The tool I would recommend is expensive but a very nice tool...

https://www.eastwood.com/professional-brake-tubing-flaring-tool.html?wickedsource=google&wickedid=Cj0KCQiAr5nKBhCpARIsACa_NiOCxo9Tdb7ZxmHMruB2h5o6q90RPhM5N2lJ1bggqy0RMY7xCKeZeJwaAjSrEALw_wcB&wickedid=730838757115&wcid=22174107587&wv=4&wickedsource=google&wickedid=Cj0KCQiAr5nKBhCpARIsACa_NiOCxo9Tdb7ZxmHMruB2h5o6q90RPhM5N2lJ1bggqy0RMY7xCKeZeJwaAjSrEALw_wcB&creativeid=730838757115&wcid=22174107587&wv=4&gad_source=1&gad_campaignid=22174107587&gclid=Cj0KCQiAr5nKBhCpARIsACa_NiOCxo9Tdb7ZxmHMruB2h5o6q90RPhM5N2lJ1bggqy0RMY7xCKeZeJwaAjSrEALw_wcB

It's pretty difficult to make the correct flair if you don't have a really quality tool

I repaired (replaced) a rear brake line using a prefitted piece of brake tube from OReilly Auto. They had a large selection hanging on the wall that they let me browse through. Take the old one with you to match it. A piece of string or wire run down the ends will let you get the correct straight tube length. Use wood screws in a piece of wood to get a smooth bend.

That line only runs down to the warning light switch. Not too long.

https://www.oreillyauto.com/detail/c/american-grease-stick/american-grease-stick-steel-8-inch-brake-line-adapter/ags0/paay311?q=brakeline+repair

Edited December 21, 2025Dec 21 by Zed Head

42 minutes ago, Zed Head said:

I repaired (replaced) a rear brake line using a prefitted piece of brake tube from OReilly Auto. They had a large selection hanging on the wall that they let me browse through. Take the old one with you to match it. A piece of string or wire run down the ends will let you get the correct straight tube length. Use wood screws in a piece of wood to get a smooth bend.

That line only runs down to the warning light switch. Not too long.

https://www.oreillyauto.com/detail/c/american-grease-stick/american-grease-stick-steel-8-inch-brake-line-adapter/ags0/paay311?q=brakeline+repair

This is perfect - I’ll pick this up and call it good!

Check the fittings. The one I posted is just an example. There are many different sizes. Good luck.

Edited December 21, 2025Dec 21 by Zed Head

So I threw in the towel for the first time with this car and took it to a repair shop - kinda bummed I had to do that, but it's better than getting the brake fluid bath for the 15th time.

Anyhow, I drove it down the street to the brake repair place (.5 miles away) at 10mph, with my hazards on, braking by modulating the e-brake, and got many of the 'I'm speeding past you in the left lane to show you I'm mad' folks driving by - and that's fine.

I discovered that pressing the brake pedal now does absolutely nothing to stop the car even though the drum's reservoir is full and the master/drums are properly bled. The disc's reservoir (the rectangular reservoir closer to the cabin) is empty because that is the side of the cylinder that is leaking through the fitting. Do the drums not work if the disc's reservoir cup is empty? The brake repairman is curious if it could be the proportioning valve, but that wouldn't make sense to me since pressing the brake pedal while bleeding the rears shot brake fluid out. That said, that was when the disc's reservoir cup was full and bled.

I’m not entirely sure where you’re seeing pressure. Under normal circumstances, there should be no noticeable pressure in the reservoirs. However, there are situations where a small pressure build-up can occur, usually when certain seals begin to fail.

How it works - in a nutshell:

• When you apply the brakes, piston no. 1 moves forward and passes port A. Once this happens, brake fluid can no longer return to the reservoir, and pressure begins to build. Fluid then flows through port Y to the front calipers, while the pressure also pushes piston no. 2 forward.

Note: Seal X on piston no. 2 prevents fluid from passing from the first (disc brake) chamber into the center section of piston no. 2.

• As pressure builds in the first chamber, it continues to drive piston no. 2 forward.

• Piston no. 2 then passes port B, which prevents fluid from escaping back to the reservoir. Fluid now flows through port Z to the rear drum brakes.

At this point, the system is in balance.

Leak scenarios that can cause pressure in the reservoirs

The most likely cause is seal X. If this seal leaks, pressurized fluid from the disc brake chamber can pass into the drum brake reservoir. With each brake application, fluid is transferred from the disc brake reservoir to the drum brake reservoir, causing a gradual pressure build-up. You will also notice the fluid levels in the reservoirs changing.

Another possibility is leakage past the piston no. 1 seal, located directly beneath port A. If this seal leaks, high-pressure fluid from the disc brake chamber can pass back along the piston and enter the reservoir. Because the chamber volume is much larger than the volume around the piston shaft, roughly half of the leaked fluid can end up in the reservoir, creating pressure.

A similar situation can occur with piston no. 2 and seal B.

There’s more going on internally, but this overview should help explain why you’re experiencing what appears to be pressure build-up in the reservoirs.

The conditions that can lead to pressure build-up in the reservoirs:

• The reservoirs are completely full of brake fluid

• The rubber bellows in the reservoirs are in a compressed position

Under these conditions, there is very little room for fluid expansion, which can result in pressure building up in the reservoirs.

Edited January 17Jan 17 by EuroDat
Adding scetch

4 hours ago, EuroDat said:

I’m not entirely sure where you’re seeing pressure. Under normal circumstances, there should be no noticeable pressure in the reservoirs. However, there are situations where a small pressure build-up can occur, usually when certain seals begin to fail.

How it works - in a nutshell:

• When you apply the brakes, piston no. 1 moves forward and passes port A. Once this happens, brake fluid can no longer return to the reservoir, and pressure begins to build. Fluid then flows through port Y to the front calipers, while the pressure also pushes piston no. 2 forward.

Note: Seal X on piston no. 2 prevents fluid from passing from the first (disc brake) chamber into the center section of piston no. 2.

• As pressure builds in the first chamber, it continues to drive piston no. 2 forward.

• Piston no. 2 then passes port B, which prevents fluid from escaping back to the reservoir. Fluid now flows through port Z to the rear drum brakes.

At this point, the system is in balance.

Leak scenarios that can cause pressure in the reservoirs

The most likely cause is seal X. If this seal leaks, pressurized fluid from the disc brake chamber can pass into the drum brake reservoir. With each brake application, fluid is transferred from the disc brake reservoir to the drum brake reservoir, causing a gradual pressure build-up. You will also notice the fluid levels in the reservoirs changing.

Another possibility is leakage past the piston no. 1 seal, located directly beneath port A. If this seal leaks, high-pressure fluid from the disc brake chamber can pass back along the piston and enter the reservoir. Because the chamber volume is much larger than the volume around the piston shaft, roughly half of the leaked fluid can end up in the reservoir, creating pressure.

A similar situation can occur with piston no. 2 and seal B.

There’s more going on internally, but this overview should help explain why you’re experiencing what appears to be pressure build-up in the reservoirs.

The conditions that can lead to pressure build-up in the reservoirs:

• The reservoirs are completely full of brake fluid

• The rubber bellows in the reservoirs are in a compressed position

Under these conditions, there is very little room for fluid expansion, which can result in pressure building up in the reservoirs.

Wow that’s pretty interesting - one if my seals must have been going but I don’t recall fluid levels changing between the reservoirs. That said, I suppose it’s a good thing I replaced the master even if it was my failed attempt at doing that to fix the leak where the master meets the line at port Y. The brake repairman is making a new metal line for that.

However, the rear brakes don’t seem to be working at all now, (but fluid will come out of the rear wheel cylinders when the bleeder is open and the pedal is applied). The car will stop with the e-brake pulled but the pedal does basically nothing.

I know in my triumph spitfire if a brake line loses pressure, the distribution block has a plunger that slides over and locks the leaking line so pressure no longer flows through it. In my case however, brake fluid does come out of the rear cylinders if I open the bleeder valve though.

Could that be what is happening on this car? As of now, I have no brakes in the rear for some reason.

Edited January 17Jan 17 by chaseincats

15 hours ago, chaseincats said:

The brake repairman is curious if it could be the proportioning valve,

The leak has to be fixed first. A good shop will know how to do that, and bleed the brakes. Shouldn't really be speculating until those two things happen.

If the rear brake shoes aren't adjusted correctly the piston in the MC can bottom out before the shoes make contact with the drums.

The Datsuns don’t have an excess-flow preventer like the Spitfire, so that won’t be the issue here. If the braking system were hydraulically unbalanced, you should normally get a signal from the brake warning switch. That said, these switches can deteriorate over the years and may no longer operate correctly.

I’d be more inclined to suspect a blockage somewhere in the brake line after the brake switch. This could be in the brake proportioning valve or in the single line running back to the rear axle.

The car is now in the garage, and they should be able to find the problem.

A simple step by step troubleshooting would be to loosen the brake line fittings one by one, starting just after the brake switch and working your way back to the T-piece at the rear axle near the fuel pump.

At some point, when you crack a fitting with the brake pedal applied, no fluid will come out. The blockage will be located between the last fitting where fluid did flow and the fitting where it didn’t.

The photo of the fuel pump is showing the bronze coloured T-piece just above it

Sorry I didn’t jump in earlier; we might have found the problem sooner.

Edited January 17Jan 17 by EuroDat

I just realized that, apparently, Nissan got rid of the brake warning pressure differential switch in 1978. They replaced it with the fluid level warning switch.

And, a possibility on pressure buildup might be if there is a large air bubble in the front calipers. The bubble compresses when the pedal is pressed and will squirt quite a bit of fluid back in to the reservoir when the pedal is released. That is how I figured out that my calipers were on the wrong sides, with the bleed screws on the bottom. Something to share with your brake guy if he has problems. A not uncommon problem.