Hi experts, I'm in the process of replacing the combination valve on my friend's 71 442, (power disk brake)
We have a very hard brake pedal, booster and Master Cylinder are new, good engine vaccum, but when trying to vaccum bleed
the rear, not much was coming out. So I want to buy this valve from Inline tube (see pics for old and new), is it a good choice ?

Thanks

 

Did your bleed the master cylinder? If you loosen the fitting at the master cylinder does fluid come out when you press the brake pedal? Before replacing the valve, make sure you are getting fluid to it from the master cylinder.

 

Is the brake light lit on the dash? Your issue can also be the rubber brake line from the hard line to the rear differential.

 

Thanks, yes did bench bleed it, but did not loose the fitting to test, will try that as soon as i get the car.

 

No the light is off, but is it working ? Don't know. The last time I had the car that rubber line on the differentiel looked very old, will change it and test the master like Loaded68W38 suggested.

Thank a lot your a big help.

 

In your photo above, the wire for the brake warning light is disconnected. It attaches to the pin between the front anf rear lines coming from the master cylinder.

 

Usually it is connected, I took it off to remove one line...

 

I figured that was the case. You can touch that wire to ground with the key on to see if the light and wiring are good.

 

Yes thanks Loaded68W34.

 

The combo valve won't cause a "very hard pedal" unless it is totally plugged, which would mean that zero fluid is getting to the wheels. Perhaps more troubleshooting before replacing a part that will likely cause collateral damage (like breaking at least one of those hard lines)? And that brass ILT combo valve is likely the same imported part that everyone sells, the PV-2 valve with the one-size-fits-none calibration.

First question is, is pedal force the same with and without the vacuum line connected to the booster? If so, then the hydraulics are not part of this problem.
Second question is, if you ground the wire to the combo valve with the key on, does the BRAKE light come on? If so, that system is working and the switch inside the combo valve isn't off to one side.

Which vacuum bleeder are you using, a Mityvac or a constant-flow system like Vacula?

 

I will test as you said Joe as soon as I have my friend's car at home back from storage. For the wire if I understand, light should come on when grounded to the valve and if the switch inside isn't off to one side ?
To me is, if you ground the wire to the valve, the light should come on right away, no matter where the switch is located inside no ?

For my bleeder I use one from my auto parts store, it's PT performance..may be not the best actually

Thanks Joe for your pro tips

 

Once you disconnect the wire from the combo valve, the switch isn't part of the circuit. This is just a troubleshooting technique. Disconnect the wire and ground it to simulate the switch being off-center. This tests everything in the circuit except the switch, to verify that the circuit is operating. Now if plug the wire back onto the switch and the light still doesn't come on, that says that the switch is not off-center.





As for the vacuum bleeder, I've found the hand-pump versions to be less than satisfactory, no matter who makes them. The Vacula style (and the imported clones) use shop compressed air to create a constant vacuum in the bleeder. These are much more effective.

 

OK Joe got it, and I think I will shop for one of these Vacula. In the coming weeks I'll post what I did and found, thanks again.

 

Be aware that a real Vacula is very expensive. I found mine used at a swap meet for cheap. There are clones available for under $50 on Amazon.

 

This one should do the trick, and pretty good reviews.

 

Hi, did the pedal test, with vaccum line connected it's a hard pedal and with the vaccum line disconnected it's very very...vey hard. So that means the booster is ok right ?

Did ground the wire for the switch on the combinatioin valve with ignition ON and the brake light is ON so...the cicuit and the light is good, after putting back the wire on the switch, ignition ON, the brake light is OFF, so like you said Joe, switch inside the combo valve isn't off to one side right ?

So I think the next thing is to press brake pedal and open the line on the master to see If I have oil coming out to the combo valve. like Loaded68W34 said in an earlier post.
If it's ok what would be the next thing to check, both rear wheel cylinder are new also. And the rubber hose on the differentiel doesn't look that bad finally.
Thank you all

 

If you get flow from the M/C, the next thing to check is the next connection, and the next one and the next one. Don't buy anything until you know where the fluid stops.

 

Thanks Joe, I'll do that.

 

Hi again, ready to open the fitting on master cylinder to see if there is flow to the combination valve, if it does,
I will open the one that go to the rear brake, so my question is if there's flow, will the switch inside the
combo valve will move to one side ? I did remove the brake switch to verify that the valve is not off-center, and it's good.
So I'm afraid that the valve could move and get stuck,
I need your good advice again, thanks

 

If you don't jam on the pedal the valve won't move.

 

Ok thanks, happy to hear that, just opened the fitting on master cylinder and there's flow, so
next one on combo valve...to be continued.

 

OK got good fluid out of the rear of the combination valve, now going at the rear at the soft line on differentiel,
that's a nasty little place to unscrew a fitting! Hope to find the problem soon, I have the impression that things are not moving forward.

 

Hi again, just removed my rear rubber line and it is NOT clogged. Had to break the main line but I will replace it along with the 2 short line that goes to the wheel cylinder. The only thing left are the rear wheel cylinder and they are new !!

71 442 conv.

 

Hi,
here's a little update on these brakes. Replaced all hard and rubber hose, rear wheel cylinder are new.
Bench bleed again the new master cylinder, and put a vacuum pump to bleed the lines.
Now with a person pumping and holding the brake pedal, when I open a bleeder on the front caliper, there's a very stong flow
and pedal is going to floor. But in the rear the flow is alot less and pedal will travel about 1/3 of it's travel and become hard.

The only thing that is not new is the combo valve. I thought I could try to disassemble it for inspection and cleaning, but if I need
o-ring or something inside, not sure they are available. Any advice, I don't thrust the repop valve.

Thanks a lot