What front disc, caliper combo? Mk2a 850

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Last year I did a fair bit of work recommissioning a 1974 mk2a 850. My desire was to try to preserve its originality as best I could, and retain a fair bit of its patina. At only 10k miles from new it was in a reasonable condition and after replacing a few bits here and there it was all up and running. Doesn’t bloody stop though! :(

I had the disc refaced to remove all the surface rust, then the caliper was rebuilt with 2 new pistons and end cap. Finally a new 13mm AN master cylinder (I’d read on here about how bad the 5/8“ original is) and brake hose and fluid. All is working correctly - doesn’t bloody stop though! :(

I'm not expecting 2 finger braking like on my Busa or ZZR1400, but I do want to stop reasonably soon after deciding to, and not half a mile later.

so, suggestions please. However I will not resort to changing the forks, but just do enough to bring it a bit more up to date. What is the most viable caliper and disc to consider purchasing, the RGM disc and caliper kit? I’ve read elsewhere about Grimeca caliper (?) but if so where from?

I’m in UK
 

cliffa

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Which pads do you have? Ferodo Platinum are reputed to be the best.

There are a few upgrade options available if you search on here. But RGM, Norvil, CNW (U.S.) Madass140, do kits. Or if you speak nicely to Time Warp, perhaps he'll run you up one of these very neat carriers...



Cheers,

cliffa
 

Fast Eddie

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I had a stock disc with RGM bracket and Grimeca caliper on mine when I bought it. I was quite underwhelmed with the lack of feel and bite. Very wooden.

I changed it for an RGM disc and PFM 6 pots caliper, great performs but the pads rattle drove me nuts.

I‘ve now got Matts kit, the more subdued black version. I really can’t say enough about it. Twin discs would offer more outright power but this is really enough. On the track it gets a bit blue I confess, but it’s still Ok.

I’d highly recommend it...

99DFD456-3556-4FD3-9825-3A8853AE8524.jpeg
 

Tornado

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Last year I did a fair bit of work recommissioning a 1974 mk2a 850. My desire was to try to preserve its originality as best I could, and retain a fair bit of its patina. At only 10k miles from new it was in a reasonable condition and after replacing a few bits here and there it was all up and running. Doesn’t bloody stop though! :(

I had the disc refaced to remove all the surface rust, then the caliper was rebuilt with 2 new pistons and end cap. Finally a new 13mm AN master cylinder (I’d read on here about how bad the 5/8“ original is) and brake hose and fluid. All is working correctly - doesn’t bloody stop though! :(

I'm not expecting 2 finger braking like on my Busa or ZZR1400, but I do want to stop reasonably soon after deciding to, and not half a mile later.

so, suggestions please. However I will not resort to changing the forks, but just do enough to bring it a bit more up to date. What is the most viable caliper and disc to consider purchasing, the RGM disc and caliper kit? I’ve read elsewhere about Grimeca caliper (?) but if so where from?

I’m in UK
Other than pad choice (Fedoro Platinum is highly recommended), I believe there were differences in disc finish or material? Some old thread I recall read a few yrs ago about significant performance differences.

FYI, reasonable braking with stock caliper, disc, platinum pads, 13mm MC is achievable. My bike has roughly 80% braking performance as my modern air cooled Bonneville with single front disc. Plenty for my style of riding.
 
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Thanks for the replies. I fitted new pads as well but I have no idea who they came from, they were included with a few other spares when I got the bike. Bearing in mind the other spares came from RGM and AN they maybe just their option.

Trying some Ferodo Platinum is worth a go as they’re far cheaper than a new disc/caliper/bracket combo to start off with.

Now as I’ve not ridden it for 6/7 months it may need to be recommissioned all over again :)
 

Tornado

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For other alternative fromt braking, check out Don Pender's products here:


His MC kits can fit stock switchgear. Don is a member on this forum (@madass140).
 

johnm

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I had a stock disc with RGM bracket and Grimeca caliper on mine when I bought it. I was quite underwhelmed with the lack of feel and bite. Very wooden.

I changed it for an RGM disc and PFM 6 pots caliper, great performs but the pads rattle drove me nuts.

I‘ve now got Matts kit, the more subdued black version. I really can’t say enough about it. Twin discs would offer more outright power but this is really enough. On the track it gets a bit blue I confess, but it’s still Ok.

I’d highly recommend it...

View attachment 78682
That's exactly what I have. It works very well.
 
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I’m not sure there was any chrome to remove and it’s just a plain rusty (again) disc. I’m happy to buy another stock, or lightened, disc to remove any doubt of its worthiness. But if I then wanted to change to another disc things are getting a bit expensive. A pair of pads at £20 is worth a punt.
 

cliffa

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I’m not sure there was any chrome to remove and it’s just a plain rusty (again) disc. I’m happy to buy another stock, or lightened, disc to remove any doubt of its worthiness. But if I then wanted to change to another disc things are getting a bit expensive. A pair of pads at £20 is worth a punt.
While you're changing the pads it may be worth having a look at the state of the caliper pistons too. The chrome plating tends to flake causing them to seize.

Maybe worth considering..

 

Tornado

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"I had the disc refaced to remove all the surface rust,"

Did you remove the chrome?
This is what I was thinking had happened in my previous post about disc material differences. If resurfacing removed the plating then this would change the friction co-efficient.
My disc has surface rust in areas that I dealt with by fine steel wool , a wire wheel on a dremel, and some light oil. Once removed and degreased with brake cleaner, it seemed to not re-rust after the pads had bedded in.
 

concours

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I’m not sure there was any chrome to remove and it’s just a plain rusty (again) disc. I’m happy to buy another stock, or lightened, disc to remove any doubt of its worthiness. But if I then wanted to change to another disc things are getting a bit expensive. A pair of pads at £20 is worth a punt.
Chrome has a very poor friction coefficient versus cast iron. Makes all the difference.
 

Tornado

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Chrome has a very poor friction coefficient versus cast iron. Makes all the difference.
So what was the purpose of chroming these? Were they worried of too much bite or front lock ups leading a$$ over tea kettle?
If the OP has removed chrome from resurfacing, wouldn't this improve his braking?
 

cliffa

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So what was the purpose of chroming these? Were they worried of too much bite or front lock ups leading a$$ over tea kettle?
If the OP has removed chrome from resurfacing, wouldn't this improve his braking?
The purpose of chrome plating? In my opinion purely cosmetic. Italian bikes with unplated (therefore normally rusty) discs always stopped way better than ANY other bikes of the same era.
 
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I’m not sure there was any chrome to remove and it’s just a plain rusty (again) disc. I’m happy to buy another stock, or lightened, disc to remove any doubt of its worthiness. But if I then wanted to change to another disc things are getting a bit expensive. A pair of pads at £20 is worth a punt.
You can try better pads, but keep in mind that you're working with a 50 year old design. It was better than the previous drum setup, but the m/c required changes to increase hydraulic pressure on the caliper. Still, at least it has 2 pistons in the caliper. However, rather small diameter disc with a caliper with small pads. Replacing the brake line with braided would be about the only other benefit to your current setup. Drilling the disc would yield lightening and small amount of cooling. Still, it's a 50 year old design, so can only be optimized, not improved. Depending on how aggressive a rider you are, this setup may fail after repeated hard braking overheats the caliper.
If you want something that inspires confidence, upgrade to a setup with better m/c, caliper and rotor. If you're going to spend, may as well entertain CNW or Madass's kits.
There was a saying, "speed costs money, how fast do you want to go?"
In this case, how fast do you want to stop?
 
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Thanks to all. See my avatar ;) I am used to having excellent brakes, and on the subject of speed costs money, the engine build for my turbo Busa land speed bike was over £12k more than a decade ago.
I’ll see how I feel about how a change of pads to Ferodo Platinum in a stock system works firstly. If the difference is too marginal then I may just bite the bullet and go for a different set up.
 
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