Morris Minor Owners Club

ESM show two sizes of Master Cylinder Repair Kits in their catalogue, 13/16" and 7/8". Can anybody tell me what size I need for a 1962 948 Series 3 Moggie fitted with 7" front brakes?

Thanks.

WOO, yes, the 7" front braked cars used the 7/8" Master Cylinders. The size
should be clearly marked on the outside of the casing. (important, as you have no idea if a wrong sized replacement unit has ever been fitted).

If it is the original master cylinder, then you can trust the marking on the outside, (but as Willie mentioned - the orignal part would have been a 7/8" anyway)
The replacement parts since about 10 or 15 years have been known to have the wrong identifier on the casting, but as you have to get the m/c out to see it you may as well check the bore diameter anyway.

If the m/c is leaking, it is almost always caused by corrosion in the bore around the secondary seal. This can't be fixed with a new seal kit and the whole thing will need to be replaced.

The last m/c seal kit I had was for the later m/c and one of the seals was faulty. Hopefully you won't come across that problem with the earlier m/c.

woo wrote:ESM show two sizes of Master Cylinder Repair Kits in their catalogue, 13/16" and 7/8". Can anybody tell me what size I need for a 1962 948 Series 3 Moggie fitted with 7" front brakes?

Thanks.

My Farthing's worth would be that given that you will be doing some serious swearing to get the M/C in in the first place an exchange M/C might be better than replacing the seals .. At least if it fails and you have to take it out again you have someone other than yourself to blame

Willie / Ray / Justin

Thanks for the information, perhaps from the comments it would be best to 'bite the bullet' and go for a new M/C. Is there any advantage in fitting a 13/16 in place of the original 7/8? If not I'll put in a 7/8.

Incidently, any ideas why the put a reduced bore unit in the later cars? More pressure?

Robin

Hi Woo
As you know my mog is within a few build number of yours.

I can confirm that the 7/8 inch MC was fitted to your model.

The 13/16 got fitted when the front brakes were changed from our 7 inch to 8 inch. Better brake pedal pressure.

regards
Ty

I fitted a new M/c only 2 months ago. Its only about £36 Plus P+P so not too bad, almost not worth the mucking about replacing the seals.

If you find any Bore corrosion (highly likely) its a bin job.

(Oh I must send that old m/c to JLH)