Cleaning new brake system

Kendall · Post by **Kendall** » Sat Apr 22, 2006 8:16 pm

I just recently replaced all brake lines and two wheel cylinders (rebuilt the other two wheel cylinders and master cylinder) on my M38A1. I was reading the forum and noticed the advice about flushing the system with alcohol if using DOT 3 brake fluid. I have synthetic DOT 4 brake fluid. Will flushing with the alcohol be compatable with this fluid? Should I use regular DOT 3 fluid? Any other suggestions? Thanks, Kendall

Post by **wesk** » Sat Apr 22, 2006 9:36 pm

If you search the archives carefully here and on the g503 site you will see a ton of info praising both DOT 3 and Dot 4 and Dot 5. 3and 4 are the same base chemical makeup. Dot 5 is silicon based. IMHO the bottom line is Dot 3 has worked for me for 45 years with no rust problems. The hype on moisture and rust is a mute issue when one properly maintains his system and flushes it every two years. Dot 4 is pennies more than Dot 3 and really gives a jeep owner no visible/measurable advantage. Dot 5 is considerably more expensive and just not worth it IMHO.

The basic issues are:
1-Moisture.
3 & 4 will absorb a lot of it. This causes a deterioration in it's ability to function and can cause corrosion in the system's metal parts. This is really only a problem when poor maintenance and a LOT of time is allowed to accrue on the fluid.
5 does not absorb the moisture. When using 5 the moisture simply finds it's way to the lowest points in the system and in a very short period will start steel and iron parts to corroding.

2-Compressability: (this topic is where the smart asses hollar "A liquid is not compressable) )well they are correct. It is the air bubbles that are suspended in the liquid that are compressable and will cause a consistant spongy pedal feel.
3 & 4 usually don't have any problem with air being trapped between their fluid's molecules.
5 does have this problem.

3-Heat:
3 & 4 handle it.
5 doesn't.

PeteL · Post by **PeteL** » Sun Apr 23, 2006 11:36 am

So, Wes,

Can you help me understand why DOT 5 exists, if it is inferior in every category? What application is is designed for? I'm curious, not critical.

Pete

Post by **wesk** » Sun Apr 23, 2006 8:02 pm

Just like a new drug that ends up doing more harm than good.

It was introduced back in the 70's as the new cure all for all that ailed brake systems. It was embraced quickly by Corvette and other performance and top shelf auto manufactures then in just a little over 2 years was dumped by the same auto manufacturers. Then one of the Silicon DOT 5 CEO's suckered a cousin in congress to dupe the military into using it and we still haven't sorted that out. And today as each new classic jeep restorer enters our fold they hear this old wives tale about the glorious DOT 5 and then we old timers who have been dot 5 and left dot 5 try to explain why you don't need it.