Happy Easter,
I would like to share my mistakes, my experiences and MY OPINION regarding the brake system. I replaced the whole brake/fuel system and spent around $2200 on it. My first mistake was not bleeding the system before the engine was in - its very hard to access the proportioning valve with the engine in. The second mistake was (thought it saves me time), to buy pre-bent steel lines. From my experience on a previous project, I knew that stainless steel lines are hard to bend and even harder to get sealed. Therefore, this time I decided to go with steel lines.
My experience: The pre-bent lines didn't fit 100%, but I never expected a perfect fit and knew they will need some adjustments. The problem is, if a pre-bent brake line has a small radius bend, you can't bend it back - it would weaken the material. Big radius bends are not that big of a problem - you can make the radius tighter or wider. The same goes for the fuel line.
For example the fuel/brake lines through the cross member holes: Even though I applied grease on the lines and tried to widen the radius on some tight bends, it was almost impossible to get those lines through the holes. My car doesn't have new paint but still, I don't want to make more scratches in it. The same problems occurred on the brake lines going under the front frame rail to the brake hoses - tight radius - if not 100% correct pre-bent, hard to correct.
Anyway, I took my hours to install the brake lines with proper bends and without having tension on them. Bench bled the master cylinder and filled the system - BOOM - its leaking on several corners.
I am not a professional car mechanic and don't have a built-in torque wrench in my arm, but after 25 years working on cars and with different metals, I kinda developed a sense for torque specifications. The well-known trick of loosening and retighten worked neither, so I had to tighten most fittings really hard - too hard for my taste.
Common sense and my experience should have told me that steel and brass are not a good combination - brass is soft and steel is hard.
Even the proportioning valve itself had a leak and I really had to tighten the inline part really really hard to get it sealed.
A few years ago I worked on my Suzuki Samurai Offroad car, I redid the whole brake system with nickel/copper lines, what a pleasure to work with. They are soft, last long, easy to bend and seal right away.
My resume - an investment in a QUALITY double flaring tool (no China crap) and certified nickel/copper lines saves money, nerves, and guarantees a professional result. As I mentioned above this is MY OPINION, and I am sure if I ever remove those brake lines, the seats in the brass parts will have deep marks form that way too hard steel lines. So if someone has new paint on his car, I highly recommend thinking twice what kind of brake lines to use.
Here an example: The line to the master cylinder - way off(cross marks the point where the nipple should be), plus I had to file off some material from the nipple because it bottomed before the flare even touched the bottom of the proportioning valve.
. I used the shop manual and the technical book https://www.amazon.com/dp/1613253354/?tag=fabo03-20, those pieces of literature covered almost every subject on the 904. The only thing I noticed, the author was often focused on 70 up 904s. Therefore I always double-checked with the 69 shop manual and year specific parts measurements, offered by transmission parts suppliers.
