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

July 9th, 2018, 3:27 am #31

Beejay5169 wrote:Your brake proportioning valve doesn't have an anti-leak mechanism in it?
-As above, yes, it does. Virtually all P-valves do these days. And I'd tried "resetting" it half a dozen times yesterday, all to no avail.

If it's the front that's failed, apparently there's a "pin" that pops out the front, that just has to be pushed in to reset the thing. Mine appears to have blocked off the rear, and no such "pin" is available.

Some people have said you open the side that's supposed to be "good" and press the pedal, which pushed the piston back towards the center. A few people have said theirs wouldn't reset no matter what they did, and they eventually had to toss it and replace it with a new one. Others have said you can pull the switch and use a scribe or other sharp pointy thing to physically move the piston back into place.

If I get a chance tomorrow, I'll try the scribe thing, because we tried resetting it with the pedal a bunch of times in a bunch of ways and never saw any change.

I suppose what i could do is rig a connection to the dash light, or whip up a standalone test light, and see if I can mash it back into place- being able to watch the light at least gives an indication of what's happening.

Doc.
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Joined: October 8th, 2014, 2:06 pm

July 9th, 2018, 4:16 am #32

For submission,a full list of things I've found to be resistant to brake fluid:

Metal brake components.
This is a test. Explosions are a happy side effect.
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Joined: January 11th, 2016, 8:57 pm

July 9th, 2018, 4:45 am #33

It helps if you buy the right one of these little widgets from your auto parts store,


And insert it in place of the switch while you're bleeding the rears. It apparently resets the valve piston to its normal position, and holds the valve in that position allowing the wet stuff to reach the rear end of the system while bleeding.

"Product Description:Use our Proportion Valve Bleeding Tool when bleeding your brakes to lock the prop valve in place and keep the valve from tripping. Simply remove the warning light switch (white plug) on the valve, then screw in this tool while bleeding your brakes. After the bleeding process is finished replace the warning light switch. This item makes bleeding your brake system much easier. Works with all our non adjustable valves. Works with Combination and Proportioning Valves."
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Joined: January 1st, 1970, 12:00 am

July 9th, 2018, 6:58 am #34

Beejay5169 wrote: It helps if you buy the right one of these little widgets from your auto parts store,
-I called around looking for one yesterday when I started having this issue, and nobody locally sells them. Most of the auto-parts places had never even heard of such a thing.
I'm thinking I'll just make one, thankfully it's an imperial thread, not metric, and the dimensions aren't critical. The problem is, it doesn't 'reset' the valve, all it does is hold the piston in place during the bleeding procedure, specifically so that this sort of thing doesn't happen.
So I still have the same issue- I need to fix the valve, then use the tool to hold the piston while I bleed the brakes. Hopefully it'll be as simple as being able to worry it back in place with a scribe, through the switch hole. But if not, I'm not sure what else to do, as I've already tried about every other technique mentioned online.
Doc.
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Joined: January 11th, 2016, 8:57 pm

July 9th, 2018, 7:08 am #35

Can you block off the rear INLET to the valve, and rig up a tire pump (or some other controllable source of pressure) on the valve OUTLET to (gently) blow the piston forward, off its backseated position?

The other internet rumor is that not all PVs can be reset - some need to be replaced once they've tripped. 'It's a safety thing' is the highly technical reason frequently given.
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Joined: January 1st, 1970, 12:00 am

July 9th, 2018, 8:08 am #36

Beejay5169 wrote:Can you block off the rear INLET to the valve, and rig up a tire pump (or some other controllable source of pressure) on the valve OUTLET to (gently) blow the piston forward, off its backseated position?
-I was thinking about that. It'll probably be a last-ditch option, but I was thinking I could turn up a sort of adapter fitting that could screw in in place of one of the rear wheel cylinder bleeder screws. For just brute force, I could hook it to compressed air, but I was trying to think of a way that I could better control the pressure. A grease gun would be ideal- and get higher pressures to boot- but of course I don't want to be pumping actual grease into the brake lines.
I have converted grease guns over to oil guns, but there's some work involved. Again, it's towards the "last resort" end of the list of tricks to try. 😁
The other internet rumor is that not all PVs can be reset - some need to be replaced once they've tripped. 'It's a safety thing' is the highly technical reason frequently given.
-Yeah, I've been reading that too. Some people say it's easy, just crack open the opposite side and push the pedal 'til the light goes out, others say there's a "button" you can push to reset, still others say you have to really hammer the pedal to get it to break loose, and still more say they don't reset, or you can't get it to reset.
I rather doubt it's a case of not being able to be reset. That seems like an odd setup to me, and you'd think that it'd be mentioned in more manuals or rebuild books. No one that I've read so far has linked to an official AC Delco or other manufacturer source that says anything like "once tripped, the PV will need to be removed and replaced", etc. It's all essentially internet rumor.
I suspect what the actual issue is, is that some people with older valves do in fact wind up with a valve that won't reset, but that's due to old, hardened seals, rusty bores, and grunge in the fluid.
Which I also think may be why I've never needed one of those holder tools before, despite having bled countless brake systems- all the ones I've worked on have been at least 20 years old or more, and likely the piston in the proportioning valve doesn't move as easily as it does in this clean, nearly-new one.
Just speculation, though.
Doc.
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Joined: January 11th, 2016, 8:57 pm

July 9th, 2018, 8:39 am #37

I'd be careful using 120psi  compressed air. There's a nasty stain under the eaves in my carport where I tried to free up a frozen piston in the caliper of an ancient GSX250 Suzi by injecting air into the bleeder - and succeeded in emptying the master cylinder and reservoir vertically in a few milliseconds.... Hence the idea about using a hand-pump. (Why I thought 120psi air would move the piston when 1000psi from the master cylinder wouldn't, I don't know. Roger-level optimism, I suspect. But the grease gun DID eject it quite easily.)
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Joined: January 11th, 2016, 8:57 pm

July 9th, 2018, 9:02 am #38

The picture below shows that this particular valve has a detent to (presumably) hold the valve in the tripped position once it's fired off, using the switch plunger as the stopper. Have you tried pumping the pedal with the switch removed and the front bleeder open? It looks like there are seals on the piston either side of the switch, and hopefully it shouldn't be too messy without the switch fitted and pressure applied.

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

July 10th, 2018, 9:21 am #39

And Done! (At least provisionally, barring further proper testing. 😁 )

As above, as noted, it of course turned out that the "bias piston" (everybody seems to call it something different) had engaged, and basically had done it's job- blocking off the end that it thinks is "leaking".

The common ways to keep this from happening are either to put a block of wood under the brake pedal to prevent the pusher from pressing down on it too far, or to remove the brake indicator light switch and replace it with a tool that holds the spool in place until the bleeding is complete.

I've bled hundreds of brake systems in my life, and I've never used either of those techniques, and never had a problem. 😁 BUT, also as I mentioned above, what probably happened was those systems were all old and used, and the piston likely didn't move as easily. Which meant that it didn't engage when I'd bleed the system.

This setup is new and clean, so apparently that piston moved easily. I had never encountered the inability to bleed like I did, so of course it confuzzled me for a bit. (In my defense, I've been working on about 10 different projecys over the last couple of weeks, and I can tend to get a bit... scattered at times. 😁 )

Anyway, learn from my mistakes kids: If one end or the other doesn't want to bleed properly, check that proportioning valve spool. And grab one of those cheap tools to keep it from going haywire on you in the first place.

As for the tool, like I said yesterday, I'd already called around looking for one, and none of the auto parts stores had so much as heard of them. We were able to locate one in the computer at two of the stores, but naturally they had none in stock- it'd be a week to get one in.

Ebay and other sellers had 'em too, of course, but would take that same week.

But hey, what do I have nine tons of machine tools for if not for something like this? 😁

So I removed and measured the switch, fully expecting it to be some metric thread. Nope, surprisingly enough, it's Imperial, 1/2"-20, same as some of the tubing fittings for the brake lines.



That was easy enough. A short scrap from the bin and ten minutes got me a reasonable facimile of the switch but with a non-spring-loaded pin to positively hold the spool in place.



And installed, it looked like this:



I was able to shanghai some help again, and this time, the brakes bled easily and quickly, and now gives me a very firm pedal.

So I think we can mark this Summer Project, too, as Completed! I haven't fully tested the diff or the brakes, as it was raining pretty hard all day- I'd like to have some dry roads to make sure the brakes don't lock up one side or one end or the other, and that the posi clutches in the diff aren't going to "spool up" on me and send me off in a spin. (Both are very unlikely to happen, but it was pretty late in the day before I had time to get the bleeding done anyway, so hopefully tomorrow will be a bit drier.)

Doc.
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Joined: January 11th, 2016, 8:57 pm

July 10th, 2018, 9:30 am #40

Presumably you could tickle the piston back into the centered position thru the empty switch hole?
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