Thread: Series III dual brake conversion - which master cylinder?

There is no residual pressure valve in the late SIII dual circuit master cylinder.

Many thanks, I think I'll go for NRC8690. Are the early defender 110 master cylinders plumbed the same as the Series III 109 - i.e. front brake lines to the firewall end of the master cylinder?
cheers
Phin

You may find the difference is metric threads.

I was going to use metric threads on the brake pipes on the master cylinder end, and 3/8UNF to where the PDWA would be. I'm planning on replacing the PDWA with a T piece for the front and an in-line connector for the back brakes. Most of the reading I've done on the PDWA suggests that they aren't much good as they only actuate a warning light and are a potential fail point.

I just had a look at the parts manuals, it looks like late series III plumbed the master cylinder the opposite to early defender.

SIII - NRC6096:


110 - NRC8690:


This looks like the arrangement was reversed going from SIII to 110.

thanks again
Phin

Hi Phin,
the parts illustration you have posted for the Series 3 actually shows the layout for the 88 inch models, which used a 7/8" diameter master cylinder with the section closest to the firewall working the front brakes.
The dual circuit 109 inch models used a 1" diameter master cylinder with the section closest to the firewall working the rear brakes.
The shuttle valve/brake failure switch is fitted to comply with Australian Design Rules and is a requirement for registration standards. Removing this would technically make the vehicle unroadworthy. An alternative replacement switch is available, but you may need to change the pipe fitting nuts. (different thread)
New Series 3 109 dual circuit master cylinders are available locally.
Have you seen my posts regarding the front disc conversion?

Series disc brake conversion --- I did it my way

cookey

Thanks cookey - I had a look at your front disc conversion and must admit I was very very tempted, it's just I've already tracked down and bought all the parts for the 6 cylinder drum conversion (save for master cylinder and a decent booster as the one I have is only 6").

I was looking for a booster and came across the bigger defender 80 series models, some of which will take an early master cylinder, and others of which are set up for a later type master cylinder. If I got the later tower assembly with the later booster, would it still work with drums all round? The master cylinder I'm looking at is this one:


This would give me a bigger booster and perhaps partly solve my warning light issue, as there is a brake fluid warning actuator in the reservoir cap.

many thanks again,
Phin

I did some further reading on the later type master cylinder over the weekend. From what I can gather, the later master cylinder (STC441) was used as more or less a direct replacement for NRC8690, with the rest of the braking system basically unchanged. Bore size is apparently also the same at 25.4mm. I also read that disc master cylinders should work fine in drum applications as All this suggests to me that it should work fine - any chance I've missed something? The only thing I could think of of is possible proportioning changes putting too much pressure to the front.

cheers
Phin

When I did the Series 3 many years ago (about 96 or 97 it was an ex army series 3 with the 6 cylinder motor), just got hold of the series 3 pdwa to put the existing brake lines into and fitted the defender master cyclinder straight up to the booster.

Then got a mobile guy out to make the brake lines from the master to the pdwa, metric on one end, the old series ones on the other.

Worked a treat after that.