Which brake fluid DOT 3 or DOT 4 (in 86' 911).

slotcar · 04:58 PM

I used the search function...but thought I'd ask point blank. I'll be bleeding the brakes with a vacuum bleeder (mighty vac)....which brake fluid should I use...DOT 3 or DOT 4. I'd like to buy the stuff off the shelf at one of the local parts stores (any problems with this)?

Also, any suggestions while using the vacuum bleeder?

Thanks.

VaSteve · 12-29-2005, 05:19 PM

If you're tracking it, DOT4.

Most people use the racing blue and racing yellow. Alternate between the two.

911pcars · 12-29-2005, 06:35 PM

ATE is good. I suggest Motul RBF. It has higher wet and dry specs. A little more $$ though @ $10/liter. You might find it at your local cycle shop.

More brake fluid specs here.

Sherwood

slotcar · 12-29-2005, 06:58 PM

Thanks....I think I'll go with the Castrol products.

Sherwood...thanks for the link, very helpful.

JohnJL · 12-30-2005, 03:06 PM

Steve's point is a good one...its good practice to alternate between the 2 so you can tell when you're onto fresh fluid when you change next...just bleed until you see the new color...

911pcars · 12-30-2005, 04:53 PM

Quote:

Originally posted by JohnJL
Steve's point is a good one...its good practice to alternate between the 2 so you can tell when you're onto fresh fluid when you change next...just bleed until you see the new color...

The word the last couple of years is that ATE Blue is being discontinued because of staining. DOT likes amber or whatever. If that's the case, there must be a huge supply of ATE Blue in warehouses as it seems to be readily available. Regardless, used fluid should be more amber than new fluid.

Sherwood

slotcar · 12-30-2005, 06:02 PM

In 101 Projects it says silicone DOT 5 is not recommended for street use.

JohnJL · 12-30-2005, 06:13 PM

I believe DOT5 is silicon-based. In road cars, OK for a long-term fill but mildly compressable and so not ideal for performance braking systems like ours.

Nine9six · Nine9six's Garage

I will second the Motul RBF...

JohnJL · 12-30-2005, 07:30 PM

Sorry if I misinformed. But I know ATE Blue and Gold are tops, personally.

makaio · 09:42 PM

Dot 5 is best for long term storage or show vehicles.

Dot 4 fluid is what you want for your Porsche. For everyday street driving any off the shelf DOT 4 from your local auto parts store will suffice. If you're going to the track or auto-x, go with one with a dry boiling temp like ATE Super Blue or others.

And make sure to flush it every two years if you don't bleed your brakes regularly. I have seen lots of brake problems due to lack of flushing the fluid. One of them was a fender bender accident that could have been avoided at work.

slotcar · 12-31-2005, 12:01 PM

My partner in crime had some ATE Blue....I went with that, job completed!

SLO-BOB · 12-31-2005, 12:12 PM

I do the ATE blue/gold thing too. I do DEs and street driving. No problems in either venue.

VaSteve · 12-31-2005, 12:29 PM

Quote:

Originally posted by makaio

And make sure to flush it every two years if you don't bleed your brakes regularly. I have seen lots of brake problems due to lack of flushing the fluid. One of them was a fender bender accident that could have been avoided at work.

If you do DE's, flush it WAY more often than that! Our region requires it to be done within 180 days.

randywebb · 12-31-2005, 12:33 PM

No matter how you use the car, flush it every 2 years at a minimum - regardless of how often you bleed the brakes.

UNless you bleed them so often that you are really flushing the whole system w/in 2 years... in which case you have a problem...

sketchers356 · 12-31-2005, 02:21 PM

OK, I'm missing something. I thought that the difference between DOT 3,4,5 was that with increasing number came increasing boiling point. So why would we definately not want 5?

Wil Ferch · 12-31-2005, 02:30 PM

OK...lotsa dancing around the issues here....

"Most" DOT 5 is silicone based. Good for long term storage. Will not absorb water which is the reason to replace other types of fluid. Small amount s of water absorbed ( 1-2%) can lower boiling points by several hundred degrees F. But, has an affinity for air, cannot get a "solid" pedal with it. Also requires "complete" draining and cleaning of the original system, since it is not compatible with other fluids. Big hassle.

There are *some* DOT 5 fluids that are NOT silicone, but these are very rare and terribly expensive...like a factor of 10X. I *think* ( help here, please...)French MOTUL has such brake fluid. I also *think* these are ESTER based and not silicone based....someone help here ?

Wil

vash · vash's Garage

a racer guy told me the ATE stuff was to be used in racing applications where the fluid is really changed out often. he says it is more hydroscopic than stuff designed for the street. i have ATE gold in my car now. i may search out that MOTUL stuff, at cyclegear.

SLO-BOB · 12-31-2005, 05:03 PM

Quote:

Originally posted by vash
a racer guy told me the ATE stuff was to be used in racing applications where the fluid is really changed out often. he says it is more hydroscopic than stuff designed for the street. i have ATE gold in my car now. i may search out that MOTUL stuff, at cyclegear.

Maybe true, but frequent brake fluid changes are a good idea imo. One advantage is the bleeder nipples won't corrode shut if you excercise them on a regular basis. With a power bleeder, it's a very quick job.

911pcars · 12-31-2005, 05:29 PM

"There are *some* DOT 5 fluids that are NOT silicone, but these are very rare and terribly expensive...like a factor of 10X. I *think* ( help here, please...)French MOTUL has such brake fluid. I also *think* these are ESTER based and not silicone based....someone help here ?"

Motul 5.1 is a polyglycol-based fluid and has a DOT spec of 5.1 to differentiate itself from the DOT 5, silicone-based fluids. Motul RBF has a DOT 4 spec.

In my earlier post on the cost of RBF, it's about $26 per liter. ATE and Motul 5.1 is about $10/liter.

Sherwood