Chromed discs?

jeanster · Post by **jeanster** » 06 Oct 2006 21:07

New to Morinis. Just took charge of a 500 Strada.
Why are the discs chrome plated? Should they be re-plated if chrome worn through? Is this to show a measure of wear and allow for refurbishing rather than renewal?

Ballacraine · Post by **Ballacraine** » 06 Oct 2006 22:07

My take on it is that they were fashionable in the late seventies and this was Morini following a trend.

Nortons and Triumphs had them.
The chrome was purely cosmetic. They thought it looked better than leaving them as naked cast iron and them developing a light rust coating if it rained when they were parked.
The Brembos on the Guzzis and Laverdas were left as cast and were better brakes for it.

Now to answer your question, I give you a question....

Are you after orignality or practicality?

If the former replace or rechrome, if the latter have them skimmed, but be aware there is a minimum service thickness and be guided by that.

Hope this helps some!

Nige.

jeanster · Post by **jeanster** » 06 Oct 2006 22:31

Thanks for reply.
Might rechrome at next tyre change though agree they might perform better left as bare casting. If this is my biggest problem then I'll have a sweet bike.

What does your sign off mean? Was never all that good at Latin but feel I should brush up on all things Italian now (especially the old stuff).

Ballacraine · Post by **Ballacraine** » 06 Oct 2006 22:47

I would agree with that.

They do perform better without the chrome & obviously the fresh chrome will wear through again at some point, dependant on how generous the thickness is.

My signature translates loosely as:

'Always in the s**t, it is only the depth that varies!'

Nige

Brubru · Post by **Brubru** » 10 Oct 2006 13:13

Nige,

Are you sure the discs are chrome plated? I have always thought they are stainless steel. Even badly worn and scratched, they do not corrode.

Bruno

Post by **SteveMRC** » 10 Oct 2006 19:34

The disc on my 500 Sei were chromed. The chrome used to pull off in thin strips.
I had an engineering shop grind the remaining chrome off. They were not very happy when I came back to collect them because they had ruined three grinding tools on them, they were very very hard.

Now they go rusty if rain is forecast sometime in the next week

Weeelp · Post by **Weeelp** » 11 Oct 2006 10:32

My 500SEI has iron disks now; -a few years ago they were chomed. i never bothered getting them re-chomed when they started to go as they work so well in the wet. In fact I think they work better ( have more feel) in the wet; -Gawd know why.

moriniuk · Post by **moriniuk** » 08 Mar 2007 09:18

The reason that the cast iron discs work better is that the cast iron has higher coefficient of friction than the chrome, ie it's grippier. If the chrome is flaking or worn it should be chemically removed and not skimmed. The de-chromed disc will perform better but it will rust and wear out the brake pads quicker. In my experience using de-chromed discs when racing, the pads will wear very quickly.

EVguru · Post by **EVguru** » 09 Mar 2007 10:25

The Morini discs are pressed Steel, not cast Iron.

How much the decision to go with the plated discs was to placate the Americans, who seemed to have an aversion to rusty brakes, I don't know. I can't imagine Morini doing it if it cost more than Cast Iron.

With the right pads the HARD chrome plated discs work fine, even in the wet. With the wrong compound (EBC don't seem to work) they're useless. With the single disc setup, the master cylinder is the wrong size, fit the 250 version.

Ballacraine · Post by **Ballacraine** » 09 Mar 2007 23:01

Now that is an interesting snippet there about master cylinders, Paul.....

Would that mean the standard m/cyl of my single disc 1977 350 Sport should be sufficient for a twin disc upgrade?

Nige.

EVguru · Post by **EVguru** » 17 Mar 2007 10:03

Yes, standard 350 master cylinder is perfect for twin discs.

Many early disc brakes bikes had oversize master cylinders and are now often crisicised for a 'wooden' feel to the brakes. Sometimes this is down to the fact that the original brake material had a very high 'mu' (friction coefficient) but wore quite fast, compared to modern materials. On cars particularly there were different grades for different models and gradually all these grades have been replaced with just the hardest (most heat tollerant) one. A perfect example is the Triumph Dolomite. All models have the same discs and callipers, which were OK on the 1300, but inadequate on the 1850 and downright dangerous on the 2 litre 16 valve Sprint. Triumph simply fitted harder and harder pads and more and more powerful servos to suit.