Joined: October 24th, 2014, 10:51 pm

July 8th, 2018, 2:07 am #21

Fine, I'll do it...


"Don't forget the jackstands."

~:)P
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Joined: October 8th, 2014, 2:06 pm

July 8th, 2018, 5:31 am #22

hinermad wrote:
Don't forget to close the hood. You won't be able to see out if you don't.
If he closes the hood he won't be able to see the radiator cap. How will you expect him to aim it?
This is a test. Explosions are a happy side effect.
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Joined: January 1st, 1970, 12:00 am

July 8th, 2018, 7:42 am #23

Well, that was a day...

I'm kind of surprised nobody picked up on the missing thing, after I so carefully crafted that Monty Python parody earlier in the thread.

The missing piece was, of course, the sway bar!



(Technically antisway bar, or antiroll bar, or stabilizer bar, whatever. )

Anyway, today's task was supposed to be pretty simple, Slip the sway bar in, bleed the brakes, go take it for a test drive.

The first half went just fine- apart from having to go get more bolts, because I'd accidentally gotten ones a full inch too long- and the sway bar fell right into place, got properly shimmed and carefully tightened down.

Then I set out to bleed the brakes. An easy task in most cases, made even easier in this case because everything is either brand-new, or only a couple of years old. Except, ten hours later, they're still not properly bled. The fronts are fine, they work great. But I cannot get the rears to bleed properly.

My best guess at this point is something went wonky in the master cylinder. I don't know what, and it's odd if it did, as that part is only a few years old- I replaced it, along with everything else up front short of the booster, back in 2015 when I did the front end suspension. And it was a new manufacture part, not a rebuilt one.

I'm now trying to decide if it's worth the time to yank it, pull it apart and try to rebuild it, or just go buy another new one (maybe from a different vendor) and just bolt that one on.

Doc.
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Joined: January 1st, 1970, 12:00 am

July 8th, 2018, 7:43 am #24

Antknot wrote:Maybe contamination from the old rear breaks?
-Unlikely. The old brakes got flushed and properly bled back when I rebuilt the front end. And, the fluid doesn't "recirculate". It's a one-way system. The fluid at the rear axle end pretty much stays there- when you press on the pedal, you're sending more fluid to that end, forcing the pistons further apart against spring pressure. The brake fluid goes "back and forth" in the lines a short ways, but it'd be almost impossible for fluid- and junk- in the rear wheel cylinders to work it's way all the way up to the master cylinder.

The thing here is that for some reason I seem to recall the second time I bled the brakes back in 2015- after I had to tear the front end back apart because I couldn't get it properly aligned- that it didn't bleed as well. I couldn't get the pedal feeling as "rock solid" as it had been the first time.

It wasn't a huge difference, and obviously I didn't pay much attention to it, but it now makes me wonder if something wasn't starting to go wonky in the master cylinder even back then.

Of course, I've driven the car extensively since then, and the brakes have always performed very well.

Doc.
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Joined: September 16th, 2014, 7:01 am

July 8th, 2018, 8:18 am #25

Are you doing it the hard way with an able assistant stomping the pedal and you twiddling a bleeder wrench?Β  Or one-way check valve "Speed Bleeders" on both rear cylinders, or a old mechanic style pressure bleed system (but they waste brake fluid like a monster, you need to change the whole gallon plus in the chamber...) or a Mityvac and a catch cup, or...?Β 

You reconfigured the hard lines, if you made a high spot it'll be hard to bleed by hand (okay, by foot) - it takes a concentrated blast of flow to force an air bubble all the way through in one try.Β 
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Joined: January 1st, 1970, 12:00 am

July 8th, 2018, 8:44 am #26

Are you doing it the hard way with an able assistant stomping the pedal and you twiddling a bleeder wrench?
-That's not the "hard" way, that's the correct way. 😁 (Barring professional pressure bleeders, etc.)

When everything's working right, two guys using that method can bleed an entire system in ten minutes. Half an hour if you include all the jacking and wheel removal. (But not counting having to break rusty bleeders loose- I've spent eight or nine hours just on that part of the job. 😁 )

"Speed bleeders" do effectively the same thing. I've used them in the past, but again, this is Alaska, and I drive even this Cutlass on some of the not-so-nice days. The check valves in those things rust up/clog up way too easily.
You reconfigured the hard lines, if you made a high spot it'll be hard to bleed by hand (okay, by foot) - it takes a concentrated blast of flow to force an air bubble all the way through in one try.
-I disagree. A high spot would have to be pretty severe to not be fairly easily flushed out, and no, there are no such high spots in my lines. 😁

After prolonged attempts to push the fluid through- the lines were still dry at this point- I cracked the tube at the master cylinder and ran a short section of hose up to the MC reservoir itself. I then used a MightyVac to pull fluid through the lines, and was eventually able to get a good flush on both corners.

And while the line was off the MC, I also removed the front line and "bench bled" the master cylinder, then hooked everything back up. As noted above, the fronts bled just fine, but I still wasn't able to get more than just a basically irrelevant dribble out of the rears.

I guess I'm just going to have to "throw money" at this thing and just buy a new master cylinder in the morning. I honestly can't think of anything else it could be- and the only reason i'm not convinced it's the MC is simply that's it's so new, and was working fine- like, Monday.

Doc.
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Joined: October 24th, 2014, 10:51 pm

July 8th, 2018, 10:06 am #27

I wouldn't put it past the OEMs to cheap out on their seals, especially for stuff that doesn't sell a bunch overall anymore; nevermind the fact that it was probably made for the most part overseas...
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Joined: January 11th, 2016, 8:57 pm

July 8th, 2018, 10:45 am #28

Your brake proportioning valve doesn't have an anti-leak mechanism in it? They will prevent proper bleeding, as they see the open system during bleeding as a severe leak, and close off the flow to the rear brakes. Apparently, if there's a 'check brake' warning light on the dash, you may need a dummy switch in the valve to prevent the anti-leak system from shutting off the flow to the rears while you bleed them. There's a video atΒ  and the guy explains the system reasonably well.....
Breakfast.com halted. Cereal port not ready.
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Joined: August 3rd, 2015, 8:49 am

July 8th, 2018, 2:17 pm #29

DocsMachine wrote: That's absolutely correct.

It makes me want to unscrew your head a little bit, just to see what would happen, but you're correct. 😁

Doc.
Hee! I'm not sure it's screwed on right as it is, so who knows what could happen! 😁 Ah, that was a good giggle, thanks for that!Β πŸ˜†
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Joined: January 1st, 1970, 12:00 am

July 9th, 2018, 3:20 am #30

Okay. [cracks knuckles]

There's only two things it can be: Either the master cylinder, or the proportioning valve. Both are almost new, and both were working just fine a week ago. So as neither yelling at it or writing about it on the internet seems to have solved my issue, it's time to jump back in and get my hands dirty.

I decided to tackle the master cylinder first, as it's easiest to get to and dismantle. Thanks to rust-free stainless fasteners, it popped right off.



Drained and on the bench, we see it's unlikely it got clogged with rust or other gunk- the damn thing is only three years old.



By the way: Don't let anybody tell you- not even me, 'cause I have 😁 - that POR-15 is immune to brake fluid. I'm here to tell ya it ain't. 😁



The can says it is, the reviews said it was, I've had other hotrodders say it was... but it ain't. Basically everything on the back third of the master cylinder could be peeled off in big flakes. 'Coupla you Guilders told me about that back when I was putting this thing together, and nope, I was still goin' by what the box said. 😁

Anyway, a master cylinder is easy to rebuild- or in this case, just inspect and clean. A big snap ring out the back, and then there's two pistons and a spring. That's it.



I cleaned everything off, inspected the seals closely, probed the ports for anything that might be jammed in there, wiped everything down, lubed the seals with some fresh DOT4, and put 'er back together.



I found nothing to indicate a problem with the master cylinder. The seals were in top shape, there was zero gunk that could clog anything, there was no rust, no mechanical damage, and no missing parts.

So, I refilled the reservoirs and "bench bled" it.



This is basically just a process that recirculates fluid through the pistons, to drive out all the air. Regular bleeding on the car doesn't do it very well- it actually took me about ten minutes of cycling, waiting, cycling, waiting, topping off, and cycling some more, before I finally stopped getting air bubbles out of the ports.



To reinstall it, I just bent the tubes back up out of the way, and latched the cap in place. Then took it out to the car and bolted 'er back on.



So the master cylinder is almost certainly not the problem. That leaves the proportioning valve, and the obvious bit on the also-nearly-new P-valve is the "switch" or "differential" piston. This is a spool in the center of the P-valve that balances between the front half and rear half of the brake system. If a leak occurs on one end or the other, the differential in pressure shunts this piston to the weak side, closing it off and supposedly preventing any further fluid loss (at least at the master cylinder.)

That's basically what my system has been doing, with the fronts bleeding normally and the rears being unable to be bled at all. But we'd also tried half a dozen times to "reset" the piston- if it was indeed the culprit- but all to no effect. And I'd been able to draw fluid through with the MightyVac, so I'd kind of been leaning towards the master cylinder.

Okay, so the MC has (very probably) been eliminated as the offending part, which leaves the P-valve. And the P-valve, being nearly new, is unlikely to have spontaneously failed, which points towards this issue being something it's supposed to be doing.

Something I should have tried early yesterday (isn't it interesting how obvious things seem in retrospect? 😁 ) is to put a multimeter on the bias switch. This is a later-model P-valve, and the switch is different than that of the plug on the car, so I don't have a dash light. (Which, in retrospect, if I did have it, it would likely have sped up the diagnosis by about 20 hours. πŸ˜‹ )



And I'm sure some of you smug bastards know exactly what I found, right? 😁



Yup. Full continuity- the switch was "on", meaning the piston was indeed biased to one side.There's the problem that's been bugging me all weekend. (At least, the parts of the weekend I was able to work on the car. 😁 )

Unfortunately, that was all the time I had today to fool with it, and duty called me elsewhere. Hopefully I'll have a chance to fool with it some more on Monday or Tuesday.

Doc.
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