Solved Unable to bleed 4WABS.

[techweenie]

I need help! I've been trying to bleed the brakes on my 94 Explorer with 4WABS for over a month and haven't been able to do it. The symptoms are spongy pedal, low pedal with engine running, and constant stream of small bubbles when bleeding. I figured it had to be air in the ABS pump, so I bought the bleeder tool and used it. That actually made the problem worse and I had NO pedal after that. I then went to a junkyard and pulled another ABS pump and installed it. Ran the bleeder on it, and I was back to square one with the low spongy pedal, but at least I had SOME pedal again. No air whatsoever in the front lines, but a constant stream of tiny bubbles remained in the rear. I then did as much research on this as I could and determined it must be a stuck valve in both pumps causing fluid to fill the accumulator rather than go to the calipers or drums. Rather than gamble on another junkyard part, I ordered a brand new pump from ebay. Installed that today, and STILL THE SAME SYMPTOMS. This time I'm getting a steady stream of tiny air bubbles at all four wheels. I have the factory service manual and I've followed it to the letter on diagnosing the low pedal and bleeding procedures. I'm using the 2 person down/up method without pumping up in between (tried pumping up as well, no different). I tried vacuum bleeding but couldn't get that to work. I put a new master cylinder on it but that didn't help. It did solve intermittent brake light function though (the old one didn't have enough return pressure to keep the switch activated). I put a vacuum pump on the booster and it held vacuum. I don't know what else I can do!

 

[BKennedy]

If its the ABS pump, it probably needs power bleeding by a shop. Have you tried the gravity method? Tubing on the R/R bleeder, crack it and come back in a couple of hours. Repeat for each corner. That is what worked best for my Explorer when I had soft pedal issues after the SAS.

Did you check the entire rear brake lines for a leak? It sounds like air is getting in somewhere.

 

[techweenie]

Since I can't vacuum bleed I haven't bothered gravity bleeding. There are no leaks anywhere that I can see, and it's a California truck so absolutely no rust on the brake lines. I'll buy a pressure bleeder if that's what it takes, but I'd like to hear some opinions first.

 

[massacre]

Pressure bleeder is what I use

 

[BrooklynBay]

Did you try using speed bleeders? Those things are small bleeder screws with built in check valves.

 

[techweenie]

I just don't see how speed bleeders will help. They don't change the process that has repeatedly failed me.

 

[BrooklynBay]

They prevent air from entering the system while bleeding the brakes with one person. It simplifies the process.

 

[swshawaii]

Were any calipers removed? Sides have been switched where the bleeders were on the bottom.

Impossible to get the air out without having ALL the bleeders facing UP.

 

[techweenie]

Calipers are in correct position. Front hoses are newer, but done before I bought it. This is not my first rodeo, but it is my first older Ford. I grew up with Chevy and bleeding those was always a breeze.

 

[FR-425]

My trick is to install a front rotor with a couple of missing teeth on the tone ring, then drive slowly with the brake applied. This will activate the ABS pump every time the pickup passes the gap in the tone ring, forcing the air out of the ABS block. Then bleed as normal to get the air out of the rest of the system.

 

[Centaurious]

Are you wrapping teflon tape around the THREADS of the bleed screws? If not you will get air seeping past the threads and a stream of small bubbles when you vacuum bleed.

When I have a spongy pedal I like to have my assistant pump up the brakes 3 or 4 times, hold good pressure on the pedal, and I open the bleed screw as far and as quickly as I can. If air is trapped in a high spot in the line, cracking the bleed screw open and letting the fluid out slowly will allow the fluid to flow AROUND the trapped air and not force it down and out the line.

 

[boominXplorer]

Is there any prior brake work that was done before this problem arose or did you but the truck with this problem?

 

[410Fortune]

air trapped inside the 4wabs pump can cause a soft pedal
A shop will have to activate the ABS pump while bleeding to get that trapped air out

Also a master cylinder, even new, will blow out its seals if it is depressed too far during the initial bleeding process (bench bleeding or otherwise)

There are several threads like this have you tried the search button?

 

[techweenie]

I have searched relentlessly about this, but almost everything is rwabs. I have the ABS bleeder tool so I don't need a shop (I called around first and no local shops or dealers have the tool). I only bled the master cylinder after installing and adjusting the push rod. I used the reverse bleed with a syringe method, and then pumped it several times with tubes running back into the reservoir. I'm confident there's no problem with it. I also adjusted the rear drums, which were quite loose. That surprisingly made no difference.

The brakes were spongy when I bought the truck, but I didn't think much of it because it stops fine and I've never had issues bleeding before.

I ordered a Speedi-Bleed system but it hasn't arrived yet. I'm hoping that cycling the ABS pump under pressure will release all the air and stop the steady stream of tiny bubbles. That's essentially what happens with the lock it up on a dirt road method, which I can't do because there's a warning light I haven't cleared yet. Diagnostics with the breakout box indicate a wiring issue, but it hasn't been driven with either of the replacement pumps.

I disassembled the valves on the original pump and they were all full of crud and nasty black fluid despite hours of bleeding and cycling it. I mainly wanted to see if it could be rebuilt easily, but the valves are machine crimped and impossible to open without damaging. I think that's why only one company touches them. The brand new pump cost less than they charge.

I even went so far as to read the bleed procedures for other makes and models with this pump and could not find anything helpful. One old certification study book claims the accumulator valve must be purged before the rear lines can be bled, but doesn't explain how and google comes up empty. I noticed there's two check ball ports on either side of the pump body, but nothing I've found mentions them. Does anyone know what those are for?

I hope by now you realize how much time and effort I've put into this. Short of pressure bleeding, I have tried EVERYTHING.

 

[boominXplorer]

In your situation I'd try to isolate the issue. I'd unhook the rear brake line and plug the master cylinder. Plugs can be bought at Napa for cheap. Even though they all run through the pump the front and rear stay separate. If you still can't get a good pedal try plugging the front and just use the rear. Of course you must use caution and keep test drives to a minimum but this should help narrow it down.

 

[techweenie]

My brakes are FIXED!!!

The secret was pressure bleeding. I ordered a speedi-bleed kit and it worked flawlessly. I started at 15psi, cycled the abs pump, and got a lot of air at all the wheels. I think I repeated that at 15psi but still had a super mushy pedal, so I cranked it up to 30psi and got a TON of air. It took another 2 or 3 cycles of going back and forth between abs and wheels at 30psi to finally get all the air out. There was less and less air with each iteration.

So for anyone with this system who finds this on google, I'm going to say you absolutely must pressure bleed it. And I highly recommend the speedi-bleed kit.

 

[BrooklynBay]

Thanks for the update! Could you provide a photo with a link to the pressure bleeding system, and the tool that you used to cycle the ABS pump?