disc brake front end for a MK3

[Scottish888]

Having ridden my 1974 250 MK3 a few times I have found the 35mm Marzocchi forks bottom out with a harsh clang if hitting speed bumps or a bump under braking.
I also find the front drum brake to be a bit stiff and not so responsive. The shoes and twin cables are new, nothing binding, just a slow heavier feel than I want. I would hate to rely on it in am emergency.
I am thinking about fitting Ceriani forks that have the front disc, can I use the same top yolk set? What other parts will I need....if this set up can be found.

Regards

[Duccout]

The bottoming out is not normal, so something is amiss there, possibly The spacers on top of the springs are missing, or you need longer ones. I think that you would be very lucky to find a disc set of forks for sale, but you never know! The disc, hub and caliper is the easy bit.

[blethermaskite]

The standard marzocchi front forks shouldn't bottom out that easily (unless you are very heavy? ) may well be that the preload spacers are not in place or someone has reduced their length, if I remember rightly the spacers should be about 30mm (ish)long, so firstly, you may be able to find a pair of ceriani 35mm desmo front legs at a cost, but while they will fit the marzocchi yokes those yokes are too narrow for the disc brake front wheel, secondly, the disc front wheel/hub will be really hard to get and will cost pretty big money because its the same hub assembly as the 1970s bevel twins, thirdly, if you can find and afford all the bits needed for the conversion there is a problem with the standard master cylinder on the singles, in that the bore ratio is wrong and believe it or not the standard desmo disc brake on a single is absolutely cr-p and the drum brake is better!
It took me years of mucking about with that double drum front brake to get it to work properly, the standard brake linings are rubbish, and the standard brake cables are not great either, you need modern competition brake linings, the brake assembly arced on a lathe, and good quality nylon lined brake cables.
I have both types of brake on my Ducati's, 250 desmo disc and 350mk3 double drum, so I have been there with all this before, just for interest I didn't like the standard marzocchi forks on the mk3 and was lucky to find a pair of new old stock genuine ceriani GP fork legs which fitted perfectly and made an already good handlind/roadholding bike into an exceptional one
Cheers,
George

[blethermaskite]

Sorry should have mentioned.......the easy fix for the desmo disc front brake mismatch master cylinder problem, is to fit the rectangular brembo master cylinder from a "modern" ss600 Ducati, instant fix.
Cheers,
George

[Jordan]

A double disc front end from a parallel twin gives amazing brake power to a single.

The Grimeca 4 shoe brake fitted as standard to some singles has bosses cast into the back plates for conversion to true 4LS, which is a very good brake.
Different levers, linkages and shoes are needed.

Other 35mm fork legs/brakes could be fitted, say from a contemporary Yamaha, although these are now being collected and restored so might be hard to find.
Something Chinese?

[themoudie]

Aye Alex,

Doesn't sound right at all and I know that you aren't as heavy as my 85Kg.

As has already been asked, what spacers do you have on top of your fork springs?

What oil weight/ATF are you using and how much have you put in each fork leg? Have you measured this by volume, or level within the fork stanchion?

The Marzocchi's tend to be a fairly stiff fork anyway and using too light a weight oil can enable them to bottom more easily. Just out of curiosity what tyre pressures are you using, as they are part of the suspension.

As for the anchors, George (Blethermaskite) knows his stuff. I had my brake shoes relined by Saftek https://saftek.co.uk/friction-products-for-classic-vehicles-and-race-applications/. I then made up new cables using materials from Venhills that use a nylon lined outer cover and clevises, rather than looped cable and various other solutions, some of which I used, to secure the cable to the brake arm. Phosphoric acid, aluminium/stainless steel cleaner as a flux, a MAP X gas torch and a large bolt made into a solder pot, filled with old school plumber's lead solder, not the modern lead free stuff or plumber's flux. If you use stainless steel cable then off the shelf plumber's materials just will not solder! I have the 'T' shirt!

Have you measured the distance from the lower edge of the cable adjuster boss to the top of the brake arm to ensure that both are the same distance.

Did you centre the brake back plates in the hub before tightening the brake stay arms onto the brake back plate?

Did you use a light coat of copper or molybdenum grease on the brake and cam pivots and either the same or a 2B pencil on the actuating cam faces? I apply mine with a small artists paint brush, not a dod on the end of the finger!

This link might also be a useful read for you: http://victorylibrary.com/brit/2LS-c.htm#adjustment

Whilst the brakes are not the same as the Honda Bros or Yamaha SRX single discs, they are as good as the chromed twin discs on the front of the Morini K2 and probably better than those in the wet. The K2 also uses Marzocchi 35mm front forks and these are quite stiff and yet can be made to bottom out over severe bumps or potholes that are unavoidable.

Hope this helps, BillR

[Scottish888]

Have read all, looks like I am better to stick with the drum brakes.
All the parts are new, good route for the cables, just a heavy feel which does not give me confidence in it.
Maybe just needs more usage.
I have the spacer fitted above the springs, I filled with the weight and volume as recommended on this forum, I think 200 ml per leg? weight was light.
It feels like very little dampening on compression or rebound, there must be some dampening but it does not feel anywhere near enough.
I can bottom out the forks under braking especially if hitting a small bump.
I'll try and dig out a photo of the forks before assembly (I had the legs re chromed)
Here is a link to a fork question I asked on this forum.
It includes photos of the preload spacer and the damper mech, I managed to sort the spring and to free up the split nylon bush.
I used 10 weight fork oil, maybe try much heavier and more volume?

viewtopic.php?f=3&t=2891&hilit=ducati+250+MK3+fork+oil

Regards

[Duccout]

Hi Alex,

I guess that whatever you do, you are going to need longer spacers on top of the fork springs.

I have owned two mkIII Ducatis with the double sided drum the same as yours, and thought that they were fantastic, but that was thirty years ago, and I may not think the same today!

Colin

[blethermaskite]

Alex, when you say the front brake is "heavy" do you mean the lever has a heavy mechanical action or do you mean you need to apply excessive force to the lever to operate the brake or both? when set up correctly the brake lever should be light to pull and when the free play is taken up and you move past the return spring pressure the lever should be firm and hard with no springyness, with new brake shoes that have not been arced on a lathe (to fit the drum correctly) the lever will feel springy until after many miles of use as the shoes eventually wear into the drum dimension. There is also a balance issue between the two drums, yes there is an equaliser but it will only compensate for a little out of balance and it is very good practice to get both drums actuating as near perfectly together as possible. As I mentioned before it is almost essential on these brakes to fit good quality competition linings as most replacement linings for these are just no good, also these brakes being small have a tendency to fade under pressure and whilst it is a "bit off the originality path" opening up the air intake scoops on the brake plates and cutting exhaust holes in the plates to let the hot air out again, will certainly helps if you start to use this brake aggressively.
Cheers,
George

[themoudie]

Aye Alex,

I used 10 weight fork oil, maybe try much heavier and more volume?

Try a 15 weight fork oil, but be very careful about "more volume", you can blow the fork seals! The previous owner of the Morini 350 K2 that I now have had put 30 weight fork oil in the Marzocchi forks of the same design as on the Ducati and it was like riding a jack hammer! Fine if you are on a smooth circuit and trying hard, but not suited to our less than smooth roads up here.

Longer spacers will just increase the preload on your springs, NOT the damping of the forks.

I agree with all that George has said in his post of Fri Sep 11, 2020 5:15pm and have made the modification that he suggests for extra ventilation through the front brake drums. Though I don't use the brake as George might on a circuit, it helps on twisty downhill descents, my "bottle" isn't what it used to be!

Good health, Bill