Well the new master cylinder came in for the Monte Carlo and one thing I can at least say about this part of the whole brake situation with the car is that replacing the MC in the MC was pretty easy. Two nuts hold the MC in and there's only two brake lines going to the unit. The thing really took about 5 minutes to put in. I did gravity bleed the MC first though. Instead of doing the MC bleeding procedure (This is where you attach short brake line runs from the ports on the MC that bend right back up and into the oil chambers so when you pump the brake pedal it pushes the air out into the reservoir of brake oil while sucking oil back into the line), I just filled the reservoir with brake oil then let the oil work its way down into and through the MC via gravity before putting the brake lines onto the unit. This way I can say that the MC is full of oil and not air.
I immediately tried to bleed the rear brakes, but had no luck. The whole system did the same shit where no oil made its way back to the rear brakes when I pumped the brake pedal. At this point I had already determined that the proportioning valve was bad. Well in reality it wasn't "bad" in the traditional sense of the word. After having done some research just prior to putting the MC on, I did find out on these older GM cars the proportioning valve actually has a fail safe built in where if brake pressure is lost on one side of the system (in our case the rear), when you push the brake pedal, the regular pressure on the working side will actually push a valve inside the PV that will seal the oil passages to the bad side, causing the brake light warning switch to be activated (which is built in the proportioning valve) and stop oil flow to the bad side of the system so the working side will continue to have decent enough pressure to allow for the car to be safely driven to a shop. Online forums did state that it was possible to reset this tripped valve inside the PV in order to restore operation to the PV, but there were mixed reviews on that action. Some say when the shit trips the whole unit needs to be replaced, others say the thing can be reset by removing the switch and manually moving the valve back into the standby position inside the proportioning valve. Either way this goes it will require removal of the PV, which also requires removal of the brake lines going to the unit and this in and of itself is not an easy feat due to the tight quarters made by the exhaust header and just the physical location of the PV in the first place. This is where I actually thought about getting an adjustable PV and just bypassing the stock unit altogether. I did do some more troubleshooting and other tests, like letting brake oil gravity feed to the rear brake bleeders, which in this case, did not work either since the system seemed to still be blocked. What is bizarre though is the idea that when this problem first manifested itself in the form of broken wheel cylinders, oil made its way to the rear hard, I pretty much emptied the MC with one good driving session. That's what really fucked me up because I can understand the fail safe in the PV stopping oil flow but the exact opposite had happened at first but now no oil is getting to the rear. I did a little more troubleshooting just to see if I could make something happen before I take any other measures that would cost me more time and money. I ended up using my vacuum pump to try and pull fluid down to the wheel cylinders, trying to see if maybe I can force the check valve in the PV to reset or at least open up to let fluid down. After several attempts to pull fluid down that also included pulling lines loose from multiple points along the rear brake circuit, I managed to get oil to finally make its way down to the rear wheels. Once I got oil coming out of the wheels and a brake pedal that was somewhat fair I buttoned up everything so I can try to see how things work during the next driving session with the car. We will see how things go.
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