Complex sentence: Up until the 1970s, a "cord" (although by that time it was chain) was still used, which ran the length of the carriage and connected to a valve at one end which opened the brake pipe.
Split into simpler sentences: Up until the 1970s, a "cord" (although by that time it was chain) was still used. This ran the length of the carriage and connected to a valve at one end which opened the brake pipe.