Brake fluid

[JeffR]

My 1948 Dodge B1-B brake master cylinder and wheel cylinders are empty.  How do I know what type of brake fluid was in these??

 

Thanks

JeffR

[Merle Coggins]

Better question... why are they empty? Has the system been opened up recently to drain everything? Have the components been replaced recently? Or has it just been dragged out of storage after many years and everything has seeped out? If it's an older system that hasn't been worked on in recent years it's likely just DOT3. If it has had an overhaul in recent years there's the possibility that someone used DOT5, but it's not all that common. The two types don't mix well, but unless you have a reason to suspect that the system had DOT5 in the system I would just use DOT3. 

[JeffR]

Well, the sad part is I let my truck sit for many many years and the fluid has seeped out.  I did a full body off restoration in 1986.  I  added the wrong type fluid to it a few years later and destroyed the braked system.  Then I had the brake system completely redone but I didn't keep a record of the type of fluid they used.  I assume DOT 3, but after seeing what happens when the wrong fluid is added I am paranoid.  Do you think there may be some fluid left in the lines to test?

[Plymouthy Adams]

for the cost of any test...one would probably be best advised to just take the system down for a reseal...if the prior fluids caused reaction....the only real peace of mind here is to flush and start anew....

[Merle Coggins]

Yea... what he said... 

[JeffR]

Yes, I've been reviewing the process of flushing out the system.  Do you have any suggestions as to the process.  IE:  some say denatured alcohol etc.  and how to do it??

[T120]

If you're unsure what brake fluid is now in the system, you might draw a bit out of the master cylinder using a syringe  and empty it into a small jar then add some DOT3 or DOT4. The combined fluids should visibly separate if they are incompatible...OOPS! Going back, I see now that the system is empty.?

 

Edited August 4, 2020 by T120
correction

[JBNeal]

Ya might need to pull each wheel cylinder apart and rinse with aerosol brake cleaner, as well as the master cylinder and each short hose and hard line, with long lines flooded with brake cleaner then chased with compressed air to purge, 3 times might do the trick...allow to dry, reassemble and bleed + pressurize with DOT 3...I've read about filling and purging a system with denatured alcohol and I wonder if that damages the sealing cups in the master + wheel cylinders during pressurizing...its quicker but at what cost?

 

Doing the complete teardown allows for inspection of components which can remove some ambiguity about system component condition.  These hydraulic system either work or don't and having found out how one doesn't work while rolling down a steep hill is not something I ever want to experience again...better safe than sorry, it's cheaper in the long run

[Plymouthy Adams]

been empty for a spell, fluid unknown.....my answer is the default to good shop practices that will not waste your time and money with stop gap measures...a flush could only work if you were sure of the prior fluid...without that knowledge, tear down and clean and start anew would be my only recommendation based on cost and time involved and the assurance (as best one can get) on a good braking system.

Edited August 4, 2020 by Plymouthy Adams

[Los_Control]

I would just add some basic dot 3, figure out whats wrong and correct it ... then flush the system and install the fluid of your choice.

Flushing it is good maintenance.

Life is to short to worry about which brake fluid to use on a 70 year old vehicle. Stock brakes, they did not have choices on fluid back then.

 

You did not say how long the truck has been sitting to leak the fluid. Since it did leak, is time for maintenance anyways.

[PT81PlymouthPickup]

Jeff, If your vehicle has been sitting for many years, especially if in an unheated or UN-air conditioned garage and it had DOT3 (hygroscopic) fluid in the system there's a high probability water has entered the system. DOT 3 absorbs water and that will corrode things. I used to watch my dad (professional mechanic) check drum brake systems. He would remove a drum and first peal back the wheel cylinder dust seals to take a peek to look for excessive corrosion, then he would take a couple of pry bars or large screwdrivers on each side of the shoes with the end of screwdrivers inside the lip of the backing plate. He would rock the pry bars back and forth slightly to see if the pistons were moving freely in both directions. On cars that had been sitting for lengthy periods it was common to find stuck pistons. You might want to try that first?    DOT 5 which repels water is good for vehicles that sit for long periods, but it has disadvantages as well, most notably expands with heat more than DOT3 and can give a spongy inconsistent pedal. As far as flushing, it's not a good practice to flush the system with alcohol or other solvents. It can damage rubber components. Alchohol is good for individually flushing lines and washing metal parts before assembly. DOT 3 and DOT5 don't mix and if that should accidentally happen you'll have to do a complete disassembly to clean it all out. If you can get any fluid from your system you can add a few drops of water to it in a jar. DOT 5 will not mix with water, but DOT 3 will. New DOT 5 does have a purple color, but over time it can change to yellowish, so not a reliable way to check. I had DOT5 in my truck for thirty some years and just recently switched back to DOT 3 due to stated shortcomings. I will say that the system was like new after all that time. It has it's merits for vehicles that sit for long periods. I'm much happier with my braking performance with DOT3 but I will need to be more diligent about routinely replacing the fluid. Most car manufactures recommend changing brake fluids at prescribed intervals, but almost no one does it. If you're cylinders are all free and in like new appearance you may have had DOT5 in there. If you see some minimal corrosion but pistons are still free your probably safe with DOT 3.  Make sure to bleed thoroughly and in your case look for leaks. Sounds like you likely had one.

[JeffR]

Very good, thanks for the thoughts.  I am hoping I can find some of the old fluid in a line and will do as you suggest.