Disc brake fitting.

[midget]

Just need to check this as I am just about to prepare my new original mowog brake master cylinder for fitting in the van chassis which will have disc/callipers fitted later. I am aware that a valve cup has to be removed to prevent the brakes binding on.
Having studied the workshop manual and I assume this is 7H 7022. Is this correct please?

[les]

It's a rubber seal shaped like a top hat.

[philthehill]

John
The recuperation cup is the item that has to be removed when disc brakes are fitted Pt No: 7H7022 up to LCV Com No: 149536.
Item No: 14 in the BMC parts list. I do not have a Pt No: for the cup fitted to the later master cylinder but it makes no difference as the cup on the early and late cylinders is still item No: 14 and has the same purpose.
The item in question is shown as valve cup in Fig. M.8 in the BMC Minor Wksp Manual Section M.
Phil

[midget]

Thanks for confirmation. That is what I thought.
Never stripped an M/C previously. but I assume that you reassemble with brake fluid liberally applied? On that point, what is the preferable type to use..Mineral Girling or new age synthetic?

[philthehill]

Cover the seals and moving parts liberally in brake fluid on assembly.
I would recommend UNIPART universal DOT 4 or similar.
I have never felt the need to use silicon brake fluid.

[les]

Silicone seems to be down to personal choice, some say it gives a soft pedal. Having used it for 15 years I have been pleased with my choice, a little expensive but less inclined to absorb water, which certainly in my case has eliminate seized components. Although dot 4 seems to prevail.

[midget]

Many thanks. I'll stick to dot 4.
Used to use racing fluid in my comp days, but doubt if I will need to worry about boiling it in the van

[midget]

More woes with this episode. My original Lockheed (still in its greased paper and MOWOG box) tuned out to be u/s due to the corrosion in the bore. Supplier changed it for a modern one at little cost,but I will be more careful with "original" parts.
For anyone else contemplating this job for the first time will be advised that the "cap" (correctly identified by Phil) and has to be removed, is not obvious to find from the diagram in the manual. It is inside the larger seal and needs digging out.

Question is... is it worth resleeving the "original" one (which I was allowed to keep) in either S/S or Brass? If so which company please?

[philthehill]

John
Personally I would ditch the corroded master cylinder and fit a new unit.
I would use a small bore master cylinder as you can get a slightly better line pressure at the caliper. The slight increase in pedal travel does not detract from the brake operation and is hardly noticeable.
I use the small bore cylinder with Marina disc brakes on my Minor and without servo and the brakes are very good and you can feel the road through the brake pedal.
Phil

[midget]

I have a replacement from same supplier Phil. Not aware of small bore types--tell me more please. Were these for pre 8" brakes?

[philthehill]

John
There are or where two different master cylinders fitted to the Minor and each had a different ID bore size.
I will quote the relative part numbers relating to the 1/4 ton LCV.

17H7423.................finished at com number 149536
17H3621.................commenced at com number 149537.

The small bore master cylinder is 13/16" ID (later M/C) and the large bore master cylinder is 7/8" ID (early M/C)
I understand that the bore size of the master cylinder is marked on the side of the master cylinder.
Phil

[>Thomas63<]

Screenshot_20171219-164729.jpg (1.28 MiB) Viewed 1462 times

Rubber bit I'm holding comes out of the plastic cup I've pointed out.

[midget]

Yep,that's the one Thomas. Thanks for pictorial evidence.