• Hello Guest, welcome to the initial stages of our new platform!
    You can find some additional information about where we are in the process of migrating the board and setting up our new software here

    Thank you for being a part of our community!

Brakes build pressure, junction box dripping 1988- 240

OwlJerky

New member
Joined
Mar 16, 2024
Hello all,

First post here, been wrenching on my 240 for a while now but this break problem is a real curveball.

When driving the car, every time I press the breaks the break pressure seems to build until it gets to a point where the car barely crawls while my foot is off the breaks.
I used a laser thermo on each rotor and found my driver side rotor was the hottest after a fair drive around town. I also noticed when inspecting the caliper that one of the lines attached the break junction box had a drop of break fluid hanging from it and my break fluid revivor was low.

My question is which part of my breaks would you suspect is causing the issue? Usually when I read form posts about break pressure its that they are spongy when this type of leak is present but that isn't the case here.

My neighbor said it may be restriction in the soft line leading to the driver front wheel because I recently changed my master cylinder out for a new one.

Any ideas?

Thanks!
 
The Junction boxes are a known failure, the sensor tends to start leaking, and could be letting fluid go from one circuit to another
 
You probably have two issues going on. A seized caliper due to corrosion or the soft line restricting the flow till the caliper failed. So you need a caliper, a set of rubber flex lines or the stainless steel ones. Rubber is fine for a daily driver. Then the brake junktion internal seals have failed and you need to replace that. Bleed the brakes thoroughly using DOT4 fluid.
 
Took the wheel off and the break pads out yesterday. Seems like the top two pistons move a bit but not as much as the bottom two pistons. I'm going to replace the rubber line and try to work some break lube behind the rubber boot to see if that helps the top two pistons. I think the leak from the junction box was from a build up of pressure.

After putting some break lube where the pads move across the caliper I noticed the problem isn't as apparent for the first half of a short drive. But after driving for a while the pressure eventually builds.

Will report back with more findings soon.
 
If you're not going to just replace the sticky calipers along with the hoses, I'd at least get a caliper rebuild kit and do the job properly.
 
Anyone have a source for a Genuine Volvo brake junction box? After some research people advise against going with the after market.
 
Last edited:
I've never had an problem with the aftermarket ones. The ones I bought were made by Bendix the supplier to Volvo so look for that brand if possible. If you get one supplied by Beck Arnley that should be reboxed oem.
 
Avoid MTC parts at all costs, it's the MTC junction we're having issues with, it's cheapest and probably most common one.
 
MTC is the only one out there. Hiperfauto and planetman were rebuilding the originals. You could also try rebuilding yours. Have you looked at the cleanflametrap site?
 
... Have you looked at the cleanflametrap site?
I don't think you can find it referenced there, but this is the compilation picture you probably recall.

octopus6.jpg
 
You probably have two issues going on. A seized caliper due to corrosion or the soft line restricting the flow till the caliper failed. So you need a caliper, a set of rubber flex lines or the stainless steel ones. Rubber is fine for a daily driver. Then the brake junktion internal seals have failed and you need to replace that. Bleed the brakes thoroughly using DOT4 fluid.
Agreed. I've experienced both. In my experience the caliper issue will sort itself as the pad wears and the piston moves outward. I'm leaning toward hoses, but good idea to rebuild calipers while brake system is open. semi-pro tip: press the brake pedal to the floor immediately after opening brake system and the master seals will close off the outgoing lines, so you won't drip dry as fast, or at all. If your master is old, this may also kill the seals, so you might consider budgeting in that for replacement too.
 
I recently discovered a leak in my junction block as well. I was going to replace the o-rings in mine, but it looks like that won't work. One of the pieces of the shuttle valve is pitted (the lighter areas on the left piece in the pic below), and there was some chunky gunk in each end of the junction block. Chalking that up to not flushing the brake fluid often enough.

AP1GczMaDbb0qsnyqc3pB3a3_Fl9XG_tsExRCfbb0X1nvtBXNUtQrlbNn5bJ9sZVatHouDgV1NzeL5W-2S2yplugWXrp9F3td-KrGl4nyJppgYRg9dOwdihWMaD9swdtCcUOoxKy-AZwpwWt9iBaBvdn9cYsmw=w1588-h893-s-no-gm


Very sad that this didn't occur before Hi Perf Auto stopped selling the non-sensor block due to NLA.

Does anyone have the part number for the ATE reservoir cap with the float sensor handy?

I'm going to approach this by sealing the area where the shuttle valve resides permanently to maintain 2 separate brake circuits. Plug and crush washer for the sensor port, M12x1.0. Downside is the brake failure light won't indicate an issue with one of the circuits, just low fluid in one of the reservoir chambers (right?) , but I suppose it's better than nothing. Would a reservoir with a single large chamber be better? Does this exist?

The aftermarket MTC option doesn't seem great given multiple reports of leaks not that long after installing them. Maybe they just need better o-rings - has anyone opened one up after they started leaking to see what failed internally?
 
Here's the BMW part number for the brake fluid reservoir cap with float switch that I was including with the brake distribution block.

34321153157
 
Back
Top