Which DOT brake fluid (3 or 4) should I use for my 86 GXL? Does it even matter? I am replacing the master cylinder and the instructions said to be sure you use the correct fluid.

 

Any DOT 3 or 4 should be fine if you're just driving around. If you plan to take it to the track use Motul 600.

 

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You have a sports car, use 4.

Basically the differences are the fluid boiling point. I car with DOT 3 fluid will get squishy under intense braking long before a DOT 4 fluid will. Sometimes it's like a few dollars more expensive for the entire brake system. I thinkit's worth it.

 

^ The exception to the rule being Ford Spec DOT 3 fluid which has a dry boiling point of 550F. If you are going to take your car to the track I highly recommend it.

Brake fluid absorbs water over time which lowers its boiling point. When the fluid boils it effects it's ability to stop the car. Ford Spec DOT 3 is compromised severly by water absorbtion and thus it needs to be changed fairly frequently. DOT 4 fluids can last quiet a while before needing to be changed. There is also 5.1 fluid which is compatable with DOT 3 and 4 and lasts even longer. Often you will see Wet boiling points mentioned on the bottle. This gives you an indication of fluid performance towards the end of its life - when it has absorbed a fair bit of water.

 

Comments I've seen is that you should not use a DOT 4 fluid if your system was designed for DOT 3. Apparently the chemicals that make up the fluid are different and may not be compatible w/ the seals/alloys used in your brake system (i.e. faster corrosion, etc).

Check this article out:
http://www.stoptech.com/tech_info/wp...fluid_1a.shtml

 

DOT3/4/5.1 are fully compatible. Cost wise, DOT4 is what I recommend. Other then the Motorcraft DOT3, there aren't any other DOT3's worth using. DOT 5.1 is too expensive and a lighter viscosity to allow ABS pumps to cycle faster. Motorcraft also has a DOT4 brake fluid. There are also lower visc DOT4 fluids.

Stoptechs warning is generic. Avoid silicon DOT5 fluids and any racing fluid that isn't DOT certified. And, don't use a DOT4/5.1 as an excuse not to bleed your brake fluid at least yearly.

For street use, dry boiling point is almost meaningless. The brake fluid is ONLY dry when in the bottle. Once you open the bottle or use it, it starts pulling moisture, which depends on moisture levels in your area and brake seals condition. The more humid your environment, the more frequently you need to bleed the brakes.

Avoid using racing brake fluids that are compatible, but may not meet the DOT3/4/5.1 specs. Be careful of bottle labelling. Compatible with a spec and meeting a spec are two different things.
Racing vehicles are maintained more frequently and don't require the "corrosion" prevention addtives and PH control that we need because NOONE on the street changes their brake fluid enough. Racing brake fluids love those high dry boiling temps because they are never allowed to become 'wet'.

Also, don't use the brake fluid as an 'upgrade'. If you exceed the dry boiling temp specs of a lowly DOT3 fluid, you need to upgrade your situation(improved pads, larger rotors, better cooling, lighter car). If you exceed the wet boiling temp specs of your brake fluid, you need to bleed your brakes more often.

If the fluid, in either of your master cylinders(brake/clutch), is dark, you are overdue for a brake bleed.

 

what brake fluid would be best for the fc?

 

ANY DOT4. There is NO best. Just bleed it frequently enough(minimally once a year) to keep it dry. IMO, DOT4 is a worthy upgrade and neither DOT4 or 5.1 is an excuse not to bleed regularly.
If using a DOT3, bleed it more often.
If living in a humid environment, bleed it more often.
I also siphon/refill my master cylinders every 3 months. This helps keep the moisture level, throughout the system, down.

 

Ate Super Blue / Ate Gold is the best street track brake fluid available for the price. Then Motul RBF 600 then Castrol SRF.

better --> Best

 

Motul RBF is slightly better than Castrol SRF, if you bleed before every race.

Castrol SRF is the king of the "I'm leaving my brake fluid in for 2-3 years without changing" category.

 

for the price ive heard fords brake fuilds are one of the best for its super high boiling point?

 

http://www.rotorwiki.com/index.php/R...id_Master_List

Other than that, read the bottle for boiling points.

 

it's good before it starts sucking in water. Then it's like all the other brake fluids.

Yay for $79.50/liter (litre) bottles of Castrol SRF!

 

Yes, there is no best for everyone, just a best for each situation and budget.

I prefer valvoline synpower simply because it is pretty much a top DOT 4 with high dry and wet boiling points. And I can get it at the local Oriellies cheaper than dirt.

Lotsa bang for little bucks.

If I was tracking or autocrossing regularly, I don't know what I would use, probably Motul 600. But maybe not, since you change it before every outing anyway...

 

i work for Lexus and we are replacing all the fluid in all the cars with DOT4 when they come in for service, so the bullshit that they arent compatible, is just that...bullshit

 

dot 3 and 4 are fully compatible... but if not seriously tracking the car or driving like a mad man... dot 3 should be fine with the ocassional flush and fill