Flushing/changing brake fluid

[earntaz]

Just looking for some input -- I have read many articles/accounts of the pros/cons of flushing old brake fluid from the system and replacing. I have never done this and have never had a brake system failure that can be attributed to brake fluid "breakdown". Would anyone from this GREAT forum care to chime in on their experience(s)??

Thanks -- TAZ

[69 Post Sedan]

If you do change it and are by yourself, just do it the old fashioned way, gravity feed. Jack the front of the car up, start at the farthest point from the master cylinder which is usually the right rear, add new fluid to the top of the reservoir. Place a hose over the bleader and run the hose into a jug/container. Open the bleader and let the old fluid run out. You should notice the color of the new brake fluid. Once the new fluid is at the right rear, close the bleader and do the same thing to the left rear.

When the rear is done, lower the front of the car and jack the rear up. Do the passenger side then the driver's side. It takes a while but it's an easy way to do it alone.

<span style="font-weight: bold"><span style="text-decoration: underline">The most important thing to remember is to keep the reservoir full at all times.....DO NOT let it get too low as air can get in the brake line and you'll have to start all over again.</span></span>

Below is a video....not the best but it gets the idea across.

YouTube Video (https://www.youtube.com/watch?v=K__9lR8yW6Y)

Kurt

[bbbentley]

Hi TAZ,
I am kind of interested to hear what the &quot;cons&quot;(you mention) are when it comes to doing basic maintenance to a car? I am not touting myself as an expert or an authority although I have wrenched on old cars for almost 40 years, was ASA certified Master Tech, and trained Mercedes-B Authorized Technician. Mercedes recommended (back in the day, I should ad, I.E. DOT 3 era)to flush brake system once a year, preferably in the Spring. That was their exact advice. Why Spring? Humidity is lowest and DOT3 fluid is a desecant (absorbs moisture) this is why most brakes on old cars fail. I have spent a good part of my life literally swimming in fuel and brake problems on antique cars as that is the majority of work I do these days. Take my advice and replace the fluid. It don't cost much in time or material and safety should be a priority to all in the hobby. I have also read where DOT4 or Silicone fluids (can't remember if that is one and the same off the top of my head) do not have the problem of moisture absorption that old DOT3 fluids have, and if a car is used infrequently (stored), it is recommended to convert over to this fluid (old has to be completely removed). I have not tried to convert, but plan to try this out on Camaro resto I am doing. I am &quot;Old School&quot; and living in the past, so I have little to no experience working on anything made after the early 80's or as I refer to the pre-Chinese era.

[firstgenaddict]

The issues are as BBBently stated moisture in the fluid, and lack of driving, the moisture pools and condenses then causes corrosion and then failure, second is that petroleum based fluids will eventually swell rubber brake lines, and the rubber seals/o-rings in the system.
Most of the original rear rubber lines (from body to rear end) I have removed have been so swollen they will not allow any fluid to pass.

If the system is currently not leaking and operational, I drain, replace any single crimp rubber lines and any old looking rubber replacements, then refill with silicone fluid. Since I am usually pulling and replacing the rubber lines I blow the old hard lines out with clean dry air, open the bleeders and blow all the old fluid out.
We have been using silicone fluid for 30 years and have never had any issues with brakes, including rarely used Corvette 4 piston calipers.

[earntaz]

So are there any issues with draining the system and changing to DOT 4?

[earntaz]

BBBentley -- &quot;I am kind of interested to hear what the &quot;cons&quot;(you mention) are when it comes to doing basic maintenance to a car?&quot;

I think the &quot;cons&quot; in some discussions are brought by those with the attitude &quot;if it ain't broke -- don't fix it&quot; ... TAZ

[Verne_Frantz]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: earntaz</div><div class="ubbcode-body">So are there any issues with draining the system and changing to DOT 4? </div></div>

Just a note: DOT-4 is just a high temperature version of DOT-3. Silicone fluid is DOT-5.

Verne <<GRAEMLIN_URL>>/biggthumpup.gif

[Lynn]

I don't see that as a &quot;con&quot; when it comes to maintenance. By its very definition, nothing has to be broken to maintain. I don't wait until the engine locks up to change my oil. I don't wait until the gutters fall down to clean the leaves out. I don't wait for the pool pump to lock up before cleaning the filters and skimmers.

I knew a guy that claimed he could replace the enging in his car cheaper than changing oil over and over for a period of years. Maybe, but I doubt it.

I would not change from dot 3 to dot 4. I have limited experience with dot 5, but from what I understand, not a good plan unless all parts are new and lines are flushed.

I change brake fluid in the german cars every 3 years (dot 4), and in the murcan cars every two (dot 3). Just in case you need another reason, it is not likely, but possible for steel brake line to rust from the inside out. I have seen it twice, both times on cars that had zero fluid changes over the years.

Kurt's approach is great for a 4 wheel disc car. Rear drums will usually not gravity bleed because of a little check valve in the mc.

[earntaz]

I guess I have been pretty lucky -- never had the &quot;apparent&quot; issue with moisture in lines. Only problem I had is with Corvette calipers leaking because of being parked too long -- drive them some and the leaks seem to fix themselves. So it appears there is no real advantage going from DOT3 to DOT4 or even DOT5.1 if the vehicle is not raced ... normal street driving will be OK.

AS far as gravity bleed -- I think a hand vacuum works well ... thoughts?

[Lynn]

My experience with the hand vac is that it works best if you seal the threads on the bleeder screws.

[njsteve]

Flushing is a wonderful thing. Your brakes will thanks you.

I usually use a hand-vacuum syphon and pull out 90% of the fluid from the master cylinder with the tube so it sucks up all the rusty gunk that has accumulated at the bottom of the reservoir. Don't pull all the fluid out otherwise you'll have to bleed the master cylinder again.

Then fill it with fresh stuff and go from there.

If you don't think you need to change brake fluid, look at this photo which is of the internal piston in my 73 after 40 years with the same brake fluid.

http://www.yenko.net/ubbthreads/pics/usergals/2013/12/full-1359-8538-p1010288.jpg

http://www.yenko.net/ubbthreads/pics/usergals/2013/12/full-1359-8540-p1010289.jpg

[Bill Pritchard]

I don't think you will find any one overwhelming consensus of opinion on this subject. If Mercedes recommended to flush brake fluid every year, I would say they were concerned as much about flushing cash from your wallet as fluid from your brake system <<GRAEMLIN_URL>>/rolleyes.gif

I know the only time I have ever used silicone (DOT-5) brake fluid in a car is on the Hemi Challenger I restored back in the 1980's. The brake pedal always had a very different 'feel' to it in that car, as compared with a car with DOT-3 fluid. Over the years since, I have read about many other people who had similar results.

[SS427]

Dot 5 does in fact does have a different feel in the pedal and almost always feels a little mushy. It is also prone to 'seepage' due to the difference in viscosity. However, I feel the benefits of silicone not harming paint and not holding moisture far outweighs the cons and have used it on all my restored cars since the 80's with only one complaint.

[jasonL78]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SS427</div><div class="ubbcode-body">Dot 5 does in fact does have a different feel in the pedal and almost always feels a little mushy. It is also prone to 'seepage' due to the difference in viscosity. However, I feel the benefits of silicone not harming paint and not holding moisture far outweighs the cons and have used it on all my restored cars since the 80's with only one complaint. </div></div>

I second Dot 5. From what I am told Dot 5 can't be mixed with Dot 3 or 4. So the best time to change over would be when everything is new. You will never get all the fluid out of the calipers when trying to change over. The only thing I would say is a problem is Dot 5 consistancy is a lot thinner. Sometimes your fittings won't seal 100%. If any piting is in your flared fittings say caliper or master your will get some leakage. Again Dot 5 don't eat paint either. Pro's and cons for both.

Just my 2 cents....

[earntaz]

What is with the Chinese post???!@#$

[earntaz]

What is with the Chinese post???!@#$

Am I the only one that can see these two post??

[firstgenaddict]

Silicone is a smaller molecule.... thus will seep where others will not.
I have found that with double flare stainless lines I have had to &quot;burnish&quot; or &quot;lap&quot; the flares by inserting the fitting together and hand snugging the nut then spinning the line in the fitting, then snugging a little more and spinning again, then after tightening I have had no problems, this seems to seat the flare.

[BJCHEV396]

I've never had a problem flushing out DOT 3 brake fluid and replacing with silicone.Use gas line antifreeze for the flush and then fill with silicone.Has worked on a '66 Corvette,'68 Camaro and a '70 Nova.