Sharpie_Eastern
New member
- Joined
- Sep 5, 2020
- Location
- Portland, OR
Making a Brake Junction Block for a Volvo 240 (1991 Style)
Hey everyone! I wanted to share a DIY mod I put together that could help people that have a faulty brake junction block (or octopus) and cannot source a hard to find 1991 unit. If you are gonna replace your brake junction block, don't waste your money on cheap replacements that are as bad as the original design and also I go into more detail about why you should avoid band aiding your problem with a sensor plug cap. There is better solutions available.
The Parts List
Let just get straight into this. There's only 3 main you really need to make this partJunction block: https://us.gktech.com/products/ss-4-way-brake-union
-You'll need two of these. Get'em while they're hot. M10x1.0 thread pitch and built for a concave fitting (euro style)
Flat bar: https://a.co/d/epseEjg
-I used 1" wide 14 gauge stainless steel for mine. I recommend using some sort of steel because the junction block is also made of steel. You need about 4 inches of this.
Brake reservoir cap: https://www.fcpeuro.com/products/bmw-brake-master-cylinder-reservoir-cap-320i-318i-325e-34321153157
-Standard BMW e30 brake reservoir cap. This is a must-have if you case about the brake failure light.
Miscellaneous: M6-1 x 25mm | M6-1 Nylon Lock Nuts | U Nut (Optional)
-You'll need some bolts to hold this thing together. Use whatever your local hardware store has. The optional bit here is the U nut. I bought one to put on the bracket where the junction block is held. It originally is held in with a self taper style screw, which would probably work fine but the U-nut makes everything more secure. I used an M6 U nut and bolt.
The Bracket
The bracket is pretty straight forward. It's just a piece of steel flat bend bent into the shape of a U. My first go around with this bracket used no measurements, I simply eyeballed the entire thing. I've since made a template for making a bracket and drilling holes that you may use for making your own bracket. Although fair warning about my bracket image. It's made off of my already made bracket which is bolted to the car. I can't bother to remove it to get accurate measurements but this should get you close enough if you must have some sort of template. The bracket is not exactly a science, as long as both junction blocks are straight and your center hole is relatively offset from you side holes, you should be okay.Download bracket template here:
The Removal & Installation
This may sounds a little tricky but it's actually pretty simple and forgiving.Removal: Firstly, the very first line you should remove are the master cylinder lines. Just go ahead and disconnect them from the master and plug the holes on the master so you don't leak all your fluid out and have to re-bleed the master (Use m10x1.0 bleeder screws!). This will also in turn make less of a dripping mess while removing the junction block, it's as clean as you can make this process. After you've done that go ahead and remove all the lines for the junction block. This may be self explanatory but if not, start on the bottom ones first then work you way up.
Installation: Once you've got the old junction block removed, go ahead and line up the middle bottom lines and screw them in. You should be able to screw the lines in by hand, no tools required, these are not lines you want to strip out. If you cant get them in by hand, try cleaning the threads and don't use a tool till you're absolutely sure you've started the threads by hand. Once you've got those middle bottom lines in, you can go head and start bending the lines and get the junction block loosely bolted to the car. Once you've got the junction block pushed up against the mounting bracket on the car, you can start screwing in the top lines and the bottom lines. Again go by hand here, take your time and don't strip it out. Once you've tightened everything up, you should be left with only the top middle lines disconnected from the junction block. These lines go to the master and they should have been dangling this whole time. Start threading them into the junction block first, snug them up, and then go up top and bend them towards the master. Install the remaining lines back into the master. Double check everything is snug for good measure. You don't need crack down on them, just enough that they're seated and snug.
Here's a quick reference list in-case you don't like reading novels:
- Disconnect lines from Master Cylinder.
- Plug master cylinder lines (m10x1.0 bleeder screw works perfect)
- Disconnect lines from brake junction block.
- Unbolt old junction block.
- Connect middle bottom lines to junction block.
- Bend into place and attach junction block to car bracket.
- Reconnect top and bottom lines.
- Reconnect top middle lines.
- Reconnect lines to master cylinder.
The Wiring: Lastly would be the reservoir cap. This is a incredibly simple setup. You remove your old cap and install the BMW cap. For wiring you re-route your existing wire for the junction block all the way up to the master cylinder (It's plenty long enough to do this) and then you run a ground wire for the other spade on the BMW cap. If the fluid level drop below the the minimum, the reservoir will ground the brake failure wire and indicate to you on the dash that you've got an issue with the brakes.
But Why Not Just Plug the Sensor Port Old One? (Additional Information/Rant)
Now I know that it’s popular to cap off the sensor port on the original junction block, but let's explore what that means a little bit and talk about split braking systems.Understanding the plug: Firstly, the sensor port on the junction block should never have fluid in it. It was not meant for fluid and if there is a presence of fluid, it's a ticking time bomb. Fluid within the sensor ports means the O-rings have failed internally on the pressure sensitive plunger. Also where ever fluid can leak out, air can get in. In an ideal world, that plunger is suppose to push to one side if unequal brake pressure is applied to it. In reality, that plunger gets stuck from generations of old/bad brake fluid and just flat out doesn't move/work. The newest 240 with a junction block is now pushing 34 years old, (Written in 2024) that means the O-rings that have started to become hard/swell and are leaking fluid into your sensor port have become unreliable. Now you could just cap off the sensor port that is leaking but what about the plunger in the middle? You may be able to stop the leak with a plug but how certain can you be that the plunger is still dead center in the middle after 34 years? It's very possible for it to be pushed to one side after a bad brake event and not return while not tripping the light, especially if you cap off the sensor port. In that regard, you've essentially created a whole new issues that could make diagnosing brake issues very tricky. Lets look at the original brake junction block for what it is, an overly complicated way to trigger a light in your dash. Volvo must have realized this in 1991 because they ditched the idea completely and went with a regular junction block and put a sensor inside the master cylinder reservoir. Having a sensor for brake pressure sounds like a neat idea, but it's ultimately not needed. If you're having pressure issues from a loss of fluid then you don't really need to know the pressure, the lack of available fluid does the same purpose for tripping a light.
Split Brake Systems: Now there is also misconception that the brake junction blocks adds a level of safety when it comes to the split brake system. The idea being that the plunger is able to move and cut off supply to one side of the system if a brake pressure issue is present. Well again, sounds like a good idea in practice but that's not actually what happens in reality, and even with the plunger pushed to one side, a failed O-ring still leave potential for fluid to leak past and out of the system if not dealt with appropriately. So in my mind, it's actually adding more danger to the brake system because of the peskiness related to the O-ring sealing ability. The only thing retaining the split brake system in a pre-1991 240 is that plunger. So another common "fix" I've heard related to that plunger is to remove it when capping off the sensor port. That way there's no possibility of it pushing to one side of the system and creating brake pressure issues of it's own. While this may fix your issue, this basically the equivalent to having one brake line for the entire braking system, something cars manufactures haven't been doing since the Summer of Love.
The big reason not to do this is because if you experience any brake fluid leak (Which is possible on a 34 y/o car), you'll lose all your fluid entirely and have no back up solutions coupled with zero brakes. I see this fact rarely acknowledged when this method comes up as a solution related to fixing the brake junction block, there are inherent risk involved that circumvent the trouble Volvo went through to create the triangle-split dual circuit brake system and those risk should be understood before taking the route of gutting and capping your old junction block.
Hope this helps! Let me know if you have any questions or improvements
Last edited:
