Brake performance? Problem solved

[Hyper]

Herein, I reveal the root cause for my e31's substandard brake performance.

**** Back story ****
For the longest time, probably since I took ownership, I had the impression that my e31 brakes did not compare well with anything else I was driving.
As evidence of something amiss, I observed that it was difficult or impossible to invoke ABS.

As a result, in the second half of 2016 I developed the means to install larger, stronger brakes (See -> e60 rotors front, and -> rear caliper survey, collectively know as BBKonBudget)
Unfortunately, the results were still disappointing and in December the project was shelved, due to this disappointment combined with a packed itinerary which left me no time to investigate further.
'Round about June, I got back on it and my first action was to sample Alex840's, who graciously allowed his Red to act as a beta site for a 2nd install which occurred back at the beginning of this year.
I immediately found everything to my liking, which brought up the question, what is wrong with my car?

My second action was then to start disassembling my own brake system and reverse some previous component swaps, especially the master cylinder and the brake booster.

*** Long-short ***
It was discovered that the screen at the boosters input port was clogged with both chunks and fine contaminates (chunks not shown).


With the screen cleared, and the brakes upsized, the performance is now 'good' or even 'great' and we can now get into ABS without too much effort.
This success has then released the BBKoB for continued development and roll out.

**** More details, even more back story ****

Further back in time was the incident where both the steering assist went away and the brake pedal would kiss the floor.
During that repair project we...
- Inspected the hydraulic pump
- Replaced the hydraulic pump with salvage
- Replaced the regulator with new
- Replaced master cylinder with new
- Rebuilt the H31 brake booster
- Replaced the (pentosin) hydraulic lines. (Surprise, they were leaking)
- Inserted pressure sensors into the (pentosin) hydraulic lines and monitored using my Hyperdrive-ETV computer.
- Replaced the ZF steering box with salvage



The last two items revealed that 1) the problem was with the steering box, and 2) that the hydraulic system was in a state of low-pressure-high-flow.
The original ZF steering box was then overhauled (meaning that seals were replaced) and this returned that box to 'operational'. Details at HowTo->Overhaul a ZF steering box.
So what was wrong with the seals? Don't know, but my observation at the time was that seals in the control section looked contaminated with metallics.



The other significant action in this earlier repair project was the insertion of pressure sensors into the pentosin lines.
This involved welding 1/8-NPT Tee's into the tube leading to the brake booster.
In retrospect, this was probably a further source of contaminates that would end up in the booster input screen.
Ironically (because it was a potential source of trouble), the brake line sensor, being upstream from the blockage, would give a false report that the booster supply pressure was OK.



Notes regarding filters...
- In the above schematic for the 840 there is a filter in the system, on the return line from the steering and shown below. This will eventually clean up the debris in the fluid, but only after it has circulated through the steering box rather than getting trapped there.
- Afaik, the 850 has another/additional filter on the output of the pump. It could catch debris, either from the reservoir or generated in the pump, from traveling further on to the steering or brake components.
- In either case, these filters will not trap debris generated/sourced in the (rubber) lines immediately prior to the steering or brake component.




How the blockage was found...
While swapping back in my original MC, the H31 booster suddenly started gushing pentosin. (Reason, failure of the garter spring seal at the forward/MC end. Yet another adventure.)
This then required that I pull the booster, dismantle and repair it. (Details from the past at HowTo->Rebuild the 840 brake booster).
Fortunately (for this brake diag project) I inverted the booster, draining the pentosin out onto a clean bench top, and thus revealing the contaminates.
While I had the booster dismantled, I could blow out / clear the screen from the inside using air.

This opens several serious questions...
- When and how to inspect for blockage at this location?
- How to clear blockage without the inconvenience of removing, dismantling and/or inverting the booster?

Regarding the accumulator...
It's the one item missing from the laundry list above.
At no point in diagnosing any of the steering/braking problems did the system performance symptoms match something the accumulator is theoretically capable of.
That said it would be about time (since built) to freshen up this component.

Does this fix now make BBKoB irrelevant?...
Unfortunately, the migration to BBKoB is not conveniently reversed (I've discarded the stock rotors, done some machining), so I won't be going back to review the performance of a stock system vs the BBKoB.
Rather, I'll just continue with BBKoB rollout.
There is interest, isn't there?


**** Pad pressure testing ****
Finally, we come to "the buck stops here" pad-pressure sensing tool.


This was brought in at the time the BBKoB was shelved in December, and never used until after the blockage problem was discovered and removed.
Therefore...
- This tool did not figure into the resolution of the problem but eventually would have, by localizing the symptoms to the point of obvious.
- I can not compare pad pressures before and after the fix, but I can report the current numbers for this particular tool and my particular Brembo caliper (it ranges from 3500 to 4500psi). As of this time, I don't have the equivalent numbers for the ATE-60/30.

A couple of tool tips...
- The tool reports in PSI, a curiosity. Why not units of force?
- The tell-tale feature on this particular product is unreliable. This is highly unfortunate.
- You'll be more interested in comparisons rather than absolute numbers. Left vs right calipers, inside vs outside on the Brembos anyway. Kit instructions provides further analysis projects and guidance.

For the first topic I compared the pad pressure reported in PSI against my hydraulic press reported as a force and found that 4000 psi corresponded to 2-1/2 US tons (=5000lbs).
Since the pad diameter on the tool is 1-1/8 inch, we are at least happy about the math, just not the reporting style.


For the second topic I became suspicious when I inserted both units into the same caliber, one inside, one outside, and they reported vastly different readings on the tell-tale.


This deserves investigation because for this to be the true situation it implies that there is either hydraulic proportioning occurring within the caliper, or two pistons are conspiring to bind on one side. Could happen, but only a remote possibility.
Since this was a one-man op, a camera was used to catch this capricious lying on video, showing that during pedal pumps, the gauges would flop around wildly on the hoses and the indicator needles would skip over rather than push their tell-tale tracker.
The result would be that, while the gauge needle (briefly) hits 4500, the tell-tale was left behind at say only 400.

[72tpik5]

Wow! I can see that you won't take "NO" for an answer. Good for you and your attention to detail to figure this out.

[toomanyparts]

Thank you for putting all this together. Very helpful.

Regarding the 840 master cylinder, where does one find one of these for less than the $700+ BMW is asking? Seems this has gone to "backordered" on a few sites.

[tvjake2]

Thanks, Hyper. I've added this to my "things to do sometime" list. My brakes work ok for now, ABS is reachable under hard braking.

[dragon850]

Where do the contaminants come from? Disintegrating PS pump seals?

[Hyper]

It would help to know the composition, which I don't.

But based on hypothetical, here is my guess as to an associated source...
* Metal (?) in the steering box seals: Pump vanes or recirculating ball & screw?
- Pump run dry or just normal wear.

* Rubber (?) in booster port: Accumulator bladder, pentosin hoses, steering box internal seals, booster internal seals?
- Rubber has a half-life and I'm reminded of how toilette valves and the inside of fuel hoses get after say 20 years.
- The vane pump would have a shaft seal (and little or nothing else), but this always sees pressure from the inside, even when not running.

* Metal oxides (?) in booster port: My sensor Tee's, TIG welded without back purge!
- However, the brake performance was tagged long before I installed hydraulic sensors. So this can't be the total story.

* Any combination of the above.

{ed: And of course, anything that enters through the reservoir and gets by that primary screen.}

[wolfebrian2120]

Dragon probably over time bits of the rubber hoses break off from the inside. Good reason to flush the pentosin system every couple years.

Hyper, I'm still interested in BBKoB. Can't wait to get my hands on a couple of those brackets. Thanks for putting the time to write this up, letting us all know how you identified your problem.

toomanyparts, I was able to order a rebuilt one for my 850 from rockauto. I know they offer rebuild services as well.