I've worked on a customers EX100 several times in the past few years, but it's one machine he doesn't have a manual for yet. Now the EX100, like most excavators, has two main pumps. The way the pumps work is that each provides power for several functions. For example one pump runs say the boom, swing, and left track, while the other runs the dipper, bucket, and right track. Because of that, when your walking, both pump flows are merged together to maintain straight travel. If the flows weren't combined, the flow robbed to operate the second function would cause a lower flow to one track than the other, in turn causing the machine to travel to one side.
That said, the best I can remember, the EX100 is also like most excavators in that it has one system relief, and then each function has it's own port relief.
As a result of the way the system is designed, the only way to 'setup' the system is to have the proper tools/gauges to check the pressures and insure all of the relief valves are adjusted properly, and to know what those settings are. Too, it never hurts to have a flow meter that would allow you to actually check the gpm flow off the pumps at the specified pressure. I have seen many cases where the pumps seem to work just fine at lower pressures and temps, but bypass and 'fail' when the oil gets hot, causing a drop in both pressure and flow.
In other words it could be wear in the pumps, or a weak port relief, or even the main if conditions were right, that could be causing the problem your seeing with the thumb seeming weak. The same goes with the tracks. In fact, problems are often amplified with the tracks due to the fact that they always take the largest continuous flow, and often the highest pressure to operate. In fact some other brand machines actually have a two stage main relief who's lift pressure is raised hydraulically just for travel, and then allowed to go back to normal for all other functions.
Another thing I have seen with the tracks being weak is the seals in the center swivel going bad. The one I worked on was working/traveling fine the first time I worked on it. As time went on and it got worked more and more, the tracks gradually got weaker and weaker until it got to the point the only way it would barely move to travel. When I got the swivel out and torn down, what I found was that the seals had pretty much disintegrated. A new set of seals and the travel hasn't had any more problems.
In the end, without a manual to tell you what each relief valve setting is, and the tools to insure those settings are correct, there's not really much you can do. If you've got the tools, then you'll still need the manual because the settings for the valves can be varied between the different functions. In any case, if you've got the manual, all your questions will be answered.
I know this probably isn't exactly what you wanted to hear, but having worked on construction equipment most of my life, it's pretty much all anyone will be able to tell you without having the actual service manual for your machine in front of them...or having done enough of them to remember everything. Hope this helps at least a little, and good luck.
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