[shrike77]

Dumb question, should it loop upwards like I believe it should or downwards? Here's a pic of the driver side front wheel where it loops upwards. Can someone confirm if this is right or not?
Still trying to chase low and spongy pedal. After capping all four brake lines I am at 85% sure the problem is from the front brakes. I replaced hoses, bushings, sliders and bled 3 times and pedal is still low.
I'll remove calipers again and check for sticky piston, but car doesn't even see the rain so I doubt it's that.

Just trying to check everything before I start replacing the calipers or the knuckle.

 

[bigm57ict]

I believe up is correct.
Have you looked at the master cylinder as a possible culprit?

 

[shrike77]

thanks for the reply. I capped the brake hard lines to isolate the wheels from the rest of the system. Started the engine and pedal was hard. That eliminates the MC, that's why in my opinion the problem is at the wheels

 

[deVille33]

When did this start? Had you opened the system before this started? You replaced the hose?
The directional control valve, which is positioned on frame rail below the MC, will trap air if the system is opened upstream. If you crack the line going to the rear brakes, with someone standing on the brake pedal, you can get the air out. Sometimes you have to tap on the valve body to move the valve off the seat. This happens the valve is angled downward and will trap the air on the underside of the valve.

 

[shrike77]

Yes the hoses were replaced. The rear end was swapped with one from a Caprice with rear brakes. I am not sure now if it got worse right after the swap or it was already as bad. But I definitely remember the pedal sinking a bit before the swap.
I gutted the combi valve of both the valve at the rear and the bleeder nipple at the front. I plugged them.
I wanted to do the stealth bolt mode known on the impalassforum.com
But I also cracked the nut for the rear line today as you said.
Anyways, fluid comes out at every caliper. I capped all four hard lines on the frame to isolate the wheels from the system and the pedal seemed to stay up and hard, it sank but very slowly because one of the caps was leaking a bit. So to me this means that the master cylinder and the combi valve are fine.


I bled the calipers upside down , at differents angles too and nothing.

I removed the lines from the MC and plugged the outlets, started the engine and the pedal doesn't move a hair. It is very solid. so this means MC and booster are fine, right?


When I bleed the brakes with engine on, there is a bit of turbulence and I can see a bit of dirty fluid from time to time that is mixing with the clean fluid.
If I bleed them with the engine off, there is no air and fluid is clean.
Is it normal to have a bit of turbulence while bleeding with engine on?

The booster valve seems to only let air one way only.

Also when pressing on the brake pedal with the engine on, there is a powerful jet in the MC reservoir close to the firewall. Is that normal?

Also if I give it a bit of gas, when pressing the gas pedal, the brake pedal seems to sink a little more but it can be barely felt. When the RPM's go back to idle, the pedal seems to raise, again it is a very very slight movement

 

[deVille33]

For some reason your engine draw is affecting the vacuum to the booster. Check the grommet at the canister. Make sure it isn't cracked and allowing vacuum signal loss.
Disconnect the bolts that hold the MC to the booster, and pull it forward. Don't have to remove the lines. If there is fluid in there, your rear seal is seeping. The MC will work fine as long as the inner seals maintain in place along the bores. Particles ( dirt ) that gets into the valve passages can cause the seal to fail. Essentially, because the bore is in the low end of the MC you can get mud in there. Here is a trick that may cause damage or cure your problem.
Remove the brake lines from the master. Use a syringe and remove the fluid in the reservoir. Fill the master with denatured alcohol. Denatured alcohol will not effect the rubber seals. Run lines from the master to a bottle to catch the denatured alcohol / fluid mix. Put the cover on and pump the brake twice. Do not allow the reservoir to be pumped when dry. You will damage the seals. Refill the reservoir and pump twice more. See if the fluid starts to clear. Do this until the fluid clears. Get the mud out. Once the fluid clears up, pump the reservoir down low. Let it set and blow it out with air pressure set at 18 to 20 pounds on your compressor. The DA will dissolve quickly. Fill with new brake fluid and follow normal pre-bleed procedures. Reconnect the brake lines. Crack the lines at the master to remove air.
Many masters start that pedal fade because of the mud that affects the seals. If you don't want t do all this to save $35.oo, get a new master. I never buy rebuilts and rarely remans. Only new units from EIS, Rayloc or a reliable brand I trust.

 

[shrike77]

Thnk you very much for that detailed procedure. I don't have access to a compressor unfortunately.
I forgot to mention something that I think might make a difference. The car is only driven sunny days in summer so I completely forgot about that detail that makes me think is the booster. When I press the brake pedal, there is a very audible woosh from the booster, under the dash. How audible should it normally be. I am not sure that when I got the car 5 years ago it was that loud. I remember one evening when I heard something strange under the dash but I think I was really paying attention to be able to hear it. Now you can hear it with my louder exhaust.
How loud is the hissing normally?

----------

today I took 5 min to unplug the hose frome the booster check valve and try to press hard on the brake pedal. I know the brake wasn't assisted anymore but it really didn't go down that much. I couldn't drive it because I removed the driveshaft.

 

[Robin Banx]

I don't think that one should hear any hissing or whooshing upon applying the brakes.

Cheers...........R.

 

[shrike77]

ok thanks. I'll make sure nothing is unplugged and that the noise is really from the booster and get a new booster if that is the case. When I searched 3-4 years ago about this I think I read somewhere that a small hissing was normal but now the noise is very audible

 

[shrike77]

Which booster is right? With or without vacuum switch? Is the vacuum switch used only for electric pumps?

 

[deVille33]

The vacuum comes off the back port of the carb. Not aware of a vacuum pump used on Cadillacs and not aware of a switched application. The noise could be from a cracked diaphragm. Make sure it not coming from the vacuum hose for the automatic brake release. That hose has a tendency to dry out and harden over time. Will cause significant vacuum loss to affect engine operation and other vacuum signals.

 

[shrike77]

The hose for the autommaticparking brake was plugged already but I will make sure it's still good. The car has a FI engine now, the hose goes to the intake manifold. But the idle is fine so it's probable still ok.
By the way, while looking for brake boosters it seems that mine is missing the filter for it. It actually never had it otherwise I would have kept it. If the booster is really dead, it could be the root of the problem.
I was asking about the vacuum switch because rockauto lists a booster with vacuum switch and others without.

 

[shrike77]

changed booster today. still hear wooshing noise while applying brakes. when pedal reaches end of travel boosteer is quiet. Is that normal? the noise comes from the filter from around rod that attaches to brake pedal.

 

[bigm57ict]

I think that's normal. I'll have to listen next time I drive it, but I recall hearing that sound.

 

[deVille33]

The carbureted systems had no filters. Yes, you may hear the canister when the pedal is depressed, but it should not be loud enough to distract from operating engine. Once you get used to it, you shouldn't notice as much.

 

[scurling]

Shrike77: I've been searching some brake problem posts to get some ideas for fixing my soft brake pedal. I had to replace one hard line coming off the Bosch distributor box to the front left wheel. Then I had a caliper rebuilt on the front right.

I see you capped the lines at one point in your investigation. How and at which connection did you cap the lines. I haven't seen any specific cap fittings in the parts store, so I'm thinking you made a connector to cap the line.
My thought on locations was where the 3/8 in. flex line connector meets the inboard hard line. That's seems to be an easy access on the front end. I'm not sure about the rear lines.