I am going to change my master cylinder and when I do I plan on switching to synthetic brake fluid. How much fluid will I need to buy in order to refill the system with synthetic? Thanks.

The obvious is what make/model? 1 pot or 2 pot master cylinder? Power brakes? Disk brakes or all drums?

I seem to recall when I did my 65 darts brake flush it took about one larger bottle. (not the costco size) Maybe a little more/less. I seem to recall buying 2 and using 1 or maybe it was 3 and 2. but I could be totally wrong.

If your going dot 5 you don't have to worry about it absorbing water after you open the bottle so buy more not less.

1970 Dart, manual front disks from a 73 and rear drums. Mopar Performance master cylinder.

Old post, but the exact question I need answered.
How much brake fluid is needed to bleed and completely fill system.
Front disc, rear drums and the newer styled aluminum master cylinder.

Looking at Amazon,
1 - 32oz bottle, $22 (is 1 enough?)
6 - 12oz bottles, $45 (probably way too much, 72oz)

Thanks

I have always been able to drain and refill with some left over on the big autozone type bottle.
Just don't remember how many oz. I know the parts stores sells the 2 sizes, half bottle size and full bottle size. the full bottle size is plenty.

I just replaced the master (OE style) and bled system to switch to Dot5. '73 340 chall. I used just a couple of ounces short of full Qt. I did have to re-bleed the front though.

I think one big bottle (?32 oz) should do it... but I always seem to use more, especially starting with a dry master. I either have a problem or just feel better hitting each wheel at least twice. I like to have 2 quarts on hand before starting the job.

Also, as a suggestion, you might check your local AP store or Walmart... it seems with fluids that is often a better deal than "on line".

32 oz's here on a empty system.

It can be a workout getting all the air out of a completely new dry system. I would not start with less than 2 litres/quarts. You may get lucky and use only one, but don't count on it. If you don't have to open the 2nd bottle, it'll keep until you change the fluid every 2 years as we all should, but never do...

Thanks for the replys,

Autozone, Advanced Auto or Walmart don't even list Dot 5 on their websites.

Since I'm purging the existing system filled with Dot 3, I'm going to err on getting too much.

I'm going to get the 6 - 12oz bottles, that way the leftovers will be in sealed containers for future use.

Should I hook up the vacuum bleeder and suck out as much as I can before adding?
Or just add the purple stuff and bleed each wheel until it looks like only the purple coming out?

Thanks

Sealed bottles that are plastic aren't sealed. Moisture migrates thru the plastic contaminating the fluid. Just get enough to do the job and i the future if you need some buy fresh.

always drain and refill, don't try to purge it out.
dilution/fill and purge uses way more fluid.

plus as I recall you need to use some sort of denatured alchol to purge the system first or you don't fully get the benfits of dot5.

Sounds like you are using silicone (purple) fluid which is the most common DOT5. Simply bleed until it runs purple seems to work very well. Good idea to have extra.

FWIW NAPA offers DOT 5/Silicone. Don't know if it is a better deal.

http://www.napaonline.com/Catalog/Catalo...5032_0424509960

Ah, yes, silicone brake fluid. Not quite as appealing as one of the major uses of silicone, certainly not as interesting.

Rick Ehrenberg would have most of the answers, being a long time silicone brake fluid user.

Now to the install: The DOT brake fluids are supposed to be compatible, so you wouldn't need to flush for that. However, DOT3 is hygroscopic, picking up water from the air. It is possible that little drops of DOT3 could carry enough water to make problems either by corrosion or by the water vaporizing from the heat of many brake applications. I had this happen to me in the Rockies, but that was with really old DOT3.

One problem that used to occur is getting air entrained in the silicone fluid. So not shaking the bottle, letting it sit for days after shipping, etc used to be standard. It'd be cool if there was an anti-aeration additive, but I haven't heard of one.

R.

I want to say that I bought one quart at Car Quest for my Challenger. The system was completely dry. After bench bleeding the master, I hooked the lines up and left the bleeders open. Within 10 minutes I had fluid at all four corners. I'll look at the bottle tonight but I'm sure I have close to 1/3 of it left. It was about $25 per quart. I seem to remember recovering the fluid while bleeding. No point in wasting it when the system was perfectly clean to start with.