need some help my 1990 240 wagon is having some issues... to say the least
but its now having a brake failure issue the light on the dash is on and i checked the fluids and its fine. it started with the light coming on then it started to loss pressure but the car still stops. it now continuing with that every time i start it.

p.s i don't think it matters but the main fuel pump is going out too i plan on replacing it soon. So i don't think that they are related.

 

these cars have dual brake circuits, the light comes on when the pressure in the circuits is unequal. one circuit goes to half of each front brake, and to one of the rear brakes, the other circuit goes to the other half of each front brake, and to the other rear brake, so even if one circuit fails completely, you have half braking power in front plus one rear wheel.

you probably need to replace or rebuild your master cylinder, and maybe the slaves (in the calibers) too.

 

There is a brake bias valve in on the lower frame rail left side if I remember correctly. Follow the brake lines down from the master cylinder and you will come to a block with an electrical connector on top- that should be it.




The failure light could be on for one of several reasons.
Does the car pull left or right when you brake or do you have any leaks from the braking system?


Have you had any work done on the braking system?


I think you can remove the wire from the bias valve and the light will go out. This is a diagnostic step to see if you are on the right track. DO NOT UNPLUG AND IGNORE this as it is telling you there is an imbalance in the braking system. Since this is related to the hydraulic portion of your braking system I would STRONGLY suggest that you have a professional work on this. It may be difficult to diagnose exactly what the root cause is and if you make a mistake then the brakes could fail; not a scenario anyone wants to be in.


Now that you are aware of the importance of this, it is a relatively simple system. Brake fluid from the master cylinder goes in each side and acts on a shuttle valve. If all is working as designed the pressure on each side is equal and the shuttle valve stays in the center. If there is an imbalance then the shuttle valve moves to the side of less pressure and grounds the sensor, causing the light to come on. Something as simple as having air in the system could cause it but, as I stressed previously, the braking system is essential to your survival so treat it as such.