mk1-forum.net

Hi

I have an early (the car was registered in September 1964, I don't know when it was made as Gaydon do not have the files for this car) 998 cooper that needs the brake master cylinder replacing. Does anyone know what is the correct master cylinder bore size for this car?

It has the earlier centre pivot sun visors and black crackle interior mirror (dry suspension).

The reason why I ask is I have been told two different sizes!

Thanks for any help.

Nathan

Hi Nathan, I've never heard of different bore sizes for that cylinder, there is a difference in the size of the fluid reservoirs on the single line cylinders, GMC171 being the standard one & GMC172 having the larger reservoir as fitted to the Cooper S & early 1275GT. I always used the larger GMC172, but for originality, I believe that the standard GMC171 is correct.

The 998 Cooper used a .625" bore cylinder, and was the only Mini to do so. It was used from 382832 on (Austin) and 382183 (Morris). I don't have the BMC part number at hand, but the Unipart number was GMC105 and the AP/Lockheed number was 4222-921. An old stock specialist like Nick Rogers (Min-E-Bitz)
may be able to help.

Thanks for the help. The bore size you suggest is the one I thought it should be, but I became uncertain after a few vendors said it should be another one.

I will get in touch with Nick and see if he has any available.

Nathan

Sorry Nathan, I am obviously like one of those people who said it should be another one, I must admit I obviously have never encountered a genuine 998 Cooper cylinder, I bought a 1966 Cooper in 1969 & by then it had already been fitted with a Cooper 'S' master cylinder, which seemed to work very well. I hope I didn't mislead you & that you find the cylinder that you need.

Nathan, I think I already replied to this on another board. As Mike says, I have NOS of these 0.625 bore cylinders.

Is it possible to have a large reservoir 0,75" ?
I wanted to reassamble my new one with new minispares kit,but the rubbers look to small?
Is the first step in the cilinder a larger diameter?
I meassured about 5 mm inwurths.And saw 19mm equals 0,75"?

Yes. The Austin/Morris 1300GT (the ADO16) used a tall can reservoir with a 0.75" bore cylinder. Its Lockheed number is 4222-138.

Yes the first part of the bore is the same size, so that the washer and circlip on the push-rod are the same for all cylinder sizes. (All cylinders of that type, that is)

Am I right in thinking that the 997 / 998 master cylinder changed when the "Brake intensifier" was deleted?

I don't know when it was made as Gaydon do not have the files for this car

If it is one of the cars in Gaydons missing production record ledgers it was built in August or the first half of September 1964. There were no changes to the brake master cylinder during this period.

About the brake intensiefier.
Are there any rebuild kit's for those?
I've got 2 of them and like to restaur them a bit.
Didn't yet take them apart ,because i don't need them.