Series 3 Dual circuit brake fittings sizes

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TheMegaMan

TheMegaMan

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I'm now moving on to the brakes on my rebuild. And I know I've got a bit of a mule, here.

It's a 1978 SWB, so has the 10" brake drums all round and imperial 3/8 fittings on the slave cylinders and flexi hoses.

However, the quirk is that it's got dual circuits and a servo, which I understood came with the brake upgrade that put 11" drums on the front. I suspect a previous owner decided to improve safety a bit, by going dual circuit. This includes a 5-port shuttle valve as well as a dual-circuit master cylinder.

The bit that's puzzling me is the fitting sizes. Both the master cylinder and the shuttle valve seem to have the same 3/8 UNF (24 tpi?) fitting as the slave cylinders on one circuit, but has slightly larger ports on the other circuits.

Does anyone know off hand what size this is? Metric?! And why are they different sizes, anyway?

I'm making up my own pipes, so just need to know what fittings to get.

Cheers,
Adam
 
You'll have to be careful a bit, you may have a metric dual circuit system (from 80 or 81 on) or something dual circuit from an older LWB. If it's had a metric system fitted then everything should be metric apart from the wheel cylinders. Be careful with the UNF as it will screw into a metric master cylinder and make you think it's right but will blow out under pressure. I seem to remember from my metric system that one port on the Master Cylinder is bigger than the other. Maybe buy a some metric and UNF fittings and carefully try them in the ports to see where you're at.
 
Agreed, be carefull and do your best to stick with one system. Mine was a mix and I found it easier to go to imperial (which was right for the year too) as the master cylinder and wheel cylinders seemed easier to get in imperial. The master cylinders have a standard and a large size to prevent the pipes being put on the wrong way around. If you google it you will see plenty of posts on the issue. I seem to recall its 3/8 unf and 7/16 unf, they are easy enough to get hold of but often people make up their own lines and re-use the existing nipples. The flares and the cylinder holes are not the same for metric and imperial. Avoid copper pipe, buy curpo-nickel and pay for a decent in-situe flare tool.
 
Yeah, I am aware of the 3/8" vs 10mm fitting similarity. I have some 10mm fittings, too, and I'm 95% sure that the smaller holes really are 3/8" imperial.

I've been looking at what other fittings are available that I can try (got a selection coming from ebay), and am now guessing the larger holes are 7/16" UNF. 12mm is a possibility...

A problem I have now is that the fittings at the wheels are 3/8", so I've been using 3/16" copper tubing. However, if the other end of the pipe (at the shuttle valve) actually is a 7/16" fitting, then they need 1/4" tubing. So bang goes my plan of just fitting the appropriate fitting on the same pipe...

I wonder where the 'official' pipes would switch from one size to the other...
 
rob1miles said:
Agreed, be carefull and do your best to stick with one system. Mine was a mix and I found it easier to go to imperial (which was right for the year too) as the master cylinder and wheel cylinders seemed easier to get in imperial. The master cylinders have a standard and a large size to prevent the pipes being put on the wrong way around. If you google it you will see plenty of posts on the issue. I seem to recall its 3/8 unf and 7/16 unf, they are easy enough to get hold of but often people make up their own lines and re-use the existing nipples. The flares and the cylinder holes are not the same for metric and imperial. Avoid copper pipe, buy curpo-nickel and pay for a decent in-situe flare tool.
Click to expand...

Ah, I'd already replied before I saw your post..

Why do the pipes need to be the 'right way around'? Don't they share a common bore in the master cylinder, so the pressure from both master cylinder ports will be the same - it's the size of the slave cylinder that determined the effective brake bias, isn't it? I need to google this, I can see!

The existing nipples are too corroded and mangled to use again. I do have some new ones on order, but that's not going to solve the issue I have with the pipe bore.

Avoid copper pipe? Hmmm....Wish I'd heard that before I made up almost a complete set! :-( Any particular reason? I have borrowed a fairly good flaring tool that seems to be doing a pretty good job, but it's not in-situe.
 
Firstly the larger fitting (7/16) is still sized for the 3/16 tube ( you can get a 1/4 tube fitting in 7/16 so make sure you get the right one). Some masters have the same bore but I would be wary of assuming all do, but also I think it may be about which get pushed first. Its extremely confusing as several sources of info disagree about which way around to pipe the unions. On a LWB I have front line to rear brakes.
 
+1 on Rob's post. I encountered this issue when I did the brakes on my LWB but only after I bought enough 3/8 fittings and none of the 7/16 ones!
I've used both copper and cupro-nickel and both are fine - copper is a bit easier to bend but quickly tarnishes, especially when it gets splashed with road salt.
The bore is indeed the same in the master cylinder and there's a lot of views on whether it's important to pipe the front of the m/c to the front circuit or vice versa. Personally, I don't think it matters, but probably best to replicate the setup you had before.
 
Thanks again. The fitting suppliers I had been looking at on ebay were only listing 7/16 fittings for 1/4 pipe, so I assumed that's all that was available. But looking specifically for 3/16-compatible fittings has now listed a few for the smaller pipe - exactly what I want. Ordered both 24tpi and 20tpi versions, so should be sorted whatever. Only this is where I probably discover they're metric after ali! :)

I am intending to hook up the larger ports (most rearward on the master cylinder) to the front brakes, as that's how it was before I dismantled it (using the 3 x 7/16 ports on the shuttle valve to feed two pipes to the front brakes), and that's what everyone seems to suggest...but I'm just puzzled why it would make a difference and why they go to such lengths with different sized fittings. Seems a pointless restriction. And also means I have to cross pipes over each other. But never mind...it shall be done!
 
If you have a master cylinder designed for the TLS 11" setup its probably going to be a bit large for a standard 10" SLS setup. It should still work but the pedal will be heavier.

A agree that it should make absolutely no difference which port goes to the front or back, the correct small bore master cylinder for the servo assisted 10" drum setup has the rear port going to the rear brakes but apart from the bore size it looks almost identical to the 11" master cylinder which is traditionally plumb the same as yours.
 
If you look in the workshop manual you will see diagrams of the various brake pipe set-ups with the various splitters and valves.
 
The problem with that is I don't think Land Rover ever fitted the domestic market civilian 10" drum SWB with a dual line servo assist setup. I might be wrong but the only references I've seen for this are in a Series 3 Lightweight.
 
Rodeo Joe said:
If you look in the workshop manual you will see diagrams of the various brake pipe set-ups with the various splitters and valves.
Click to expand...

I can see a few diagrams, but it's rather vague, and I can't see anything as specific as which master cylinder port goes where. Maybe I have a different workshop manual or I'm looking in the wrong place...?

I've been using the parts catalogue as a indication of how things are connected up, but it doesn't really cover my combinations.

Citizen Kane said:
The problem with that is I don't think Land Rover ever fitted the domestic market civilian 10" drum SWB with a dual line servo assist setup. I might be wrong but the only references I've seen for this are in a Series 3 Lightweight.
Click to expand...

Yes, I think this is true. I'm pretty sure this was a conversion by a previous owner, that seemed to resemble the last diagram in the book, with the two circuits feeding down to the 5-port shuttle valve, two ports feeding along separate pipes to the front wheels, and one smaller port feeding to the rear (T-piece mounted on the diff). The routing of the pipes to the front wheels was pretty atrocious (just sort-of running diagonally across under the battery base), so I'm doing a much tidier job this time. I'm sure Land Rover would never have routed the pipes like that. It also looks like my shuttle valve is fitted upside down compared with the diagrams I've seen.

I've got a new 569671 master cylinder to fit. https://www.lrdirect.com/569671-Brake-Master-Cyl.-Dual-Circ-Swb/?keep_https=yes describes this as "Dual line brake master cylinder part number 569671. This fits the Land Rover Series SWB models to 1980. This is for servo assisted brake models, also fits the Military lightweight models." so I hope will be compatible with SLS 10" drums all round. I've checked and it appears to have 3/8 and 7/16 UNF ports, so matches the shuttle valve.

I've read a few comments about leaking shuttle valves/PDWA causing problems, so while it's off, I'm planning to give it an overhaul. I don't suppose anyone knows what the internal oil seals are, do they? Are they simple O-rings or more complex/specific seals? I'm loathed to take the old one apart and risking damaging them in case I can't get replacements, and I've not seen any kits or parts for these. And the whole unit is rather pricey.

Sorry for the rambling. I obviously know I need to get the brakes right, so it's comforting to hear your suggestions and comments, that will help me get this sorted.
 
The PDWA switch has a couple of o rings inside. It can be a pain to take apart and spare parts are non existent as far as I can tell (if anybody knows different please say so because I need to overhaul one as well!) so if its working don't mess with it.
You can still get the switch part for it though.
pdwa brake valve.jpg
 
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Do correct me if I'm wrong on this but my understanding was that the shuttle valve really only makes sense on a single circuit system, on a dual circuit it just makes bleeding more difficult. My S2A LWB has been retrofitted with an S3 servo and dual master cylinder and the shuttle valve has been removed.
 
Thanks, Joe. I think I'll take your advice and leave it alone until it causes a problem. If/when it fails, I guess I need to consider repairing, replacing or bypassing. A decision for another day...

I know it's a controversial device, but I was planning on keeping it as it's a handy connector to save me having to make up exceptionally long brake pipes. :)

Rob, I think they *only* work on dual circuit systems, as they work on the pressure difference between the circuits. In a single circuit system, there's no other circuit to compare against.
 
Some years back I had a 1979 SWB that had 10" drums all round and a servo, so this was available as a standard option, maybe only for a short while until the 1980 move to 11" TLS brakes. And yes, 569671 is the correct m/c listed for this combination of dual-circuit 10" with a servo.
The PDWA may be difficult to overhaul. Even if you can find the o-rings, the internals are likely to be corroded and I've never seen any spares listed for it. They are still available new, but at a hefty price.
@rob, you need two brake circuits for the PDWA - basically it detects a difference in pressure between the circuits and activates a warning light (although you're likely to know when you lose a brake circuit without needing a light to tell you - assuming the light is working in the first place). In my opinion, a fluid level switch in the m/c cap is a better idea because it alerts you to a slow leak, but not all dual-circuit master cylinders will accept a float switch, as I found out after I bought one...
 
ExMil109 said:
Some years back I had a 1979 SWB that had 10" drums all round and a servo, so this was available as a standard option, maybe only for a short while until the 1980 move to 11" TLS brakes. And yes, 569671 is the correct m/c listed for this combination of dual-circuit 10" with a servo.
Click to expand...

Thanks for confirming.

ExMil109 said:
In my opinion, a fluid level switch in the m/c cap is a better idea because it alerts you to a slow leak, but not all dual-circuit master cylinders will accept a float switch, as I found out after I bought one...
Click to expand...

I was planning on having both...belt and braces! That's assuming the contact type (normally closed or open) means I can wire the cap in series/parallel with the PSWA switch. I've not got around to checking whether I can fit a float cap to my new master cylinder reservoir, yet. Are the caps a standard size? Assuming there are no mouldings below the cap, is one of these likely to fit? https://www.ebay.co.uk/itm/174064844968 Yeah, I know it's a 'how long is a piece of string'-type question, but just wondering how you went about finding a cap for yours.
 
I second throwing the shuttle valve it is only an indication of a circuit failure does not stop loss of fluid from that circuit you can get the same warning from a level switch on the fluid reservoir. The fluid reservoir has a internal baffle in it so all the fluid can not go to the failure.
 
Well, I tried one of these:
0017512_brake-fluid-reservoir-cap-with-2-pin-plug-and-fly-leads.jpg

https://www.carbuilder.com/uk/brake-fluid-reservoir-cap-with-2-pin-plug-and-fly-leads
and the cap part fits on the master cylinder no problem, but as Blackburn said, there's a baffle inside the m/c that separates the two fluid compartments, and the float tube hits the baffle. So, no joy...
Various Defenders have a dual-circuit m/c and a fluid loss switch, so there may be a later m/c that can be used, but I never investigated this (and Defenders all have disc brakes, so maybe that isn't an option). It might be possible to trim down the float tube to clear the m/c baffle, but this is on the (long) list of tasks waiting for a rainy day...
 
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