Brake Pedal Slowly Sinking When Braking

[workingonit]

Originally Posted by Peezen

Ok so I took it to the shop and they said the bled the brakes and machine bled them but the pedal is still soft.

Said that they suspect that the MC is faulty or wasn’t bench bled properly before install. It is a brand new MC and I did somewhat bench bleed the MC though I’m not sure if I did it enough.

Is this not something a shop could take care of?


How aggravating!

Tell me about it; at my age (73) and having bad knees and back, undercar brake work is now farmed out to a pro shop, after 55+ years of me doing it all on my own.

I just (today) got my wife's '98 GMC back from a shop where I had them replace rear drum brakes (wheel cylinders, shoes, drums), replace broken/rusted bleeders on the front calipers (pads & rotors still 70%), then replace all the old fluid and powerbleed the system. The truck only gets used 2-4 times a year, and I needed pros to get everything unstuck for me (I can no longer crawl under a truck repeatedly to do the brakes by myself anymore) so it was worth a few hundred to get it done for me (they also had to replace a couple of wheel studs, etc.).

The mechanic that handed it back to me said he bled the system three times and wished he could give it a better pedal feel (actually, it feels as it did 20 years ago, so no problem), but it's certainly better than the pedal feel I got after I did much the same procedures on my wife's other car, an '08 Cobalt (it also got a new MC, new front pads and rotors, all done by me). I could not get a totally firm pedal even after using a Motive Products powerbleeder and my NT510 Elite scan tool, multiple times, over three years. I sold the Cobalt last month, and the proceeds paid for the brake work and new tires on the GMC (with some left over $$).

If you don't like the pedal feel, by all means get a second opinion. In my opinion, the Cobalt brakes felt good enough, but my wife didn't agree, and I was just about to put it in the pro shop for a second look at my handiwork, when the wife bought a low-mileage (55k miles) '14 Lexus ES350 from an acquaintance/friend of a friend, and I sold the Cobalt within a week. I certainly took advantage of the extra cash to upgrade her truck, so I wouldn't be second-guessed by the wife (who thinks I'm too old to be crawling around in the driveway, on sand and rocks, at my age). She may be right!

[Peezen]

Originally Posted by workingonit

Tell me about it; at my age (73) and having bad knees and back, undercar brake work is now farmed out to a pro shop, after 55+ years of me doing it all on my own.

I just (today) got my wife's '98 GMC back from a shop where I had them replace rear drum brakes (wheel cylinders, shoes, drums), replace broken/rusted bleeders on the front calipers (pads & rotors still 70%), then replace all the old fluid and powerbleed the system. The truck only gets used 2-4 times a year, and I needed pros to get everything unstuck for me (I can no longer crawl under a truck repeatedly to do the brakes by myself anymore) so it was worth a few hundred to get it done for me (they also had to replace a couple of wheel studs, etc.).

The mechanic that handed it back to me said he bled the system three times and wished he could give it a better pedal feel (actually, it feels as it did 20 years ago, so no problem), but it's certainly better than the pedal feel I got after I did much the same procedures on my wife's other car, an '08 Cobalt (it also got a new MC, new front pads and rotors, all done by me). I could not get a totally firm pedal even after using a Motive Products powerbleeder and my NT510 Elite scan tool, multiple times, over three years. I sold the Cobalt last month, and the proceeds paid for the brake work and new tires on the GMC (with some left over $$).

If you don't like the pedal feel, by all means get a second opinion. In my opinion, the Cobalt brakes felt good enough, but my wife didn't agree, and I was just about to put it in the pro shop for a second look at my handiwork, when the wife bought a low-mileage (55k miles) '14 Lexus ES350 from an acquaintance/friend of a friend, and I sold the Cobalt within a week. I certainly took advantage of the extra cash to upgrade her truck, so I wouldn't be second-guessed by the wife (who thinks I'm too old to be crawling around in the driveway, on sand and rocks, at my age). She may be right!

Oh man, I hear you!

Well I definitely don’t like the feel because it slowly keeps sinking to the ground when I push the pedal, though the brakes do work.

I just said screw it. I’m replacing the parts under warranty and will start again being far more careful than I ever have so that I can rule out the parts.


I have been watching videos for the e39 and feel that I need to do a better job bench bleeding and installing.


I have the BMW specific Foxwell, I have ISTA, and I have INPA. I should be able to get the right bleeding procedure down.


It doesn’t sound like Canadian Tire really knows how to do the proper technique, but then again it could be a faulty MC.


I have never had this much of an issue with brakes before but I love my 4.8is!

[workingonit]

Originally Posted by Peezen

• 1) I have been watching videos for the e39 and feel that I need to do a better job bench bleeding and installing
• 2) I have the BMW specific Foxwell, I have ISTA, and I have INPA. I should be able to get the right bleeding procedure down
• 3) I have never had this much of an issue with brakes before ....

My points of agreement:

• 1) I've been trained at a GM tech school in '71-72, and done dozens of brake systems over the following decades, on my vehicles and others (I never worked as a pro auto mechanic, but went in another direction, so I never had my own "shop"), but I know that I bled the MC and brake lines as good as I'd ever done before
• 2) I bought my Foxwell with GM software installed a few months prior to getting the X5 (it was still being worked on by the PO, before we traded cars...my Chevelle for the X5 he bought specifically for the trade), added the BMW software to it, and have used the NT510 Elite many, many times on the X5 and all four of my GM cars since then, so I should've been able to get the right bleeding procedure down on the Cobalt
• 3) I too, never have had a soft pedal problem I couldn't resolve, before the Cobalt

So far, I've had no brake problems with the X5, but I would assume that the Foxwell autobleed procedures found in both GM and BMW software has been satisfactorily successful for others prior, and perhaps both you and I were just unlucky when we were trying to bleed our respective brakes.

[80stech]

I think some have said that doing some ABS panic stops has been the trick ??

[nick325xit 5spd]

Originally Posted by 80stech

I think some have said that doing some ABS panic stops has been the trick ??

For me, I generally like to run the INPA bleed procedure a couple times, followed by a traditional "two man" bleed. Note this burns a LOT of power. A 10A power supply is often not enough to get through it.

Triggering the ABS isn't a bad strategy, but it's hard to do that extensively enough to get things totally clear.

Fun fact: Windows 11 ARM x86 emulation works so well that I can actually run INPA in a VM on an Apple Silicon Mac.

[workingonit]

Originally Posted by nick325xit 5spd

...Fun fact: Windows 11 ARM x86 emulation works so well that I can actually run INPA in a VM on an Apple Silicon Mac.

My Arm64 processor laptop isn't nearly as powerful as even a VM application. It has a total 4gb memory (most of which ...usually 60+%...is eaten up by Windows Defender), so I can hardly run INPA, can't get ISTA+ to load, and it won't even download the Windows 11 Microsoft Android Emulator (which I wanted to use for my Android automotive apps.

I'm sure you paid 5-10x for your Mac what I did for my laptop, which I sorta regret buying now, but you've got functionality! As Joker said: "Where does he get those wonderful toys?"; I feel the same about my budget devices.

[Attacking Mid]

To follow up on this, I spent countless hours bleeding my brakes to no avail. I replaced all the rubber hoses that connect to the calipers (they were showing cracks anyway), I replaced the master cylinder, and I followed the BMW bleed procedure to a "T" several times. If anything, I made it worse. I also observed some weird phenomenons with just getting endless bubbles. More searching forums revealed others who have fought this issue to no avail. A couple people mentioned they had success by wrapping their bleeders with teflon tape. Since one of the weird things that was happening was... after shutting the bleeder, bubbles would continue to flow through the clear hose attached to the bleeder nipple, I considered this. That was a head scratcher that indicated air was somehow getting in the line even with the bleeder shut.

I had little hope, but back up on jackstands she went today. All the wheels removed AGAIN. I started by removing each bleeder nipple and carefully wrapping about 3" of teflon tape around each. I then reinstalled the nipples and ran the BMW bleed procedure as I had before. I have a homemade pressure bleeder, and I ran the bleed procedure in ISTA+ for each wheel separately with the bleeder open. I didn't seem to get many, if any, bubbles out of the rear brakes, but the RF brake had a lot of bubbles. I ran the ISTA procedure a couple of times with 5 brake pedal full pumps following each time. Eventually the bubbles stopped, and I moved on to the LF where I got fewer, but still significant bubbles. I then shut the bleeder and put my foot to the pedal and GLORY BE!!!! we had a firm pedal!

Ultimately, the problem was all caused by air leaking around the threads of the bleeders. Intuitively, I seriously doubted that could be my issue, but I was proven wrong for the second time in a decade (sorry, corny dad joke). This problem was really grating on me, as it just shouldn't be this hard to bleed a brake system and get a firm pedal. Anyone need a perfectly good, used master cylinder? ;-)

AM.

[andrewwynn]

Great follow up it will for sure help somebody


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