Topic: Better brakes wanted: Dual front disc?

[GodFather13]

I would really like better stopping power from my 750. Its amazing to think back in the early 70's this braking system was one of the best there was. I truly believe the rear brakes on my bike stop better then the front.

Anyways, I was wondering who out there has done the dual disc conversion on the front and what parts did you use? Or is there another route I could go? I current just have the stock brake system with a 76 supersport master cylinder/brake lever and dot5 silicone purple fluid.

Thanks in advance.

[Hush]

When I was tought to ride the rule was always 80/20 ie the rear brake was accountable for 80% of the braking and the front only 20%.
This was because the front brakes only really were used to keep the bike in a straight line when braking.
Both my CB650'S have twin front disc systems and I still get more stopping power from my drum rear brake, I guess I'd haul on the fronts if a truck stopped suddenly in front of me but then you also run the risk of flipping the bike.
Wet weather and twin front discs can be fraught with danger too as stopping the front wheel turning is one thing but actually coming to a stop is another.
I really don't think twin front discs would be too much of an advantage but I see a lot of forum users doing these converts so maybe it is a form of psychological security rather than actual stopping power.

[MCRider]

When I was tought to ride the rule was always 80/20 ie the rear brake was accountable for 80% of the braking and the front only 20%.
This was because the front brakes only really were used to keep the bike in a straight line when braking.
Both my CB650'S have twin front disc systems and I still get more stopping power from my drum rear brake, I guess I'd haul on the fronts if a truck stopped suddenly in front of me but then you also run the risk of flipping the bike.
Wet weather and twin front discs can be fraught with danger too as stopping the front wheel turning is one thing but actually coming to a stop is another.
I really don't think twin front discs would be too much of an advantage but I see a lot of forum users doing these converts so maybe it is a form of psychological security rather than actual stopping power.

With all due respect, I have to correct you. It is 80/20 for sure, but 80% front and 20% rear. You can check with the Motorcycle Safety Foundation and any other professional riding/ training outfit you like. The rear is used to keep the vehicle straight not the front.

That's why all performance bikes have twin fronts, cars put discs on front and drums rear.

If you're having trouble with this you are doing something terribly... and dangerously...wrong.

Please take some rider training.

As to godfather's question, this site is rife with threads on the dual disc conversion, including parts lists. A properly functioning original disc is very powerful and should always be used properly to stop the bike. I seldom use the rear, and that's what the pros will teach you.  The second disc only adds marginally to gross power (one disc will lock the wheel) but two discs are easier to modulate, won't fade as quickly etc.

[j-conn]

but 80% front and 20% rear

agreed. or some ratio similar...


on bicycles its even more to the front

[Deltarider]

Less is more IMO.
To much braking power can be dangerous. I'd prefer learning and training the right braketechnique. Besides there are simple improvements you can make. Personally I see no advantage in adding unsprung weight and I am amazed so many go that route. Don't get me wrong, you can improve stopping power by double disks, but I would never want another of them stock disks that are very heavy indeed.

[cafe750]

Less is more IMO.
To much breaking power can be dangerous. I'd prefer learning and training the right breaktechnique. Besides there are simple improvements you can make. Personally I see no advantage in adding unsprung weight and I am amazed so many go that route. Don't get me wrong, you can improve stopping power by double disks, but I would never want another of them stock disks that are very heavy indeed.

+1
I'm doing everything that I can to maximize the single brake, because I don't want to add all of the unsprung weight that a stock twin disc will add. Add to that the additional gyro effect of that second disc, and you may not be happy with how it effects the handling of the bike.

[MCRider]

Less is more IMO.
To much breaking power can be dangerous. I'd prefer learning and training the right breaktechnique. Besides there are simple improvements you can make. Personally I see no advantage in adding unsprung weight and I am amazed so many go that route. Don't get me wrong, you can improve stopping power by double disks, but I would never want another of them stock disks that are very heavy indeed.

In Godfather's case yours is good advice. He should be sure that his front brake is operating properly AND he should learn how to use it if that's a problem. He will not find a professional trainer or book written on the subject that will tell him to use the rear over the front.

As to why a duallie, fade resistance, modulation, uniform fork flex, etc. important for those of us who fancy the twisties.  My stock discs were thinned and drilled, 2 weigh little more than one.

And there is a cool factor.  

[Duke McDukiedook]

MC is right about the braking, you barely use the rear for correct braking.
Do you want to keep period correct brakes? Dual disc is probably the way to go.
If you want modern brakes, just swap out a modern front fork and triple, there are a few guys on this forum that did just that. That will probably give you the most braking power.

Hey, these brakes were state of the art back then, technology has come a way since then. They were the first mass production bike out there with disc brakes.  

[MCRider]

Less is more IMO.
To much breaking power can be dangerous. I'd prefer learning and training the right breaktechnique. Besides there are simple improvements you can make. Personally I see no advantage in adding unsprung weight and I am amazed so many go that route. Don't get me wrong, you can improve stopping power by double disks, but I would never want another of them stock disks that are very heavy indeed.

+1
I'm doing everything that I can to maximize the single brake, because I don't want to add all of the unsprung weight that a stock twin disc will add. Add to that the additional gyro effect of that second disc, and you may not be happy with how it effects the handling of the bike.

My HawkGT is a single disc bike. A larger diameter disc adds stopping power, multiple pots in the caliper help with fade and modualtion. A fork brace helps with flex. So a single disc can do the job.

Once you have enough power to lock the wheel, improvements are for other reasons. One is to be able to come to near lock over and over, hence the multi pot duallies.
I'm thinking my next project will be a single front disc. 76CB750F Cafe Racer

[cafe750]

As to why a duallie, fade resistance, modulation, uniform fork flex, etc. important for those of us who fancy the twisties.  My stock discs were thinned and drilled, 2 weigh little more than one.

And there is a cool factor.  

I found a drilled and thinned rotor at a salvage yard...it was a pound and a half lighter than a NOS stock rotor, which amazes me...It works just as well as the stock one did.

We twin disked my little brother's 550, as well as flipping the calipers behind the fork ears. All that rotational weight destroyed the light, quick tip-in and flickablility of the bike, which is what I based my previous post on.

[MCRider]

As to why a duallie, fade resistance, modulation, uniform fork flex, etc. important for those of us who fancy the twisties.  My stock discs were thinned and drilled, 2 weigh little more than one.

And there is a cool factor.  

I found a drilled and thinned rotor at a salvage yard...it was a pound and a half lighter than a NOS stock rotor, which amazes me...It works just as well as the stock one did.

We twin disked my little brother's 550, as well as flipping the calipers behind the fork ears. All that rotational weight destroyed the light, quick tip-in and flickablility of the bike.

Like my HawkGT (similar in size and power to a 550) one disc is enough. If you  had skads of horsepower (speed) and were approaching multiple turns way too fast, then twin discs wouldn't fade. If you're being reasonable about it, riding the pace, then the twin is overkill, from a performance point of view.

ITs still cool.   

[GodFather13]

All good info. Yes I know most of the braking comes from the front. I've had my brakes checked twice by my mechanic (who builds/restores only cb750's) and he's assured me they are fine. It just seems to take a long time (longer then it should) to bring the 750 to a complete stop with only the front brake. I can bring the bike to a stop much quicker using only the rear (for comparison purposes, not what I do everyday riding).

Im thinking what might be happening is I also spend a lot of time on my cousins Softail Duece and Wideglide both of which have motor work done and great braking systems. I've never locked up one of their front wheels nor I have I locked up my 750's and I know the newer Harley brakes are much better then a 40 yr old Honda but thats the stopping power Im comparing it to and thats the stopping power I wished the Honda had. I ride the same mountain roads on both bikes and I have to slow down a LOT earlier on a turn in with the Honda then I do the hog. Maybe a bad comparison, but either way, Im looking for that type of grab and feel that the bike is going to stop soon, not sloooowly come to a stop.

Does that make sense?

[lordmoonpie]

If you guys can tell the difference in addign the unsprung weight of a second disk then you must be fantastic riders and that I'd propose means you should have the second disk to match your abilities! Two will always be better than one for stopping purposes it's plain physics - twice the frictional swept area. If you seriously think that affects your handling noticeably because of the tiny bit of unsprung weight addition I'm amazed. Put two brakes and discs on and cut out the Wendy burgers for a month and there's twice the stopping power and less unsprung weight than you started with. It's your riding weight that affects handling more than a small extra bit of metal!

We could open up the old race vs road debate here with Young Eldar again - do you think Valentino Rossi would prefer one front disc? I think not!

[TwoTired]

I recommend you do a few things before changing to dual disk.

1 - Change the brake lines to Stainless Steel braided type.  While old, or rubber, lines may not leak, they are not as rigid under pressure as the SS type.  So instead of expanding under pressure, the energy robbed by expansion instead goes to your brake pads.

2 - (And I'm sure I'll catch flak for this), drain and flush the DOT5.  One of the complaints I've read about this fluid type is a spongier pedal or lever as the silicone is more compressible than DOT3 or DOT 5.1.  Again, you want all the energy to go toward those friction pads, not compressing a fluid.

I don't know how long you've had DOT 5 in your system.  I also read reports that DOT5 is not always compatible with the old style rubber components originally intended for use with DOT 3 fluids, with swelling being the symptom.  Further, water collects at the bottom of the system (where the caliper piston is) and can corrode bits down there, making operation less than ideal.  I've not tested the Honda brake parts for DOT5 compatibility.  I only pass on what I've read about DOT5.

I have a 550 with a smaller disk than the 750.  I also have a big Vetter fairing on that bike, bringing the weight up.  New, clean pads, SS lines, and Dot 3 fluid allow me to squall the front tire, (with admittedly high hand pressure).   But, it's there if I need it.   However, I don't WANT to stop the wheel from turning altogether, as that would just make the front end slide.  In a panic stop, almost all the weight of the bike shifts to that front tire.  And the lever is rock hard, with no doubt as to when the pads are engaging disk.

Cheers,

[MCRider]

All good info. Yes I know most of the braking comes from the front. I've had my brakes checked twice by my mechanic (who builds/restores only cb750's) and he's assured me they are fine. It just seems to take a long time (longer then it should) to bring the 750 to a complete stop with only the front brake. I can bring the bike to a stop much quicker using only the rear (for comparison purposes, not what I do everyday riding).

Im thinking what might be happening is I also spend a lot of time on my cousins Softail Duece and Wideglide both of which have motor work done and great braking systems. I've never locked up one of their front wheels nor I have I locked up my 750's and I know the newer Harley brakes are much better then a 40 yr old Honda but thats the stopping power Im comparing it to and thats the stopping power I wished the Honda had. I ride the same mountain roads on both bikes and I have to slow down a LOT earlier on a turn in the Honda then I do the hog. Maybe a bad comparison, but either way, Im looking for that type of grab and feel that the bike is going to stop soon, not sloooowly come to a stop.

Does that make sense?

A big part of stopping distances is weight transfer. The less the better. It is weight transfer that dictates that the front brake does the most work. First I'll say that if you stop a cb750 shorter with the rear than the front, you are doing something seriously wrong. That's it, period.

Now about your second pragraph. Back to my statement on weight transfer and stopping distances. The last such test I read in Motorcycle Consumer News had a Suzuki Marauder, a single front brake cruiser, in the top 5 of ALL motorcycles for stopping short. MANY sportbikes scored lower and only a few scored higher. Reason, cruisers have relatively little weight transfer. Several cruisers in the top 10. Now likely they couldn't repeat the performance due to brake fade, but for a one time stop, they are the best.

Your CB750, a "standard" is never likely to give you the slowdown feel of a cruiser. Too much weight transfer, weight is carried too high. If you're drawn by the feel of a cruiser for any one of a number of reasons, you'll likely never be happy with a CB.

My buddy that's helping me with my current project had a Marauder, a Harley before that. We were out riding one time, me on my Hawk GT and we switched bikes. His Marauer couldn't turn itself around in a country mile. I hated it. He said his first impression of the Hawk was "where's the front wheel?" He was so used to being able to see it on the Suzy, the Hawk front wheel like most sport style bikes is tucked in the front. But never having been on anythng but a cruiser it shocked him.

Within a few months he had traded the Marauder in on a low mileage used FJ1200 he still rides and loves. Tucked in front wheel, fairing, dual discs, transverse in line 4, high CG. It does have ABS.

But I'll finish by repeating, regardless of the style of motorcycle, you will get your best performance from emphasizing the front brake. If you can't do that, you really need to look into training.

[GodFather13]

Well I just got the bike back Sunday with the dot 5 in it. And that wasnt for performance purposes but so it would never eat through my paint if it was to ever spill on the tank. I rode for over a year with the regular fluid in it. But I had it in the shop because my oil sending unit started leaking and I installed a new triple tree, fork boots, and some other goodies.

[USN20]

Im looking for that type of grab and feel that the bike is going to stop soon, not sloooowly come to a stop.

Along with the other advice posted, a fresh rotor surface can also help improve brake feel.

SOHC member: "Speedracer741" offers rotor surface grinding:

http://cgi.ebay.com/ebaymotors/HONDA-CB500-CB550-CB650-CB750-BRAKE-DISC-ROTOR-SERVICE_W0QQitemZ300294782776QQihZ020QQcategoryZ111105QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Also, a good read from an old thread: http://forums.sohc4.net/index.php?topic=44155.0

[GodFather13]

I understand what you are saying, and while I have taken a motorcycle riding course in my lifetime, I would never admit to knowing everything. However, I know how to brake, when to brake and how to emergency stop. Ive put over 5,000 miles on the 750 in a short period of time and have never once locked up the front wheel, hit anything from stopping short or any other senarios.

BUT... I would like the bike to have the stopping power "or feel I should say" of other more modern bikes that I ride as well. While they might not transfer the weight like mine does, I know when a bike stops better then mine. I could care less about adding a little extra weight, hell I took a 800 mile trip with a carryon suit case and my bookbag strapped to the back and was fine with it. My WISH is to have it stop better then it does now and if that means dual disc then thats the way I want to go.

Maybe I should ride another 750 and compare it to mine back to back to see if there really is something wrong with my system???

[GodFather13]

While were at it, lets throw out the cross-drilled v/s solid disc comparison. Crossed drilled was originally made to let out gasses caused by the pads against the rotors but most modern applications do not do that in regular riding conditions. More surface means more braking power, however less weight could mean shorter stopping distances.

Whats everyones take on this? Anyone ever known a cross-drilled rotor to crack from the heat?

[MCRider]

I understand what you are saying, and while I have taken a motorcycle riding course in my lifetime, I would never admit to knowing everything. However, I know how to brake, when to brake and how to emergency stop. Ive put over 5,000 miles on the 750 in a short period of time and have never once locked up the front wheel, hit anything from stopping short or any other senarios.

BUT... I would like the bike to have the stopping power "or feel I should say" of other more modern bikes that I ride as well. While they might not transfer the weight like mine does, I know when a bike stops better then mine. I could care less about adding a little extra weight, hell I took a 800 mile trip with a carryon suit case and my bookbag strapped to the back and was fine with it. My WISH is to have it stop better then it does now and if that means dual disc then thats the way I want to go.

Maybe I should ride another 750 and compare it to mine back to back to see if there really is something wrong with my system???

If you're comfortable squeezing the front brake lever hard, and still have these concerns, I have to suspect your brake. I for one always liked the feel of DOT5, though now I use DOT4.

Without rereading I forget what you said you've done to your brakes. But a showroom stock brake should satisfy all Sunday drivers. As others have mentioned, the disc may need surfacing, (elbow grease and emory paper can do this) try a different style puck, etc. New rubber lines would feel fine, but likely yours are old. Switch out to stainless steel braid.

But the hunker down stop right now feel of a cruiser won't be had.

Good luck

[MCRider]

While were at it, lets throw out the cross-drilled v/s solid disc comparison. Crossed drilled was originally made to let out gasses caused by the pads against the rotors but most modern applications do not do that in regular riding conditions. More surface means more braking power, however less weight could mean shorter stopping distances.

Whats everyones take on this? Anyone ever known a cross-drilled rotor to crack from the heat?

Yeah the drilling was OT, but that happens. But I will correct one thing "more surface means more braking power". Not true. The braking power remains the same, if all that has changed is drilling the disc.

I led a thread on this very subject. It got very technical with mathmatical calculaiotns and all sorts of things. Bottom line is, the master cylinder puts out a certain amount of pressure. Period. That pressure is transferred to the disc as PSI. IF there is less surface area the PSI goes up as surface area goes down. Net result is braking force remains the same.

If you think about it, what the master cylinder puts out cannot disappear. In a drilled disc, it just becomes more focused.

That's why some bikes (like mine) have swiss cheeze discs with no drop in braking force. The increase in PSI does tend to heat up the pucks and wear them out faster. THAT is the downside, not loss of force.

And I've never seen or known first hand of a drilled disc failure. I have read that it is possible, but never read of a case. Someone here has.

[GodFather13]

Thanks. I'll for sure try to resurface the rotor for starters and check out the SS lines. Anyone you recommend to purchase these lines from?

[MCRider]

Thanks. I'll for sure try to resurface the rotor for starters and check out the SS lines. Anyone you recommend to purchase these lines from?

No I've always had mine done local. There is a shop here in Indy which stocks everything in bulk. They make them tailored to fit different bars, applications etc. On the bike or off. Different anodize colors on the fittings etc.

But plenty of sources, someone will speak up I'm sure. Or Google it.

[Krixxer]

While were at it, lets throw out the cross-drilled v/s solid disc comparison. Crossed drilled was originally made to let out gasses caused by the pads against the rotors but most modern applications do not do that in regular riding conditions. More surface means more braking power, however less weight could mean shorter stopping distances.

Whats everyones take on this? Anyone ever known a cross-drilled rotor to crack from the heat?

this is my SM set-up 320mm. These get so dam hot spit will sizzle on the caliper and I've never seem any crack. As for brake fluid I think DOT 5 is silicon and a big NONO for anything that was not specifically designed for it. Something about the silicone eating away at some of the rubber bits. I use DOT 4 and with this set up I've never felt any fade.

 As for the crossdrilling; it's just like a cheese graded for brake pads.

Forgive my ignorance but can't I just outfit my 550 with a bigger rotor and fab up a bracket to accommodate my choice of calipers?

[MCRider]

While were at it, lets throw out the cross-drilled v/s solid disc comparison. Crossed drilled was originally made to let out gasses caused by the pads against the rotors but most modern applications do not do that in regular riding conditions. More surface means more braking power, however less weight could mean shorter stopping distances.

Whats everyones take on this? Anyone ever known a cross-drilled rotor to crack from the heat?

this is my SM set-up 320mm. These get so dam hot spit will sizzle on the caliper and I've never seem any crack. As for brake fluid I think DOT 5 is silicon and a big NONO for anything that was not specifically designed for it. Something about the silicone eating away at some of the rubber bits. I use DOT 4 and with this set up I've never felt any fade.

 As for the crossdrilling; it's just like a cheese graded for brake pads.

Forgive my ignorance but can't I just outfit my 550 with a bigger rotor and fab up a bracket to accommodate my choice of calipers?

That is a way cool set up. That large diameter disc has to give a lot of power. The more I see and think about it, a single big disc multipot system makes a lot of sense.

AS mentioned I used DOT5 in my CB750 for well over 15 years no problem. Several changes and flush throughs in the period. AS this article mentions, Silicone is chemically inert and does not attack anything. http://www.dnd-automotive.com/chassis/brake-fluid.htm  Used in antique cars to preserve the system.

The real problem (confirmed on Wickipedia) is that it doesn't mix with DOT 3,4,5.1. So switching is a problem. But if you start with a fresh clean system, all parts free of DOT 3,4, or 5.1, then DOT5 is fine. AS mentioned elsewhere, it doesn't absorb water, so the water will puddle in the system over time. No problem if you change the fluid regularlly. DOT 3,4, or 5.1 DOES absorb water, so what is worse? Both need to be changed regularly to purge the water.