Post by: SpannerBrat on August 27, 2018, 08:46:43 AM
I seem to have managed to fettle an extra (rhs) calliper into life & fit it to the 750SS forks I got with the “box of rusty bits” bike I originally bought. All “looks” decent (i’v not had anything working yet) but I need to buy new levers & so I wanted to find out from you guys what size of master cylinder I need to hunt for ont’interwobble? Searches are throwing up 5/8” as a likely candidate. If any of you have any cool looking alternative suggestions for levers, i’m all ears.
Also, have any of you advice on the best twin disc hose arrangement? I prefer the look of looping a link hose from one side to the other but suspect that this could a) not be as powerful as running a full length hose to each side & b) could also be more problematic when it comes to bleeding (but both of those are guesses).
As ever, thanks for any input. This forum has been a great help in keeping my build going (& importantly, going in the right direction).
Post by: Bryanj on August 27, 2018, 08:58:17 AM
Post by: SpannerBrat on August 27, 2018, 10:44:25 AM
The bore of the GL MS seems to be 14mm but 16mm is the number being thrown up by searches for 550/750 MSs. Could you educate me on which I should be tending towards & why (i’m assuming from your recomendation of GL, the smaller bore is better)?
Post by: Bryanj on August 27, 2018, 02:59:55 PM
Post by: petermigreen on August 27, 2018, 03:20:16 PM
be carefull of big handfulls on very wet roads as you fall off! Got the tee shirt and video for that oneAny chance of posting the video? ;D
Post by: cb750stu on August 27, 2018, 07:01:42 PM
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Post by: SpannerBrat on August 27, 2018, 07:34:50 PM
I’d be ok using anything that works well tbh (GL, CB, whatever). I’m just a bit confused on the bore size situation. Is there a simple rule of thumb like “the larger the bore, the less grip force required (or visa Verda)?
There’s so much choice out there from cheep (£20 & even less) units that have surely got to be made of cheese, to ridiculous (£hundreds) & from onboard reservoirs to “remote” styles. The bike’s a mixture of all sorts of parts & is planned as a brat/cafe so anything goes really. I’m just trying to understand what exactly I’m looking for to give me decent performance. I’ll not be blasting around the N.Yorks moors wearing out knee sliders at every opportunity but equally, i’d like to know i’ve got some effective anchors if/when needed.
Post by: cb750stu on August 27, 2018, 07:56:42 PM
Thanks for the comments.This is what I use , one brake line coming from M/S then into splitter to the two calipers , works really well plenty of braking power
I’d be ok using anything that works well tbh (GL, CB, whatever). I’m just a bit confused on the bore size situation. Is there a simple rule of thumb like “the larger the bore, the less grip force required (or visa Verda)?
There’s so much choice out there from cheep (£20 & even less) units that have surely got to be made of cheese, to ridiculous (£hundreds) & from onboard reservoirs to “remote” styles. The bike’s a mixture of all sorts of parts & is planned as a brat/cafe so anything goes really. I’m just trying to understand what exactly I’m looking for to give me decent performance. I’ll not be blasting around the N.Yorks moors wearing out knee sliders at every opportunity but equally, i’d like to know i’ve got some effective anchors if/when needed.
Regards
https://www.davidsilverspares.co.uk/CB750F1-(Single-overhead-cam)/part_123909/
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Post by: Bryanj on August 27, 2018, 09:44:33 PM
Post by: Bryanj on August 27, 2018, 09:53:11 PM
Post by: matthewmosse on September 02, 2018, 01:01:53 PM
Post by: kevski on September 02, 2018, 01:08:05 PM
Post by: Colonial-Clive (yindi) on September 02, 2018, 01:12:39 PM
PS I also updated to braided hoses.
Post by: Johnwebley on September 02, 2018, 01:51:48 PM
I used a gold wing one when i twinned up my 500k3 in the late nineties.
same for me,and only £30 from David Silver
Post by: SpannerBrat on September 02, 2018, 04:37:56 PM
Thanks for the comments & suggestions so far. I thought to try the std cylinder/lever arrangement that I have here but on offering it up to the bike, it turns out that the cylinder exiting from the brake unit fouls against the clip-ons i’m using. So i’m expecting the GL unit wouldn’t work either & therefore it seems a plan C might be needed. That being the case, the BMW option (thx Matthew) is worth investigating but I find myself wondering what a radial setup would work like (with remote “sample pot” - fortunately i’m not completely adverse to the look). Has anyone any guidance on what I should be looking for there (appropriate model, year, part generally from a larger capacity bike or does it really matter)?
Post by: Colonial-Clive (yindi) on September 02, 2018, 06:17:29 PM
Post by: SpannerBrat on September 02, 2018, 11:06:30 PM
Post by: SpannerBrat on September 03, 2018, 07:19:21 AM
That link looks like the right kind of thing (although I can’t see the bar dia mentioned in the description) but i’m always rather suspicious (rightly or wrongly) about unfamiliar / non-branded parts. I’d prefer a 2ndhand Nissin or similar from an actual bike ideally (i’ve always thought of braking as a part of a bike you want to get “right”) but would consider strong recommendations of reliable alternatives.
Post by: SpannerBrat on September 04, 2018, 03:27:06 PM
Post by: Johnwebley on September 04, 2018, 07:51:29 PM
I am not an expert on brakes ,but surely you need to calculate caliper piston area,and MC area,
on sohc bike a single caliper has a 12mm bore MC,( I think)
a Gold wing with 2 calipers ,(same caliper as SOHC ) it has a 16mm bore,again I think,
basic thought,each of the 2 caliper pistons need to move to squeeze the disc,and will need twice as much fluid to cause that,
hence the dual caliper MC has a larger bore,
a quick calculation show a 122mm bore has an area of about 113square millimeters,and 16 is just over 200 ,
nearly twice as much for the same piston stroke .
hope it helps ,or gives you food for thought
Post by: SpannerBrat on September 12, 2018, 02:15:04 PM
Thanks for the reply & I believe you're right (regarding needing to calculate what's needed). Unfortunately I've become increasingly confused as I've looked into what I should be looking for in the new MC. From this link - https://www.vintagebrake.com/mastercylinder.htm - as I've got 2 x 38mm pistons (I'd forgotten I was using CX calipers....sorry. Perhaps I should really have started the topic on the CX forum but hopefully it's something some of you can still help with) & based on that page/chart, I should be looking for a MC with an 11mm bore size to give me a "preferred" 23.87 ratio. Taking that as correct (& I've no idea if it is), I'm struggling to find a MC that will be suitable. My hunt is made more difficult because the exiting cylinder - where the fluid is pushed out - of the old style MCs is in line with the bar & as can be seen on the photo of my bike (further up this thread), the mounting end of the clip-on gets in the way of the cylinder.
So, I have 2 questions:
1) Is that ratio figure "correct" in relation to getting the right feel (I appreciate that "feel" is a subjective term but there must be a figure that's widely understood as being inbetween bartouchinly spongy & oak-like wooden)?
2) Taking the ratio as correct, does anyone have a suggested solution to solve the need for an 11mm bore radial MC to clear my clip-on by any chance?
I'll get there in the end but it's resisting me at the moment.
Andy
Post by: K2-K6 on September 12, 2018, 08:12:50 PM
That obviously doesn't come near the preferred ratio on the vintage site, but those brakes work quite well with decent power, progression and feeling on a 19inch front rim.
Smaller bore master will give you more travel but lighter lever pressure required for same stopping effort. So softer, longer and more potency.
Larger bore master, obviously the opposite. So harder shorter and more effort required at the lever to get same braking.
They were quite conservative in that era for master cylinder bore ratio so going somewhere near to 16.0mm I feel would be a good start point. There is a caveat though, radial operated master can use different mechanical lever ratios placement of the bore relative to the lever fulcrum. So it depends what the design has done here that can change the effort required.
Post by: SpannerBrat on September 12, 2018, 09:10:07 PM
Thanks. it seems like a bit of a minefield when it comes to messing about changing / mixing braking system components (& not a comfortable field at that). It sounds like i’m going to have to take a bit of a punt on a 16mm radial MC (Nissin seems a good solid option), hook up some new braided hoses & test that when it comes to the bike moving under its own steam. It’s not running yet so I was hoping sorting the front end out would be a relatively simple & inexpensive job before getting round to the pricier jobs like sending the carbs off to be rebuilt (that’s a task that’s well outside my comfort zone / pay grade). It seems a shame not to act on all this useful info i’ve gathered so will scour eBay for a suitable MC (& matching clutch lever if possible).
Post by: K2-K6 on September 12, 2018, 10:01:36 PM
As the bore size increases it moves more fluid and puts you (your hand) progressively at more of a mechanical disadvantage.
It's like using shorter spanner/ratchet to turn the sale size bolt, longer lever makes it easier to exert force on bolt but moves further. Shorter lever, hand moves less but can't make the same force.
That's why you can spin a loose nut up quickly with your fingers but need a lever to tighten and loosen it when under load.
Post by: Trigger on September 12, 2018, 10:26:38 PM
I have always said, bigger the bore, sharper the brakes and you don't want sharp brakes.
The more up to date bikes with 8 pistons on the front use a small bore and the reservoirs are getting smaller all the time.
Post by: K2-K6 on September 13, 2018, 09:52:20 AM
Going back to that vintage chart, they are focusing on race stuff with twin piston calipers generally for the desired ratios. He puts a condition in his text for single piston calipers near the end saying ratio of 12/14 to 1 is most desirable.
16mm takes you very close to that range and in reality you'll probably end up somewhere from that down to 13mm as a workable range if you where able to test them individually.
With your calipers, 16mm will make a good baseline and probably won't need to be altered.
Post by: Johnwebley on September 13, 2018, 10:37:48 PM
So are you saying that because the lever stays further out and it travels less because it's pushing more fluid that your hand is at a disadvantage because the fingers are extended and you get more force as the hand contracts ?
I did this mod many many moons ago and used a Yamaha MC, bore size was bigger but the lever had an adjustable screw where the lever meets the end of the piston, so you could adjust the lever to sit closer to the bars, TBH it felt quite hard which was a big change from the Honda MC which was always a bit spongy and had loads of lever travel, I did change the lines to Braided at the same time to stop the infamous rubber line expansion the early Honda fours were known for. I raced that setup for a few years, had plenty of feel without much lever travel, it could lock up the front wheel if pulled really hard but it didn't feel even remotely dangerous, in fact it felt safer as the braking improved tremendously.
its more to do with finger pressure and strength,the bigger the bore will increase the amount of power needed by the fingers,
a smaller bore will give long travel and lighter pressure needed to lock the wheel,
its all to do with mechanical advantage
Post by: K2-K6 on September 14, 2018, 08:58:28 AM
Going back to the leverage. If you first strip out the brake lever and just look at the hydraulic section it makes it easier to see what's happening. If you extended the piston to the same area of the calipers (extreme for illustration purposes) then you have no ratio advantage at all, and probably wouldn't be able to get any appreciable force on the brake pads, this would be a 1 to 1 ratio. Then you leave the calipers alone and keep reducing the bore of the mastercylinder to a point at which you have the ratio advantage you want. This shows that by reducing the mastercylinder bore you create a ratio that trades movement against leverage, so better able to pressure the pads but you now have to move the mastercylinder piston further to achieve it. In other words a mechanical advantage.
Then you add the lever back into the mix. If you measure the distance from lever pivot point to centre of piston and compare it too the lever length, it will give you another ratio that will act as a multiplier on top of the hydraulic one.
So depending on the area of the caliper's pistons, if you use a mastercylinder of (obvious used range) between 10/16mm to get a ratio you want then manipulate that total with a different lever ratio, you end up being able to produce a similar brake line pressure but with different "feel" to the lever.
The newer radial type mastercylinder seems to go for lower end bore size (as Trigger mentioned) to get the most potent hydraulic advantage but then use a variable/ adjustable lever fulcrum ratio to alter feel for rider preference.
The screw on those old Yamaha levers just moved the lever to accommodate differing hand sizes and not the ratio. If you move your hand out to the end of the lever you do increase the leverage though, compared to using your two principle fingers nearest to the pivot point.
Post by: Yoshi823 on November 12, 2018, 11:07:26 PM
(http://i666.photobucket.com/albums/vv23/WiNot_Rhencullen/Honda%20750/My%20bikes/Earlydays034.jpg~original)
A few years later I swapped the double discs over to Mrs. Yoshi's 550F2
(http://i666.photobucket.com/albums/vv23/WiNot_Rhencullen/Honda%20750/My%20bikes/Earlydays047.jpg~original)