91' 850i braking fine, then barely any brakes after rotor replacement. Hints?

[lockeed]

Hey guys, I would love to get your feedback on something. I've done plenty of research but I'm not sure I found someone who experienced what I'm seeing now on my 91 850i with ABS/ASC.

Monday, I brought my freshly restored car to my local shop (drove great) and had the front rotors and pads replaced for ATE OEM parts. I got a call later and the guys told me the car didn't brake anymore... pedal goes straight to the floor. They suggested a failure of the master cylinder, but keep in mind they are not familiar with the E31 specific braking system... I was quite surprised as you can imagine, as I just drove the car there myself a couple hours prior and it drove perfectly. They also mentioned they tried purging the front brakes, but it didn't produce any results...


At the moment, the car has just a tiny bit of brakes, when you have your foot on the floor. My brake fluid reservoir is full. I do get a firm pedal after about 10 push on the pedal while the car is off, telling me that the accumulator must be doing it's job... I tried purging the brake lines starting from the rear right wheel, only a very small amount of oil came out, then nothing. I tried the other side, same thing. It's like the master cylinder is unable to build up pressure to send fluid towards the back...


I see no visible leaks at the master, or on the interior of the car. I'll try to open the wheel arch cover to check the accumulator and regulator tomorrow... I'm quite puzzled!


Let me know if there's anything that I'm missing?


Thanks!
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[shogun]

what some do without tool, get the car on a lift and switch into gear, ASC/ASC-T will activate and open/close valves, then bleed once more.

from shop manual:
34 00 048 Bleeding brake system with ABS/ASC+T
Note: Conform with filling and bleeding procedures when replacing or repairing the, - Tandem-brake master cylinder, - Hydraulic unit ABS/ASC+T, - Accumulator ASC+T, - and components which are installed between these units.
The procedures of "Bleeding brakes with ABS",refer to 34 00 047 are also applicable for ASC+T vehicles when performing other jobs on the braking system (e.g. replacing brake calipers).
Caution! Note "General Data", refer to 34 00 ...

1. Connect bleeder on expansion tank
Note: Check relevant Owner's Manual for each device. Charging pressure should not exceed 2 bar.
2. Bleed braking system in advance
Connect bleeder hose with bottle to rear-right brake caliper. Open breather valve and flush brake system, flush volume approx. 50 cm 3 (brake fluid must emerge without bubbles). Close bleeder valve. Bleed brakes in the same manner at left rear, right front and left front.
3. Bleed hydraulic unit ABS/ASC+T
Connect BMW Service Tester to vehicle diagnosis connector. Select number 50 "Teves Slip Control System" from control-unit overview, followed by number 5 "Special Functions" from the menu and finally number 1 "Bleeding Routine for ASC+T".
4. Bleed braking system
Connect bleeder hose with bottle to rear-right brake caliper. Open bleeder valve and flush braking system while operating brake pedal as far as it will go at least 10 times (escaping brake fluid must be free of air bubbles). Keep brake pedal pressed down, close bleeder valve and release brake pedal.
Bleed brakes in the same manner at left rear, right front and left front. Installation: Use dust caps on bleeder valves.
5. Bleed accumulator ASC+T (only vehicles up to 09.93): Remove liner from inside of front-left wheel house. Connect bleeder hose with bottle to bleeder valve (accumulator). Caution! Pressure in accumulator will be approximately 120 bar.
Carefully open bleeder valve. Start bleeding routine in selected menu item of special functions (BMW Service Tester) and flush accumulator until escaping brake fluid is free of air bubbles.
If necessary, repeat bleeding routine several times. Close bleeder valve. Install dust cap. Install liner on inside of wheel house.
6. Remove bleeder
Check and, if necessary, correct brake-fluid level. Screw cap on expansion tank (ensure that rubber seal (1) is installed in cap).

[dragon850]

Guessing you need a new master cylinder, you can use 750il E32 one.
Cheers

[lockeed]

As I told Shogun, these old beemers fix themselves...!


Before I tried INPA, I tried hooking up my Foxwell tool using my 20 to 16 pin round adapter, for some reason the diagnostic port in the engine compartment had power but I couldn't get it to communicate. (I tested my tool and adapter on my E38 and it worked perfectly). Anyhow, I started the car let it sat for 10 minutes at idle... Came back in the car, I had brakes and a pretty good feel on the pedal too... What the hell! To be honnest, I don't get it ? Maybe having the car idling for a while, the abs and asc pumps were operating and may have been able to purge out an air bubble... I don't know? What do you think?

[rjjablo]

Bubbles do purge themselves.

However the fact that you were not able to bleed the right rear indicates a problem

I would rebleed the brakes just because

[sshivaram]

As I told Shogun, these old beemers fix themselves...!
...tried hooking up my Foxwell tool using my 20 to 16 pin round adapter

I was able to use Foxwell NT510 scanner on my M73 using the 20pin to 16 pin adapter, and it worked just once perfectly.
I have contacted Foxwell many times after that, telling them a combination of the Foxwell scanner with that softaware
version worked perfectly to read the error codes, and since an upgrade happened to Foxwell, it has stopped scanning.
They are unable to understand why, and I do have an open ticket with them, many emails from China, and with no
resolution. The NT510 is supposed to work with the E31s.

[lockeed]

I doubt it's the scanner itself... more than likely a slightly bent pin, dirt or corroded prongs... I tested my Foxwell NT630 pro with my e38 and again today with my E39, worked great. But the E31, although I was able to use it last winter, doesn't seem to be working at the moment...

[sshivaram]

I doubt it's the scanner itself... more than likely a slightly bent pin, dirt or corroded prongs... I tested my Foxwell NT630 pro with my e38 and again today with my E39, worked great. But the E31, although I was able to use it last winter, doesn't seem to be working at the moment...

I tested connectivity from the 16 pin adapter to the back side of the 20 pins, perfect and snug. My NT510 stopped after i did the software upgrade from their support website. Sadly, they are unable to give me back the older software. They just don't respond at all.

[lockeed]

Try this: Bat. charger on, igition on, then plug scanner. Manually select the car with the build date, do an auto scan for all modules, once done, clic Save. It wil download a bunch of files, be patient... afterward you should have access to the various module in the car.

[CD05001CIA]

As I told Shogun, these old beemers fix themselves...!


Before I tried IN .... .... I had brakes and a pretty good feel on the pedal too... What the hell! To be honnest, I don't get it ? Maybe having the car idling for a while, the abs and asc pumps were operating and may have been able to purge out an air bubble... I don't know? What do you think?

If it was the case that a bubble entered into the brake line system( Brake bomb, ABS module, master cylinder, brake pistons) it is possible to have gravity move the fluid downward as the air bubble moved upward wrt gravity. The viscosity of the brake fluid and any point in the system where a bubble could stall(interim relative high point) would delay that bubble's travel upward. Vibration could help move the bubble along. {THEORY}

[sshivaram]

Brake fluid should be like water....
"Empty your mind, be formless. Shapeless, like water. If you put water into a cup, it becomes the cup." - Bruce Lee.

After successive use, the brake fluid should "settle" down correctly. Keep pressing it slowly, multiple times, till you get the firm feel. Don't drive it out - just keep it parked and make sure the pads are gripping 100% before you drive.

I had pressed the pads, and it took about 5-6 brake pedal activation before they clamped correctly.