Converting from DOT 3 to DOT 5 brake fluid

Sneaks

Since my backup solenoid valve failed on the Pacific trailer, I'm considering a switch to DOT 5 while it's down for repair.

The DOT 5 label procedure involves draining the DOT 3, "flushing" and then filling and bleeding with DOT 5. Flushing with what? Some say alcohol, some say DOT5 (at $30/qt.)

There are a few tech articles like this one around but none really pertain to boat trailers which, IMHO, are perfect candidates for DOT5.

Bottom line: Has anyone here done the DOT3/DOT5 conversion? Any tips? I'm encouraged by the fact that any possible mixing isn't the "end of the world", so I'll probably do as NAPA recommended: Drain the DOT3, pour in and flush with a few bottles of alcohol normally sold to remove water from fuel, blow out the lines and start filling/bleeding with DOT 5.

Don

Adeline · Posted: Tue Nov 14, 2006 9:27 pm Post subject:

I just replaced my wheel cylinders(one was stuck) and considered the switch to DOT-5. I opted for a compromise. DOT-4. I'm convinced that my W.C. stuck due to water in the fluid. It was ugly when I drained it. Dot-4 is puportedly less hydroscopic than DOT-3 and less expensive than DOT-5($12.99/QT). It is also compatible. I never heard of using alchohol for flushing. I assumed I'd flush with DOT-5. That MIGHT have changed my calculations.

journey on · Posted: Wed Nov 15, 2006 10:46 am Post subject:

There is a big difference in the viscosity between DOT 4 and DOT 5. Dot 5 is much thicker.

Changing from DOT 3 to DOT 5 is acceptable, but changing from DOT 3 to DOT 4 may have unforseen cosequences. I found this out the hard way on a KTM bike. The rear brake would not work when I changed from DOT 4 (recommended) to DOT 5.

It may work, but I'd stick with the manufactures recomendation. They know the difference. If your brakes don't work, the cost difference is immaterial.

Boris

Sneaks · Posted: Wed Nov 15, 2006 11:12 am Post subject:

mcolp

I have a 1982 shorelander tandem axle trailer under my SeaRay and
after inspecting the wheel cylinders and master cylinder they were
severely rusted. I replaced all of the wheel cylinders and master
cylinder (Atwood) in 1995 and flushed out everything and used DOT 5
Silicone brake fluid. I did not notice any deterioration of stopping
performance. The inside of the master cylinder looks like new
inside and I have not observed any water when I flushed the system.
Note: Silicone does not absorb moisture like conventional glycol
based brake fluids. I am very picky when it comes to brakes.
That's my $.02 worth.

Mike