My son has been complaining that the brake failure idiot light on the dash of his '90 240 sedan has been flickering. Sometimes it gets a little brighter but for the most part, it is very dim and flickers slightly with the engine vibration.

We checked out the braking system and there are no indications of any leaks, brake fluid is up to the top and there doesn't seem to be any diminished braking. Car stops fine, etc. We found that by disconnecting the wire from the "octopus" that the dash light goes out.

Has anyone out there had a failure like this? I'd hate to go replacing the octopus if it isn't failing but that is my prime suspect at this time.

Any input would be greatly appreciated.

 

No ideas??????

 

Do we assume that the octopus is the brake proportioning valve. If so and when you remove the wire and the light goes out? If this is the area you are talking about then at some time the valve has shifted because of one of the brake pistons possibly sticking. You would have to center the valve if this is the problem. If this is not the area you are talking about then you need to be more descriptive. The resident mind reader is off this week. Things like year and model would also help.

 

Hmmm... Year and model was in my first sentence - '90 240 Sedan.

What I am referring to as the 'octopus' is the valve that separates the two brake circuits in the car (my understanding the brake proportioning valve is under the rear of the car and reduces the braking of the rear wheels in proportion to the front). The octopus has a little piston that divides the two braking circuits. If one of the circuits develops a leak, the piston will slide towards the leaking circuit since the circuit without the leak will have higher pressure. When it slides, it also makes a connection that turns the brake light on.

What I am trying to figure out is if this is a problem with the octopus or if there is some other underlying problem.

 

The valve has shifted and the wire has been grounded. That is what turns the light on. You also may have a bad switch. You should be able to remove the switch to check it out . If it is OK you would need to recenter the piston in the valve assembly. If the valve is OK then you would need to check each brake caliper to see which one is the problem. Although there may not be a leak one of the calipers is weaker causing the pressure difference to shift the valve.

 

Is there any sort of leak at the brake junction block valve area? They fail quite often...possibly leaking on one side would cause this if the piston shifted?

 

Thanks for the replies...

Jagtoes - how can I check the switch to see if it is bad? Also, what would be the procedure for repositioning the piston? I thought perhaps opening a bleeder on one of the circuits would shift the piston but I don't know how I could re-center it.

Swift - no leaks are detected on the octopus. From what I have read, that leaking is the typical failure of this component. Since it isn't leaking, I'm hesitant to replace it.

 

I don't recall off hand but either you can unscrew the switch or it will just pull out. If it is in a rubber bushing it will pull out if it has a hex on it then it will unscrew. There should be no brake fluid coming out of this location. On some units there used to be a tool that you insert to recenter the valve. The other method had end caps that you removed and pushed the valve back in. Check the bottom of the switch and you should see the reed type contacts. Make sure they are not pushed together.

 

To check for leaks at the junction block, be sure to peel the rubber boot back from the switch...even a little is too much. Early models had a screw in brass switch which was much less prone to leaking. Later models are plastic and I believe, a friction fit. Removing these later style switches is self defeating, my experience is they will never seal again, even with a new repair set up. There are large cap screws on either end that can be used to recenter the switch. They are extremely tight! IMHO, they are the Achilles heel of the 240 brake system. I do not spend much time trouble shooting it frankly. Often, they reset themselves with brake bleeding. When they don't, I replace them. Speaking only for myself, I don't need a brake failure light. My experience has been the light comes on as the pedal hits the floor! So...I replace the brake junction block with the one used on 91 non ABS 240's. It has no switch...