View Full Version : Dot 5 ok in brake system?

07-13-2012, 01:06 AM
Brakes on 2001 205v trailer were rusted and full of water and not working. Just ordered new actuator and 4 new calipers. Was thinking of using silicone dot 5 when putting it all back together to minimize moisture adsoption into the fluid. One of the folks on the malibu forum says his a-60 ufp based system (what i have too) has a sticker saying ONLY dot 5 can be used. Is anyone on the forum using it and had any problems?

Also was deciding whether to replace or just flush the brake line/hoses instead of replace. Is it much work to install all new using a kit like from pacific trailer and worth the effort?

Thanks to all. Ive learned tons from folks on the forum!


07-13-2012, 01:15 AM
My new UFP manual (which also applies to yours) says Dot 3 or 4 only.

07-13-2012, 04:09 PM
My new UFP manual (which also applies to yours) says Dot 3 or 4 only.

Yes, i read the UFP maintenance and service manual. It does indeed say dot 3 or 4 but it doesn't say NOT to use dot 5! As i mentioned someone on the malibu forum has a ufp actuator and sticker on it says to only to use dot 5. Since dot 5 can cause some problems (depending on the o-ring and seal material). I was wondering if anyone had switched and if so, did they have any problems...


07-13-2012, 04:36 PM
If any water gets into the brake system, DOT 3 or 4 will absorb the water, degrading the fluid. So, you should change it on a regular basis.
DOT 5 won't absorb the water, so it won't degrade the fluid. However, the water will remains as little droplets that will cause rust and pitting on the internals, more so than the absorbed water in the DOT 3. DOT 5 is also more compressible, which probably isn't very important in this application.

DOT 3 will tend to degrade more by absorbing atmospheric water that wouldn't impact the DOT 5, but remember that you're dunking the whole system into the lake.

Frankly, I'd stay with the mfgr's recommendations here - DOT 5 isn't necessarily better just because it has a bigger number. Use the DOT 3 or 4, and change it every year or so.


07-13-2012, 05:59 PM
Semi-related cautionary tale: When I got The Boy's KTM, the former owner had used Dot 5. Not sure what happened, but some of it became little globules of orange plastic-like hard whatever in the master cylinders. My guess is it was mixed, but who knows. I'd avoid the stuff, unless it is specifically required. Like above, Dot 3 or 4 and change it every year. Plus, if you find yourself 5 miles just shy of BFE, and you are low on fluid and the only place in town is Grandpa Jone's Gas-n-Food-n-More Gas (because of the food), they probably aren't going to have Dot 5 on the shelf.

07-13-2012, 07:36 PM
OK, so have never heard to change the brake fluid every year, so of course I have never done this on my trailer. (3 years old) How do you do this, just suck it out of the reservoir and replace or what?


07-13-2012, 10:17 PM

I use a bleeder on my trailer that connects to my compressor. You are welcome to use it during MC bash 3 ...... Keep the reservoir full with a funnel, while using vacuum to pull fluid through the lines.

If you don't have a vacuum bleeder you can always pump fluid from the actuator from underneath the tongue with a flat blade screw driver, much like pumping brakes in a car.

I can give more details if you want .... I thing I have a tech note on my PC from A while back.


07-13-2012, 10:19 PM
Some synth brake fluids are less prone to absorb water than others ..... Regardless flush and fill every 2 years.

Worth the $$$$ in peace of mind.

07-18-2012, 09:27 PM
Heard back from UFP today. They recommend dot 3 &4 but also indicated that the parts are compatible with dot 5 and that some trailer mfgs they sell brake systems to use dot 5 in their trailers when shipped new. They did indicate that absorbing water may be better than having water drops floating around if using dot 5. If it turns out that dot5 is heavier than water (and any water would stay at the top of the mastercylinder) think i'll go that way since i'm using all new parts.


07-18-2012, 11:59 PM
As long as all parts are compatible with DOT 5 - I have replaced all the parts in a brake system that contained rubber from customers who swapped over to DOT 5 fluid in their Hondas. I don't really see the big advantage to DOT 5 - regular brake fluid is so cheap and easy to swap out when needed, why risk it? :twocents:

07-19-2012, 11:40 AM
Seems on boat trailer brakes, the fluid looks crappy pretty quick.
My 06 trailer was 4yr old from date of mfg when I bought the X2. SPent it's life in the driest climate possible. Rarely even dunked in the lake (guessing the boat was off the trailer 10 times maybeee) and the brake fluid was BROWN, dark brown.
I swapped fluid in the reservior a half dozen times (after every trip to the lake for a cpl months) and got it cleaned up. 2 years later, brown again.
I find it's easier (if the fluid isn't too bad/rusty) to just empty and refill the reservior multiple times. After doing that, most of the old fluid is gone and if you keep up with it every year or 2 it keeps good fluid in the brake system. Waaay easier than bleeding.
I do this with all my vehicles/toys and knock on wood, in hte last 15+ years I've not had to replace any brake components other than pads and rotors on any vehicles.
I also use only dot 4 in everything because it absorbs moisture better. Brake fluid is cheap and easy to replace.
Can empty and refill a reservior for $1or 2 while you're waiting for the oil to drain.

08-12-2012, 02:07 AM
Well ended up going with new actuator and calipers as well as dot 4. Bled everything today so will test it out in the morning to see if working ok.