Brake fluid in brand new system: is it synthetic?

Hey all

A local Mechanic says he put Dot 3 in my brand new brake system but when I researched and finally asked the shop owner, he said he thinks he put synthetic in...

I’ve seen threads on how to identify synthetic from non

Please see my photo and let me know what you think

Thanks for any and all feedback!!!

All brake fluids, except one made for Citroen combined hydraulics system, are synthetic. The confusion comes about because of people confusing silicone (DOT 5) brake fluid with synthetic brake fluid. Basically all DOT 3, 4, and 5.1 brake fluids are synthetic and are glycol-ether based, whether they are labeled synthetic or not, and can be mixed. DOT 5 is silicone based and cannot be mixed with DOT 3, 4, or 5.1 glycol-ether based brake fluids. You need to find out what is in yours. If the shop owner doesn't know what they use, I would find another shop.

So, are you trying to find out if you have silicone based or glycol based brake fluid?

Hi don

Thanks for that clarification And they dint seem to know!

Yes I’m going to learn and do these things myself as I have another mechanic that is very busy but does know this stuff well.

I assume that since it’s coagulated at the top and is purple, that it is Silcone based Dot 5 and not 3 as they stated

The vid is very good and I’ll try another test and not shake the cup this time

I really hate think I’ll have to flush the system or worse!!

Thank you for the insight!!

Hi don

Thanks for that clarification And they dint seem to know!

Yes I’m going to learn and do these things myself as I have another mechanic that is very busy but does know this stuff well.

I assume that since it’s coagulated at the top and is purple, that it is Silcone  based Dot 5 and not 3 as they stated

The vid is very good and I’ll try another test and not shake the cup this time

I really hate think I’ll have to flush the system or worse!!

Thank you for the insight!!

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Ok finally got to the bottom of this. The shop used a freelancer who specializes in classic cars and he confirmed he used Dot 5 silicone based fluid. He uses this because some cars sit most of the time and it’s a precautionary step. So mystery solved. I did suggest that they put a label or something in the car dated and describing fluids used if not standard products... so it’s purple, it coagulates and has been verified

thanks again Don for the insight!

You're welcome, glad you got it solved. I can understand and agree with using DOT 5 in seldom used vehicles and classic cars, it's not hygroscopic and it's paint friendly. The only thing I don't like about it is that it can cause a soft or spongy brake pedal because it can absorb air, making it difficult to get the brakes bled. I believe that using a vacuum pump, with too much vacuum, at the wheel cylinders and calipers can cause it to aerate.

Hopefully they completely flushed the entire system, glycol-ester and silicone fluids are not compatible and can cause the fluid to gel, as well as damaging seals.

You're welcome, glad you got it solved. I can understand and agree with using DOT 5 in seldom used vehicles and classic cars, it's not hygroscopic and it's paint friendly. The only thing I don't like about it is that it can cause a soft or spongy brake pedal because it can absorb air, making it difficult to get the brakes bled. I believe that using a vacuum pump, with too much vacuum, at the wheel cylinders and calipers can cause it to aerate.

Hopefully they completely flushed the entire system, glycol-ester and silicone fluids are not compatible and can cause the fluid to gel, as well as damaging seals.

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Yes for the readers benefit, the entire system was new so we shouldn’t have any cross contamination issues here.

From the LEED Brakes website:

Silicone Brake Fluid Caution:

While silicone brake fluid has its many advantages it also has a few weaknesses with today’s brake systems. In order to use silicone brake fluid your entire brake system must be composed of all peroxide cured EPDM seals. Silicone brake fluid will distort and break down standard rubber seals causing your system to leak and fail. Silicone usually will break down standard seals in a very short amount of time. If you are not sure if your seals are peroxide cured EPDM seals check with the component manufacturer before using silicone fluid.

From the LEED Brakes website: 

Silicone Brake Fluid Caution:

While silicone brake fluid has its many advantages it also has a few weaknesses with today’s brake systems. In order to use silicone brake fluid your entire brake system must be composed of all peroxide cured EPDM seals. Silicone brake fluid will distort and break down standard rubber seals causing your system to leak and fail. Silicone usually will break down standard seals in a very short amount of time. If you are not sure if your seals are peroxide cured EPDM seals check with the component manufacturer before using silicone fluid.

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Great note Bill.  Puts it in black and white.  I would rather stay with dot 3 than take any chances of brake failure or having someone else accidently put in the wrong type if I was having the car service by an shop.

Ok so next question is if someone didn’t know it had dot 5 and bled the front brakes like the shop said they did because a hose had a leak, and topped it off with dot 3...

What should be done now?

I assume it’ll be evident if we purge the system and we’d see dot 3 floating around. Can we go back to dot 3 now?

This is worrisome because it’s all brand new lines, calipers, hoses and booster

Please advise

Ok so next question is if someone didn’t know it had dot 5 and bled the front brakes like the shop said they did because a hose had a leak, and topped it off with dot 3...

What should be done now?

I assume it’ll be evident if we purge the system and we’d see dot 3 floating around. Can we go back to dot 3 now?

This is worrisome because it’s all brand new lines, calipers, hoses and booster

Please advise

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You would need to flush the lines and wheel cylinders with dot 5 and refill.  I like many other do my own maintenance so I know what I'm using.  If I was using a shop to service my car I would put a bold label in plan sight that had the type of fluid to use. 

The difference in the dot's 3, 4, and 5.1 are the boiling points.  You can  use a higher number in a lower number system but not the reverse.  So if you had dot 3 in your brakes and someone added dot 4 it would not create a problem.  But if you brakes system called for a dot 4 or 5.1 and you added dot 3 it could cause brake failure due to the boiling point.  You need to use at least what the manufacturer calls for. See below

Ok, well I think I’m going to totally flush and refill with 5 and make sure I put that label somewhere..

Thanks everyone for the great advice!!

Ok, well I think I’m going to totally flush and refill with 5 and make sure I put that label somewhere..

Thanks everyone for the great advice!!

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Final question for you.  Did you verify what Bill had posted about the peroxide cured EPDM material needed for dot 5.  More than likely you are ok but I would double check the manufacturers web site to see if it states it or what the type of dot you can use.  If you find out that any part of the brake system will not take dot 5 I would flush with any of the other dots and use one of them. I would probably go with the 4 or 5.1

Ahh ok... well I can’t remember what brand brake calipers and wheel cylinders are so I’m thinking it may be best to flush it like crazy and do 4

I don’t think I’d be able to determine if the runner parts have been treated

Thanks for the input!!

Back in 2007 I was finishing my 69 Mustang vert restomod and installed DOT 5 thinking it would be advantageous for all the usual reasons (resistant to water since it spends more time sitting than not, won't hurt paint if it develops leak, etc). It had a SSBC drum to disk conversion kit. In 2014 I needed to replace a defective booster and figured I might as well change the Master Cylinder at the same time. As I discussed the issues with LEED, they mentioned to me they no longer advocated DOT 5 since they had encountered so many system issues with seal failures. They basically said use of DOT 5 would void any warranty with the MC I purchased. I did not install the new MC at the time due to a mis-match in the line fittings.

I flushed my system 3 times with 90% isopropyl alcohol before installing new DOT 3/4 (has slight advantage over DOT 3 with water absorption) after installing the new booster. BUT I had to replace my rear wheel cylinders (2007) two years ago when the seals failed - found puddle of fluid under one wheel when taking out of winter storage. As I began to pressure bleed the system with the new wheel cylinders I was very surprised at the traces of purple fluid I kept seeing in the fluid I was getting out of the rear lines. So I re-flushed the entire system with an entire quart of new DOT 3/4. I also replaced all flex lines with new stainless wrapped lines a couple months after the wheel cylinder change and did another system flush at the time.

Now I'm in the process of finally changing the (2007) MC since the piston seals have failed causing the brakes to lose their hold after a few seconds of pedal pressure. I will be interested to see the condition of the seals in the old unit.

So my experience with DOT 5 has not worked out very well over time. My 73 vert always had Dot 3 or DOT 3/4 and there were never any issues with seals over 25 years & 30K miles of driving. I should note the 69 system only has 6K mileage since 2007.

You will also need to rebuild your distribution block if you haven’t don’t it already. The original o rings are not compatible. I know from experience. I put dot 5 in when I put my car into storage 25 years ago. When I restarted my project 2 years ago every single seal in the brake system had failed. Wheel cylinders, front calipers, and the distribution block. Rebuild kit and instructions for that is here:
www.muscle car research.com/valve-rebuild-kh

I would also pull apart the master cylinder as well, since those o rings may also not be compatible. I put a brand new MC in the car before storing it, and the o rings on the piston failed and leaked into the power booster, so I had to replace that as well.
PS, fire that mechanic after you make him repair everything. Any “Classic car” mechanic should know that older cars can’t use DOT 5 without modifications. At least I had the option douse of being an amateur mechanic working on my first restoration