dot 3? or 5.1

[grash2]

Need to add some brake fluid in the 2, i know i should fill with dot 3, but a friend of mine that works at Toyota and has an mk1 gave me Toyota dot 5.1 fluid to add in there

Is there a problem if i mix the stuff, what about the rubber seals, can they handle dot 5.1?

[Jim-SR]

DOT 3, 4 and 5.1 are all compatible. rubber seals will be fine with all of them, no problems at all really. obviously mixing 5.1 in with 3 is still only going to give the performance of DOT 3, youd be better flushing the system and running brand new DOT 5.1 (especially if it hasnt been done in the last 12 months, brake fluid should be renewed every year at minimum).

the only incompatible fluid is DOT 5 (NOT TO BE CONFUSED WITH 5.1!!!), which is silicone based. it isnt compatible with any other type of fluid, and also offers poor performance. its basically to be avoided at all costs IMO, it just needs changing less regularly

[grash2]

thanks!!!

haven't flushed the system for at least 5 years ooups... that goes in the to do list :)

[AlunJ]

5.1 will do the job nicely :)


which is silicone based. it isnt compatible with any other type of fluid, and also offers poor performance. its basically to be avoided at all costs IMO, it just needs changing less regularly
Using dot 5 after previously using dot 3 or 4 will destroy your braking system too.

Dot 5 fluid meeting any trace of dot 3 or 4 (residue on brake cylinder etc) will cause solids to drop out of the brake fluid, potentially plugging brake system internals and damaging seals due to restricted movement. You'd have to strip your entire brake system, clean each piece with brake cleaner then rebuild the lot before putting dot 5 in there (and the same again going from dot 5 back to dot 3/4)