Topic: Getting dual discs adjusted properly (new pics added 10/9)

[Scott S]

 Long winded post, but please bear with me. I'm trying to give as much info as possible...


  Bike is a '78 550K with dual disc conversion and braided steel lines. Since doing the conversion, I haven't been able to get the brake or lever feel that I think it should have.

 I'm confident that it doesn't have air in the system. I've bled three bottles of fluid through it. I tried bleeding it at the banjo bolts. I bench bled the master cylinder. I tried three different master cylinders: stock (known good...came on the bike with the single disc), a GL1000 and a modern aftermarket 14mm bore master cylinder that's currently on the bike now.




 The lever is soft and the brakes don't have the "bite" they should, IMO. Today, I installed new EBC pads on both sides. Put it all back together and the front wheel is locked. Ok, that's sort of to be expected with new pads.
 I confirmed that both calipers are working and both pistons are moving. I pushed the pistons back in as far as I could by hand, hopefully forcing any remaining air back UP to the master cylinder (I've had excellent results using this method on my XS650's).

 I loosened the caliper on the RH side and adjusted the stock, LH side as usual . I can make the LH side completely loose, tighten until it drags, then back off and set the lock-nut. Good...now I know that side is OK.
 Try to do the same on the RH side and the wheel locks up again. I have to loosen the caliper arm adjusting screw WAY out. I also have to loosen the caliper halves to even turn the adjusting screw, then re-tighten.

 Took a good look around and saw that the bottom of the caliper arm had begun to touch the fork leg. "Aha!", I thought....it's bottoming out on the fork before I can get it adjusted correctly. I remember the DDC instructions saying that shimming may be necessary.
 Found a washer to shim it out and ....no luck. Better, but still locks the wheel up. I can turn it by hand, but with much force.

 The new EBC pads are MUCH thicker than the stock pads, even accounting for wear. Especially the stationary inner pad. I'd say it's twice as thick (sorry, didn't get pics).
 I remember my Dad encountering this same thing when he installed EBC pads on his XS650. Properly adjusted, it still had too much drag. His solution was to ride it for a couple hundred miles and re-adjust. I rode up and down my street about five times and the RH rotor got pretty hot. I don't want to warp the rotor.

 All visual inspections show that everything lines up. Caliper arms are the same side to side, pad thickness is the same side to side, clearance between the arm and the forks is the same side to side, etc., etc.

 I'm seriously considering removing the inner pad on the RH side and taking a belt grinder to it! I think if I could get the thickness down some. I could get the RH side to adjust properly. Or, I could just take it out on the highway and ride it for 100 miles, keeping good air flow on it.
 Opinions? Options? Ideas?

[Greggo]

About the pedal feel: How is the stopping?  I guess it's hard to tell with the pads dragging, but once you get that settled go out and give the brakes a good romping...Does it feel stronger?  Does it stop sooner?  Pedal feel will change with the dual disc, but as long as the stopping power is there, you should be okay. 

[bjbuchanan]

I think the EBC stuff is slightly oversized

I changed my rear shoes, i know diff idea but still, they were tight as sh!t. I had to sand the shoes just to get them to go in the drums. Then my rear wheel was tight as all hell, I had to ride it out and then clean all the dust out

Works great now but I think part of the problem may be the pad size overall, not enough adjustment designed in to the system to compensate

[Scott S]

About the pedal feel: How is the stopping?  I guess it's hard to tell with the pads dragging, but once you get that settled go out and give the brakes a good romping...Does it feel stronger?  Does it stop sooner?  Pedal feel will change with the dual disc, but as long as the stopping power is there, you should be okay. 

 Haven't really ridden enough with the EBC pads to tell. With all of the above set-up and stock pads, stopping was OK. But only OK. Not like I think it should be with dual discs. I've had better single disc set-ups.
 I tried bedding the old pads with no real change. I need to get this RH side sorted and I'll do it with the EBC pads.

[Scott S]

I think the EBC stuff is slightly oversized

I changed my rear shoes, i know diff idea but still, they were tight as sh!t. I had to sand the shoes just to get them to go in the drums. Then my rear wheel was tight as all hell, I had to ride it out and then clean all the dust out

Works great now but I think part of the problem may be the pad size overall, not enough adjustment designed in to the system to compensate

 It sure seems that way. I've used EBC pads in the rear before and been really happy with them. My Dad swears by them. His XS650 pads seemed oversize and these do, too. I may pull the RH side off for grinding and get some comparison pics.

 From what I can tell, the lever didn't get much firmer, but the "bite" seems better. I really want to get the RH caliper sorted out before I get into the final tuning, bedding, etc.

[JohnG]

Questions:  when you had a single disk did you have the same master cylinder as you are using now?

Do you happen to know what the diameter of the piston in the new master cylinder is?

When you say you are unhappy with the feel, what are you comparing to?

(I did this conversion on a 750F )

          John

[Scott S]

 The bike originally came with stock set-up: single disc, stock M/C, rubber lines, etc.

 I tried the stock M/C with the dual dics and SS lines and didn't like it.

 The lever on the bike now has a 14mm bore.

 I'm comparing the feel to other bikes I've built or ridden. Most have been single disc. The lever seems soft. When sitting in the garage, I can actually squeeze hard enough to make the lever touch the grip. I can't get it that close on the road because the brakes are actually working, but I still feel like it's too soft.

 I spoke with Mike "Mercury" Morse of 650Central/Vintage Brake fame and gave him all the info concerning caliper piston size, stock M/C size, etc. He said the 14mm M/C is the closest to the best size, but I may not ever get the feel I want if I'm using the old calipers.

 I think they would stop better with the EBC pads, but there's something up with the RH side.I noticed some grooves/uneven wear on the inner, fixed pad on that side when I removed the stock pads. I was hoping that finding the caliper holder "cocked" was the cause of that and the cure for the dragging wheel after the EBC pad install.
 I'm really thinking now that the EBC pads are just VERY thick.

[JohnG]

14 mm  is the same bore as the master cylinder Honda provided with the CB750 and the CB450  and a single disk.  Hook it up to 2 calipers and you have to move twice as much fluid with the same motion  hence a "softer"  lever.

I added a second disk to a stock  750F  (same MC as this but slightly larger caliper pistons).  I got alot more lever travel, which I initially did not want.  But the stopping was so outstanding that I did not change anything.  (I had a GL 1000 master cylinder with larger bore as a backup plan).

In setting up the second caliper I spent alot of time with washers for shims and chalk and feeler gauges so as to get the pad as parallel to the disk as I possibly could.  The surface of the pad needs to be parallel as possible to the disk both front-back and vertically.

I have three other Hondas with factory dual disks  and only 1 of them  (an 1100F with braided lines otherwise stock) comes real close to this bike for stopping power.  I have had the bike 36 years and this was the best mod I ever made.

So my polite suggestions are 2 fold: attention to detail on the setup of the new caliper and arm,  and the decision of whether you want an MC with a bigger piston for a firmer feel.

FYI:  I used stock brake pads and new, stock lines.

I have an Excel spreadsheet with the MC piston IDs, caliper piston IDs and the ratio of caliper(s) piston  area to mc piston area  if anyone wants it.  You can toss your own number in and see how the ratio compares to 10 or so Hondas I put in there.  Just send me an email address that can accept a file attachment.

[scottly]

In setting up the second caliper I spent alot of time with washers for shims and chalk and feeler gauges so as to get the pad as parallel to the disk as I possibly could.  The surface of the pad needs to be parallel as possible to the disk both front-back and vertically.

1+ I don't know about the 550, but the right-side fork leg mounting lugs on the 750 are different from the left side; the lower lug sticks out further, and if you bolt the caliper directly to the fork leg without either shimming the top mounts, or cutting down the lower lug (or the flat on the pivot pin), the caliper will be cocked vertically.
What I would do is first remove the adjuster screw and spring, then loosen the 3 mounting bolts for the pin, so there is about 1/8" clearance. Then apply the brake, and you can see where it needs to be shimmed or cut. 

[Scott S]

 It's been a few months since we did this conversion, so my memory about what we did and why is a little cloudy.

 We did grind on the caliper holder in this area:


 It looked like this afterwards:


 It's not shown in this pic, but I added a shim here today:


 If my memory serves, the shim wasn't needed there with the old pads. When I installed the newer, MUCH thicker EBC pads, that lower part of the holder arm hit the fork when I tried to adjust it out enough to get the wheel to spin. Added a washer today and it lines up nice next the fork.....same gap as the stock side.
 My Dad is coming over in the next day or two to take a look at it. Sometimes another set of eyes is good to have.

 I really, really think the thickness of the pads is the major cause. I'll remove the RH side pads tomorrow and get pics to show you guys the difference. While I'm at it, and it's all apart, I'll check the alignment of the arm to the disc.

[scottly]

Now that you jogged my memory, I recall having to file some clearance into the arm in the pivot area to prevent it from hitting the fork leg; I don't remember for sure, but it may have been at the bottom?

[JohnG]

even if the 550 right fork leg is a mirror image of the left,  the carrier  arm for the caliper is not, so you are kind of on your own no matter what to fine tune it for correct position. You have 3 mounting points  -  2   6mm upper bolts and  1   8 mm lower.  I seem to remember having to shim 2 out of 3.  Maybe the upper,rear one to make things vertically align and the rear one to make things horizontally align.  If the fixed brake pad was alot thicker, it might make this harder. 

I think I took the attitude of getting the fixed pad to align well with the disk, then just let  the moving pad take it's natural position.

The idea of the chalk was to put it on the pad, use the brake and see how much of the chalk was left  (not much if done right). Of course some mileage helped alot.

I can double check the bike tomorrow and see what I shimmed as this is going back to the winter of 2011.

Has anyone checked to see if the lower fork legs on 550s and 750s are the same part # ?

[Scott S]

 Scottly, going from memory here....and just thinking things through....

 But we apparently had to grind the top to get the bottom to STOP hitting the fork leg. When I used the adjuster and mover the caliper arm farther inward (towards the center of the bike) in an effort to take the thicker pads into account, it started hitting the fork leg again.
 That seems correct, doesn't it.....moving the arm inward towards the centerline to make less drag? Adding a shim on the bottom got it off the leg again.

 More pics coming later today.

[JohnG]

I never installed an adjuster.  The difference in sides would have required a longer bolt than the stock one.  Works fine as is.  Once the free (floating) pad moved in on the disk, that seemed to take care of adjustment.  But this is a 750F  and I dont know what carries over to the 550 so my comments are to be taken with a grain of salt.

[Scott S]

 Okay....here's a pic showing the difference in pad size. The EBC pads are at least 2mm thicker.


 There's an odd wear pattern on the inner pad of the RH side. It was on the old pad and disc, as well as the new EBC pads. I probably don't have a full mile on the EBC pads yet. The rotors were resurfaced and I cannot feel a ridge or mark on the rotor.



 If I loosen the caliper like this, the wheel spins as it should.


 I removed the caliper halves and backed out the adjusting screw and noticed that the caliper arm didn't move or float freely. I thought maybe the washer I used was too large and when I tighten it down it was causing the pivot to bind. Replaced it with a smaller washer and the arm will still bind when I tighten up the lower bolt.
 If I loosen the lower bolt in this pic, the wheel frees up. (You can alos see that the adjuster screw is still backed out).


 The brakes definitely work better, but are dragging badly when I tighten up the lower bolt on the RH side. The LH side seems to work as it should. The rotor gets pretty hot after just a couple of passses up and down the street and I can barely push the bike around the garage without loosening the lower bolt.

 What next? What's causing the pivot arm to tighten up so much when I tighten the lower bolt?

[JohnG]

so I would stick with stock pads until I got it working correctly  (basic rule:  less variables is better).

When you say "lower bolt"  do you mean the 8 mm one that holds the arm to the fork leg?  (the upper bolts being 6 mm).   if that causes binding then you seem to need shim(s) to prevent that.  The pad should end up perfectly vertical when the front wheel is straight ahead because the disk will be.

The left side should work fine as it it 100% stock, yes ?

I put a jack under the bike and just get the front wheel a tad off the floor so I can see how easily the wheel turns as I experiment.  This will save you some gas . . .   

[Scott S]

 I think I got it!!

 Just kept loosening/tightening/adjusting...trying to compare what was different side to side. Lifted UP on the whole shebang and that seemed to help, but it was still dragging.
 That's when, after looking for about the 15th time, trying to see what was different on the RH side, I noticed that the fender itself was touching the caliper arm. I was so focused on the arm and caliper, I didn't notice the fender.
 Loosened the 6mm bolts and lifted up/back on the fender and got it off the arm. The bike rolls freely now.

 I took it up and down the street a few times, got her up to ~35 mph and grabbed a handful of clutch and brake a few times to bed the pads. Seems to work MUCH better. The lever is better, but still not quite to my personal taste. May try a 16mm master someday.
 When used in conjuction with the rear brake (also with EBC pads) it REALLY stops well.

[Scott S]

 Oh, the adjuster is still backed off. Maybe after the thicker pads wear down I'll need to use the adjuster, but for now I'm going the way JohnG did and just leave it backed out.