Hi guys,

I am currently replacing the rear wheel cylinders/hoses/shoes and was going to continue this afternoon. The car is a '63 850. The backing plates look like so, with the locating pin on the right.

The wheel cylinders I was sold are the opposite way around - locating pin on the left.

On research now, the 850 and Cooper S have 5/8" cylinders and the regular ones are 3/4". I'm assuming I can't just drill another hole on the left hand side of the backing plate to use the 3/4" ones?

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My backing plates had a hole on either side...when i went from 3/4 to 5/8 cylinders someone had already drilled the other hole for me

So yes...just drill another one. Carefully!

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1975 Clubman
1152cc, 40dcoe weber, RE83 cam, GRed head.

I had this same problem recently. I opted to drill the new cylinders on the opposite side - carefully, and importantly, no deeper than the original holes!
In the end it probably matters little whether you do cylinders or backing plates.

Matt

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'68 Deluxe w/Metro engine

The much safer option would be to drill the backing plate (mate)

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"Show me the Mini!"

It only looks easier. Hard to drill it right, if on the car (try it, haha).
It is much easier to redrill the cylinders as Matt did, IF you have the gear (which I do). PM me if you want them done, it's only 10mins work to set up and drill the 5/32" hole in the right place, on my mill.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

The reason the hole is in the wrong place is because you have the wrong cylinders - but yes, you can use the cyls you have - by drilling the back plate.

I THINK (may be the wrong way round) that the larger cyl will give increased pressure and increased risk of rear lock-up.

Cheers, Ian

Thanks guys, it might just be easier to try and return them at the shop for the right ones. I don't like mucking around to save a few dollars on brakes

Yep, I was not sure about the effect of different sized cylinders, don't want to risk it. High school maths makes me think the same hose pressure over a larger area would be less pressure on the shoes?

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In my case, I had the wheel cylinder diameter I wanted, and both were the same. At the time I just figured the spare parts system had declined such that they only made left cylinders. Or right.
Whatever the case, it shouldn't be this hard!

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'68 Deluxe w/Metro engine

5/8" rear cylinders are used on a Cooper S to prevent locking. I still had 3/4" ones on Barney after fitting S discs. Trust me, rear wheel lockup in the wet @ 110KMH on the F3 was scary stuff.
Rule #1- fit front discs, better fit 5/8" rear cylinders too.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Just checked my cars - all rear wheel cylinders have the dowell pegs on the left side - same as the pic. The 60s car backplates have 2 peg holes each, the 80s car has only one peg hole in each backplate - both on the left side.

If you have discs, as the good doctor said, you must fit these if you have discs. Returning them to the shop for different ones will be a potentially fatal shortcut.

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1975 Clubman
1152cc, 40dcoe weber, RE83 cam, GRed head.

You must have gone to a crap high school then!
Force = pressure x area.

Leaving the brake line pressure the same, if the bigger cylinders are used you'll get more braking force on the shoes - that's why they lock up easier.

Ok to clarify:

Car is a 1963 Morris 850. It still has drums at the front and back.

Standard they have 5/8" on the back

I was sold 3/4" cylinders. I was asking if these were ok to keep.

General thought is no. I'll try to return them then

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Oops didn't mean less pressure. I meant that due to the bigger cylinder volume you'll need more fluid to move it

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[quote="9YaTaH" and the Doc]

The much safer option would be to drill the backing plate (mate) [/quote]

It only looks easier. Hard to drill it right, if on the car (try it, haha).
It is much easier to redrill the cylinders as Matt did, IF you have the gear (which I do). PM me if you want them done, it's only 10mins work to set up and drill the 5/32" hole in the right place, on my mill.[/quote]

That's fine if you are an expert machinist and have "all the gear"

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"Show me the Mini!"