Master cylinder-11" brake combination - part numbers

[twodoorgaz]

Howdo folks,

I appreciate that "how do I upgrade my brakes" has been done to death - but I just want to make sure that this combination sounds OK.

I'm building a 1972 SWB SIII and this week's job is the brakes.

I would like to end up with 11" front, 10" rear, servo-assisted dual circuit brakes.

I've already have a large stock of late SWB and early LWB brakes (servos/pedal boxes/drums/backplates/etc) and will be making my own brake lines.

This is the combination I am planning:

Front 11" LWB/1980- SWB drums, backplates, wheel cylinders and sundry parts.

Rear 10" 1980- SWB drums, backplates, wheel cylinders and sundry parts.

My question is regarding the master-cylinder.

The easiest thing is to use the late, rationalised master-cylinder used on late SWB and LWB SIIIs (p/n NRC6096). However, they are expensive, and are of a slightly different design to the earlier units which wouldn't look quite right in the engine bay (I'm a bit of a rivet counter and like period upgrades over later parts). Britpart are the only replacement supplier and I'd rather have a better manufacturer (Bearmach or OE).

So, that leaves me a choice of 569671 (m/c for those pre-1980 SWBs fitted with the optional dual-circuit 10" system) or 90577520 (m/c for those pre-1980 LWBs fitted with optional dual circuit brakes). Both of which are available from Bearmach quite cheaply.

My logic says that I should get 90577520 - the early LWB m/c as I would have the same twin cylinder front/single cylinder rear combination as a 109.

Does this make sense - matching the master cylinder to the wheel cylinders?

Ta.

[secondjeremy]

2Leading Shoe brakes produce a nice self servo effect when going forward - and thus stop better for the same pedal effort as a single LS brake.

Payback is that they need adjusting more frequently - which is one of the reasons that they have a LARGER diameter master cylinder (gives a heavier pedal)

The only difference the master cylinder is going to make is to the weight of the pedal and the frequency with which the brakes need adjustment. It won't affect the balance.

I have SWB diesel S3 with the optional servo brakes - which work well but are not very exciting (mind you a 2.25 diesel hardly needs brakes as I don't use it for towing). I have had a SWB with a Prima engine and LWB brakes (with servo) which were much better.

Many dual line master cylinders have different diameter fittings for one circuit on the master cylinder (and PDWA as well i think)

[Phil Hancock]

IIRC the SWB 2 line master has a single bore size the full length and the LWB has 2 bore diameters along its length so the front/rear balance is different, also the pipe connections are different ways round depending on SWB or LWB.

I would suggest going with the std system as done by LR when they went twin line with the 11" fronts.

[Retroanaconda]

Yep, NRC6096 is what you want

One bore is larger than the other as above, and the outlet ports are also different sizes (one's M12 and one's M10 I think, or the imperial equivalents).

[ejparrott]

Yep, NRC6096 is what you want

One bore is larger than the other as above, and the outlet ports are also different sizes (one's M12 and one's M10 I think, or the imperial equivalents).

Thats the one my '83 88" had from the factory, and my 109 currently supports.