The B & M and Maine Central entered into a co-operative management agreement about 1932 with the approval of the Interstate Commerce Commission. Besides the through running of motive power on passenger trains between Bangor and Boston, most top level managers were the same persons for both roads and most were headquartered in Boston. It is my understanding that the Maine Central's financial condition was a lot worse than the B & M's at the time. The top slots in the Executive, Operating, Engineering, Finance, Purchasing and Traffic Departments were the same for both roads.
It is no coincidence that both roads had similar color schemes for diesels and style of searchlight automatic block signals.
Interestingly the Auditor of Passenger Receipts for both roads was in Portland and Freight Receipts in Boston. The Maine Central struck out on its independent course in 1952 when E(dward) Spencer Miller was elected President. It took several years for the break to be complete. People on the BRAC (now TCU --Clerks) roster had to make an election, move to Boston from Portland or move from Boston to Portland. Low seniority people probably didn't get to chose. When I started at the B & M in 1968 and for a number of years thereafter, there were still people on the B & M and MEC Clerks' rosters who had a certain notation next to their names. Caught in the B & M/MEC split they still had one bump back to their original roster.
One of the reasons for the break up might have been that by 1952, the prospects for the MEC were probably better than those for the B & M. MEC entered the 1950s with a substantial arrearage (non payment) of 5% preferred stock dividends since 1932. These were cumulative; if not paid this year, it is added onto next's years and keeps accumulating until paid. While this won't trigger a bankruptcy, it leaves the preferred holders in a very strong position in the company's management. B & M also had even more substantial arrearages on several preferred issues with almost no chance of paying them. B & M resorted to a refinancing under the Mahaffie Act which wiped out the arrearages but diluted holders of lesser stock --common. B & M became embroiled in a nasty stockholders' suit over this. It was resolved in B & M's favor but dragged out for a time. MEC's newly independent management worked throughout the 1950s and paid off a significant amount of the arrearages. In 1957 alone, MEC paid $20 in dividends on the 5% preferred--wiped out 4 yrs. of back dividends.
MEC diesels also sometimes worked to Worcester and I believe some had B & M cab signals as they sometimes went to Troy, NY to work of mileage owed to B & M.
By the way, when the B & M got hold of the Eastern about 1884, it also got control of the MEC because one of the only bright Eastern financial decisions its management made was to buy a big chunk of MEC stock. However, that was disposed of in a Mellen move orchestrated by J P Morgan.