Why do older bricks have greater clutch power?

Question

I have some pre-2000 (rough date to split the collection to old/new) System and Technic sets that are from different sources: some are from my childhood, while others have been acquired in "used" as well as "new" condition. They share a common property compared to newer sets - brick clutch power in older sets is a lot stronger. And this is something of a common observation in AFOL community.

Take Technic 8880 set for example. You can feel greater power is required to assemble and take apart Technic bricks compared to what would modern same parts needed. They are not damaged or bent, and still look the same as new part. I've also noticed, when handling the assembled model, you can hear many connection points squeak, which isn't a case with modern sets.

It is known TLG made a change from pre-colored plastic pellets to "base + colored dye" used in production these days. Newer bricks have slightly different properties too, like they doesn't yellow as much as old ones. So obviously, some changes were made to plastic formula, but it is still ABS plastic (question is about opaque colored bricks).

So I wish to understand what's the reason behind this.

• Was the clutch power always like that for bricks of that era?
• Is it because of chemical nature where some elements within ABS plastic mixture cause clutch power to change?
• Maybe some physical nature like temperature or humidity causing plastic to degrade/shrink over time?

Ideally I would like to see answers with facts, but keeping in mind TLG may be good at keeping their secrets I'm open to all the answers with some sort of proof of the statement.

Answer 1

This is a partial answer (or theory).
The moulds for most of the basic bricks have been changed over the years to use less plastic while (hopefully) retaining clutch.

2 x N bricks were given thinner walls with 'notches' for the studs. This may have slightly weakened clutch power.

1 x N bricks (and some plates) were given holes through the bottom tubes and had some supporting walls removed. Not sure how this might've affected clutch power though.

Photos taken from here.

Answer 2

I may found a hint onto what's going on with old elements made of ABS on sister website - Chemistry.SE. That question discuss other problem with ABS plastic - brittleness, however answer provide some interesting facts:

The original ABS substance is a copolymer made of acrylonitrile, butadiene and styrene. It is rather hard and brittle. To make it softer, some proportion of a plasticizer has to be added when it's hot and malleable. In the last century, the plasticizer was in general dinonylphthalate. It works well, but it is a bit volatile. So after a couple of years, the plasticizer gets evaporated, and the polymer becomes brittle again. This "illness" can only be cured by remelting the plastic and adding some new dinonylphthalate. Today better plasticizers have been discovered that are not so volatile.

The "old parts" I had in mind are from early 90's or so, which fits the description. It also makes sense that ABS becomes less plastic when it looses its plasticizer, thus no longer being flexible enough to adjust to tiny deformations during assembly. This results in, say antistuds, no longer adjusting to studs once attached and now being tiny bit smaller causing greater clutch power.

Answer 3

New bricks (having cross support) are lighter, 2•25 grammes instead of 2•68 (from my own weighing). Fits to older Lego that don't hold together well better, but new bricks not hold to 1990's as well as those of then to their top. Must be changing sizes? The ribs inside squash? Also the yellow is a different shade, can shine a light through, & the new ones light up, so there is a difference.