CB550F Double Disc's

[Trigger]

Have a question that someone out on the forum may be able to answer. Fitting double disc's to a CB550, why does everyone state that you need a master cylinder with a larger reservoir? This reservoir holds less fluid than a standard cylinder but, is a replacement for a GL1000 with twin discs.
http://www.ebay.co.uk/itm/Front-Brake-Master-Cylinder-For-Honda-GL1000-GL1100-GL1200-GL1500-Handle-Bar-New-/321185608547?pt=UK_Motorcycle_Parts_13&hash=item4ac8277363

Could anyone explain who has done a disc conversion. Cheers

[LesterPiglet]

I don't think it's because of the larger capacity, it's because the MC piston bore is a different diameter.

[Johnwebley]

it is due to the fact that you are pushing double the amount of pistons !! and double the amount of fluid,
the standard mastercylinder  may not be able to fully extend the pistons,

so a larger bore M/C is required to ensure both caliper pistons are pressed on the discs with plenty of handlebar lever clearance,

apart from the equation of dia X volume = mech advantage etc,

to much blinding with science !!

yes,it is much better to get a twin disc mastercylinder,

[Trigger]

OK, now i am scratching my head, because i have measured up the bore size on the CB550 cylinder and it is 14mm. Matched this up against the cylinder on my CX500 (which is twin disc) and that is 14mm. I must point out that the cylinder on the CB550 is one of those aftermarket jobies from DSS and NOT OEM. Another confusing thing is a rear brake cylinder (though Japanees) states 1/2 inch, which is 12.7mm.   

[Trigger]

Cheers Oddjob, that will explain it. All down to caliper piston size then. I will have to sit down and do the maths on this one, because the master in the link above states that it also has a 14mm dia. Trying to work out if the OEM master on the CB550 had a smaller dia piston in the master.

[Trigger]

Right, just buzzed round a few forums and found a member that has just bought a aftermarket master for a GL1000K1 from DSS. He says that the master piston is 14mm. Had a quick look on DSS at the aftermarket master for a CB550 and the write up states that the replacement sohc master is also 14mm. Defiantly need to do some maths on this one.
John, you are right on the dia X volume but, i am thinking what would one need for a twin caliper set up? In the way of master piston dia. 

[Johnwebley]

Right, just buzzed round a few forums and found a member that has just bought a aftermarket master for a GL1000K1 from DSS. He says that the master piston is 14mm. Had a quick look on DSS at the aftermarket master for a CB550 and the write up states that the replacement sohc master is also 14mm. Defiantly need to do some maths on this one.
John, you are right on the dia X volume but, i am thinking what would one need for a twin caliper set up? In the way of master piston dia.

I fitted a second disc to my CB500-4,using a standard caliper,and a GL1000 mastercylinder,,the feel is great,lever travel is as standard
with single disc,

and the GL1000 looks exactly the same as standard CB500

[LesterPiglet]

If you look at Silvers the 550 and Wing master cylinders are the same.

[Bryanj]

The first Wing had a master that looked identical to the 500 but had a bigger bore and the later ones had the clear, tall reervoir with a bigger bore ---I know for serpant as i got both in bits in my tool box!! No they ain't for sale, one of these days i am building a 605 with flowed head and big cam so will need the twin discs.

Many years ago when Girling still made things the started a range of japanese brake parts and i bought an early wing one, in my opinion it was a cosmetic reject from japan as the mirror boss flange had a slight dink that was anodised over

[Trigger]

Cheers for the input lads. It is all getting very interesting. After a few emails to part suppliers in the sates late last night and some Japanese this morning . Parts suppliers have stated that a master cylinder repair/service kit for a OEM, GL1000 has a 17.5 bore on the piston (well over engineered and could push any caliper piston) but, they all sell aftermarket replacement masters for the GL, 1973-1975 with a 14mm piston in the master.
Mailed DSS and asked what is the bore size on his aftermarket master for the GL 1000, lets see if it is different than the CB550. 

[LesterPiglet]

If you look at Silvers the 550 and Wing master cylinders are the same.

Just looked Lester and they aren't. They look identical but they have different part numbers plus the 550 does state it's a 14mm bore suitable for single discs whereas the GL version doesn't state the bore but does say it suitable for twin discs.

The part numbers only differ in the middle 3 numbers which I thought designated the model.
45500-410-000P and 45500-300-000P

[Trigger]

Oddjob, You can have identical Honda parts with different part numbers. CX500 had 3 different master cylinders: CX500/A had a round reservoir. CX500B came with a reservoir with 2 screws. CX500 Custom came with 4 screws. Now, back in the 90's we run out of CX500 Custom masters with a part number 45500-463-661  and found the CB250N was a identical part but, with number 45500-442-611. And at half the trade price.
We sat down and found a ton of parts by cross referencing on a microfiche. A brake lever for one Honda Model traded at £6.28. A match was found at £2.42. We also found a lot of interchangeable parts between Suzuki's as well.

The brake light switch which Honda RRP was £17.48 was made by ALPS in Milton Keynes. That switch would leave ALPS in boxes of 1000. Shipped to japan for packaging into Honda bags, Sent on to the european warehouse before been sent to the UK. I know how much that part cost to manufacturer. And it was less than the price of a box of matches.   

[Trigger]

Well, DSS never came back wih a answer to the piston bore size on his aftermarket masters for the GL1000.

[Trigger]

I am not talking about looking identical. I stripped the master on a CB250N and measured up every part to get a match. The CX500 was launched with a single disc in some country's, though using the same master as we had in the UK for the twin disc.
Some parts have different numbers just because of the colour. eg: speedo cable eyes. 

[Trigger]

Just had a reply mail from Karl at DSS. The question was could they tell me the size of the Piston bore size on the aftermarket master cylinder for the GL1000 part number ect,ect.  Karl replied with: Thank you for your email inquiry. Unfortunately we are waiting for new stock to arrive so cannot confirm at this time.