DOT3 vs DOT4

["Doug Gould" <dgould@xxxxxxxxxxxxxxx>]

My 164 has had similar master cylinder problems as AlfaBill's, so I followed
his suggestion of reverting to DOT3. I was surprised to discover improved
brake pedal "feel". In fact I believe that the brakes are more "progressive"
that when they were on DOT4.

I was discussing this with a friend last night who has been a design
engineer with some major manufacturers and a major race team. He says that
DOT 4 was developed with the objective of absorbing less moisture. DOT 4
also has less "lubricity" than DOT 3 which may or may not have been
intentional. There is some suggestion that the reduced "lubricity" of DOT4
was intended to create some "sticktion" in the brake system to help reduce
pad knock back. If this is true it would tend to explain my experience with
changes in pedal "feel".

Apparantly when DOT4 was released in the late eighties there was a lot of
trouble with it causing problems with some types of brake seals and while
this is consistent with some of the "gossip" about 164 master cylinders, one
would presume that this is all sorted out by now.

For the meantime I believe that DOT3 has improved my brakes and I prefer the
pedal feel . I  support AlfaBill's sugesstion to experiment, but can anyone
throw any objective, factual light on this collection of heresay and gossip?

Doug Gould
'91 164L

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