944Ross

I am planning to flush my systems with fresh fluid this weekend. But I was going thru the maintenance records that came with the car, and I find an entry at 17k miles, "Replaced brake and clutch fluids with DOT-5". Well hell, I have no idea if over the 20+ years since the original buyer had that done, the second owner (who was mechanically a moron) added to or changed the fluids with DOT-5, or has contaminated it with DOT-3 or 4. Whateveer is in there is pretty dark now.

If I'm doing a flush (with fresh fluid only), which would you use?

shiners780

I'd use DOT4.

Everything you have ever wanted to know about brake fluid: http://www.stoptech.com/tech_info/wp...fluid_1a.shtml

944Ross

That really had no guidance on the effects of cross-contamination (that I could see). I found some sites that claim no issues with switching between the two as long as non-synthetic fluids are used. I'm thinking I'll go with DOT3, because I plan to flush regularly, and I live in a very dry climate.

running_cold924

no DOT 5!!!!!!!!!!!!!!!!!!!!!! use only DOT 5.1 (if using anything other that 3 or 4)

http://www.braketech.com/index.php?o...:faq&Itemid=79

beentherebaby

FYI - DOT 4 cost about the same as DOT 3 and is probably just as easy to find. ATE Blue, ATE 200 are super cost effective DOT 4. Castrol LMA is also good.

If the previous owner(s) used DOT 5 which is silicone based, you'll want to flush the system really well or better yet disassemble everything, flush with spray brake cleaner, reassemble and then install DOT 4. DOT 5 silicone fluid should only be used for museum cars. DOT 5.1 which is NOT silcone based can be mixed with most DOT 3/4 fluids. Always confirm before mixing.

http://en.wikipedia.org/wiki/Brake_fluid

944Ross

Found some more threads on other sites and now believe I need to stay DOT5 <<if>> that is what is in there. I'm going to drain a little and try some tests to verify.

Just to clarify, my brakes are absolutely super, no problems whatsoever, this is purely preventative maintenance. I'm beginning to think I should leave well enough alone...

xsboost90

dot 5 is not what is in the car. Thats what motorcycles use- you need 3 or 4.

racer

While it might be possible Dot 5 is in the car, some vigourous flushing with dot3/4 will be fine. Of the two, I prefer DOT 4.

AS for "flushing regularly", unless you are tracking the car (and therefore stressing the brake system), there is no real advantage to frequent flushing. Most factory recomendations are once every 2 years for regular street use.

944Ross

See my opening post -- maintenance records say the original owner had it switched over. He was very rigorous about maintenance, changed plugs every 5k miles. I'm going to try the Paint Test to see if it really still is DOT5

Every 2 yrs is about what I had planned; the idea is to preserve system components from corrosion, not to replace degraded fluid.

beentherebaby

If it is DOT 5 then you do not want it in your car per the references.

Mark944na86

If it's "pretty dark" fluid now, it's crap, and needs changing. At this stage, it doesn't really matter whether it's DOT 4 or DOT 5 crap. Just flush it well to replace it with DOT 4 non-crap.