Brake fluid

[JACK M]

I am sure if I was better at searching I would find this answer but am asking here.

Last night at the go Kart races one guy was having brake issues. He was low on fluid.

One of the racers had a can of DOT5.

The first guy put some in his M/C and had brakes again.

My question is this. What are the long-term issues going to be if he has indeed mixed DOT3 and DOT5?

[Jolly_John]

Hey, Jack....this is likely more info than any of us want....but, here's a link with the long answer from Valvoline. Scroll down to the "CAN WE MIX BRAKE FLUIDS?" section. The short answer is that topping off or mixing DOT 3 with DOT 5.1 is O.K., but DOT 5 (not the same as DOT 5.1) shouldn't be mixed with either DOT 3 or DOT 4. 

 

I didn't know anything about DOT 5.1 before reading the article below. I learned DOT 5.1 is a non-silicone base version of DOT 5. Therefore, DOT 5.1 is compatible with DOT 3 and DOT 4 types of braking systems and fluids. John

 

https://www.valvoline.com/en-eur/vehicle-maintenance-brake-fluid/

Edited December 17, 2022 by Jolly_John (see edit history)

[Bloo]

2 hours ago, JACK M said:

My question is this. What are the long-term issues going to be if he has indeed mixed DOT3 and DOT5?

That may depend on what fluid and who you ask. I have heard stories from people who would not make it up about it turning to gel. Personally, any DOT5 I have ever used said it could be mixed.

 

The reason you wouldn't want to mix it even when the bottle says you can is that it does not actually mix. The DOT5 floats on top, so you get all the worst features of both types. The system is near impossible to bleed like a DOT5 system, and the DOT3 and water migrate down to the bottom of the calipers or cylinders where they still cause the rust damage, boiling, and brake fade problems you expect from DOT3.

 

Edited December 17, 2022 by Bloo (see edit history)

[Glen Andrews]

Dot 5 brake fluid is Silicone, and should not be mixed with DOT 3, 4, or 5.1; and, Dot 5 Silicone is not for use with Anti Lock Brake systems. Silicone Dot 5 aerates very easily, so if it was in an ABS system and you put that vehicle into an ABS stop the pedal would no doubt get mushy from the air bubbles forming as the internal ABS valves are pumping away trying to stop the vehicle without locking the brakes/tires. Dot 5 Silicone doesn't absorb moisture (water) so it will last longer without problems in antique cars that sit around and do not get driven much. 25 years ago I put Silicone Dot 5(which my fluid has a purple tint) in my 1938 Chevy pickup, and have not had any issues such as a leak, or a pull to one side when braking. Maybe not everyone will have good experiences with Dot 5 Silicone as there are other factors involved during installation, where and how the vehicle is used and stored. Dot 3, 4, 5.1 will eventually absorb moisture and cause problems as Bloo has mentioned; and, that is why these types of brake fluid should be changed every couple-few years in order to keep the brake system functioning at a high standard. However practically all "daily driver cars" don't get this done probably because the brakes are functioning by stopping the car and the brake fluid is something the car owner doesn't see, it's a mystery so why spend money on it?!  Jolly_John thanks for posting that Valvoline link on brake fluid, that is an excellent and concise explanation of brake fluid. I've done many brake jobs through the years and plan to continue doing so. I spent nearly 25 years working for Raybestos Brakes and picked up some good information about brakes along the way. Also been in many repair and tire shops and saw brake related things/problems on cars that would just about make my hair stand straight out.

 

Jack M: I'm not really sure what long term issues you will have by mixing Silicone Dot 5 and Dot 3, the two will not mix, put some oil in a clear glass with some water and shake it up, the two won't mix together and blend, and that's what will happen with two different types of brake fluid, just won't mix and blend, and will not be safe in a brake system. Dot 3, 4, 5.1 can be mixed together, but is not recommended.

(Silicone brake fluid has been discussed earlier this year on this technical forum)

[Glen Andrews]

5 hours ago, Jolly_John said:

Hey, Jack....this is likely more info than any of us want....but, here's a link with the long answer from Valvoline. Scroll down to the "CAN WE MIX BRAKE FLUIDS?" section. The short answer is that topping off or mixing DOT 3 with DOT 5.1 is O.K., but DOT 5 (not the same as DOT 5.1) shouldn't be mixed with either DOT 3 or DOT 4. 

 

I didn't know anything about DOT 5.1 before reading the article below. I learned DOT 5.1 is a non-silicone base version of DOT 5. Therefore, DOT 5.1 is compatible with DOT 3 and DOT 4 types of braking systems and fluids. John

 

https://www.valvoline.com/en-eur/vehicle-maintenance-brake-fluid/

Thanks for posting the Valvoline link, excellent and concise explanation.

[Frank DuVal]

7 hours ago, Bloo said:

system is near impossible to bleed like a DOT5 system,

I've never ever had an issue bleeding a DOT 5 brake system, and I have converted many cars to using it, both personally owned and customer cars.

[Bloo]

I'm happy for you. 😛

 

I don't have that much trouble either, but had the gotchas pounded into my head in tech school. Look around on the internet, lots of people wont use it because they "don't like the soft pedal" and will insist it is "compressible". The average person who is accustomed to bleeding DOT3 fluid never gets all the air out when using DOT5.

 

[edinmass]

We use Dot 5 in all our big pre war cars……..here is a Model JN getting a brake adjustment. Dot 5 works fine.

[JACK M]

Thanks all.

The system got drained and flushed and refilled.

Most teams will be taking the karts apart during off season so are getting fresh fluid fairly often.

As far as mixing goes, this was known that it should be considered temporary at best.

The 'doesn't mix' makes all the sense in the world. and was dealt with.

We will be considering the options next tear down. 

I know about the foaming problems with DOT5. And know that rebleeding after time will be helpful with that.

But since racers are always in a hurry this may be the deciding factor.

These are tiny systems, probably less than two ounces. The master piston is about 1/2 inch in diameter and the lines are tiny, often translucent so it is easy to see air in the lines.

Mine are two piston calipers that are about an inch and a half in diameter and push on both sides of the disc. Mine also runs two lines from the M/C, one to each side of the caliper.  There are many variations of these systems, but all are quite basic.

[Glen Andrews]

12 hours ago, Bloo said:

I'm happy for you. 😛

 

I don't have that much trouble either, but had the gotchas pounded into my head in tech school. Look around on the internet, lots of people wont use it because they "don't like the soft pedal" and will insist it is "compressible". The average person who is accustomed to bleeding DOT3 fluid never gets all the air out when using DOT5.

 

I agree Bloo, the average person used to bleeding Dot 3 (and/or 4 and 5.1), typically will have issues when bleeding Silcone Dot 5 especially when pumping the pedal in order to bleed the system. When using either type of brake fluid I like to start with gravity bleeding and finish up with one, or two, pedal pump and release. Since Silicone aerates easily the pedal pumps are done slower and more deliberate. When starting a Silicone Dot 5 brake job be careful not to drop the bottle of fluid or even bounce it on the work bench, if you do, go work on something else for a couple of days and let the Silicone fluid sit so all the tiny pin hole size air bubbles in the fluid have time to disappear, you just can't get into a rush with Silicone brake fluid.

[Glen Andrews]

1 minute ago, JACK M said:

Thanks all.

The system got drained and flushed and refilled.

Most teams will be taking the karts apart during off season so are getting fresh fluid fairly often.

As far as mixing goes, this was known that it should be considered temporary at best.

The 'doesn't mix' makes all the sense in the world. and was dealt with.

We will be considering the options next tear down. 

I know about the foaming problems with DOT5. And know that rebleeding after time will be helpful with that.

But since racers are always in a hurry this may be the deciding factor.

These are tiny systems, probably less than two ounces. The master piston is about 1/2 inch in diameter and the lines are tiny, often translucent so it is easy to see air in the lines.

Mine are two piston calipers that are about an inch and a half in diameter and push on both sides of the disc. Mine also runs two lines from the M/C, one to each side of the caliper.  There are many variations of these systems, but all are quite basic.

Jack; I realize that your post opens things up as far comments on brake fluid and doing brake jobs. The thing is you were talking about guys racing go karts, and racers just want to race when given the chance, so if someone there offered the guy transmission fluid and said it would work the guy would probably try it just so he could get out there and run some more laps; and knowing quite well that he would be redoing his brake system so he could be ready to go racing next week. Personal experience, in the late 70's I ran a half mile dirt track car in the (straight) 6 cylinder class, chevy 250", and always carried extra small parts and such. During warm ups one night a racing friend pulled back in and had a miss in his engine, pulled off the valve cover and noticed a broken rocker arm and said something like: "dang, can't race tonight" to which I told him I had two rocker arms in my stuff and gave him one. At that point about the only thing that would have made him happier is if someone else had given him a pillow case full of $100's. So like I said, racers want to race and make some laps; keep having that fun.

[JACK M]

10 minutes ago, Glen Andrews said:

Jack; I realize that your post opens things up as far comments on brake fluid and doing brake jobs. The thing is you were talking about guys racing go karts, and racers just want to race when given the chance, so if someone there offered the guy transmission fluid and said it would work the guy would probably try it just so he could get out there and run some more laps; and knowing quite well that he would be redoing his brake system so he could be ready to go racing next week. Personal experience, in the late 70's I ran a half mile dirt track car in the (straight) 6 cylinder class, chevy 250", and always carried extra small parts and such. During warm ups one night a racing friend pulled back in and had a miss in his engine, pulled off the valve cover and noticed a broken rocker arm and said something like: "dang, can't race tonight" to which I told him I had two rocker arms in my stuff and gave him one. At that point about the only thing that would have made him happier is if someone else had given him a pillow case full of $100's. So like I said, racers want to race and make some laps; keep having that fun.

This is so true in the racing community.

I ran Big block Mopars for years at the local dirt track.

On night one of my competitors was having cooling problems and found that he had a cracked head and asked if I had any heads.

Well, I did have a pair of used mystery heads but it's an hour and a half each way to my shop.

We headed out about midnight after the races to fetch them. (this was a two day show)

He put those used heads on his car the next night and finished ahead of me. 

GRRR, sometimes painful to be the good guy. LOL

Edited December 18, 2022 by JACK M (see edit history)