Ok – Brake Troubles continue!!!
replaced the master (new - not rebuilt) and the boost and the proportioning valve and two suspect calipers - I bought the pressure bleeder (on the advice of the forum), all bleeds well (master bench bleed) - brakes still go all the way down!
Ok..the car is an automatic...the master is the one with the deep hole, the rod is adjusted correctly! Is the Master different for an auto versus manual (deep hole versus dimple) and if so why would it make a difference just so the rod is adjusted correctly?
Thanks

 

im having the exact same problem so

 

Well - thats sort of nice to know (that someone else has the same problem) so I know that I am not nuts! Surely someone has a fix!

 

How did you bench bleed the master cylinder?
(procedure?)

Did you disassemble the new master cylinder before you installed it?
If they sit on the shelf for a long time they will already be rusted & pitted on the inside. As soon as the piston is activated (usually during bench bleeding), the new master cylinder piston seals grind across the rust and they are ruined & they leak. I always disassemble master cylinders (new or rebuilt) & inspect for rust BEFORE I bleed and/or install them.

I have also run across master cylinders where the internals were assembled incorrectly... but that is rare.

I have test plugs that fit the master cylinder inverted flare ports. After I bench bleed a master, I install the test plugs and pressure test.

You can make test plugs by buying tubing w/fittings. Cut off about 3 inches, leave the fitting on, and flatten about 2 inches of the tubing really well with a hammer... this will allow you to plug the master cylinder ports and pressure test the master cylinder.

Process of elimination.

 

Thanks
Bench bleed as per instructions that came with it - plugged ports and pumped until no more bubbles! - is it your contention that I should take apart the MC and have a look! - this is the second one, I took the first one back (rebuilt) and told then it was bad and they (napa) gave me a new one!

 

Also - how exactly to pressure test the MC? - I have a pressure bleeder! and the little port plugs that came with the MC
Thanks

 

I have fought this '72 of mine for about 11 years now on that brake issue, tried all sorts of short term fixes off this forum and off others, and also did my own ****-y-sis over it, and came to the conclusion there was absolutely NO where to go BUT....the damn booster, and so even though it didn't make any sense, I tried going to hydroboost, and....

after about 4 months now, the brake problems are OVER, I tore the old stock vacuum booster apart and found nothing rong...seals fine, diaphram fine, held vacuum fine, engine vac fine....just no pedal...

from what I think I wuz looking at in disgust, I noticed a spring in the line of the input shaft to output shaft....so that could compress and give a false feel is my only surmise....

all I know is, change to hydroboost and brace yourself, you going through the window, into the wheel...serious...

I did the SS calipers, hell the car CAME with those, hard to beleive any C2-3's ot there without that change these daze....and so did O ring pistons, did the run out thing, changed the freeking world under there, convinced about the 'problem' but the guilty culprit seems to be the booster....

fought that damn war, damn certain of my conclusions...

case closed....

 

Thanks
replaced the booster - problem still there, I have had 3 other C3's over the years, never had this problem before - that’s why its so perplexing!!

 

To bench bleed you need a feedback line from each port to its respective chamber. The fluid is pumped/circulated from the chamber, through the port(s), through the feedback line, back to the chamber.

"plugging" the ports won't work.

Edit: Yes.... you need to disassemble and inspect even a new M/C... they all rust while on the shelf... it just depends on how long it has been there.

 

The bleeder has nothing to do with a "pressure test".

After you bench bleed (& remove the pressure bleeder), you plug the output line ports with metal inverted flare plugs, and press on the m/c actuating rod (pedal). You should get a rock hard pedal almost instantly.. virtually no pedal travel. If not, something is wrong, no need to go any further.

Edit- the plastic plugs are no good for the test.... you must use metal plugs as described in above post.
You can buy inverted flare plugs specific to the task, or you can make them out of line purchased at an autoparts store.

 

Thanks for the reply - the new master came with plugs for bench bleeding - I do remember years ago that a master came with plugs with a hole and tubes.... the instructions that come with masters today say that the plugs are the new way to bench bleed....
Looks like I will pull that thing apart tonight - thanks for the reply!

 

That appears to be a cheap way out... to do it well you still need the tubes.

The design of the piston, seals & valving inside the m/c does not lend itself to bleeding with just plugs. The fluid needs to go all the way from the chamber through the ports to get most of the air out.

Even with the tubes, I've had problems getting a m/c to bleed good.

Add the rust problem, and it can be a PITA.
I've gotten so many rusty "new/rebuilt" master cylinders that I don't even bother installing them anymore until after I have disassembled them & checked the bores.

Good luck with it. Patience is key.

 

That's funny, I have the total opposite problem, hyper-sensitive brakes.

I replaced the master cylinder, all four calipers, brake pads and added stainless steel brake lines during my restoration. I bench bled the master cylinder to no more bulbbles came out and then bled the system with the help of an assistant pumping the brake pedal, no special bleeding procedure folowed except bleeding the calipers from the furthest to the closest.

My brakes are now hyper-sensitive. Just tap on the pedal and you will be sure to meet the stearing wheel I have been thinking that the vacuume booster might be defective since they are so sensitive.

 

Ok - got a new master and the bleeder kit with the tubes (sold not with the master, the parts guy said people did not know what they were doing so the maker stopped supplying them!)
It says in the instructions (Bench bleeding with bleeder tubes) to stroke until "the piston cannot be depressed more than 1/8 of an inch" HOW is this possible ?? with the bleeder tubes in and fluid flowing - won't the piston always be able to be pushed in???
Thanks

 

yes it will. Pump it slowly until it pushes clean fluid with no bubbles.

 

73c3-you might have a non-power master cylinder

 

Yes... your assessment is correct... the instructions are wrong.


As posted- just keep pumping until the fluid is clear with no bubbles.
Don't let the chamber(s) run dry at any time.

Then you need to replace the fittings/tubes with inverted flare plugs and test for pressure before you hook it up to the car.

Try not to let any fluid run out of the ports in the process.
A few drops is okay.

 

Tom
Thanks - thats what I thought! I notice others say that it will firm up with continued pushing but I suspect they think there are plugs in and not bleeder tubes... I have sent a note to Napa telling them their instructions are wrong - but they have not replied...
Thanks for the help!

 

Some observations...

I'm replacing my master cylinder and booster too. When you fill the master cylinder reservoirs with fluid you should pump the piston and watch for air bubbles. As the gravity bleeding guys will tell you the fluid should flow from the reservoirs out through the lines even without pumping, but a new master cylinder needs a little convincing.

Even after bleeding some master cylinders that I've tested will just spray fluid out instead of a solid squirt...this is due to the master cylinder sucking air in from the outlets instead of fluid from the reservoirs. There is more pressure in the reservoir than at the outlets so there is no reason for a lot of air to get sucked in...some air is typical, but not enough to turn the stream into a spray. It sometimes takes two or three master cylinders until I find one that works the way I want it to, but by setting my goals high I have managed to never have problems with my brakes.

So...you can bleed the brakes the easy way...simply buy like 4 quarts of brake fluid...the stuff is fairly cheap so no big deal if you want to do it this way. Fill a metal or glass container (don't use plastic or rubber) with enough brake fluid so that you can emerse the entire master cylinder into the fluid...you might need to have the master cylinder at an angle so you can use some force to pump it. Then pump it until there's no bubbles. Remove it from the brake fluid bath and pump it several times to make sure that you are getting solid streams of fluid out of the outlets. If you only get one or two pumps of solid stream then it starts to spray then I would get another master cylinder, but some people might figure that was OK because as long as there is fluid at the outlets like with a comletely filled system, then you will have no problems...but I disagree.

 

I have a '75 and had the same problems. I had newer brake lines
already in front (from the master to the brakes). I got new brake
lines from the cylinder to the back and also between the wheels -
now everything works great. Those old brake lines looked liked
they were going to burst - and might leak a little air. No more problems.