Replacing Dot 3 Brake Fluid with Dot 5

Posted By: charge70

Replacing Dot 3 Brake Fluid with Dot 5 - 07/16/08 12:16 AM

I want to replace the Dot 3 brake fluid in my 69 Dart with Dot 5.I know I have to flush the lines as the two fluids aren't compatible.My question is this,what do I use to flush the system so it won't ruin any of the hoses or wheel cylinder rubber parts.The steel lines are fairly new,and I don't want to replace them.Thanks in advance, John.

Posted By: Lemon_Twist

Re: Replacing Dot 3 Brake Fluid with Dot 5 - 07/16/08 01:23 AM

John

I just had my third car converted from Dot 3 to Dot 5. Same process for all three. Open bleeder valve at one corner, pump brakes and keep addidng Dot 5 to master cyl, being careful not to let it run too dry so you get air in the system. Continue to bleed until new Dot 5 fluid only is coming out at the wheel cyl/caliper. Its a different color than Dot 3, so you will know. Repeat for other three wheels, top master cyl when completed, and then you are done. My 71 Cuda had discs up front as opposed to drums on the 69 Runner and 71 GTX so it required a little more fluid to flush out the calipers. I think my GTX went through just about 4 pints or so to get the job done. A disc car will require a little more.

Rod

Posted By: Magnum

Re: Replacing Dot 3 Brake Fluid with Dot 5 - 07/16/08 02:15 AM

If this helps I did the same as LemonTwist.

Used the silicone fluid to push out the old Dot 3.

It was about 6 years ago on an already "aged" braking system and is still working perfectly.

Posted By: Andrewh

Re: Replacing Dot 3 Brake Fluid with Dot 5 - 07/16/08 02:23 AM

well, you are supposed to use denatured alcohol to flush the system out.

Posted By: jcc

Re: Replacing Dot 3 Brake Fluid with Dot 5 - 07/16/08 07:36 AM

What is the reason for going 5.1 when there are some pretty highly rated DOT 3's on the market?

Posted By: charge70

Re: Replacing Dot 3 Brake Fluid with Dot 5 - 07/16/08 09:44 AM

Quote:

What is the reason for going 5.1 when there are some pretty highly rated DOT 3's on the market?

Jcc,the biggest reason for swapping fluids is that the master cylinder on my car weeped fluid at the rear,ruining the paint on the firewall.I'll be taking the engine out this fall and repainting,I know that the master cylinder is the problem,but I don't want to have to do this again. John.

Posted By: 471Magnum

Re: Replacing Dot 3 Brake Fluid with Dot 5 - 07/16/08 11:05 AM

Quote:

What is the reason for going 5.1 when there are some pretty highly rated DOT 3's on the market?

Unlike DOT 3, DOT5 is not hygroscopic (ie does not absorb water). Your brake system components won't rust over time making it good for cars driven infrequently (like collector cars).

In the event of a spill, DOT 5 won't harm your paint like DOT 3 can (especially lacquer paint).

Those are the pros. I'm sure someone will chime in with the cons here before too long.

Posted By: Clair_Davis

Re: Replacing Dot 3 Brake Fluid with Dot 5 - 07/16/08 12:09 PM

There are a bunch of other threads on brake fluids, and lots of good info in those threads as well.

As for the high-rated DOT3 fluids, they must have low wet boiling points or they'd be DOT4's or DOT5.1's (assuming they're not silicone based). You CAN have very high dry boiling points in a fluid that only meets DOT3 specs because the wet boiling point is so low. Many of the highest dry boiling point fluids are SUPER hygroscopic - they suck moisture out of the air like it's giong out of style. Racers can feel the difference in their brake fluid from the start of the race to the end, and these fluids get changed out (or should) for every race.

Clair

Posted By: 6T6Cuda

Re: Replacing Dot 3 Brake Fluid with Dot 5 - 07/16/08 01:26 PM

Quote:

What is the reason for going 5.1 when there are some pretty highly rated DOT 3's on the market?

Just to be clear 5.1 is not a silicone fluid like dot 5 is; dot 5.1 is "traditional" with a higher boiling point.

5.1 will suck moisture, and will damage paint!

Posted By: CJK440

Re: Replacing Dot 3 Brake Fluid with Dot 5 - 07/16/08 02:03 PM

I use DOT 5 at the expense of a firm pedal. The DOT 5 is a little spongey no matter how much I bleed it.

The fluid is expensive too but I have some master cylinder cover sealing issues and would have lost lots of paint had it been DOT3.

Posted By: Black_Sheep

Re: Replacing Dot 3 Brake Fluid with Dot 5 - 07/16/08 02:53 PM

Quote:

I use DOT 5 at the expense of a firm pedal. The DOT 5 is a little spongey no matter how much I bleed it.

I've used DOT 5 in several cars and never experienced a spongy pedal. My '37 has had DOT 5 in it for 25 years with zero problems. IMHO using DOT 5 in an occasional use vehicle is a no brainer, especially when restoring a brake system using new wheel cylinders, master cylinder, etc...

Posted By: CJK440

Re: Replacing Dot 3 Brake Fluid with Dot 5 - 07/16/08 03:27 PM

Both cars I ran it in were manual brake cars. I bled them every which way and always the same.

Posted By: 471Magnum

Re: Replacing Dot 3 Brake Fluid with Dot 5 - 07/16/08 04:49 PM

Quote:

Just to be clear 5.1 is not a silicone fluid like dot 5 is; dot 5.1 is "traditional" with a higher boiling point.

5.1 will suck moisture, and will damage paint!

Do'oh! I should have known that "point 1" was there for a reason.

So none of the reasons I listed are valid. Not sure why you would use DOT 5.1 in anything other than a race car.

Posted By: cogen80

Re: Replacing Dot 3 Brake Fluid with Dot 5 - 07/16/08 08:01 PM

Quote:

Unlike DOT 3, DOT5 is not hygroscopic (ie does not absorb water). Your brake system components won't rust over time making it good for cars driven infrequently (like collector cars).

you will need tyo bleed the system from time to time because the moisture will gather at the ends of the system (calipers/wheel cylinders) since the fluid won't absorb it. no big deal though if you bleed them once a year or so.

Posted By: 73cudaproject

Re: Replacing Dot 3 Brake Fluid with Dot 5 - 07/16/08 09:07 PM

Quote:

Quote:

Just to be clear 5.1 is not a silicone fluid like dot 5 is; dot 5.1 is "traditional" with a higher boiling point.

5.1 will suck moisture, and will damage paint!

Do'oh! I should have known that "point 1" was there for a reason.

So none of the reasons I listed are valid. Not sure why you would use DOT 5.1 in anything other than a race car.

Don't feel alone! Thankfully I learned something today and not the hard way...

Posted By: Mr T2U

Re: Replacing Dot 3 Brake Fluid with Dot 5 - 07/16/08 11:16 PM

some info
ALL BRAKE FLUIDS ARE COMPATABLE with each other.

silicone brake fluid retains AIR like standard brake fluid hold moisture. the best way around this is to place the black brake fluid bottle in the hot sun for about 1 to 2 hours, this is why it is delivered in black bottles. this will force the air out of the fluid. if you don't do this you will never get a hard brake petal no matter how much you bleed the system.
also NEVER use silicone brake fluid in a anti-lock bracking system.

Posted By: jcc

Re: Replacing Dot 3 Brake Fluid with Dot 5 - 07/16/08 11:30 PM

Quote:

some info
ALL BRAKE FLUIDS ARE COMPATABLE with each other.

Maybe you should define "compatable". OK they are both liquid at room temp. But saying they are compatable goes against many schhols of thought. Seems my first reply reg "5.1" got by most readers. This is s critical safety issue and easy to lead the unknowing down a very dangerous path. I suggest everyone take all the above with a word of caution.

Posted By: Mr T2U

Re: Replacing Dot 3 Brake Fluid with Dot 5 - 07/16/08 11:37 PM

they will mix and not jell. you can put DOT 3, 4 & 5 together and your brakes will still work.

you can just suck out the old brake fluid from your master. install new fluid to pump out the old stuff with no bad side effects.
there is no need to flush your brake system with anything before changing fluids.

Posted By: 73cudaproject

Re: Replacing Dot 3 Brake Fluid with Dot 5 - 07/16/08 11:41 PM

Quote:

some info
ALL BRAKE FLUIDS ARE COMPATABLE with each other.

silicone brake fluid retains AIR like standard brake fluid hold moisture. the best way around this is to place the black brake fluid bottle in the hot sun for about 1 to 2 hours, this is why it is delivered in black bottles. this will force the air out of the fluid. if you don't do this you will never get a hard brake petal no matter how much you bleed the system.
also NEVER use silicone brake fluid in a anti-lock bracking system.

This is interesting. I never heard about placing a bottle of brake fluid in the sun for a couple hours. My son flushed the brake fluid on our '01 Dakota at tech school. It has never been the same since. Brakes fine at highway and even lower speeds; however at very low speeds the front brakes seem to grab much harder than they should. My company truck is identical and it brakes totally different. I might be reaching for straws but maybe they used silicone fluid...

Posted By: Clair_Davis

Re: Replacing Dot 3 Brake Fluid with Dot 5 - 07/17/08 03:21 AM

I've never let the fluid sit in the sun to remove bubbles before, I just pour it slowly in to the MC and try to not create any excessive bubbles while bleeding. I've never really had a problem with a spongy pedal at all, either. That may have something to do with the 1-1/32" MC more than anything, but I did notice an improvement in pedal feel when I swapped the front hoses to braided stainless units.

As for compatibility, I used to keep a plastic Coke bottle in my garage that was half full of a 50:50 mix of used DOT3 and DOT5 fluids. Periodically, I would shake up the bottle and see if anything would ever happen to the mix. The only thing that really happened was that the two fluids would be mixed up in to a frothy mix for a while, but within a couple minutes you could see a distinct layer between the two. After an hour or so, there were no visible bubbles in the silicone fluid, and both were nearly clear again. Never saw any trace of goo, sludge, crud, or corruption in the bottle. DOT regulations require that the brake fluids be compatible. The following is an excerpt from the 49th Code of Federal Regulations, Section 571, Federal Motor Vehicle Safety Standards, Subsection 6.10

Quote:

S6.10 Compatibility. The compatibility of a brake fluid with other brake fluids shall be evaluated by running one test sample according to the following procedure.
S6.10.1 Summary of the procedure.
Brake fluid is mixed with an equal volume of SAE RM-66-04 Compatibility Fluid, then tested in the same way as for water tolerance (S6.9) except that the bubble flow time is not measured. This test is an indication of the compatibility of the test fluid with other motor vehicle brake fluids at both high and low temperatures.
S6.10.2 Apparatus and materials.
(a) Centrifuge tube. See S7.5.1(a).
(b) Centrifuge. See S7.5.1(b).
(c) Cold Chamber. See S6.7.2(b)
(d) Oven. See S6.9.2(d)
(e) SAE RM-66-04 Compatibility Fluid. As described in appendix B of SAE Standard J1703 JAN 1995 ``Motor Vehicle Brake Fluid.'' (SAE RM-66-03 Compatibility Fluid as described in appendix A of SAE Standard J1703 NOV83, ``Motor Vehicle Brake Fluid,'' November 1983, may be used in place of SAE RM-66-04 until January 1, 1995.)
S6.10.3 Procedure.
(a) At low temperature.
Mix 50 [plusmn]0.5 mL of brake fluid with 50 [plusmn]0.5 mL of SAE RM-66-04 Compatibility Fluid. Pour this mixture into a centrifuge tube and stopper with a clean dry cork. Place tube in the cold chamber maintained at minus 40[deg] [plusmn]2 [deg]C. (minus 40[deg] [plusmn]4 [deg]F). After 24 [plusmn]2 hours, remove tube, quickly wipe with a clean lint-free cloth saturated with ethanol (isopropanol when testing DOT 5 fluids) or acetone. Examine the test specimen for evidence of slugging, sedimentation, or crystallization. Test fluids, except DOT 5 SBBF, shall be examined for stratification.

Obviously, mixing fluids diminishes the benefit the higher-rated fluid.

Clair

Posted By: Mr T2U

Re: Replacing Dot 3 Brake Fluid with Dot 5 - 07/17/08 03:38 AM

i only warm silicone brake fluid in the sun.
shake up some silicone fluid then pour it into a pan and heat it up. you will be amazed by the amount of air that is released from heating it up that you can't see when it's sitting.
this is why previous posters have spongy brake pedals that will never get firm no matter how much bleeding they do.

Posted By: jcc

Re: Replacing Dot 3 Brake Fluid with Dot 5 - 07/17/08 04:13 AM

Quote:

obviously, mixing fluids diminishes the benefit the higher-rated fluid.

Clair

but maybe not so obvious, and therefore are trace amounts due to lack of complete flushing enough to degrade the performance of a higher rated fluid if that trace amount is found in the highly heated caliper for instance?

Posted By: Clair_Davis

Re: Replacing Dot 3 Brake Fluid with Dot 5 - 07/17/08 12:27 PM

Egg-Zakly. It's not too tough to get a good flush on calipers or wheel cylinders, if you're really interested in getting the 100% full benefit of a DOT5 or 5.1 for example. Just pull them and drain them well. For most folks who want to upgrade to DOT5 for the paint protection factor, it's a lot less of an issue.

Clair

Posted By: CJK440

Re: Replacing Dot 3 Brake Fluid with Dot 5 - 07/17/08 01:22 PM

Quote:

i only warm silicone brake fluid in the sun.
shake up some silicone fluid then pour it into a pan and heat it up. you will be amazed by the amount of air that is released from heating it up that you can't see when it's sitting.
this is why previous posters have spongy brake pedals that will never get firm no matter how much bleeding they do.

I've got to pull my master cylinder this weekend and will have to re-bleed the system. I will be sure to sit the bottles in the sun to see what happens.

Should the tops be off or does that not matter???

Posted By: Mr T2U

Re: Replacing Dot 3 Brake Fluid with Dot 5 - 07/18/08 03:29 AM

i leave the top off when i do it. i am not sure if it really matters but i figure top off would be better.