MACH7

I have to change both rear wheel brake cylinders on my 85 (drum brakes). I would like to replace the brake fluid at the same time. From earlier postings I gather that most drain at each wheel until the brake fluid looks like the new you are putting in at the other end. However, the brake fluid that is in the system does not look that much different than the new. So my questions is does anyone have any advice on how to/when to know you have all the old out of that particular line? And if you are doing a complete change, how many cans (standard size) should you buy, e.g. enough to flush the system and totally refill it?

Also, any advice on where to buy the brake cylinders? Or not to buy them? British Victoria seems to have the most reasonable prices, e.g. vs. NAPA or Advance Auto Parts
Thanks in advance for any help.

LongDuck

I'd use VB if I were doing rear drum brakes. The parts will work well enough. Mazdatrix will have factory parts, but you'll be paying about 2x as much for them.

On bleeding, start at the furthest corner from the Master Cylinder (MC), so the right rear corner should be the first one that you bleed. The drum rear brakes are a single feed from the proportioning valve next to the MC, so there is only one line that goes back to the rear axle - this simplifies bleeding, also. Install your bleed kit (you have one, right?!?), and loosen the bleeder valve on the piston. Have someone pump the brake pedal - SLOWLY - all the way down, you tighten the bleeder, and then they release the brake pedal - SLOWLY, to refill the MC piston. It's going to take about 10-15 pumps of the brake pedal to displace the fluid in the line. Be patient. No real way to tell when you get all the 'old' out, but it's really not that critical - the MC and reservoir don't get that hot, and it's heat that causes brake fluid to break down (and high humidity...).

Once you have the right rear done, move to the left rear, and bleed there just like before - you'll already have worked out most of the fluid doing the long line to the right rear, so you may only need a pump or two at the left rear corner. Look behind the left rear piston to see if the other line exits to the right rear - you'll see what I mean when you get down there. Much faster to do the left rear when right is already done.

Fronts are very similiar, but each has it's own line, so must be bled accordingly. Most manufacturers don't list an interval for brake system fluid replacement, because this is usually not the part that fails. MC pistons, flexible hoses, and caliper piston seals usually go out first, which normally requires bleeding which replaces fluid over time.

Of course, manufacturer maintenance schedules are normally only given to keep cars out of the maintenance department during their initial warranty period. Any enthusiast driver will be performing a lot of maintenance that your dealer would say you don't need... HTH,

813KR$

If it looks good, then why replace all of it. I would just bleed out the air that gets in the line after your brake work.

GavinJuice

Remember, Brake fluid will readily absorb water which will cause rust in the brake line which is a big no-no and can cause a huge pain in the ***.

If you have a break in the line where you car has been sitting, or for some reason water is entered into the brake line, that is the reason to completely flush out ALL the brake fluid.

Removing and installing new brake lines aren't always the easiest chore, but will add peace of mind.

MACH7

Thanks for the input - some additional informaiton - the car has 52K original miles - this is why the brake fluid looks good - however, its never been changed - and as the last post says, its rumored that you get water mixed with the brake fluid over time - thus my desire to change it out as I replace the wheel cylinders

LongDuck = I do not have a bleed kit, just the bleed nipple that comes standard - I was going to slide a plastic hose over it to guide the fluid into a container

And are there any suggestions for blocking the brake line when I remove the wheel cylinder to keep it from spilling brake fluid?