Replacing brake master cylinder, but with what?

[JimK]

Evening all,
as per the recent thread, my brakes aren't and there's suspicious dripping liquid on the drive under the car. So, I've resigned myself to changing the master cylinder. I have a pretty good idea now of the system layout and the procedure for removal, having cross-referenced the BMC and Haynes manuals and the Techtips page from this site.

Question now is: do I have to replace the current M/C with one exactly the same? I have a '65 saloon, with Marina-based discs and 175 tyres. I currently cannot lock the front wheels on a dry road, so there's scope for improvement.

Can I beef the system up a little? What other options are out there? A servo is an obvious suggestion, but I've come to like the directly-connected feel of an unservoed system.

Ta.

[bigginger]

I can't think offhand of any option but the same. Bear in mind that there are two different cylinder bore sizes (can't remember when they changed) and the need to remove a washer from the M/C for disc brakes.

[JimK]

I know there are two different bore sizes, and I don't know which I have... I guess they might have changed with the 948-to-1098 switch?

I would guess that with the alledged extra fluid displacement of calipers that the larger bore M/C would be OK, whichever one I have.

Carlo told me at Sadmog about removing the washer for disc use, and attempted to explain which washer that was. Alas I failed to grasp what he meant so I might need a diagram with a big arrow pointing to the right one. I don't want to remove the wrong one

[lofty1000]

I've lost my instructions for mine, but if you compare your old seal setup with your new MC seal setup you will see which one needs removing.

PS. MC's is a job I most detest! why they put it there...

lofty

[RogerRust]

Dont despair yet I have heard of the banjo connector on the back of the M/C working loose and leaking. It's worth checking first.

What brake set up do you have? Even with the standard 8 inch brakes at the front it should lock up in the drywith standard tyre, but your wide tyres will have more grip.
The options are 9 inch Wolseley brakes at the front or discs. Its a matter of you pays your money you takes your choice.

[JimK]

Dont despair yet I have heard of the banjo connector on the back of the M/C working loose and leaking. It's worth checking first.

Ahh, I'll have a look. Thanks.

What brake set up do you have? Even with the standard 8 inch brakes at the front it should lock up in the drywith standard tyre, but your wide tyres will have more grip.

Standard drums back, Marina-based solid discs. 175 Dunlop SPs on 14" alloys. The tyres have massively more rubber on the road than the 145s on Wifey's Trav, the car corners like it's on rails.

[RogerRust]

Here's is a usefull hint that I got from RayO'L. Don't try to undo the banjo at the back of the master cylinder because access is very poor. Disconnect it at the joint with the rear flexible and pull it forward you can then get at it to undo it.

I've never had a problem disconnecting the torsion bar so I think I'd do that rather than try and bend it down out of the way. Its not a bad job.

[les]

I was under the impression that discs should not lock wheels.

[JimK]

I was under the impression that discs should not lock wheels.

Why would that be? Seems a little odd...

[les]

Maybe something to do with the mechanics of the design, but locking the wheels is not a good thing and will not stop the car quicker, in fact you lose control.

[bigginger]

I was under the impression that discs should not lock wheels.

I hope that I'm not just missing a joke here, but for the sake of safety I'll just say that unless you have ABS fitted, disc brakes can and WILL lock the wheels

[JimK]

Controlling the brake power such that you brake at the maximum point of friction, i.e. just before the wheel slides, is very hard indeed. If you can't lock the brakes then it's very likely you can't brake to the maximum friction point.

You should be able to lock the brakes, but you shouldn't actually do it.

[les]

If the wheel doesn't lock, I suppose you can brake as hard as you like! As I first said it was my impression. I don't want to stand trial here!

[bigginger]

My understanding too, and what ABS does for you, if you have it. Not that I've ever driven anything which did

[JimK]

Sorry Les, didn't mean to sound confrontational. It's late and I should be in bed...

[jonathon]

It has sometimes been said on this forum, that certain uprated drums are so good that they can lock up all four wheels. In saying this, the point of better brakes seems to have been misunderstood, and that a locked wheel equals good brakes or increased power of them. My view is that a locked brake is totally useless in stopping the car, and what you need is improved clamping pressure for a given rate of braking efficiency. Discs both servo'd or non servo'd in my view can offer this combination with a greater degree of feel and repetition.

[JimK]

improved clamping pressure for a given rate of braking efficiency.

I need an explanation of this, I can't get my head around what it means.

Locked wheels are not as good as rotating wheels at stopping, that is certainly true. What I meant was that if you can't lock your wheels it's incredibly unlikely that you are able to brake to the point just before the wheels stop rotating.

[bigginger]

Eeerrrr - you're agreeing with each other

[JimK]

I had a feeling that we were, but I couldn't grasp Jonathan's comment about clamping pressure so I wasn't sure...

[jonathon]

Yep we do agree Jim. Now I've written it like I have I cannot think of another way of saying it. I know what I mean just as well I don't teach!!!