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Discussion Starter · #1 ·
:whiteflag

Folks -

I have been lurking here a while and I got some excellent info (props to Shadowfax and TophersWorld.com!!!!) and help by searching this site, but I have a problem that I cannot seem to find an answer to. Here's the situation:

Vehicle: 1994 EB

I replaced front rotors, calipers, pads and bearings. Much of the brake fluid drained out, but the reservoir was never empty. I bled the brakes thoroghly (1/2 a quart). When I got ready to test them out, there was some pedal feel when the truck was off. After I started the truck, the pedal is soft all the way to the floor and then it locks up the wheels at bottom.

So, here's where I'm at:
1. I found a leak and fixed that. No more leaks as far as I can tell.

2. I bled some more almost a quart total.

3. The pedal is soft all the way to the floor, and then locks up the brakes.

4. "Pumping" the pedal does NOT build up feel or pressure. It ALWAYS operates as descibed at 3.

I was watching the reservoir while someone else pumped the pedal, and it looks like fluid is coming back into the reservoir. Is it possible that the ABS valve is jacked up and diverting fluid?

Any help is greatly appreciated.

KC

P.S. No dash lights at all. When there was a leak, the brake light stayed on, but once I fixed the leak, no more lights.
 

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and by entire system. i think he means all lines.....had to do that with mine.....air got way back into the system....after bleeding all lines they felt like new......
 

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Just echoing the others. Bleed all the lines starting with the right rear, left rear, right front and then left front. That should take care of the problem.
 

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Discussion Starter · #6 ·
2 quarts through it starting from the right rear and proceeding per Hayes and AllDataDiy.com and the same problem persists. I really don't think this is air. As I said before, I can pump and pump and pump and no pressure builds up.
 

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Satyr of the Midwest
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So it'll bleed fine, as in fluid will be forced out the bleeder, but you still can't get a firm pedal? Something's not adding up here...
 

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Possible bad MC. buy a brake line clamp, clamp one line at a time looking for a bad wheel cyl/ caliper. If no change, change the MC.
 

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Discussion Starter · #9 ·
Ok - more info:

All the stopping is from the back brakes. In the initial post, I mentioned that there was no pedal feel and then you get all the way to the floor and it locks up. So I investigated this behavior further by putting the front on jack stands and spinng the wheel by hand while the wife slammed on the brakes and I'm getting nothing from the front calipers at all. Even with the brakes to the floor.

So this tells me that the calipers aren't moving right?

If the MC is screwed up would the rears still work?

I wonder if I missed some packing material or instruction on the new caliper installation?

Thanks for the tips so far.

KC
 

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All modern MCs are "dual piston" type, which means if 1 part fails, the MC will still operate the other brakes. The vast majority of vehicles are split by axles, meaning F & R. Very few are split diagonally. So yes: it's theoretically possible for the MC to be bad & still work the rear brakes.

It's just not very likely.

So do you get fluid pumping out of the front calipers when you bleed them, or are you using a vacuum-bleed technique? Either way: if you get fluid out, there's nothing blocking them off.



kellyjcook said:
...the wife slammed on the brakes and I'm getting nothing from the front calipers...
What are the rears doing? What happens if she applies the pedal slowly?

Just to be 100% sure:
You have new calipers installed on new pads & new rotors fully assembled as shown here, right?



Or do you have floating calipers like this?



And you adjusted the wheel bearing nut like this?



If the nut looked like this, there's a different procedure, which I don't have posted yet...

 

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kellyjcook said:
Ok - more info:

All the stopping is from the back brakes. In the initial post, I mentioned that there was no pedal feel and then you get all the way to the floor and it locks up. So I investigated this behavior further by putting the front on jack stands and spinng the wheel by hand while the wife slammed on the brakes and I'm getting nothing from the front calipers at all. Even with the brakes to the floor.

So this tells me that the calipers aren't moving right?

If the MC is screwed up would the rears still work?

I wonder if I missed some packing material or instruction on the new caliper installation?

Thanks for the tips so far.

KC
Did you bleed the front lines??
 

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Discussion Starter · #13 ·
Steve83 said:
So do you get fluid pumping out of the front calipers when you bleed them, or are you using a vacuum-bleed technique? Either way: if you get fluid out, there's nothing blocking them off.
Pressure bleed - I don't have a vacuum pump. I'm using a wife-pump-the-pedal which seems to work well (but I gotta get this fixed pretty quick cause she's starting to develop body builder thighs...;) ).

Steve83 said:
What are the rears doing? What happens if she applies the pedal slowly?
The rears seem to be operating normally. Appling pedal slowly stops the rears as expected.


Steve83 said:
Or do you have floating calipers like this?

I have the floating calipers, and I have new rotors, calipers and pads installed per this drawing.


Steve83 said:
And you adjusted the wheel bearing nut like this?

Correct. I have the outer lock nut, holy washer, inner lock nut requiring large 4 tooth socket type of hubs.

To the other questions, yes, I have bled all four wheels, and if I'm not mistaken, the Proportioning/Combining valve is about a 1" long lug-nut looking thing that comes out of the side of my MC on the line closest to the firewall.

I tested my ABS and Brake lights, and they seem to function correctly, so I don't think there are any codes being thrown or system malfunctions that are being detected.
 

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So the MC is pumping fluid to the fronts. Are you opening the bleed screw, then telling her to pump the pedal, or are you having her pump & hold, then opening the screw? If the latter; does the fluid spray out with some force? Are you bleeding it with the key on or off?
 

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Discussion Starter · #15 ·
Steve83 said:
So the MC is pumping fluid to the fronts. Are you opening the bleed screw, then telling her to pump the pedal, or are you having her pump & hold, then opening the screw? If the latter; does the fluid spray out with some force? Are you bleeding it with the key on or off?
I've only bled with the key off and bleeder open before any pressure is applied. I'll try the other scenarios you suggest when I get home this evening.

If I get pressure with the key off and less or non with the key on, what does that mean?

Thanks again for the suggestions.

KC
 

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To save your wife's thighs from getting any bigger, get some speedbleeders from summit. They're only $10 an axle, and worth every penny.

It sounds like you might have air in the ABS HCU to me. You can't bleed that out without a special tool, or magical knowledge of how to make the pump start and solenoids switch.
 

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Discussion Starter · #17 ·
sewiv said:
To save your wife's thighs from getting any bigger, get some speedbleeders from summit. They're only $10 an axle, and worth every penny.

It sounds like you might have air in the ABS HCU to me. You can't bleed that out without a special tool, or magical knowledge of how to make the pump start and solenoids switch.

I ordered the speed bleeders yesterday...;)
 

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If it changes with the key on, it would indicate a hard fault in the 4WABS ECU, triggering an isolation valve (or 2) in the HCU. If that turns out to be the case, just unplug the 2 connectors near the HCU/ECU beside the PS box.

It actually doesn't take "magical knowledge" - you just have to be able to read & understand the wiring diagram & apply 12V/ground to the HCU inputs to make them do what you want.
 

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you've got the bleeder cracked before you start the wife pumping??????? if you do, you need to have her pump, hold, then crack the bleeder...........
 
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