I took a hike for 5.5 years when someone started editing my posts. Of course this is someone else's party.  Steve (CTR)

MM edited YOUR post !??
Holy shyte....either delete (and explaiin) or post a rebute...not edit someone's words

That was not me editing my own post at 4:56AM!

I hope MM does not take sly action to make us question the integrity of this forum. Really Don, you found it necessary to remove the link to my YouTube channel?? When I mention and tag you all the time?? After all these years of being complimentary to my friends here, and giving credit and promoting their business, this sort of thing may have me change my tone, and start explaining WHY I no longer work here!

It's easy enough to get around this distasteful action. Search "Jemal shows" in any browser to get to my YouTube. And note how complimentary I am to Mini Mania.

Depends on the offset

Oh yes, the wheels will fit! Absolutely swap to disk brakes... Ian didn't mention that when drum brakes get wet, they're not much better than Fred Flintstone dragging his feet! Even Mini Mania's "budget" kit is very complete, with all ball joints, seals, hoses, calipers, etc. And really, I don't find the disk brakes any harder to pedal... even with the later bigger ones made for 84 and up Minis with bigger wheels. Not nearly as hard as when the drums have reached the point of not dissipating heat! It's a light car and having that clumsy booster unit in the engine compartment getting in the way of EVERYTHING you do will subject your Mini to lots of foul language! I probably have a video on my channel installing disk brakes on The Mighty 67 Moke that I built. It originally had the 850 and tiny wheels and the S brakes fit just fine... I'll try to post it here, or go to my channel.... nearly 250 mostly Mini how-to-videos that should help pass the time, and teach you almost everything you can do to a Mini! Lots of new content... I'm stuck at home too! 

I was unaware that you had aftermarket rims. They may fit or may not?

So I need to change wheels too? Currently there are 4.5 x10  minilite copies all around  ('S/T' in center hub).  Thought as long as I got the 7.5" version I would be ok?
Kim

Your 850 rims won't fit with Cooper S disc brakes.

Hi Kim,I guess I'm answering for the same reason you're asking.... it pretty quiet round here too.

Q1. Generally I would agree with Steve that discs are a good idea .. but its worth asking why discs are considered an upgrade.  Basically discs didn't really stop as well as drums but they continued to work when the drums were giving up.  Its all about heat dissipation.  

This is best illustrated on a long downhill run with sharp bends.  For the first couple of corners the drums on my Daughter's 1100 Clubman were probably as good (or maybe even better) than the S discs on my Traveller.  However, by the fouth or fifth ...and definitely by the tenth.. heavy slow it is obvious that discs are the way to go.

If you spend your time in the way suited to an 850 (my first car and something I did a lot of miles in) then drums are a good idea. Although, they do need a bit more maintenance than discs.  However, if you live in a hilly area and drive in a way that the original designer didn't intend, then discs are worth considering.

Q2.  You need to think about a booster system.  Many people will poo poo the idea; but you fit discs for their fade resistance.  And harder pads handle fade better but take more effort to produce the same retardation. I've done both and definitely prefer the boosted approach.

Fitting has (IMH no real  gotchas.  Assembly is the reverse of disassembly.  The only tricky bit I can think of off the top of my head (depending on your mechanical ability) is shimming the ball joints - although you can use the ones you've got if they're in OK condition.

Q3.  Its up to you to look around and see what might do with freshening up..  Inner lower arm bushes??  Tie rod bushes?  You're going to get new bearings and seals anyway (discs uprights/hubs are different from those you currently have .... and may or may not be part of the kit you are considering..) If your current master cylinder is OK I see no need to tamper with it.  ..And I didn't bother to change the rear wheel cylinders on my Traveller when I changed to front brakes .. the rear brake limiter seems to look after things; I've run it like that for years without any concerns.

Good luck, 

Ian

PS Just remember that once you move away from "standard" (even though the bits might be standard on another model) everything may not line up perfectly in your application and you have to be prepared to do a little problem solving beyond what you can find in the manual.

1.  Any upgrade that will improve safety is a good upgrade.  Back in '63 my 850 suffered from brake fade, etc.
2.  Take off the old, put on the new, but then we are talking about a 50+ year old car.
3.  The conversion to disks on the front adds around 1" to the track.  This is why the Cooper 'S has a spacered rear drum.  You might consider 'S drums, new shoes, and Steve has already mentioned the rear slave cylinders.  

Until you get into the project you won't know what issues/gotchas/hard spots there are.  You will probably need new seals - but then are they included with the kit?  The suspension cones - might be time to replace them, track rod ends? Check what tools are needed torque wrench, cone compressor, etc.

My first mini was an 850 with drum brakes. Yes 7.5s would be a perfect upgrade for the basic 850 or most any power upgrade
you may consider. I'd go ahead and install a new master cyl. You need to balance the rear wheel cyls to your disc. 1/2 if light
never run full tank or passengers, 5/8 if using 165 tires or heavier car. Care should be taken installing front brake hoses. Some
are handed side for side. Be prepared to replace hard pipe it can be old. I'm about to remove Metro vented Turbo brakes from
a mini and install non vented four pot alloy fronts and super mini fins rear. Send me a cell number and I'll text you pics. Contact
info in profile. Steve (CTR)

Hope all are well,

MK1 850 Morris 10" wheels, magic wand

Thinking of converting to 7.5" discs in the front from the drums.  Not sure why beyond I can social distance in the garage.   Looks like I can order a kit with all the front end bits that need to be swapped.  1) Is this a good upgrade?   2) What are likely issues/ gotchas/hard spots in the conversion? 3) What else can/should I do as long as I have everything apart? (seals?)   No particular problems just idle hands looking for entertainment.......

Kim