Brake Failure - Stiff Pedal & No Assist (Solved)

[crystalworks]

**Solution**

Putting this here for those who don't want to read the whole thread. The problem turned out to be a bad brake booster. The subsequent repair TRW (OES) booster was bad out of the box as well, because that's my luck. Had a small vacuum leak that would cause it to lose vacuum overnight, or consecutive braking actuations.

So TLDR, brake assist loss (and stiff pedal) was caused by a failed booster.

**Original Below**

So there are plenty of threads about this and I'm going to diag the issue in the next couple of days.

But just wanted to post to get some thoughts, and to just vent a little I suppose. I am assuming (you know what they say when you do that) that at 168000 miles the vacuum pump seals have failed on our 2010 X5d and taken out the booster. It doesn't leak externally, but I have not looked at the vaccum line or internals of the booster. I'm still waiting for the tow truck to bring it home from the dealer where it was getting state inspected. I'm guessing it failed during the ABS lockup test being done by the tech as it drove and broke fine on the way there. I have that kind of luck though...

If you've been following along I've been fighting this X5 for the last 2 years. First the trans went out, so I spent a year(+) trying various things, and eventually just replacing the trans. It shifts wonderfully now. Then, SCR inefficiency popped up, reset that, which led to DDE forced no start condition. Spent almost a year trying to figure that out myself, got ISTA running, unknowingly installed counterfeit NOX sensors, then installed real NOX sensors from the dealer. But not before my mileage and reset were used up so I could not continue ISTA test plans. Sent out the DDE, CAS, and key to have the DDE unlocked. And finally got it all back together which brought me to taking it for its state inspection today so I could start driving it again. And list it for sale so it could pay me back some of the love I've given it. Well... I guess it's not ready to leave yet and wants more money, sweat, and tears.

[josiahg52]

I have almost 169k on my diesel. So far no huge issues. Do have a current NOx system inefficiency DTC; 04D16 / P20EE. I've looked at your threads with interest. Hope repairs go smoothly.

[sgrice]

Fairly easy to diagnose with a vacuum pressure gauge. The vacuum pump on what is now my son's 35d went out last year at I think something like 140,000 miles. Symptoms of stiff brake pedal and poor braking. In our case the booster was fine. Replacing the vacuum pump solved everything. Not too hard of a repair as I recall - everything is right up front and fairly easy to get to.



Good luck with what I hope is your last repair!


Stephen

[crystalworks]

Originally Posted by sgrice

Fairly easy to diagnose with a vacuum pressure gauge. The vacuum pump on what is now my son's 35d went out last year at I think something like 140,000 miles. Symptoms of stiff brake pedal and poor braking. In our case the booster was fine. Replacing the vacuum pump solved everything. Not too hard of a repair as I recall - everything is right up front and fairly easy to get to.



Good luck with what I hope is your last repair!


Stephen

Thanks Stephen! I would prefer it be the vacuum pump itself that failed rather than it leaking oil into the line which finds its way to the booster and takes it out. As you said, it's right up front and easy to get to. Will be using a Mighty Vac to check both the pump and the booster's ability to supply/hold vacuum. Will update after I get the oil changed on our E61 and get the E70 back into the garage. If I let the X5 idle for awhile, I do get a few good braking tries so perhaps the pump is failing to produce vacuum or there is a vacuum leak somewhere. *Fingers Crossed*

[andrewwynn]

Post the results curious minds want to know


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[crystalworks]

Originally Posted by andrewwynn

Post the results curious minds want to know.

Will do. For now... I'll just leave this here. Ah, BMW life.

[crystalworks]

Well guys, got some diag in. First pictures show the vacuum being provided by the vacuum pump with the brake booster disconnected. 27 inches of mercury, which seems more than sufficient to me. I checked this at the check valve that connects to the booster.



Then, I took the check valve line off the truck so I could do the blow test for the check valve. It passed. I could suck (from the vacuum pump side), but not blow through the line. So valve is good.

I took the line off the vacuum pump to check for oil in the line. There was some, but nothing major. I am going to replace the seals anyway. I checked further down the line at the joint and at the booster check valve. No oil was present so I don't think the booster seals were fouled by oil.

Then I T'd into the line with the mityvac/gauge so I could see vacuum with the booster connected. This leads me to a couple of questions, but I am leaning towards a failed booster rather than a failed vacuum pump. I think the vehicle sitting for so long in hot and cold over 2 years through the seasons with the vehicle very rarely being used and brakes being actuated led to the booster diaphragm being brittle. Then the ABS lockup test being administered during the inspection testing caused it to rupture/tear. Does this sound plausible? Here is a video I took of vacuum behavior with the entire circuit hooked up.



Questions:

• Max vacuum reached was about 25 in Hg rather than 27 with no booster in circuit. Assuming none of my joints were leaking (hah), does that mean it's leaking from the booster?
• How quickly should the vacuum climb after engine start? I should have noted that when I was testing without booster in circuit, but did not have a helper.
• How quickly should vacuum exit the system after the engine is shut off?

Thanks for any thoughts/suggestions. I still have things hooked up so can run any testing suggested. Am getting a parts order ready...

[crystalworks]

Update: So I went ahead and cut the booster out of the circuit by removing the check valve/line. Then I capped that.

After starting vacuum climbs very quickly (2-3 seconds) to 27in Hg as compared to climbing very slowly (90 seconds to 25in Hg) when the booster is in the circuit.

I'm going to call it a failed brake booster. Ordering replacement parts now. If it's not one thing, it's another with this thing. Does not want to leave.

[crystalworks]

Update #2: Still have a problem, but what a friggin mess. I ordered blockoffs for the master... made basically no difference. Brake fluid spills everywhere. Fortunately I stuffed plastic lined "diapers" around under the booster area and it caught everything so I was able to lift the mess out just as if I was lifting out an old cloth diaper. Very little fluid actually made it to paint on the truck. Phew.



But I did manage to get the new booster in and everything reinstalled without much fuss other than the mess. I hate messes.



Here's what came out of the RR caliper. Guess someone had ATE Super Blue in it at some point. I ran through the bleed procedure. "Flushed" the lines and then used ISTA to trigger the DSC/ABS pump during the second run of bleeding.

Now, my problem. My pedal no longer feels stiff all the time. It feels mostly normal, maybe slightly too much pedal travel compared to normal? Hard to say. But my braking, while feeling better than before... a bit, still feels really bad. Like unsafe for driving. Do I just need to keep bleeding fluid out of this thing because air is still in the system? So far I've ran through 2 quarts of brake fluid. Just keep going?

Let me know your thoughts, I hate doing anything involved with brake fluid for this very reason. Seems like some weird black magic to get all the air out of the system... or maybe I'm just an idiot. That's always a possibility too. But now using the pressure bleeder and ISTA I thought I would have the right recipe...

[80stech]

Nothing beats a second man with some experience and a feel for what they are doing to bleed brakes. Sometimes there are high spots for which a fast flow is needed to purge the air and your pressure bleeder is no replacement for a good man on the peddle.