Spondon Rear Brake for MK3

I just finished this change to the MK3 project previously detailed here,

https://www.accessnorton.com/NortonCommando/new-mk3-project-for-nc-rally-maybe.19259/

and thought it might interest other MK3 owners.

The caliper is a Spondon substitute for the AP Lockheed caliper popular with vintage racers. They are pretty much the same form factor as the Lockheeds, but are monoblock construction, and are a bit lighter too. I had two of them that I used on my PR race bike back in the day, and had already used one of them with the Norvil disk on the front of the bike. We used the stock rear caliper to get the bike done in time for the rally, but it really didn't work well, and I'd always intended to replace it with the other Spondon, to have matching front and rear brakes. All it took to replace it was making a new caliper bracket, a new brake hose, and an AN fitting at the brake light switch lump. Everything else stayed the same. I have a Norvil splined hub rear disk (smaller diameter than the fronts) that will eventually replace the stock disk, but didn't want to spend a lot of time on the bike right now. I'll probably get to it before next year's rally.





Ken

lcrken said:

......... and are a bit lighter too. .......Ken

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Looks "tidy" as they say, very nice installation. thx for posting. It is amazing just how heavy the stock caliper is.

lcrken said:

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That's a nice looking brake! One quick question; with all the grief the front stock calipers give us when it comes to bleeding, how is this one? It looks from the picture as if the bleed screw is below the top of the fluid passages. Do you have to remove the caliper and tip it forward to raise the bleed screw?

Thanks,
Nathan

Nater_Potater said:

That's a nice looking brake! One quick question; with all the grief the front stock calipers give us when it comes to bleeding, how is this one? It looks from the picture as if the bleed screw is below the top of the fluid passages. Do you have to remove the caliper and tip it forward to raise the bleed screw?

Thanks,
Nathan

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Yes, I do have to raise the caliper to bleed it properly. I considered putting the caliper below the axle, but decided I liked the idea of keeping it in the stock location with the same lower shock bolt fixing point. No great technical reason. I just liked doing it that way. Raising the caliper to bleed the system also helps get the air bubbles out of the brake line, which has its high point above the caliper with the current axle adjustment location. I did the brake line with fittings I already had, and in a way that allowed me to keep the original rear brake light switch hardware. I may change the line in the future to a more tidy configuration, using 90 degree fittings, maybe when I change to the Norvil disk.

Ken

It's been a while since we made any changes to this bike, but we had the rear wheel off for a new tire, and decided to replace the stock rear disk with a Norvil one to match the front. It's a stock PR front disk, with a 5-bolt carrier from Norvil (original PR front used 6-bolt carrier), which we turned down to the smaller diameter of the stock disk, and drilled with lightening holes to match the front. While we were at it, we made a new on-piece titanium axle and bored some holes to lighten the sprocket casting. We also had to modify the carrier to replace the original cup locating the disk from behind with washers. The original arrangement was meant for a front hub, and didn't work on the rear. We also rebuilt the Works shocks, which were both leaking, and painted the springs black for a little more period look.





The next step is installing the new electronic Smiths gauges. The stock speedo and tach died, and the used replacement tach I installed is dying rapidly. We replaced the stock speedo drive with a machined cup that holds a seal for the double row bearing in the sprocket. The new speedo will get it's signal from a reed sensor in the caliper bracket and a magnetic bolt on the disk.

Ken

ludwig said:

Ken , I see you bolted the bracket with the lower shock bolt .
I believe this is not nessecary .
I made it ( modified Honda) so that it just rests against the shock bolt .
It makes routine maintenance easier :

image share

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Indeed it isn’t necessary to secure it with a second mounting point that way but theoretically the complete brake assembly is prone to tilt backwards when you are on hold with your bike on an uphill road

Ken, does the Spondon caliper provide 44.5 mm pistons like the original Lockheed caliper? Do you know its weight? I read somewhere the Locheed-Norton caliper checks in a 1.1 kg (less pads), quite a bit more than todays lightweight Brembo and Nissin calipers which weigh in at 350-400 grams (less pads).

Is your master cylinder still 5/8"? There is a 13mm upgrade available which A-N recommends for those wanting a more powerful rear brake.

- Knut

ludwig said:

Ken , I see you bolted the bracket with the lower shock bolt .
I believe this is not nessecary .
I made it ( modified Honda) so that it just rests against the shock bolt .
It makes routine maintenance easier :

Click to expand...

You are quite right, Ludwig. It really isn't necessary. I just copied the stock MK3 bracket configuration, and it never occurred to me to do it differently. I might change it next time we have the rear wheel off.

Ken

mdt-son said:

Ken, does the Spondon caliper provide 44.5 mm pistons like the original Lockheed caliper? Do you know its weight? I read somewhere the Locheed-Norton caliper checks in a 1.1 kg (less pads), quite a bit more than todays lightweight Brembo and Nissin calipers which weigh in at 350-400 grams (less pads).

Is your master cylinder still 5/8"? There is a 13mm upgrade available which A-N recommends for those wanting a more powerful rear brake.

- Knut

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They do indeed use the same pistons and pads as the Lockheed. In fact, I rebuilt both of them with Lockheed kits, and fitted Ferodo pads meant for the Lockheeds from leftover race spares.

I haven't weighed them, so I can't answer about that. They are magnesium, so should be lighter than the aluminum Lockheeds, but maybe not the magnesium Lockheeds. There are lighter modern calipers and rotors, but we wanted to keep as much period look as possible. Besides, I had these left over from the racing days, and liked the idea of re-using them.

The master cylinder is a new replacement, but is still the stock 5/8". It works quite well for both my grandson (for whom we built the bike) and me, so I don't think we will change it.

Ken