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Discussion Starter #1 (Edited)
It may be OK in a hydraulic clutch system,but NOT your brake system.
Most military vehicles (NEW)came with DOT 5 to avoid corrosion issues in storage.

From what I have read,ALL of the rubber components must be replaced to do this.
It's still very difficult to flush out ALL of the DOT 3 or 4.
If it mixes with DOT 3,it turns to Jello and may clog up ports to cause failure.
DOT 5 is usually purple in color.It does not absorb water like DOT 3/4.

If you wanted to do the clutch system,the master and slave and ANY rubber parts must be cleaned/flushed with isopropyl alcohol.

Some owners report 2-3 replacements every 5 years with a DOT 3 system.Live with it.

Bottom line: It's best to flush your system every year with DOT 3 or 4 and skip the changeover.
See this link below.




http://www.britcycle.com/Manuals/DOT5.htm

I forgot about DOT 5.1
https://www.motul.com/us/en-US/products/dot-5-1-brake-fluid
 

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This is actually good to know, I had never thought about that but it makes sense.

Is the DoT5 Silicone based instead of petroleum base? I have not done any research on it, just curious.
 

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I looked into it for my 84 back in the day. Decided to go with the Castrol GT LMA fluid instead.
 

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Don't bother with DOT 5 - it is silicone, yes - so will not absorb water. But it has a fairly low boiling point, so not great for sports cars.

DOT 5.1 is the 'replacement' for standard fluids, but most racing fluids are still labelled DOT 3 or DOT 4, both of which are fine in our cars. Use Castrol SRF or similar, or Motul RBF for a high boiling point and expect to flush every 1 to 4 years depending on the humidity in your location (I get away with 4 years or so, but we have quite a dry climate. Coastal climates expect to change every year or two). If you don't expect high brake temps (and for the clutch), a normal parts store DOT 3 or DOT 4 is just fine, generally the higher temp racing fluids are more affected by water.
 

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Still my preferred brake fluid...X 30 yrs

I looked into it for my 84 back in the day. Decided to go with the Castrol GT LMA fluid instead.
 

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The fact that it turns into Jello is true, and it does this just over time. In my other car, (M5), the PO had put some in it. I did not know about that, until it started to turn into jelly, holding the calipers at stop signs & lights. It had been very difficult to restaure the proper operation of all systems afterwards. Back to DOT 4.
 

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Discussion Starter #7 (Edited)
I have seen Super DOT 4.So that may be 5.1.
DOT 5 is bad news.All silicone based.
If there is moisture in the system,it puddles in a low spot a eats a hole into the steel brake line.

DOT 3,4 and 5.1 absorbs moisture evenly. Yes,it can boil off the moisture,but that may lead to massive brake fade.

What prompted me to do the looking into this was a recent post about a clutch slave failure.
Just flush both systems to get rid of any moisture that will cause corrosion due to moisture.
Our automotive master & slave cylinders have a VENTED cap.
To lessen moisture absorption,I used some desiccant bags wrapped over my M/C cap.
I'm on my third master cylinder in 12 years.I may get more than 4 years out of this last one.

Now,B-4 you flush your system........

Brake bleeding tip:
Do...NOT ever push the brake pedal to the floor during brake bleeding. The forward piston seal never "sees" that part of the cylinder bore and it will pick up all of the crap in there.You may ruin it. I've had assistants do that for me and blew the M/C.

Put a 2 X 4 under the pedal or your other foot. Same deal with speed bleeders.
I use an adjustable hood rod stuffed into the drivers seat cushion. The pedal will not go all of the way down to the floorboard.
Do the final bleed with the engine RUNNING-you will get more bubbles out with the extra system pressure.:thumbsup:

On a NEW one,it won't matter.Go ahead.

It's much easier to bench bleed the M/C B-4 installing and there are a few ways to do this.
Some are supplied with tubes and instructions.
I use a large plastic syringe and force fluid into the out put ports and it works fine.
http://i.ebayimg.com/images/g/~B4AAOSwvg9XTo9p/s-l1600.jpg
 

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Miss the Yahoo groups page days that Bob the Oil Guy was on...
 
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