I have a bad combination valve on my 87 dakota that has been in a garage for tge past 15 years. It onky has 44xxx miles. My question is am I able to just run off the master cylinder straight to my calipers? Or is it imparitive I replace it?

 

Combo valve does two things. It restricts flow to the rears, so they are not locking up before the fronts even start to grab, and it is also a safety, if one circuit fails, a valve will move to block it, so you still have *some* brakes. That said, the valves rarely fails..... what makes you think it is bad??