Brake system flushing

[russcc]

I rebuilt the MC, front wheel cylinders, and replaced some lines and hoses and will be doing the rear wheel cylinders in the '40 soon. I will convert over to DOT 5 fluid when all is ready. My question is what is the best way to flush the entire system out ? I was thinking of filling the MC & opening all the bleeders to drain the system, would that work ? Thank you Fordbarners.

[Kube]

Originally Posted by russcc

I rebuilt the MC, front wheel cylinders, and replaced some lines and hoses and will be doing the rear wheel cylinders in the '40 soon. I will convert over to DOT 5 fluid when all is ready. My question is what is the best way to flush the entire system out ? I was thinking of filling the MC & opening all the bleeders to drain the system, would that work ? Thank you Fordbarners.

It would not work very well.
Plus, if you are intent on changing to DOT 5, you'll need to "wash" the hydraulic system.
I would suggest you power bleed the entire system- removing all of the old fluid. Then flush with denatured alcohol. And then power bleed with Dot 5.

[KGS]

Originally Posted by russcc

I rebuilt the MC, front wheel cylinders, and replaced some lines and hoses and will be doing the rear wheel cylinders in the '40 soon. I will convert over to DOT 5 fluid when all is ready. My question is what is the best way to flush the entire system out ? I was thinking of filling the MC & opening all the bleeders to drain the system, would that work ? Thank you Fordbarners.

I use denatured alcohol to clean out the system if it is a new or clean brake system. Then thoroughly bleed with DOT5. If it's an old cruddy system, I do as you have done and replace everything. Be sure to search back and see how others bleed their brake system with DOT5. Slow and easy will be the order of the day.
Ken

[russcc]

Thank you Mike & Ken. Good idea on the alcohol flush, and power bleed. What would you recommend for a "power Bleeder" ?

[Aarongriffey]

I use DOT5 in my old cars. Have for the last 20+ years.
Dot 5 will leak where nothing else will.
When I replace all 5 cylinders I use DOT 5.
If I rebuild any cylinders I NEVER use DOT5 in That car again, until I replace the rebuilt cylinder with a new one.
There’s nothing wrong with rebuilding a cylinder that was not leaking. There’s also nothing wrong with using DOT3 or 4.
You can flush a brake system that was not leaking, bleed it with dot 5 and there will be a good chance that it will have some leaks. I have done it, more than once.
I’ve worked for companies that had fleets of cars and trucks. I’m telling you , it’s risky to change over to Dot 5 on a car with used or rebuilt cylinders.

[Kube]

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Originally Posted by Aarongriffey

I use DOT5 in my old cars. Have for the last 20+ years.
Dot 5 will leak where nothing else will.
When I replace all 5 cylinders I use DOT 5.
If I rebuild any cylinders I NEVER use DOT5 in That car again, until I replace the rebuilt cylinder with a new one.
There’s nothing wrong with rebuilding a cylinder that was not leaking. There’s also nothing wrong with using DOT3 or 4.
You can flush a brake system that was not leaking, bleed it with dot 5 and there will be a good chance that it will have some leaks. I have done it, more than once.
I’ve worked for companies that had fleets of cars and trucks. I’m telling you , it’s risky to change over to Dot 5 on a car with used or rebuilt cylinders.

Very good advice indeed...

[ursus]

I have a complete 1940 rear end that came out of a car that used dot 5 in the braking system. I plan to install this in my car that uses dot 3 fluid and rebuild the rear cylinders. How do I flush the DOT 5 from the system?

[Scott52]

I am replacing all the wheel and master cylinders. Went to buy some denatured alcohol and Home Depot says California outlawed it 6-8 months ago. side note:Tried to buy some turpentine and it had been outlawed 6-8 years ago. I still had some in a 1/2 qt container and had no idea it was so precious. Any fluid suggestions for cleaning out the system without using denatured? How about Ethanol. They use it at the family Nail Salon but was hard to come by just before we were Covid shut down.

[kevinanderson]

I used brake cleaner with the straw on the nozzel and blew out the lines, one at a time. Then blew good clean air thru it.

[Aarongriffey]

Kevin (above) does it the most practical way. Getting every drop of dot 3 out is not that critical. Getting dirt out is.
Before you blow through a line be sure to tie a rag around the other end of the brake line so you do not get brake fluid on anything painted.
DOT 5 does not harm paint but 3 and 4 will eat right through to the primer.