switching to DOT 5 brake fluid??

[Alexander]

Would like to run something by you.....

I am in the process of changing my master cylinder, and would like to use this opportunity change out the brake fluid with DOT 5 (silicon) brake fluid.

To purge the system, I plan to open the wheel cylinders and use compressed air at the master cylinder side to push out the old DOT 3 fluid from the lines. Will this be enough? I am assuming, some minor residue will be left behind. Is this acceptable? I really would like to avoid changing the lines.

[Brad Lustig]

I believe you need to flush the system with something like alcohol to remove all traces of the DOT3.

[Brad Lustig]

http://www.mustangforums.com/m_1448221/tm.htm

[Alexander]

The mustang forum (link posted by brad) seems to suggest against it.

But I know many people who love it and would not have it any other way.

My car had a frame off restoration and the leaky master cyl made a big mess. I would like to aviod another mess if I get another failure in the system.

I took apart the wheel cylinders and cleaned them good. The lines I blew with compressed air.

I really would like to know for sure if I now need to flush with alcohol. I don't have an easy way to do it, and would like to avoid it if i can.

Thanks

Alex

[grey beard]

When I did my B1B brakes, every component was new and I switched to dot 5. Like it very much. I believe that if you replace your master cylinder, blow out all your lines well with compressed air, and remove and wipe out each wheel cylinder, you will be good to go. After that purging, any small amount of the old stuff would be so miniscule as to not be able to cause any problems. I would really encourage you to clean out those wheel cylinders. You will not believe how much fluid they still contain. JMHO:)

[kevinanderson]

Flushed my 55 bel air with alcohol and compressed air. Then used silicone in it. Wouldn't do a complete rebuild without it.

[Dodgeb4ya]

I use Dot 5 too for my old cars that sit a lot of the year (winter time). No problems since, no corrosion of the wheel cylinders ect. Wouldn`t use it on newer cars - 90`s up ect.

Bob

[Alexander]

Thanks guys

so whats the final? Do I really need to flush with alcohol or just blow everything out with air?

If I really need to flush with alcohol, whats the best way?

Thanks

Alex

[55 Fargo]

Just for curiosity sakes why would you not use them on more modern cars. I have silicone in my stock brakes in my 47 Chrysler, it's viscosity is different, harder to bleed, but his stuff is great for old cars that don't get used a lot of the year.........glad I used DOT 5 Fred

[kevinanderson]

I used a fogger canister hooked up to dryer/filtered compressed air, filled the canister w/ alcohol. Plugged the back lines and just let it blow thru the front metal lines till clean. Plugged the front lines and blew things thru to the back until clear. Let things set for for a few hours and then blew straight air thru and then hooked things up.

[55 Fargo]

That would get the crud and brake fluid moving out of those lines, and heck you can have a beer and watch the machine do it's work........LOL Fred

[Dodgeb4ya]

Newer cars with ABS brakes-- DOT 5 is a big no-no because silicone will bubble with the accumulator pump pulsing during operation! Non ABS systems could use dot 5 but for every day driving of a newer car unless otherwise required DOT 3 or 4 is good. Also there is I believe a 4.5 and or 5.5 brake fluids being used!

Bob

[Alexander]

Update:

to everyones suggestion, I went ahead and flushed the system with 4 bottles of rubbing alcohol. to do the flush the system I opened all the wheel cylinders, then pumped alcohol in to the lines at the MS side. I plan to let the lines air dry for about 3 hours, then install the new MS. I am reusing the rubber seals and boots as they are only 1 year old.

Any thoughts or coments are welcomed.

Thank you all for the input.

Alex

[kevinanderson]

Alex-Did you get alot of crud out?

[Alexander]

Update:

The flush went great with no major surprises. The alcohol started to run clear out of the wheel cylinders in 2-3 sec. No major crud came out.

The system is still trying but is most likely dry by now. We hit 100 degrees today so I called it quites and will continue tomorrow.

Next step:

To install the new master cylinder, seals and boots.

Fill with silicon dot 5 and pump slowly.

Hope it all works out.

Thanks

Alex

[Alexander]

Update:

filled the system with silicon dot 5 and all went well. It started to run clear right from the start. seems I did a good job at flushing out the old stuff.

One key point to remember: its very important to pump slowly as you bleed. DOT 5 seems to be very sensitive to agitation. The bubbles do not escape very easily once created.

No leaks and the system seems to be working well. However the breaks feel week. Perhaps I need to adjust the shoes or is there more air deeper in the system? I allowed aprox one cup of fluid run out from each wheel before going on to the next

[bob westphal]

Can someone tell me the purpose for using Dot 5? I maintain 15 old cars only one has Dot 5 in it. It is also the only car I have any brake trouble. I need to add fliud every year. There are no leaks! It gets driven about 400 miles a year same as the rest.

[TodFitch]

Can someone tell me the purpose for using Dot 5? I maintain 15 old cars only one has Dot 5 in it. It is also the only car I have any brake trouble. I need to add fluid every year. There are no leaks! It gets driven about 400 miles a year same as the rest.

The theory is less corrosion on vehicles that are not driven a lot. Conventional brake fluid is hydroscopic, that is it absorbs water easily. As the temperature in your garage changes during the day a little air is drawn in or expelled from the breather in your master cylinder. This fresh air exchange brings in some moisture that is absorbed into conventional brake fluid but not into the DOT5 stuff.

Anyway, once water is in the brake fluid it leads to corrosion.

Supposedly if any water gets into a DOT5 system it will stay separate. That might be a bad thing but since it is not absorbing water from the air I think this is a less likely scenario.

I have noticed that newer cars (maybe 1970s or so and newer) have a rubber diaphragm under the cap on the master cylinder. I believe that this is to keep the moist air separated from the brake fluid. But our old cars don't have it.

I have DOT5 in my 1933 but run whatever the factory/dealer puts in my new cars. I have not lost a drop of DOT5 from the 1933 since I got it back together in 1998. I can't vouch for methods of switching from one brake fluid type to another as I was starting with a brand new system including all tubing. As mentioned earlier, you have to be careful when bleeding to keep from getting bubbles in the DOT5. Once in there they are a pain to get out.

Possible other pitfalls for DOT5: 1) It has a reputation for damaging hydraulic brake light switches (so far I have not had this happen to me). 2) Some racers I know say that it gets too spongy when the brakes are used to the maximum. That should not affect street use but apparently is an issue at the track.

On the plus side: Conventional brake fluid is a very effective paint remover so spills are a pain. DOT5 does not affect existing paint. Since it has silicon in it I suspect that repainting areas that have had DOT5 spilled on them might be a problem.

[Alexander]

I dont use my cars very often. They sit in the garage aprox 85% of the year.

The DOT3 fluid seems to absorb lots of moisture which then corrodes my wheel cylinders. I find myself rebuilding the wheel cylinders and or master cylinder every year or 2. Since DOT 5 is silicon based it will not absorb water. its good for "old" cars that don't get used often.

Cheers

[Merle Coggins]

Wish I had thought about this when I did the brakes on my truck. I was basicly starting from scratch. New master cyl, new lines, new wheel cyls. That would have been the time to put in DOT5. I don't think I want to go through the trouble of flushing the system for a fluid change.

Merle