Topic: Dual disc on 550 help

[Greyhound]

When you say “sliders” do you mean the fork lowers?

The mounting holes on the 750 brackets won’t line up with the mounting holes on 550 forks lowers?

It is my understanding that the larger (K7-K8) 750 calipers and mounting arms will bolt directly onto 550 fork lowers, but need the larger (295mm) rotor, which also just bolts onto the 550 hub without issue.

[RAFster122s]

I believe as bryanj states, Distance from axle to the caliper mount points is different on the 750, this along with the shorter swing mount of the caliper accommodate the larger rotor. The 750 fork assembly is a couple inches longer than the 550 forks.
Imagine you could use the 550 fork tubes with the fork lowers from the 750 but never messed with it.
RaceTech gold emulator valves will improve the fork dampning performance. It won't be modern fork perfect but will be much improved.
But, modern fork swap often runs you $1000-1500 or even more.
Depending on how much you have to pay for the donor and access and skills for getting custom machine work done to do the swap. CognitoMoto can make it easy if you want to shop their solution for a modern fork...if you can swallow the price tag going that route.

[Greyhound]

Ya I’ve considered the modern upgrade, but if I went that route, I’d want slightly wider rims (if I’m respoking a hub anyway), plus would likely need to stiffen up the rear end and frame if the front is going to be that stiff… all for a bike that’s putting out 50hp in its current iteration.

So, as cool as it looks, and as well as it would perform, seems like overkill (including on my wallet), so planning to just upgrade the vintage capabilities (indeed w/ Racetech).

[Greyhound]

In reference to the thread I’ve linked below… is where I’m getting confirmation of attempting this 750 brake swap with 550 forks. Am I missing something? Or are they incorrect?

http://forums.sohc4.net/index.php?topic=101345.0

[754]

I know the difference is in the brake hanger  for small 550 disc vs 750....  the 500 bracket puts caliper closer to axle..
 So without measuring I would say... very strong chance.... mounting points are  the same on both the 500/550 and the 750 K from 73 to 76..

[scottly]

I think you need the 750 sliders or complete forks as mountings are a different distance from wheel spindle

This is NOT correct; the mounts on the fork "sliders" or lowers is the same distance on both the 550 and 750. A 750 rotor with it's matching caliper is a direct bolt-on to the 550 fork.

[Greyhound]

Ok I’m going for it!

[bryanj]

Scotty you are probaly correct, ive never had a 750 with the "newer" sliders so never compared them side by side, i was going off the markedly bigger disc diameter.

Bake in the mid 70's i actually ran a 500 with twin discs which as i said had to have one caliper in front and one behind as in UK we did not get 550 with mirror image mounts till later.
Braking was better than the single cast iron disc i tried and better with the GL 1000 master but that was my opinion.
Because i reversed a slider i probably did not have the alignment issues with the caliper that i have since heard of if using 550 sliders, will find out when i do the next one next year.

[Greyhound]

Did you have any issues with the mounting arm on the reversed slider?

I’m really considering flipping both around to run the calipers in the rear, but somehow deep down concerned on whether this will be okay, given that it was “designed” to be “pulled”, not “pushed.”

Although many people have ran them flipped around for decades, and I haven’t heard of a single problem resulting from it, so must be okay (idk why I’m paranoid about it).

[bryanj]

I had no problems at all, only mod was to the mudguard braket that i cut the end off, flipped it and rewelded it as the retaining bolts are at an angle

[RAFster122s]

Fender rivets you can drill out and flip bracket so fender still bolts to reversed/swapped side to side fork legs. You will lose the ability to use the shield that trailed the caliper when mounted in stock fashion.
The fender brace also serves as a fork brace, not super rigid but you pull the fender off a 550 or 750 and take it through some twisty roads and you feel the difference.
You can use short dome headed socket screws with lock nuts to secure the fender to the brace then...

[bryanj]

If you fit 2 500 brake sliders the one is reversed and the fender brace wont fit without cut and shut, look at the aangle of the bolt holes. Yes you can flip the blade if BOTH calipers face one way but in my case due to non availability of 550 sliders i had one in front and one behind

[scottly]

The GL 1000 and the F2/3 used a Huge 17.46mm master, coupled with two 38mm calipers. Thousands of dual disc conversions have been done using two 38mm calipers with a stock 14mm master, and my last dual disc setup on my 750 used two 42.8mm calipers with a stock 14mm master. I do consider that to be about the limit of piston surface area a 14mm master should used with.

[jonda500]

Putting dual 550 discs on my 550, I have all of the parts, however realize that I will need to modify the speedo drive plate to make it work…

I know there was a member on here (rangelov) who used to sell a modified speedo drive plate to make this work, but looks like it’s no longer available?

Are there any other options aside from modifying yourself?

What does modifying the speedo drive plate entail?

This is the only part I had to modify when I did this.? The only non honda part I needed to source was longer bolts - button head or countersunk would be ideal but I just got standard hex heads and ground down the heads until they cleared the speedo drive.
If using 750 discs/calipers/arms the extra arm needs to be aligned with the disc by shimming out with washers where it mounts to the fork because 750 arms are non-symmetrical.
John

[Greyhound]

Thanks for posting that. What year is your 550?

[jonda500]

My 550 is made from parts, the frame is a '75 F.
note: After looking at that chrome piece I modified, I see I must have used washers between the extra disc and the chrome piece (the same thickness as the raised bits that go over the tabs).
John

[Greyhound]

So if there were notches in the rotor mounting plate area to allow it to sit flush with the hub, would the speedo drive plate even need to be modified at all?

[robvangulik]

I didn't use that anymore, so have five of those lying around somewhere in my parts chest.

[Greyhound]

Five of what laying around speedo plates?

[robvangulik]

Yep, the modified rear of the disc makes that plate superfluous. See the pic I posted earlier.

[Greyhound]

I’ll be honest, I had to check the dictionary for “superfluous” … Glad I learned it!

You don’t happen to know they exact mm dimensions of the notches… Do you??

[robvangulik]

  What would you call it when something isn't needed anymore? Unnecessary? Is superfluous too fancy? English isn't my native speak, ever learning
And no, I just filed the alu disc inner until the driving parts did fit...

[Greyhound]

Vocabulary choice is spot on!

I wonder why the consensus isn’t to just file the carrier of the rotor, as opposed to modifying the speedo plate.

Is it 6065 aluminum or 7075?

[bryanj]

Because filing the carrier may well end up with it off centre and therefore unbalanced