Topic: CB750 AHRMA Superbike Heavyweight Racer

[slikwilli420]

BTW, anyone ever take a modern rotor's disc and build their own carrier? Maybe converting a floating design to rigid give floating wasn't on the scene in the 70s , (was it?) ??  Maybe even buying the rotor from EBC, etc directly without the carrier. Might be less expensive than having your own made if you can come up with a solution that way?  Or, is a floating disc not going to play nice if trying to make it a rigid disc?  I don't know, just thinking out loud and pondering the expense and effort involved in custom rotors.
But, you may need a custom solution for your Astrolites.

Thanks for following along David! The Ferodo race pads play well with cast iron, so as long as I can get them, I am golden.

Floating rotors are not illegal in this class, but dont really fit the build I am after. I can get similar braking from a 12" cast iron disc as one could from the same 12" floating disc in SS, possibly better.

I have found a source for rotors and they are around $100 each, or $165 if cross-drilled. No one else so far has been able to come close to that figure. They will let me submit a design and will make to my thickness spec. I have already fit the carriers to the bearing adapters and only need the actual discs to mount the calipers in the right position. Bearings should be here today and I may have time to get the adapters bored for them this weekend yet. Then I can start building things back up on the front end.

[simon#42]

the spondon calipers used the same seals and pistons as the ap calipers so no problems there , the ap adjustable ratio master cylinder is just a standard master with a crude slider that alters the leverage they dont work any better or worse than normal one . the leavers used to cost a fortune though . master cylinder ratios were understood perfectly well in the 70´s my rg500 came with 3 size options depending on use .

[Tintop]

the spondon calipers used the same seals and pistons as the ap calipers so no problems there, the ap adjustable ratio master cylinder is just a standard master with a crude slider that alters the leverage they dont work any better or worse than normal one . the leavers used to cost a fortune though . master cylinder ratios were understood perfectly well in the 70´s my rg500 came with 3 size options depending on use .

Interesting, and would make sense given they are both from the same period.  Question is....Is Chris @ MotoGP using the AP parts as well?

[MRieck]

the spondon calipers used the same seals and pistons as the ap calipers so no problems there , the ap adjustable ratio master cylinder is just a standard master with a crude slider that alters the leverage they dont work any better or worse than normal one . the leavers used to cost a fortune though . master cylinder ratios were understood perfectly well in the 70´s my rg500 came with 3 size options depending on use .

I have an adjustable ratio AP front master and it certainly doen't look like that. had it for year after a trade for some work. I should throw it on the CB with the DOHC calipers I have.

[slikwilli420]

Still lots more research to be done on calipers. If I go with the AP instead that's still going to be a killer setup that I would be thrilled with.

Bearing adapters all done except a quick smoothing of the sides where the water jet left it's mark them off to vapor blast.

[scottly]

the spondon calipers used the same seals and pistons as the ap calipers so no problems there

What about the pads?

[slikwilli420]

the spondon calipers used the same seals and pistons as the ap calipers so no problems there

What about the pads?

Not 100% sure but I believe all those period calipers from AP, Grimeca, Spondon, and Scarab all use the same pad. I need to confirm though before going with the spondon ones.

[scottly]

If the pistons are the same, and the pads are the same, all those calipers should perform the same. Not as well as a twin piston caliper from 1982, I'd wager. Still in the "period" for your class. How much do the calipers cost? I picked up two 32mm calipers with brackets from a breaker in Phoenix for $87, plus the 180 mile round trip. One is now on the Seeley, and the other is on the "ditch pump" FT500.

[slikwilli420]

These calipers were in use well into the 80's so I'd imagine they are superior to a factory 2 piston caliper. They range in price from about $150-300 depending on brand.

[simon#42]

ok have had a look at a few calipers  and will post some pictures , weights , piston sizes and pad friction area ,  hope this helps
first though some details about adjustable master cylinders , two pictures are of a standard period master the rest are of an adjustable ratio master , you should be able to see that when you adjust the screw in the leaver it alters the position it presses on the slider , this increases or decreases the leverage ratio . pretty crude but it does give you some adjustment

[simon#42]

.

[simon#42]

.

[simon#42]

the monoblock spondons

[simon#42]

more

[simon#42]

two sizes of brembo

[simon#42]

lockheed 2 piston calipers

[simon#42]

and finally some slightly later 4 piston sponden and lockheed , i have included these to show that spondon were so pleased with there monoblock calipers they dumped the idea when they went to 4 piston , also some spondon caliper mounts that i think mat was talking about

[simon#42]

ok weights ,
all have no pads fitted and all have alloy pistons

lockheed  1lb 11oz
spondon   1lb 9oz
large brembo  1lb 13oz
smal brembo  1lb
4 piston lockheed  1lb 8oz
4 piston spondon  1lb 9 oz

piston sizes

spondon / ap  40mm
large brembo  38mm
small brembo 32mm

pad size 

spondon / ap  57mm x 38mm
large brembo  55mm x 38mm
small brembo  38mm x 35mm

all measurements done quickly and are approximate  !!

[scottly]

These calipers were in use well into the 80's so I'd imagine they are superior to a factory 2 piston caliper.

Imagine in one hand and #$%* in the other and see which fills up first. The Honda two piston calipers work very well; I first started investigating them when I noticed how much better the front brake on the ditch pump was than a single 750 caliper, despite the same 295mm rotor and 14mm master diameters.
An opposed piston caliper has no hydraulic advantage over a single piston caliper. The chart from Vintage Brakes is confusing, because they double the ratio for opposed pistons, but in reality, they recommend the same size MC for a single piston caliper and a two piston opposed caliper of the same diameter. It took me a while to get my head wrapped around that.
The 32mm twin piston caliper is roughly the same as a 45mm caliper, hydraulically speaking.
The advantage to opposed piston calipers is less drag, as each piston retracts from the rotor, instead of only on one side: twice the clearance.
The pads are about 89mm x 29mm, minus the corners; I would estimate the surface area to be about 2460mm sq. Most of this area is near the OD of the rotor, where it's most effective.
 

[simon#42]

pad area is important but pad compound has a very big effect , is there a range of racing compounds for these calipers ?  . the good thing about using a racing caliper is the pads are always available in the correct compound . i would use two of the small brembos with 260mm discs on a 250 and with a soft racing compound pad be able to lift the rear wheel entering every corner . the pads would  last around 100 miles

[bwaller]

I use the small Brembo's with race pads too. Mind you on a heavier bike than a 250, but they're lightweight and plenty adequate. Build them with good brakes in mind, then use them sparingly on the track. 

I like to "dress" the discs with a rotor flex hone every few races.

[bear]

I too use the Bremdo's. We use the larger 08's on the sidecar in conjunction with ion disks mounted on a floating carrier.
We settled on this setup after mix and matching many different combinations over a lot of years.

[slikwilli420]

Wow, time flies when you have a bunch of bikes to work on and not enough time or money! Well, I sold my '09 Thruxton so one of the those problems is partially alleviated, at least short term, which means Im back to this one.

Chris at motogpwerks was gracious enough to sell me his last swingarm and the only 4-2-1 exhaust he had. I now have some sweet Calfab and MGPW pieces to add to the bike.

Arm, will be getting a custom pivot bolt, hollow axle and aluminum chain adjusters:



Didnt unpack the exhaust all the way, but here is the end can:



Bike as it sits:



The AHM trees from Chris are absolute jewelry and fit my goals nicely. They only need steering stops to be ready to rock. My front forks are still in pieces but will be going back together soon. The tank is a pickup from Mid Ohio this year for like $50 and the seat was bought last year.

I was really struggling to make adapters for the rear wheel for brakes and sprockets, and happened on a set of 18" GSXR wheels that will be going on their place, at least for now. ISR has ceased all communication on my custom rotors and I have not heard from them in a few months now. It really sucks to be out $350 but what can really be done with an international company that I paid via bank transfer? Either way, I can get ZX7 Kawi rotors for the GSXR wheels, 310mm and readily available. They won't look the part quite as well as the Astralites and custom rotors on vintage carriers, but that can be remedied later.

I should be getting my Ohlins piggyback shocks back from rebuild soon and then I can get a roller together. This is still a long, long, long term project but I am trying to make progress on all my bikes a little at a time.

[seanbarney41]

Sounds really good matt...love that seat,and want one for my orange f.  Was it a used part find or what?

[slikwilli420]

Sounds really good matt...love that seat,and want one for my orange f.  Was it a used part find or what?

Thanks Sean! Seat was a grab from a bike getting parted on the forum here last year. Seat cover job isn't great but it'll work for now and has the shape I wanted.