the rain. The following weekend found me in the garage, flipping them back to the top.

...just thought I'd mention it, just in case...

HM : Why do you think the rear position would be worse at shedding water? I find that surprising.

When riding in heavy rain, the water flings off the disc straight at the oil filer's finned housing (I've watched in on many a friend's bike during tours in the wet). This meant that the water was about 1/4 of the way up into the brake pucks: when I went to flip mine back over to the top I found lots of sand and grit already packed in around the (then front) of the pucks. I had flipped them on a weekend and rode it 2 days before rain (commuting to work, about 24 freeway miles/day then) and then 2 days in the rain, followed by 1 day with no rain. In just that much time it had collected quite a bit of debris in the front side of the pucks. That made me pretty wary of it, so I flipped them back the next weekend.

That reminds me of my ride back from Daytona 1980 to Goldhill CO on my K6 with rear side calipers. It had rained all day coming north through the Mtns of New Mexico  and turnd to freezing rain, lots of rain and puddles going up the dirt roads from Boulder. I got up to Goldhill in the dark, parked it on the hill side drive of where my friend lived so grabbed a handful of front brake to hold it while I got the kickstand down, in the cold freezing rain, soaked to the gills and shivering. Knocked on the door no one home,  so I walked over to the town watering hole to find my friends and found out they moved up the street to another house. So I walked up to their new place and got warmed by the fire with a hot drink with a kick. We went to collect the bike and found the brakes were locked solid so I unloaded it and hauled the gear in my friend's truck, covered the bike until the next day, it snowed 6 " that night. Anyhow, I  freed up the caliper with a screwdriver and then I had to rebuild the calipers. Lots of mud in them. I left them on the rear without problems and sold the bike 3 years later. I thought I had much better braking performance on the rear side of the forks.

[HondaMan]

Won't the speedometer turn backwards? Will it cause you to time travel? Will the bike be new after it zeroes out again?

Yes! It's much easier than rebuilding everything.

A comment about the brake: the dual-disc mod fits well except on the K0 bikes made before 4/69 (and a few later than that). Those don't have the right-side of the hub machined off to accept a disc.

My other comment about flipping the calipers to the rear: I discovered, during a [quite rapid] descent from Mt. Evans, 14,259 feet high, that if it sleets and rains together while you're doing this, the pucks don't grab well until for 3 times longer than when the pucks are up over the top of the discs, in the rain. The following weekend found me in the garage, flipping them back to the top.

...just thought I'd mention it, just in case...

HM : Why do you think the rear position would be worse at shedding water? I find that surprising.

When riding in heavy rain, the water flings off the disc straight at the oil filer's finned housing (I've watched in on many a friend's bike during tours in the wet). This meant that the water was about 1/4 of the way up into the brake pucks: when I went to flip mine back over to the top I found lots of sand and grit already packed in around the (then front) of the pucks. I had flipped them on a weekend and rode it 2 days before rain (commuting to work, about 24 freeway miles/day then) and then 2 days in the rain, followed by 1 day with no rain. In just that much time it had collected quite a bit of debris in the front side of the pucks. That made me pretty wary of it, so I flipped them back the next weekend.

That reminds me of my ride back from Daytona 1980 to Goldhill CO on my K6 with rear side calipers. It had rained all day coming north through the Mtns of New Mexico  and turnd to freezing rain, lots of rain and puddles going up the dirt roads from Boulder. I got up to Goldhill in the dark, parked it on the hill side drive of where my friend lived so grabbed a handful of front brake to hold it while I got the kickstand down, in the cold freezing rain, soaked to the gills and shivering. Knocked on the door no one home,  so I walked over to the town watering hole to find my friends and found out they moved up the street to another house. So I walked up to their new place and got warmed by the fire with a hot drink with a kick. We went to collect the bike and found the brakes were locked solid so I unloaded it and hauled the gear in my friend's truck, covered the bike until the next day, it snowed 6 " that night. Anyhow, I  freed up the caliper with a screwdriver and then I had to rebuild the calipers. Lots of mud in them. I left them on the rear without problems and sold the bike 3 years later. I thought I had much better braking performance on the rear side of the forks.

The one performance improvement I noticed when I had them on the backside was: less nosedive  in hard stops. Essentially it jams the fork lowers into the tubes with increased side-loading. In roadrace conditions I could absolutely agree this was the superior method, but in the 1970s rules we had it wasn't allowed.

[newday777]

"The one performance improvement I noticed when I had them on the backside was: less nosedive  in hard stops. Essentially it jams the fork lowers into the tubes with increased side-loading. In roadrace conditions I could absolutely agree this was the superior method, but in the 1970s rules we had it wasn't allowed."

I usually rode it hard into the corners.
They were acquired from a race bike, possibly were taken off because of the rules(1977 when I got them), I don't remember the details as one of the guys in the shop knew of their availability and set them up on my bike with the motor work he did to it, gonna go faster, gotta be able to stop too.

[MauiK3]

I don't ride much in the rain, many years ago I did and I didn't seem to have braking issues but I was always extra conservative when it was raining.

[Don R]

 When I did the double discs on my 76F I scalloped the front tire practicing emergency stops. When I pushed it out of the shop, I could hear the tread squishing on the floor.

[scottly]

I thought this would be mostly a bolt on affair.......

It would be if you didn't try to flip the calipers to the rear. The off-set in the forks matches the off-set in the hub. It's like Honda planned a second disc from the start!!?? 

Tim, make the right side caliper mount on the fork leg match the left side, so the caliper spacing stays the same as before. With the left side fork now on the right, you will need a spacer equal to the amount removed from the right leg, as well as the previously mentioned fender brace/spacer at the top.

[Don R]

 When you move the calipers to the back and reverse the forks, you also have to flip the fender around on the bracket right?  For anyone reading along that is gathering info. I think in this case he is removing the fender.