Matthew Perry's death has put a renewed focus on the dynamic of his old costars -- and one anecdote about David Schwimmer is resurfacing ... touching on his one-for-all spirit.

The Guardian dug up this sweet tale in Perry's memoir from last year -- 'Friends, Lovers and the Big Terrible Thing' -- in which the late actor recounts how money started to change on the set of 'Friends' while they were filming back in the '90s.

In his book, MP says all the stars were making about $22,000 an episode for Season 1 -- but by Season 2, Dave and Jennifer Aniston had begun earning a bit more ... on account of their popularity on the show due to the whole Ross/Rachel romance story line.

When Season 3 rolled around, WB wanted to throw even more cash at the 2 of 'em -- as they were now fan faves -- but Schwimmer put his foot down on behalf of his castmates. Apparently, Dave floated the idea of them collectively bargaining together ... so everyone could make the same amount of money, even if it meant a pay cut for him and Jen.

Matt says that's exactly what ultimately happened, writing ... "David had certainly been in a position to go for the most money, and he didn’t. I would like to think that I would have made the same move, but as a greedy 25-year-old, I’m not sure I would have."

He adds, "But his decision served to make us take care of each other through what turned out to be a myriad of stressful network negotiations, and it gave us a tremendous amount of power ... We had David’s goodness, and his astute business sense, to thank for what we had been offered. I owe you about $30m, David."

By Season 8, MP revealed that each of the 'Friends' actors were making about a million bucks an episode ... and he credits Schwimmer with establishing that precedent early. Apparently, they continued to hammer out salary negotiations as a group over the years.

This story, which technically came out last year, is making the rounds right now ... and just speaks to how close the 'Friends' really were on set -- adding to the devastation of Perry's sudden loss. TMZ broke the story ... he was found dead last weekend at his L.A. home.

As we reported ... the cast attended a small, private funeral for Perry Friday near the Hollywood Hills -- as did Perry's family and loved ones, including his parents.

Schwimmer, Aniston, Courteney Cox, Matt LeBlanc and Lisa Kudrow all released a joint statement addressing Perry's passing ... saying the tragedy was "unfathomable" and that they were still processing it as a group. They've laid relatively low in the days since.