Nowadays it is easy to run several diesel locomotives in tandem since all their controls are connected together, allowing the engineer to basically operate each engine from a single cab console, but I've always wondered....

How in blazes did they operate more than one steam locomotive on a consist as a helper or pusher? How do the engineers keep the two locos operating in sync without one dragging or beating its brains out against the other engine? What mechanical clues and indications were observed by experienced engineers to keep both engines working in sync?

Probably with a lot of experience and feeling for the movements of the loco.

Whistle signels were also used in the days of steam. Of course in gets complacated when as on one section of the old WM where they had to use 3 mid-train helpers and 2 on the rear to get up the Blackwater grade near Thomas, W.Va.

I'd guess it was done with practice and experience, and whistle signals between the crews
This was done in the days before radios too.

Read an article on how the D&H operated with mid-train and rear helpers.
As I recall the lead engineer whistled a signal to the helpers and then cracked his throttle.
The mid-train and rear helpers then opened their throttles.
The rear helper opened his throttle until the rear of the train started moving, actually taking up
the slack in the couplers.
With the rear helper pushing forward, some of the trains weight came off the mid-train helper
and he started moving forward, so he could open his throttle and start pushing the front half
of the train.
Now with the back 3/4 of the train moving, the lead engine would start moving too.l
Now, here's the tricky part. Each engineer has to increase throttle without slipping.
Guess they did it by "feel" and the sound of their locos to know how hard to work 'em.

Isn't it amazing it even worked at all???

That is what impresses me with the whole operation, running in the days without radio or even speed gauges. Obviously, one did not put a helper or pusher engine in the hands of a tyro. This required skill and art.

The article [TomW] was fascinating. Anyone else have further descriptions? I'd be fascinated to read them.

The article also reminded me of something about the trains in St. Louis & N. Arkansas never experienced in other routes. They actaully have slack in the couplings that can be seen and must be exploited when starting a very heavy train. Nice touch.

Steve:
If you'd like, I'll dig-up the article and scan you a copy.
I think there was another on running a D&RGW articulated in helper service.

Oh yes, I'd be very interested.