That makes sense to me.  The extra (second) hard gasket seems to be about the right play.  It was a matter of using two gaskets which was slightly thinner than the shim washers I used for the test.  If brakes again start to lock I will have to try three, but will evaluate based on your wisdom in the previous post.  Everything presently appears to point to the master cylinder linkage not having the right distance of travel with my stock install.

There is no adjustment in the pedal assemblies so if that has been altered you will see where it has been heated and or welded, afaik all the later model manual pedal boxes are the same except the later servo type ones they have a different brake peadal i believe. As far as shimming the master up to make things work it is possible but you need to make sure you have the play/looseless needed as it is in the other Mini you have and comparedd it to. You could do it with a gasket or shorten the rod from the pedal to the master or make that rod adjustable but if it were my car as it is the brakes i would want to know why i have the problem and resolve it correctly.

I've delayed my response as I'm trying to get a grasp of the suggestion the master cylinder is essentially manufactured wrong?  Currently this  is the second new master cylinder being used.  I'm sending the car off for a few days for timing and carb tuning so can't remove the MC yet again for the suggested comparison.  I'm therefore not able to release the pedal assembly from the MC just now.  I do think the pedal assembly is ok.  It is possible I suppose that I have altered the play somewhat by a DIY install of a electric brake switch, instead of using the classic pressure switch.  Since the pedal assembly is one that didn't come from this vehicle it seems possible that it may too be the culprit for messing with tolerances.  So ... if adding a second hard gasket appears to remedy the issue, and braking appears normal for a very brief test drive... what danger is it to permanently, so to speak, shim up the MC?

As you have the plate and gasket in place there must be another issue here, you should not have to shim up the master to make it work and imo it is not the right thing to do as a permanent repair. If you still have the old master cylinder remove the new one and compare the linkage lengths, also the brake pedal on a Mini always sits higher than the clutch make sure it still does before dissasembly. If the master cylinder linkages are the same length then i believe you have an internal issue with the new Master cylinder. You could just shorten the linkage but i would return the one you have purchased and get another one.

this thread is a continuation of another thread with some pictures "rear brakes locking up.......".   Hopefully that helps. 

Yes I realize the test suggested a couple weeks ago addressed the length of stroke of the master cylinder.  But I guess in my naivety,  I only understood and assumed it related to the correct install of the sponge gasket, the metal plate, and the hard gasket.  Since I had the correct parts I moved on.  Believe me I would like the $300 back for the new parts that replaced new parts.  I do appreciate your patience with my limited mechanical perceptiveness.  I never in a thousand years would have guessed (and obviouly didnt understand) that I needed to raise the master cylinder more than stock.  I only understood that there was the perception I was missing a gasket or even the metal plate.  Anyway that is my perspective today and still appreciative of that help with my brake situation In a location where Mini services are almost nil.

This thread is confusing to me. I think it would be worth the effort to upload some actual photos of your carand the brakes. Could be something simple that we could just spot by looking at it. Probably not, but maybe. 

Not having a go at you (really but this was the first solution offered to you by cupcake 2 weeks ago....

Paint is not your problem..  that would only make things better....

Cheers, Ian

Sorry for not getting back sooner, just had to do some work, beside getting this brake issue figured out.  Hey, I looks like the master cylinder needed more spacing!  For testing as suggested, I added the width of a thick washer between the master cylinder and the hard gasket.  The washer is about the thickness of the hard gasket, or just a bit thicker.  There is much more suitable play at the pedal.  And after a brief test drive of about 4 blocks, (I don't have time to do more presently) the braking feels right, and no grabbing.   A longer test drive is needed, of course, but there seems to be a solution.  Interestingly, the assumption that the parts are all to spec, must be an incorrect assumption; particularly (perhaps) the pedal assembly is off just enough to cause the problem.  As I type this, I'm thinking the POR 15 paint brushed on with two or three coats, that I used for the pedal assembly is in fact quite thick, compared to just a coat of spray paint.  Fractions make a difference! (that is my new saying for the week!)   Thanks to all for bearing with me on this marathon of two threads about rear and front brake "tight" issues.  We may be able to drive the PUP more confidently, soon. 

Yes loosen the nuts and tempararly spave up with washers and tighten back down. if there is no clearence the brake fluid/pressure cannot exhaust back to the master cylinder causing the brakes to "stick on"

As the master cylinder is a bit of a pia to remove just for $hits and giggles and to prove whether or not the master cylinder is good why don't you loosen the master cylinder up enough to duplicate the plate thickness and drive "carefully" around the block to see if it makes a difference.

Well I don't know if the police got close enough to see more than my tail. Your story is amusing, thanks!

There is a soft sponge gasket, the metal plate, and the gasket between the plate and master cylinder.  There was free  movement of the master cylinder linkage before installation.  If I am checking correctly, with  current install, I find the linkage has no looseness at the pedal connection.  When depressed the pedal moves linkage about 5/8" to 3/4" ( by hand) On the PUP.  There is no other play.    I tested the same on my Saloon and found quite a contrast: some looseness at the pedal to linkage connection. And about 1 1/2" play before pressure is felt (by hand).  The pedal assembly was a used replacement (rhd) for the original, lost sometime during the 5 years of body work at body shop.  I'm pretty sure the firewall is original so those demensions should be original.

The policeman was just trying to figure out what car that was!  When I had bought my Mini, I temporarily lost the title but just drove it with the English plate.  I stopped at a light next to a police car.  They wound their window down, so I felt obliged to wind mine down.  They then said " what kind of car is that?  What size wheels are they?" " cool!"  I smiled and let them pull ahead when the light changed!!

Well if the brakes are binding I wouldnt worry about the overheat just yet! If all four are binding then the issue is probably with the master cylinder, do you have any free play in the linkage at the master cylinder? there should be a plate and gasket under the master cylinder where it meets the bulkhead is it present? if not their it will cause this issue.

Ok.  rogress thus far. Got the pup on the ground.  Made two circuits around the block.  An all four (for sure the rears) locked up without touching the brakes on this circuit.could not move vehicle the last twenty feet into the garage.  Jacked up front and and rear and couldn't turn any wheel.     Released pressure at the master cylinder conection.  Rears then turned free!

Went for a second drive.  Went around the block four or five times.  Used brakes several times on this drive with success. Stop and start felt close to normal at most attempts.  Sometimes maybe a bit tight.  Interestingly, unexpected as I pulled into the garage there was again significant resistance, as,I tried to  park.      I think a side issue, I'm overheating and lost coolant as I parked.  And it is apoorly tuned 850 at this point.  Trying to get it to run across town 1 miles to a guy who can tune it. I may have to trailer it!  He used to race Minis.  Now into Hondas, etc.  Not sure he will want to tackle more.  I was hoping to give an all ok, but not do.  And amusingly, the next plan is to do a custom exhaust.  It is a bit too noisy for my around the block ventures.  As I went to park the second time I caught a policeman patrol car heading my way.  robably too noisy for one particular neighbor on our block.  The  policeman didn't follow me down the alley.  Whew!

On 7.5" and 8.4" Mini calipers the `dust shield' is a rubber wiper, retained by a metal ring. These can eventually load up with dust, dirt etc and jam the piston from returning freely. Time for a new kit then, even if the main quad seal is not leaking.

Almost but not quite, ever wondered why caliper seals are square (quad rings) and not O rings? well originaly they were but they soon found that the pads would stay in contact with the disc's and cause excessive heat build up so they came up with the quad ring. The square section seal actually rocks over when the piston moves out and the piston is pulled back when the pressure is released by the quad ring returning to it's natural position. It's amazing what you remember from tech school 40 odd years ago!!

Good info.  Thanks all.  Yes I meant calipers not the Discs were upside down.  And the two pics were examples.  I  think the info that the hand turning would be hard, helps clarify.  Definitely will put paws on the ground, hopefully this afternoon.  All new parts throughout ... including the braided lines to calipers.

thanks again.

His car is (apparently) the one with the bleeder down, braided cable and Yokohama tire, BEFORE he corrected as suggested by Chck Heleker. The other photo with the caliper correct and new rubber hose is somebody else's, posted for comparison. The way I read it, he has his calipers on right way round and has bled it successfully. His remaining problem seems to be dragging pads when up on stands, but has not test-driven as of his last post, as suggested he do by Minimike1.