OK, here is the story.

Thursday afternoon I notice my brake pedal was really low. I did not see any leaks so I checked the brakes for adjustment, since I just did the brakes in July for inspection. Turned out my rear adjusters are not working so, I adjusted the rear brakes and all was well.

Friday I am returning from lunch and the pedal feels a little low again so I chalk it up to the rear brakes maladjusted again and go into the office. I come out quitting time and try yo adjust the brakes but, they are still adjusted from the other day. The pedal is really low now but still holding some pressure. I notice there is brake fluid at the passenger side caliper so, I call my wife and have her go pick up the parts while I drive home.

I vise gripped the brake line on that side so I would not lose anymore fluid or pressure. The truck got me home where my wife had the pats waiting. I figured I would just replace both calipers at the same time.

I replaced the calipers as usual. I vise gripped the lines to let as little air in the lines as possible and then usually I just bleed the calipers and I am on my way.

Not this time. I can build no pressure at all. I figured it must be the Master Cylinder so I buy a new one, bench bleed it, install it and nothing, no pressure at all. I bled the system from the passenger rear to the diver rear to the passenger front to the driver front. Nothing but fluid coming out of the lines but still no pressure.

Here is the question, the only thing left to replace is the power brake booster and the proportioning valves. Can these be the culprit or is it time to call the scrap man for my $200 in scrap metal?

Pulling my hair out!

 

Acording to my Haines manual it could be the proportioning valve. I would also check the vaccume line to the booster as well. Even if you have to replace the booster it would be better than selling it for a meesly $200 after putting so much money into it with everything youv'e already done to it. Your nearing the finish line as there can't be much else to replace. I'm sure someone else will chime in with some other advise that i haven't come up with. Good luck and hang in there.

 

I can't see it being the brake booster. If the brake booster were bad, the pedal would feel rock hard and you would just about have to lay on it with both feet to stop the truck.

Also, these trucks don't have a dedicated proportioning valve. It is a combination valve that includes the proportioning valve and ABS hydraulics. If you haven't yet, try bleeding it. If that doesn't work, replace it.

 

Ii sprayed up all the fittings last night. Good thing I did, I will try the combination valve today. More suggestions are welcome. Thanks guys!

As far as the booster is concerned, what's up with that check valve?
I thought it might have been the booster too but, I had my helper step on the pedal with the master cylinder off and it pushes the rod out and I cannot push it back in so that clears the booster as the culprit, I think, unless I am missing something.

 

I've bought new calipers before and had them bad out of the box. Try pinching off each line one at a time and try to determine which one has the pressure loss.

 

Alright, here is the latest update on this issue.

I was able to free up all four fittings at the combination proportioning valve and ABS valve. I managed to free up both of the fittings at the rear wheel cylinders but the passenger side twists the steel line when it turns so I can barely do anything with that one.

Now that everything has been freed up I started from the beginning in this order.

1. I removed the master cylinder and bench bled it again. I had air bubbles in it. I replaced the master cylinder after bleeding and began to bleed the system.

2. I started bleeding at the combination valve and got no air there. Refilled the M/C and moved on.

3. I bled the rear brakes, passenger side first then divers side. No air there. Refilled M/C and moved on.

4. I bled the front brakes, passenger side first then driver side. No air in the lines there either. I refilled the M/C.

There is no brake pedal.

Now, if I have no pressure building at the pedal, that would dictate there is a leak somewhere, correct? The problem is, I can pump that pedal all day long and the fluid level in the M/C does not go down. As a matter of fact, it actually went up last night. How the hell does that happen?

I tried pinching off the rubber lines at each of the calipers to see if I could build up pressure but, the problem remains, so I am thinking the calipers are good. I have also replaced the M/C twice so, that rules a defective M/C out, I would think.

I have never had this problem before.

 

OK, I have taken the rear wheels off to check the wheel cylinders for internal leakage. Nothing. Dry as the Sahara freakin desert. I have checked the lines over and over again and have found no leaks, anywhere. JFC, I am at wits end with the freakin truck. I am out of ideas and days off. My boss told me if I am not in tomorrow, not to bother coming in at all. The scrap man is looking better every freakin hour I waste trying to get the brakes working on this truck. If I didn't have to stop, I would drive this truck into the ground but, that pesky little stopping thing might get some people a little agitated.

I priced out that ABS valve, is it really $236. Holy crap!

The proportioning valve is like $35 but, how can I tell if it is bad and why would a bad proportioning valve cause no brake pressure. AAAAAAAAAAAHHHHHHHHHHHHHHHHHHHHHHHHHHH!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!:ic on_brr::ic on_brr:

 

I had the exact same problem as you with my '95 V6 last year after I replaced my front calipers. I replaced my brake hoses for the front calipers also. A weak brake hose will cause a spongy to no pedal. After that, bleed the brakes.

After I replaced my calipers, master cylinder, brake hoses, etc., I still had no pedal, so what I ended up doing is getting a pressure bleeder and bleeding all four wheels for like an hour and after that, I had a pedal. If you don't have a pressure bleeder, you can use a vacuum bleeder that runs of compressed air and suck the fluid out of each bleeder. Just keep your eye on the master cylinder, don't run it dry or you'll be working double hard.

 

Much more information can be found in the service manual, section 5, but some key points are below.
Is your brake light on the dash lit up?

I had an issue with bad brake feel after I replaced my entire brake system (except for the combination valve), the pedal pretty much went to the floor easily. Part of my issue was a leak at a brake caliper (bad copper washers), but some of it was also...
You said "I bled"... did you do a one-man bled job (with a vacuum bleeder), or a two-man (you at the wheel, the other at the brake pedal). I initially did a one-man bleed on my brakes (via vacuum bleeder), but it was still not good. I had to use a friend.
Also, make sure you keep a good eye on the Master Cylinder level. If you run low on brake fluid (and remember: as the brakes are applied, the fluid level decreases!), air WILL enter the lines, and the whole process needs to be done again. I had to redo my bleed because of that.

Taken from the Service Manual:

PEDAL FALLS AWAY
A brake pedal that falls away under steady foot pressure is generally the result of a system leak. The leak point could be at a brakeline, fitting, hose, or caliper. Internal leakage in the master cylinder caused by worn or damaged piston cups, may also be the problem cause.
If leakage is severe, fluid will be evident at or around the leaking component. However internal
leakage in the master cylinder will not be physically evident. Refer to the cylinder test procedure in this section.
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MASTER CYLINDER/POWER BOOSTER TEST
(1) Start engine and check booster vacuum hose connections. Hissing noise indicates vacuum leak. Correct any vacuum leak before proceeding.

(2) Stop engine and shift transmission into Neutral.

(3) Pump brake pedal until all vacuum reserve in booster is depleted.

(4) Press and hold brake pedal under light foot pressure. (a) If pedal holds firm, proceed to step (5). (b) If pedal does not hold firm and falls away, master cylinder is faulty (internal leakage).

(5) Start engine and note pedal action. (a) If pedal falls away slightly under light foot pressure then holds firm, proceed to step (6). (b) If no pedal action is discernible, power booster or vacuum check valve is faulty. Install known good check valve and repeat steps (2) through (5).

(6) Rebuild booster vacuum reserve as follows: Release brake pedal. Increase engine speed to 1500 rpm, close the throttle and immediately turn off ignition.

(7) Wait a minimum of 90 seconds and try brake action again. Booster should provide two or more vacuum assisted pedal applications. If vacuum assist is not provided, perform booster and check valve vacuum tests.
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As per the Service Manual, the proper bleed sequence is:
master cylinder
combination valve
rear antilock valve
right rear wheel
left rear wheel
right front wheel
left front wheel

Make sure you bleed the system without the aid of the Power Brake Booster (ie engine not running, and the brake booster vacuum depleted).
Also, make sure to check ALL connections for ANY leaks. This included the front brake tee, rear brake tee, the front brake hose unions, etc.
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Re-reading part of your original post, you said something about "low pedal"
The service manual has this to say:
LOW PEDAL
If a low pedal is experienced, pump the pedal several times. If the pedal comes back up, worn lining and worn rotors or drums are the likely causes.
A decrease in fluid level in the master cylinder reservoirs may only be the result of normal lining wear. Fluid level will decrease in proportion to wear. It is a result of the outward movement of caliper and wheel cylinder pistons to compensate for normal wear. Top off the reservoir fluid level and check brake operation to verify proper operation.
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are you sure your rear brakes are adjusted tight enough? when you put on the emergency brake does the emergency pedal go all the way to the floor? would indicate rear brakes need to be adjusted tighter....maybe when you push the brake pedal it bottoms out before the rear brake shoes contact the drum??????????????
just adding to the pot of things to think about??????