DAF-YA-126 Recovery

[BigCountry001]

Saving this post for new adventures... hopefully

 

[BigCountry001]

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That's sad, but it makes sense. Logically I would imagine that the wheel cylinders will be next. Hopefully you can find a rebuild kit for them and the MC as well. A little bit of very fine grit emery cloth to polish any rough spots will be useful as well.

Seems good though. You found the weakest link, then you found the next one. No need to waste any more brake fluid. Go ahead and replace the cups in the wheels now before you soak your brake shoes in fluid. (hate to be the bearer of bad news)

You caught me mid post! lol. Lightning Fast!
I accidently submitted when looking at the preview. It's been edited with more detail now. I'll put the cups on the maintenance list if I ever get it road worthy! Thanks!

 

[Mullaney]

You caught me mid post! lol. Lightning Fast!
I accidently submitted when looking at the preview. It's been edited with more detail now. I'll put the cups on the maintenance list if I ever get it road worthy! Thanks!

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Interesting how that works. I spotted your post, then went back to look again and saw your new information. Glad to see that you had already started working on the MC rebuild. Sounds like you will be making steady progress and I offer good wishes for success!

 

[Terra1936]

Some time after the move to Texas, the rubber brake lines started weeping. I get it, it was a 57 year old truck, and the best I could tell the brake hoses were original. The brakes got so squishy that it wasn't safe to drive anymore. Luckily, I was able to find replacement rubber hoses from my supplier in the Netherlands.

After replacing the hoses, we were bleeding the air from the lines. When the system finally built a good amount of pressure, the brake pedal suddenly dropped to the floor, and refused to build pressure. After crawling under the truck, I found that the master cylinder was squirting fluid out of the front of it with every pedal push. It seems the new hoses allowed it to build more pressure than the seals would hold...

Welp, now we order more parts from my regular supplier and wait for shipment from the Netherlands. After receiving the gasket kit, I took the master cylinder to a friend's house that knew more about replacing seals than I did. We disassembled the cylinder and honed the rust from the walls. We reassembled it with the new seal kit and I took it home and re-installed it. After another bleed-session, it never built pressure.... We looked all over and finally noticed that when we pushed on the pedal fluid was shooting straight up, out of the reservoir!

Not fully understanding what the problem was, I assumed that the seal for the piston was letting fluid leak past it. I pulled the cylinder out and replaced the piston seal with the old gasket (because hey, it was the front cylinder seal that was the leaky one, right). It still shot out of the reservoir. Still not thinking it through too much, I ordered another seal kit from the same retailer that Swfb mentioned above. Swapped out the seals, and it happened again. I had probably pulled the master cylinder on/off the truck 30 times by now and was getting disheartened. After a little while, I took a closer look into how the cylinder worked. The YA126 has a similar master cylinder design to it's bigger brother, the YA328. The important difference is what's inside the piston... Photo credit to Hoppa69 at http://www.ya126.nl/forum/viewtopic.php?p=39861&hilit=hoofdremcilinder#p39861.


View attachment 864459

Some of the things in the pic are hard to see, but I had been focusing on the black rubber seal in the center, which seals the piston/cylinder interface. However, if you look to the left of the piston, you'll see 4 (5 if you can see the circlip) small pieces. These pieces form a cylindrical check valve inside the piston. On the return stroke, it will pull fluid from the reservoir to backfill and small leaks. The hole in the side of the piston feeds this valve, and the hole in the left end is where it all fits. From right-to-left, the small rubber seal fits on the end of the brass square-ish check. This is held down by a lightweight conical spring. (this spring is like 10% of the spring in a ballpoint pen, it's light folks). That's held in place by the copper plate that interfaces to the piston itself and held in by a circlip. The circlip in is the center of the picture next to the copper plate with holes, it's almost the color of the table.

After countless times of installing/removing the brake master cylinder, I noticed the small brass piece was crooked in the piston. I started re-installing it flat every time. Every time I removed it I found that it was crooked again. I finally found the problem! This brass piece was difficult to remove the first time, and I'm sure that I damaged it. It is such a tight fit inside of the piston, I'm that was the design feature to keep it in proper alignment. When I forced it out, I probably rounded off a corner just enough to let it turn sideways.

Welp... You are all caught up. I haven't found anyone that sells the small brass piece, and I haven't found a whole replacement brake master cylinder assembly yet. So, it's sat for 7-8 years at least now. I had lost hope finding parts and really stopped looking for a while. I'm starting to get a little more motivation to work on it again, so if anyone has a line on a replacement DAF YA 126 brake master cylinder, let me know! I'm not really wanting to rig up a different part in it's place. It's a critical safety system part, and don't want to sacrifice any braking ability. Also, the truck is mostly original, and I've been inching my way back to 100% stock/original.

Hopefully my hard learned lesson can help someone before they damage anything!

Can a local shop make one? Can it be 3D Printed? Can you fit another master cylinder? Just throwing ideas out! My rear wheel is leaking and I have no pressure now. Next months project.

 

[Swfb]

I recieved your parts today and will try to ship them tomorrow!
I'm not sure what time it takes to get from the Netherlands to you, it might be 1 to 2 weeks.

I hope after that you can continue working on it!

 

[Terra1936]

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That's sad, but it makes sense. Logically I would imagine that the wheel cylinders will be next. Hopefully you can find a rebuild kit for them and the MC as well. A little bit of very fine grit emery cloth to polish any rough spots will be useful as well.

Seems good though. You found the weakest link, then you found the next one. No need to waste any more brake fluid. Go ahead and replace the cups in the wheels now before you soak your brake shoes in fluid. (hate to be the bearer of bad news)

How did it all work out?