Hello everyone, I got a 2001 Dakota (SLT, 4.7, RWD, 16" rims, Rear ABS only) that has a brake problem I've been trying to fix.

When I bought the truck a few years ago, the brakes were crap. So I put new rotors and pads on, new wheel cylinders and shoes on the back, adjusted the parking cable and called it a day. They still were bad. Specifically, the pedal would go down pretty far before any decent braking happened. If The car was off and I pumped the pedal, it would be rock hard, and only go down about 1-1.5".

I read about the brake upgrade, so I just did another overhaul. I got 2003 durango spindles, calipers, new pads, new rotors, new flexible brake lines (I even replaced the back line). Bled the system, and the problem remains.

I noticed when I tried to bleed the brakes, all lines (front and rear) would not really drip brake fluid, other than the first couple of drops. I used my harbor freight vacuum brake bleeder kit, and got a little bit out of the passenger rear, but then it stopped sucking the brake fluid out. I even tried connecting it straight to the brake line, still no dice. Had to resort to the 2-person bleed method to really get much out. I didn't bother using the vacuum on the other brakes, but I did it the way I understand you're supposed to RR, LR, RF, LF

If I stand on the brake pedal when the engine is off, it holds...the pedal doesn't go down, so that would make me feel like the MC is fine. When the engine is running, like I said, the pedal goes down pretty far. I also notice that when I pull my foot off the brake pedal kind of quickly, the pedal has a delayed return, whereas if the car is off, it has a fast return as you would expect it.

I pulled off the vacuum line on the booster, and it is as expected, no power brakes. I threw a gauge on the vacuum hose and got 20" Hg and is very steady, so I think there isn't anything wrong with the vacuum.

So is there air in the lines? I bled quite a bit of fluid out of it, I did empty the MC with a syringe so I could replace all the old brake fluid. I'm thinking it might be the booster - it has yellow writing on the side of it making me thing it was a junkyard replacement before I bought the truck. It is a bosch unit. I dropped over $700 in it with all the brake work I've done, so I don't feel like guessing any more.

Any ideas? Not much left to replace - ABS unit, Proportioning valve, booster and master cylinder.

Thanks again

 

My understanding is if the system bleed out bone dry then air got in the ABS valves if that happens the only way to get the air out 100% is by taking it to a shop that can do it or a dealership.

DIY will never remove the trapped air.

 

x2. I hate ABS.

 

Thanks guys for the replies. As far as I know, the system was never completely dry. When I took off the front brake lines from the old calipers, I let them hang for about 2 weeks to be honest. The fluid in the master cylinder never went down (Didn't leak out as you would expect). After I got the brakes put all back together, I first sucked out all the nasty fluid in the reservoir with a syringe, but that was not low enough to affect the ABS components because they are lower in the system.

When I finished bleeding the brakes, I stood on the pedal (Which was very hard) and fired up the truck. The brake pedal went down almost to the floor and the ABS and (Brake) light came on. I shut off the truck after a few minutes and restarted it (This time without pressing the brake pedal) and I didn't have any warning lights.

I've been doing a lot of reading and thought of two more things:
the RWAL module is stuck in the "dump" position, but I would think that it would be felt even when pumping the brakes with the car off (If it was stuck)

The brake booster pushrod was never set correctly. But I would think that if it was set incorrectly I'd also have a low pedal even when the car was off.

I'm thinking if the brake booster was bad, I'd have no power assist (And I definitely do...pedal is not hard when running).

I'm thinking if there was a MC leak, when I stood on the brakes, it would go to the floor, but it's not doing that either.

The only thing I can think of is that maybe some of the things don't show up when the car is off is because I can't push the MC pushrod with nearly the same force that the booster can when the car is running?

I can't think of anything though that would be causing the slow pedal return (Only when the booster is assisting, e.g. engine running). I read about an internal to the booster check valve that could cause the problem, but I haven't found much on it.

Thanks again if you have any other ideas...

 

Their is no adjustment for the brake booster pushrod its a set length. I dont see the rear ABS sensor as the problem either.

As weird as your problems are I say air in the ABS valves only thing that says its not the ABS is the slow to return pedal that says master or booster.

Take a look under the dash at the brake pushrod do you have anything stuck or broke around the pushrod?

 

More likely than you might think. I just took my ABS valves off. After opening and disassembling, i found why it was hung in the dump mode.

20161228_140331.jpg

 

i think you may have gotten air in the MC and now you 'll need to bench bleed it. Once thats done then you'll still need to go to a dealer to have them computer bleed the ABS valves. P.S. Many Snap-on code readers(even the older ones) can do the ABS bleed procedure.

 

Thanks guys. I was thinking about bypassing the ABS all together (Pull the fuse and connect the proportioning valve directly to the rear line with a couple) to see if that fixes the issue.

I can only imagine how much the dealer would charge to spend 10 minutes letting a computer do all the work. They hear/see DIY and then you have to pay...

I thought about lifting the rear axle, putting it in drive, and then slamming on the brakes a few times to cycle the ABS. I think the RWAL system is relatively stupid because there are no speed sensors anywhere else, other than the one on the rear diff. So I think the computer activates the ABS if the back wheels "slow down too fast". I remember reading elsewhere that if you find a dirt/gravel road and do some panic stops that will cycle the abs valves as well. It's my understanding that the only thing the bleed function does is cycle them.

If I had some snow/ice here, I'd be in good shape. Too bad I'm nowhere near snow...

 

I checked and everything looks good. There appears to be some grease on the pedal pivot point, which I think is normal. When I do push down the brake pedal, and the engine is on I hear a hissing sound only as I push the pedal down (e.g. once the pedal is down I don't hear it). I've been reading that's normal, it's just the booster sucking in vacuum to assist. I looked at the booster from inside the truck and I don't see anything obviously bad there.

As far as the booster itself, it is a bosch unit, and doesn't show signs of any brake fluid leaks near the MC. There is yellow grease pencil writing on part of it, which makes me think that the previous owner might have got a junkyard booster replacement - but that's purely a guess.

 

Wow that's nasty. Yeah that'll definitely explain it.