No Brakes - how hard to replace master cylinder plus lines?, looking for some guidance before I dig into my manuals... Options

[potomacmidget]

Merry Christmas everyone,

So, my brakes have been really soft, and I figured they were due a bleeding so I bought a pressure bleeder (watched Ian Karr video) and put my car on jackstands and removed all the wheels. Topped off the reservoir with fluid, then when I inspected the master cylinder and observed it was visibly "wet" with what I could only suspect was fresh fluid. First thought was "ok, not good, that must be my pedal problem" then I reached in there with an open end wrench to see if I could snug the connection, and the tubing (vertical) was not even connected to the MC, it just swung away when I touched it, then all the fluid poured out. I guess the threaded part of the tubing rotted away in the MC?

Regardless - looks like I need a new MC, and will have to inspect/replace sketchy lines, etc., and all that comes with that project.

Prior to diving into my collection of service manuals, any guidance on the challenges of this job? Do's and Dont's? It looks a bit nightmarish to access the MC, and since my simple job turned a lot harder, I will wait until my garage is warmer than 30F. All advice appreciated...

thanks,
Reg

[technicalninja]

(IMG:style_emoticons/default/agree.gif) Well done Fiacra.

That tapping trick works on the master as well. Fill it, lightly tap the master till no more bubbles in reservoir, I loosen line fittings at master till they drip, tighten. Tap master again, loosen line fitting and watch when bubbles stop. Tighten fitting.

I HAVEN'T bench bled a master in 2 decades. I can do the above with a cloth dish towel to catch the fluid and not get any on the car. You don't have to drip very much if you get it right.

Now, most of the time I'm in the engine compartment of an appliance car and the master access is better but you can be super clean under a 914 too.

I can change a master cylinder on a Honda Accord, and get it perfectly bleed, without ever touching the bleeders at the wheels doing it this way.

One thing I've decided to add to 914 bleeding is a "stomp" procedure to clear the air out of the rear control valve. It has a section similar to an accumulator and the only way to clear an accumulator is to fill and release it.

Bleed master and front brakes. Open feed fitting at rear control valve until it drips, connect and tighten. Bleed rear brakes until you think you are good, tighten bleeders.

At this point you should have a hard pedal. Stomp it hard 4-5 times. This should operate the rear valve which has to reach 525+psi before it does its thing.
Re-bleed rear brakes, you should get a few more bubbles.
Lather, rinse, repeat...
The 19mm master should do two things, harder to push (not bad, many prefer) and raise the pedal height.
You should be HIGH and HARD when complete.

That rear control valve always gets overlooked, never gets serviced and I'd bet money yours is original. PMB is the only source for me there.
If I was re-doing "hydraulics" that would be the second item on the MUST replace list after the master.
They can rebuild yours; they may have completed units done for "swaps" which you would do a core return of your old one after you completed the job.

A pressure bleeder such as Fiacra suggests makes the above process quicker and easier (and maybe messier too). My method will work with gravity.
Personally, I use a "Vacula" and suck the fluid through the lines/bleeders.
It's really the same either way. Using a pressure differential to move the fluid.


Do look at your pedal assembly. If it needs redo, I'd go Bruce Stone and I can do that myself...

Most important tip: DON'T GET ANY ON YOU!!!
Brake fluid absorbs easily via skin, the liver can process it, but the kidneys cannot, it stays forever, and is cumulative. Water is the solvent.

I only use DOT4, I NEVER use DOT5 (True silicone) but am fine with DOT5.1
Street cars don't really need 5.1 IMO.

Check/Set master cylinder free play properly.