Brakes not binding hard enough

#21

Well, it’s not quite eureka.

I put the gauges on the output of the ABS pump and front pressure was low. That’s pretty much a smoking gun. The ABS pump has to be the problem.

I removed the ABS pump, which required that I cut a brake line, then I flared the end of the brake line and fastened an old rear flexible SS hose to it. That allowed me to connect everything up to a spare ABS pump.

I’ve never flared and repaired a steel brake line before so that was kinda cool.

But the fun kinda ended there.

My gauge connected to the LF caliper wouldn’t read any pressure. I bled my pressure gauge hose and bled it and bled it. Behavior didn’t change. Then went to the RF and bled it too. Got more air out but the behavior still didn’t change, no pressure on the gauge connected to LF. Then the LF just quit bleeding. Fluid wouldn’t come out. I pulled the pressure gauge hose off the LF caliper and tried to bleed at the caliper. Nope. That’s when I realized what was going on. My spare ABS pump is apparently bad, but it’s messed up in some way that is stopping fluid to the LF. What I can’t understand is why it bled for a little while, but then quit. But the bottom line is that the RF seems to be fine but the LF isn’t getting pressure from the pedal nor pressure from the 10psi bleeder.

Who knew that ABS pumps had so many failure modes?

Tomorrow I’ll go out to my trailer and see if I have a spare ABS pump in it. If not, I’ll just put a T in the line and bypass the ABS pump for next weekend’s racing at Rd Atl.

#22

Better bring some extra tires. I’ve spent 4 years learning how to not lock up at max braking and I will be spending the weekend unlearning that.

#23

Scott, I’ll check for an extra pump when I get home today.

#24

I got my 2nd spare ABS pump out of my trailer today and installed it right after work. And it didn’t function. WTF, over? Nothing is coming out of it’s rear port…the port that goes to the rear wheels. It makes me wonder if there’s some trick to installing an old ABS pump. How can it be that I have 3 broke-dick ABS pumps?

#25

This effort has continued for hours every night. Sunday and Monday I put huge hours into it. Nothing conclusive yet. Mostly what I’ve been doing is trying to test theories, play with variables and look for patterns.

Rich gave me an ABS pump on Friday and I bought 2 more on ebay. Every one of my 4 ABS pumps seemed to cause different low pressure problems for the front. I felt strongly that was telling me that there was a problem with my testing protocol, but I couldnt’ figure out what the problem was. 4 gauges, some hoses and some fittings, “how can I be messing this up?”, I thought over and over again.

Monday morning I thought that I’d nailed the problem down to…“Whenever fluid is going to RF caliper, all front pressure is lower than rear”. But then I found the exact same behavior when I changed the test to isolate the LF caliper.

The next theory to test was "what if the MC, for some unknown reason, struggles to provide enough fluid to fully pressurize both front slaves? One slave ok, but both slaves a problem. So I swapped MC’s for the 3rd time…this MC being a different brand then the identical first two. No change of behavior.

So I figured that if I couldn’t get the MC to cause the behavior, I needed to again bypass the ABS pump and test, but this time I’d put a pressure gauge on both the front L and R outputs. Then I’d test a front output vs. a front caliper.

They I bypassed the bias valve and tested.

I still was not getting anywhere. It seemed like whenever I put a pressure gauge on a caliper I had the problem, but when I put the pressure gauge earlier in the system, I didn’t have the problem. I racked my brains trying to come up with a scenario where pressure at the caliper could be different then pressure elsewhere.

I did a bunch of testing where instead of testing pressure at the caliper bleedscrew, I pulled the brake line off the caliper and tested there. I still didn’t find anything conclusive.

Monday night I seemed to spot the fact that the problem seemed to travel with a specific hydraulic hose. I’d already had to make 2 trips to the local hydraulic shop because one of the short hoses they made me yesterday was plugged. Because of the problem with that hydraulic hose, I was ready to consider that some weirdness was going on with a hose to a gauge, whereas that idea would not have occurred to me before. I mean heck, a hose is a hose. How can it cause pressure to drop? There wasn’t anything leaking.

So my current theory is that testing for the problem is getting “hosed up” by a hose that maybe I can’t trust. I need to do more hose swapping around and confirm that the behavior follows the hose. A big downside of this explanation is that it does nothing to understand why my braking distances were so long at Sebring last month. Why the hell did I have to stand on the brakes as hard as I possibly could?

I’m kinda exhausted over the whole thing. I’ve spent 2 weeks bleeding brake lines and hydraulic hoses, covered in brake fluid up to my shoulders. Every time I close my eyes, I see a bleed hose being held over a brake bleed nipple and a little wrench. I need to get the car and the gear ready for Rd Atl. I think I’ll just get everything together and see how the car does at RA. I’ll bring lots of parts and fittings so I can work a bit in the paddock. Altho the current ABS unit doesn’t seem to impact pressure, that doesn’t mean that it actually works.

#26

Feel free to use our lift to make things easier. That goes for anyone btw.

#27

Couple questions that may or may not be helpful, but figure I’d ask.

  1. What kind of hoses does Rich use? The front calipers are fed by a longer hose vs. the rear’s two shorter hoses, so maybe that makes it more susceptible to bulging? (Edit: Seems unlikely the more I think about it, but maybe?) If you’re seeing the front pressure flat-line despite adding pressure, I wonder if there would be a visible indication in the hoses. Is it worth measuring the OD of the hose with a caliper with no pedal/first moment it hits 700psi/subsequent pedal pressure?

  2. Have you tried replacing the ABS control box? I imagine a failure there could result in the valves in the pump not opening up predictably – and hence why maybe your 4 ABS units appear to not work right. Or is there some kind power sequence that needs to happen to have the unit “open” the valves? I can only find dotted line diagrams of the ABS control unit (meaning only partial wiring is being shown), and I can’t remember if there are any wires that run to the ECU. Curious if you’re powering on the car between your tests to have the control box inform the ABS pump to open up.

Som

#28

[quote=“Som” post=81012]Couple questions that may or may not be helpful, but figure I’d ask.

  1. What kind of hoses does Rich use? [/quote]

I use the OEM like hard lines up to the front fenders then switch to -3 AN braided lines to the calipers. To the rear, I have a hard line to just above the differential then switch to -3 AN braided lines to each of the calipers.

#29

That’s interesting – so you don’t have the 2 hard-lines on the trailing arms? You just run 2 long hoses straight from the split to the calipers?

Curious how old Scott’s lines are…

#30

I deleted the hard lines onthe trailing arms. It’s a nice setup and uses standard lines which are easy to find at most parts outfits. The problem with most E30 brake line kits is that you have to buy a complete kit each time you need to replace a line.

#31

I deleted the hard lines on the trailing arms. It’s a nice setup and uses standard lines which are easy to find at most parts outfits. The problem with most E30 brake line kits is that you have to buy a complete kit each time you need to replace a line.

#32

Som[/quote][quote=“Som” post=81012]Couple questions that may or may not be helpful, but figure I’d ask.

  1. What kind of hoses does Rich use? The front calipers are fed by a longer hose vs. the rear’s two shorter hoses, so maybe that makes it more susceptible to bulging? (Edit: Seems unlikely the more I think about it, but maybe?) If you’re seeing the front pressure flat-line despite adding pressure, I wonder if there would be a visible indication in the hoses. Is it worth measuring the OD of the hose with a caliper with no pedal/first moment it hits 700psi/subsequent pedal pressure?

  2. Have you tried replacing the ABS control box? I imagine a failure there could result in the valves in the pump not opening up predictably – and hence why maybe your 4 ABS units appear to not work right. Or is there some kind power sequence that needs to happen to have the unit “open” the valves? I can only find dotted line diagrams of the ABS control unit (meaning only partial wiring is being shown), and I can’t remember if there are any wires that run to the ECU. Curious if you’re powering on the car between your tests to have the control box inform the ABS pump to open up.

Som[/quote]

My brake lines are all standard steel and flexible SS. Nothing unusual. SS hoses are a couple years old. It’s not the SS flexible hoses. In order to lose 1000psi I’d have seen huge hose distortion. Significantly tho, recall the tests where I did not get the behavior if I blocked off one of the front calipers. Didn’t matter if it was left or right. So if I blocked off the right front line, the left front had equal pressure with the rear. Conversely, if I blocked off the left front, the right front had equal pressure with the rear. Only when the test had fluid going to both calipers did the front have less pressure than the front.

Right now what fits the symptoms best is to be suspicious of my 8’ hydraulic hose that I’ve been connecting to various points. The common thread, in the example above, is that (I think) only when that hose was in play did I have low pressure. The problem is that in all of these many days of testing, I wasn’t really paying attention to how that hose traveled around my various setups. I moved (the 4) gauges around to confirm they were reading predictably, but I never thought to move hoses around. In order to do the test described above with both front calipers getting pressure, I think I always used the now suspect hose.

I don’t accept that the ABS units need power in order to allow open passage for fluid to the calipers. No engineer would design an ABS pump that degraded braking in a power-off condition. All my tests have been done with the car both on and off. The only change is that the behavior is easier to see with vac in the booster helping the legpress. Bypassing the ABS pump didn’t change behavior, just like bypassing the bias valve didn’t change behavior.

I’ve long since burned my way thru all the easy explanations. Now it’s a matter of 1) thinking out of the box, and 2) finding different ways to test the same idea to make sure that the test isn’t providing bad info. Like the possibility that there’s a problem with one of my custom hydraulic lines.

#33

If the suspect hydraulic hose is indeed the cause of the low front brake pressure reading, then nothing I’ve found explains the problems at Sebring that opened up this can of worms. Sigh.

At this point I’m kinda inclined to just go to RA this weekend and see what the hell happens. Maybe the brakes will be fine and I’ll just say “fuck it”, add it to the list of other E30 mysteries and move on.

#34

I think you need redundant gauges to confirm that your gauges read correctly and more hoses to confirm that your test hoses are correctly testing the actual brake lines correctly. On a serious note, I do applaud you for your efforts, but I’m seriously confused and not sure what component failures you ruled out.

#35

Warning: More random thoughts of questionable helpfulness. :slight_smile:

I guess I’m having a hard time believing (as you do) that 4 different ABS pumps all seemed to not work for various reasons. If you’re transferring an ABS pump from one system to another, aren’t there specific things you need to do to ensure a full bleed of the pump itself? I’m looking at this thread, for example: http://www.r3vlimited.com/board/showthread.php?t=251112. The cycling of the pump fluid wouldn’t really explain the problem you were having on the track, unless maybe somehow you got air into the ABS pump during a flush (poor seal on a power bleeder maybe?). Even then, I’m not really sure why you’d get 3 good laps and then poor performance after that. I’m curious how much heat from the calipers makes its way back to the fluid in the pump. I would guess not much, but I don’t know.

Also, while I agree that an engineer would ensure that a loss of power wouldn’t eliminate brake capabilities, I wouldn’t be so sure that there would be an assurance that braking capabilities couldn’t “degrade” as a result of power loss. I mean, hell, our braking ability is “degraded” from power loss simply due to losing the booster. You can still brake, but it’s harder. The engineering philosophy around the pump may have been the same way. That said, I wasn’t sure how the solenoid valves in the ABS work, either – (I’m restraining myself from adding “talking out my ass” caveats to everything I write, so I hope you’re doing this for me), so I thought maybe there are valves that require power for both “full open” and “full closed” – lack of power resulting in maybe a more “floating” state that might result in less predictable behavior. Looking more into solenoid valves (thanks wikipedia), it seems that there are generally NO/NC valves, with the power pushing the solenoid closed/open. So I would expect our ABS pumps to have 3 NO valves that require power to close.

Given this, there would still be a potential for the ABS unit to cause problems – if your tests were consistently done with the electrical power on (12V, not necessarily motor running). If the unit is sending an incorrect signal to close a valve, for example. I’m guessing it would be possible to partially close a valve, too, depending on how the return mechanism works. So… I’m not sure, when you said you did your tests with the car “on and off”, if you meant engine on/off or simply power on/off.

Som

#36

Oh, and per Rich’s message, I had to create this for you.

Som

#37

me likes Som!

#38

Figuring out that I couldn’t trust one of my hydraulic hoses was a big deal. That forced me to run thru my memory banks re. my many tests and retests and make some decisions as to which I could trust and which I couldn’t. Significantly, figuring out how (and getting the fittings) to test the brake system at any point, makes it easy to, in the future, to rigorously test the system to my heart’s delight.

But I was totally burned out on the effort, and I needed to break contact, pun intended, and get my shit ready for Rd Atl.

What I do know is that my early conclusions re. insufficient front pressure are suspect. Deciding that my 2 spare ABS pumps were bad because I couldn’t get fluid to bleed thru them needs to be tested again.

A booster related problem is back on the table as a possibility. I have a spare booster and checkvalve.

It’s a little tricky trying to come up with an explanation as to why the brakes seemed to be better on the first lap of each session, but maybe it’s because I was going a lot slower in that first lap. A lot of those first laps were under yellow. Maybe I was fooling myself in that my brakes weren’t working so well in general but it just wasn’t obvious until I was hauling ass on lap 2. Potentially I could imagine them as being sort of ok and moderate speeds but kinda sucky at high speed, simply because I was demanding so much more of them at high speed.

I’m not sure yet what the problem is. But I do know that I learned a lot and I’ve all the spares I need to figure this out.

At RA this weekend, if you see me right behind you going into 10A, look hard. If you see my eyes wide with alarm, move to your left so I have a straight shot into the gravel trap. The safest place, of course, would be behind me.

#39

Not even an acknowledgement of Som’s joke? Really?

#40

The effort was ultimately interesting, but it was also frustrating and grueling. In a year I’ll look back at it and smile. I’ll compare the 100x I hooked up something differently, night after night, bled the system and then tested again and struggled to understand the bizarre gauge readings, to the 10? engines in 18 months back in '09 and '10. Not tonight will I smile about it tho. Next year.