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| Re: [GMCnet] Disc brake project still in failure mode [message #282402 is a reply to message #282401] |
Sat, 18 July 2015 13:41   |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Neil, one more thought crossed my mind. Do you have a flexible line between
the forward and rear bogies, or are they rigid ones. I have seen both types
used. The possibility exists that you have an internally collapsed flex
line, or, a pinched or kinked rigid line there. It seems highly improbable
that hydraulic pressure would vary much from one end of a line to the other
end, or, in the case of the rear brakes, from side to side. All the rear
brakes are fed from a single line. If you do have a P-30 master cylinder,
you had to reverse the two lines that go to the distribution valve to make
the fittings match the threaded ports in the MC. That would make the
reservoir towards the front of the coach feed the front brakes, and the
other one feed the rears. The pv4 should have enter and exit pressures that
are the same. There is nothing inside the valve to alter pressure or flow.
The pressure differential, if any, should activate the spool valve and
close the brake warning light circuit. There should be equal pressure on
both sides of that spool, or it will move one way or the other and operate
the warning light.
Jim Hupy
On Jul 18, 2015 11:10 AM, "A." wrote:
> Neil Fonville wrote on Sat, 18 July 2015 12:09
>> I did not read the front pressure because the fronts are solid and seem
> to be working. Since I had the front working, no leaks, etc I did not
>> want to open that part of the system up. Not really sure why that would
> tell me more? 800-900PSI at the MC and 300-400PSI at the caliper. Huge
>> loss somewhere in the rear system and the combination value seems
> likely. From what I have read, the PV2 value will cut the pressure by 1/2
> within
>> a certain range. I¹m thinking I got sold the PV2 instead of the PV4
> when I replaced it.
> It is understandable that you don't want to open up the front since it is
> working. But I have made the mistake of thinking the line farthest from the
> booster is the rear and the other is the front, which was backwards (or
> vice versa, I have to trace the lines to tell, since I can never remember).
>
> That's why I asked if you are sure the line you checked at the master
> cylinder is actually the line to the rear brakes. I don't know what can
> happen
> to cause 800 psi at one end, and half that at the other end. Doesn't seem
> plausible if they were the same line.
>
> If you have the OEM type combination valve, at light pedal pressure you
> can have less pressure to the FRONT than the rear. And in that case, you
> could
> have less pressure to one set than is coming out of the master cylinder.
>
> To summarize the thought process here: Something LIKE what you are
> describing COULD occur with an OEM type combination valve, and the lines
> from that
> valve that are supposed to go to the front going to the rear, and vice
> versa. But not the numbers you are reporting
>
>
> http://www.gmcmhphotos.com/photos/deciphering-the-combination-valve/p5331.html
>
> There are also cases where folks had to reverse the lines at the master
> cylinder to get the fittings to work (because one is larger than the other).
> --
> '73 23' Sequoia For Sale
> '73 23' CanyonLands For Sale
> Upper Alabama
> On "marriage equality": Once you define the direction that society is
> headed as "forward", you can call it progress.
>
> _______________________________________________
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| Re: [GMCnet] Disc brake project still in failure mode [message #282405 is a reply to message #282402] |
Sat, 18 July 2015 14:17 |
Neil Fonville
Messages: 68
Registered: May 2014
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Yes, I have the P-30 MC and the front port feeds the front brakes, etc. I
do have a flexible type hose between the bogies. They are steel braided
but certain they are rubber on the inside.
In response to Ken’s comment: I took the readings after holding the pedal
down for a few seconds or so and continued to hold for about 1 min. They
are were very consistent and did not see any movement of the needle during
the reading.
If I still had some air somewhere in the rear, would I see a lower reading
at the caliper than the MC? I would think do. I wanted to take the
reading at the MC to rule it out. This is my 3rd one from O’rilley.
On 7/18/15, 1:41 PM, "Gmclist on behalf of James Hupy"
wrote:
> Neil, one more thought crossed my mind. Do you have a flexible line
> between
> the forward and rear bogies, or are they rigid ones. I have seen both
> types
> used. The possibility exists that you have an internally collapsed flex
> line, or, a pinched or kinked rigid line there. It seems highly improbable
> that hydraulic pressure would vary much from one end of a line to the
> other
> end, or, in the case of the rear brakes, from side to side. All the rear
> brakes are fed from a single line. If you do have a P-30 master cylinder,
> you had to reverse the two lines that go to the distribution valve to make
> the fittings match the threaded ports in the MC. That would make the
> reservoir towards the front of the coach feed the front brakes, and the
> other one feed the rears. The pv4 should have enter and exit pressures
> that
> are the same. There is nothing inside the valve to alter pressure or flow.
> The pressure differential, if any, should activate the spool valve and
> close the brake warning light circuit. There should be equal pressure on
> both sides of that spool, or it will move one way or the other and operate
> the warning light.
> Jim Hupy
> On Jul 18, 2015 11:10 AM, "A." wrote:
>
>> Neil Fonville wrote on Sat, 18 July 2015 12:09
>>> I did not read the front pressure because the fronts are solid and
>> seem
>> to be working. Since I had the front working, no leaks, etc I did not
>>> want to open that part of the system up. Not really sure why that
>> would
>> tell me more? 800-900PSI at the MC and 300-400PSI at the caliper. Huge
>>> loss somewhere in the rear system and the combination value seems
>> likely. From what I have read, the PV2 value will cut the pressure by
>> 1/2
>> within
>>> a certain range. I¹m thinking I got sold the PV2 instead of the PV4
>> when I replaced it.
>> It is understandable that you don't want to open up the front since it
>> is
>> working. But I have made the mistake of thinking the line farthest from
>> the
>> booster is the rear and the other is the front, which was backwards (or
>> vice versa, I have to trace the lines to tell, since I can never
>> remember).
>>
>> That's why I asked if you are sure the line you checked at the master
>> cylinder is actually the line to the rear brakes. I don't know what can
>> happen
>> to cause 800 psi at one end, and half that at the other end. Doesn't
>> seem
>> plausible if they were the same line.
>>
>> If you have the OEM type combination valve, at light pedal pressure you
>> can have less pressure to the FRONT than the rear. And in that case, you
>> could
>> have less pressure to one set than is coming out of the master cylinder.
>>
>> To summarize the thought process here: Something LIKE what you are
>> describing COULD occur with an OEM type combination valve, and the lines
>> from that
>> valve that are supposed to go to the front going to the rear, and vice
>> versa. But not the numbers you are reporting
>>
>>
>>
>> http://www.gmcmhphotos.com/photos/deciphering-the-combination-valve/p5331
>> .html
>>
>> There are also cases where folks had to reverse the lines at the master
>> cylinder to get the fittings to work (because one is larger than the
>> other).
>> --
>> '73 23' Sequoia For Sale
>> '73 23' CanyonLands For Sale
>> Upper Alabama
>> On "marriage equality": Once you define the direction that society is
>> headed as "forward", you can call it progress.
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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> _______________________________________________
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| Re: [GMCnet] Disc brake project still in failure mode [message #282406 is a reply to message #282405] |
Sat, 18 July 2015 14:46 |
A Hamilto
Messages: 4508
Registered: April 2011
Karma: 39
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Neil Fonville wrote on Sat, 18 July 2015 14:17...If I still had some air somewhere in the rear, would I see a lower reading at the caliper than the MC?... My gut says the presence of air is irrelevant. If you have a pipe (container) under pressure, the pressure is the same anywhere in/on the pipe (container). At least for this case, since we can neglect the height difference.
If the pipe was vertical (instead of mostly horizontal), you could add the weight of the fluid pressing on the bottom of the pipe, which would be a psi or so, maybe.
WARNING. SCIENCE CONTENT FOLLOWS. PROCEED AT YOUR OWN RISK.
Pascal's Principle: Any external pressure applied to a fluid is transmitted undiminished throughout the fluid and onto the walls of the containing vessel.
[Updated on: Sat, 18 July 2015 15:58] Report message to a moderator |
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| Re: [GMCnet] Disc brake project still in failure mode [message #282463 is a reply to message #282406] |
Sun, 19 July 2015 12:32 |
Neil Fonville
Messages: 68
Registered: May 2014
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Member |
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So I went back out again today to collect a bit more info. So I put the
pressure gauge on the output of the combination valve. I got a consistent
reading of 500psi.
My procedure was engine running, pump 5 times and hold for 1 min. Gauge
went to 500 with every press and held at 500 without fluctuation. When I
did this same procedure on the MC got 800-900psi. So do I have a clog in
the combination valve?
Thanks for the input
Neil
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| Re: [GMCnet] Disc brake project still in failure mode [message #282477 is a reply to message #282472] |
Sun, 19 July 2015 13:44 |
Neil Fonville
Messages: 68
Registered: May 2014
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I¹m not sure I have the plumbing parts to connect to the input of the
combination valve. I¹m certain I¹m testing the same line. The output of
the MC and combination valve for the rear brakes is a 9/16 connection. I
guess the line may have an issue from the MC to the valve but does not
seem likely.
On 7/19/15, 1:31 PM, "Gmclist on behalf of A."
wrote:
> Neil Fonville wrote on Sun, 19 July 2015 12:32
>> So I went back out again today to collect a bit more info. So I put
>> the pressure gauge on the output of the combination valve. I got a
>> consistent reading of 500psi.
>>
>> My procedure was engine running, pump 5 times and hold for 1 min.
>> Gauge went to 500 with every press and held at 500 without fluctuation.
>> When I
>> did this same procedure on the MC got 800-900psi. So do I have a clog
>> in the combination valve?
>>
>> Thanks for the input
>> Neil
> You definitely have something strange happening between those two test
> points. Call me a nag if you want, but it sure seems like you are testing
> two
> different lines.
>
> To verify it is the combination valve, repeat the test with the gauge on
> the input side of the combination valve.
> --
> '73 23' Sequoia For Sale
> '73 23' CanyonLands For Sale
> Upper Alabama
> On "marriage equality": Once you define the direction that society is
> headed as "forward", you can call it progress.
>
> _______________________________________________
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| Re: [GMCnet] Disc brake project still in failure mode [message #282480 is a reply to message #282478] |
Sun, 19 July 2015 14:04 |
Neil Fonville
Messages: 68
Registered: May 2014
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I have the P-30 MC and the back port of the MC is the rear brakes and is
the larger of the two fluid lines. Do I have that wrong?
On 7/19/15, 1:56 PM, "Gmclist on behalf of A."
wrote:
> Neil Fonville wrote on Sun, 19 July 2015 13:44
>> I¹m not sure I have the plumbing parts to connect to the input of the
>> combination valve. I¹m certain I¹m testing the same line. The output of
>> the MC and combination valve for the rear brakes is a 9/16 connection.
>> I guess the line may have an issue from the MC to the valve but does not
>> seem likely.
> Other than the pressure differential switch, the combination valve for
> disk brakes is just a straight through pipe to the rears, and a "tee" to
> the
> fronts. The pressure drop you are seeing is in the line to the valve, or
> the valve. If you are pretty sure it isn't the line to the valve, then it
> has
> to be the valve. Replace it.
>
> OTOH, nag warning, you are measuring two different lines.
> --
> '73 23' Sequoia For Sale
> '73 23' CanyonLands For Sale
> Upper Alabama
> On "marriage equality": Once you define the direction that society is
> headed as "forward", you can call it progress.
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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| Re: [GMCnet] Disc brake project still in failure mode [message #282483 is a reply to message #282481] |
Sun, 19 July 2015 14:54 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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I am saying that IF you still have the original metal brake lines that went
to the ORIGINAL MASTER CYLINDER, when you install the P-30 master cylinder,
in order to install the lines without adapting anything, the OEM line
fittings must be swapped in order for them to screw into the P-30. AS THE
ORIGINAL RESERVOIR IN THE FORWARD MOST POSITION IS FOR THE REAR DRUM
BRAKES, IF YOU SWITCH THE LINES, THE RESERVOIR THEN BECOMES THE FRONT
BRAKES. I didn't say that was right or wrong. That is the way I install the
P-30. Haven't had any issues just swapping the lines. When I have to
replace the lines, as is often the case when you mess with the distribution
valve fittings, I use the same size lines. I personally cannot tell the
difference either way it is done.
If you are seeing different pressures at the distribution valve, you
either have a step bore in the P-30 MC or a restriction somewhere
downstream from the MC.
JIM HUPY
Salem, Or
78 GMC ROYALE 403
On Jul 19, 2015 12:33 PM, "A." wrote:
> Neil Fonville wrote on Sun, 19 July 2015 14:04
>> I have the P-30 MC and the back port of the MC is the rear brakes and is
> the larger of the two fluid lines. Do I have that wrong?
> Mr. Hupy said the larger goes to the rear. JP Winger's gallery on the
> photo site says the larger goes to the front. Since that is conflicting
> info,
> you need to trace the line yourself. If the line with the larger
> connection on the master cylinder goes to the end of the combination valve
> that
> splits to the fronts, it is the line to the front.
> --
> '73 23' Sequoia For Sale
> '73 23' CanyonLands For Sale
> Upper Alabama
> On "marriage equality": Once you define the direction that society is
> headed as "forward", you can call it progress.
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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| Re: [GMCnet] Disc brake project still in failure mode [message #282485 is a reply to message #282483] |
Sun, 19 July 2015 15:28 |
A Hamilto
Messages: 4508
Registered: April 2011
Karma: 39
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James Hupy wrote on Sun, 19 July 2015 14:54I am saying that IF you still have the original metal brake lines that went to the ORIGINAL MASTER CYLINDER, when you install the P-30 master cylinder, in order to install the lines without adapting anything, the OEM line fittings must be swapped in order for them to screw into the P-30. AS THE ORIGINAL RESERVOIR IN THE FORWARD MOST POSITION IS FOR THE REAR DRUM BRAKES, IF YOU SWITCH THE LINES, THE RESERVOIR THEN BECOMES THE FRONT BRAKES. I didn't say that was right or wrong. ... It gets confusing since the P-30 fitting sizes are reversed from OEM.
Everything that I know about pressurized fluid in a system is screaming at me that Neil is measuring the output to the front brakes at the master cylinder, and the pressure in the line to the rear wheels everywhere else he has taken measurements.
I think he still has air, or an obstruction, in the rear part of the system. I am leaning towards it being air, but we have to get past the problem if the differential between the points where he is reading pressure. And I think there is still air in one or more of the rear calipers. That is assuming the master cylinder is ok, and I do, despite so many new parts being from China and all that.
But we got to get that difference in pressure figured out before going on to finding the bubble(s). Once we find that the low reading exists all the way from the master cylinder to the rear calipers, we got a good idea there is nothing wrong with the lines, or the combination valve. The problem is either the master cylinder, or air one or more rear calipers. Once we establish which line from the master cylinder goes to the rear, if he has a way to put a gauge on that port and plug the line out of it, we can pressure test the master cylinder.
One step at a time. I found out long ago that most people read the first sentence and the rest has to be repeated.
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| Re: [GMCnet] Disc brake project still in failure mode [message #282486 is a reply to message #282483] |
Sun, 19 July 2015 15:27 |
Neil Fonville
Messages: 68
Registered: May 2014
Karma: 0
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Member |
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Yes I did swap the lines. Front line on the old moved to Back on new MC.
And vice versa.
What is a Step bore in the MC?
On 7/19/15, 2:54 PM, "Gmclist on behalf of James Hupy"
wrote:
> I am saying that IF you still have the original metal brake lines that
> went
> to the ORIGINAL MASTER CYLINDER, when you install the P-30 master
> cylinder,
> in order to install the lines without adapting anything, the OEM line
> fittings must be swapped in order for them to screw into the P-30. AS THE
> ORIGINAL RESERVOIR IN THE FORWARD MOST POSITION IS FOR THE REAR DRUM
> BRAKES, IF YOU SWITCH THE LINES, THE RESERVOIR THEN BECOMES THE FRONT
> BRAKES. I didn't say that was right or wrong. That is the way I install
> the
> P-30. Haven't had any issues just swapping the lines. When I have to
> replace the lines, as is often the case when you mess with the
> distribution
> valve fittings, I use the same size lines. I personally cannot tell the
> difference either way it is done.
> If you are seeing different pressures at the distribution valve, you
> either have a step bore in the P-30 MC or a restriction somewhere
> downstream from the MC.
> JIM HUPY
> Salem, Or
> 78 GMC ROYALE 403
> On Jul 19, 2015 12:33 PM, "A." wrote:
>
>> Neil Fonville wrote on Sun, 19 July 2015 14:04
>>> I have the P-30 MC and the back port of the MC is the rear brakes and
>> is
>> the larger of the two fluid lines. Do I have that wrong?
>> Mr. Hupy said the larger goes to the rear. JP Winger's gallery on the
>> photo site says the larger goes to the front. Since that is conflicting
>> info,
>> you need to trace the line yourself. If the line with the larger
>> connection on the master cylinder goes to the end of the combination
>> valve
>> that
>> splits to the fronts, it is the line to the front.
>> --
>> '73 23' Sequoia For Sale
>> '73 23' CanyonLands For Sale
>> Upper Alabama
>> On "marriage equality": Once you define the direction that society is
>> headed as "forward", you can call it progress.
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
> _______________________________________________
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| Re: [GMCnet] Disc brake project still in failure mode [message #282489 is a reply to message #282485] |
Sun, 19 July 2015 15:34 |
Neil Fonville
Messages: 68
Registered: May 2014
Karma: 0
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Member |
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I¹m going out later today to visually confirm the rear port of the MC is
plumbed to the read port of the combining valve. I¹m fairly certain it is
but I¹m going to double check.
On 7/19/15, 3:28 PM, "Gmclist on behalf of A."
wrote:
> James Hupy wrote on Sun, 19 July 2015 14:54
>> I am saying that IF you still have the original metal brake lines that
>> went to the ORIGINAL MASTER CYLINDER, when you install the P-30 master
>> cylinder, in order to install the lines without adapting anything, the
>> OEM line fittings must be swapped in order for them to screw into the
>> P-30.
>> AS THE ORIGINAL RESERVOIR IN THE FORWARD MOST POSITION IS FOR THE REAR
>> DRUM BRAKES, IF YOU SWITCH THE LINES, THE RESERVOIR THEN BECOMES THE
>> FRONT
>> BRAKES. I didn't say that was right or wrong. ...
> It gets confusing since the P-30 fitting sizes are reversed from OEM.
>
> Everything that I know about pressurized fluid in a system is screaming
> at me that Neil is measuring the output to the front brakes at the master
> cylinder, and the pressure in the line to the rear wheels everywhere else
> he has taken measurements.
>
> I think he still has air, or an obstruction, in the rear part of the
> system. I am leaning towards it being air, but we have to get past the
> problem if
> the differential between the points where he is reading pressure. And I
> think there is still air in one or more of the rear calipers. That is
> assuming
> the master cylinder is ok, and I do, despite so many new parts being from
> China and all that.
>
> But we got to get that difference in pressure figured out before going on
> to finding the bubble(s). Once we find that the low reading exists all the
> way from the master cylinder to the rear calipers, we got a good idea
> there is nothing wrong with the lines, or the combination valve. The
> problem is
> either the master cylinder, or air one or more rear calipers. Once we
> establish which line from the master cylinder goes to the rear, if he has
> a way
> to put a gauge on that port and plug the line out of it, we can pressure
> test the master cylinder.
>
> One step at a time. I found out long ago that most people read the first
> sentence and the rest has to be repeated.
> --
> '73 23' Sequoia For Sale
> '73 23' CanyonLands For Sale
> Upper Alabama
> On "marriage equality": Once you define the direction that society is
> headed as "forward", you can call it progress.
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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| Re: [GMCnet] Disc brake project still in failure mode [message #282491 is a reply to message #282486] |
Sun, 19 July 2015 15:39 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Neil, a step bore would be two different sized bores. In a closed ended
cylinder, the bore that was deepest would be a smaller diameter than the
end closest to the booster. The pistons in the bores would match their
bores. The results would be a different displacement volume of fluid from
each bore. They are rarely seen, but are possible. If that were the case
with yours, it could account for the variation in pressure as well. This
stuff makes my head hurt. It is nearing 100° in my shop. Is it 5:00 yet?
Jim Hupy
On Jul 19, 2015 1:28 PM, "Neil Fonville" wrote:
> Yes I did swap the lines. Front line on the old moved to Back on new MC.
> And vice versa.
>
> What is a Step bore in the MC?
>
> On 7/19/15, 2:54 PM, "Gmclist on behalf of James Hupy"
> wrote:
>
>> I am saying that IF you still have the original metal brake lines that
>> went
>> to the ORIGINAL MASTER CYLINDER, when you install the P-30 master
>> cylinder,
>> in order to install the lines without adapting anything, the OEM line
>> fittings must be swapped in order for them to screw into the P-30. AS THE
>> ORIGINAL RESERVOIR IN THE FORWARD MOST POSITION IS FOR THE REAR DRUM
>> BRAKES, IF YOU SWITCH THE LINES, THE RESERVOIR THEN BECOMES THE FRONT
>> BRAKES. I didn't say that was right or wrong. That is the way I install
>> the
>> P-30. Haven't had any issues just swapping the lines. When I have to
>> replace the lines, as is often the case when you mess with the
>> distribution
>> valve fittings, I use the same size lines. I personally cannot tell the
>> difference either way it is done.
>> If you are seeing different pressures at the distribution valve, you
>> either have a step bore in the P-30 MC or a restriction somewhere
>> downstream from the MC.
>> JIM HUPY
>> Salem, Or
>> 78 GMC ROYALE 403
>> On Jul 19, 2015 12:33 PM, "A." wrote:
>>
>>> Neil Fonville wrote on Sun, 19 July 2015 14:04
>>>> I have the P-30 MC and the back port of the MC is the rear brakes and
>>> is
>>> the larger of the two fluid lines. Do I have that wrong?
>>> Mr. Hupy said the larger goes to the rear. JP Winger's gallery on the
>>> photo site says the larger goes to the front. Since that is conflicting
>>> info,
>>> you need to trace the line yourself. If the line with the larger
>>> connection on the master cylinder goes to the end of the combination
>>> valve
>>> that
>>> splits to the fronts, it is the line to the front.
>>> --
>>> '73 23' Sequoia For Sale
>>> '73 23' CanyonLands For Sale
>>> Upper Alabama
>>> On "marriage equality": Once you define the direction that society is
>>> headed as "forward", you can call it progress.
>>>
>>> _______________________________________________
>>> GMCnet mailing list
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>>>
>> _______________________________________________
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| Re: [GMCnet] Disc brake project still in failure mode [message #282514 is a reply to message #282492] |
Sun, 19 July 2015 17:58 |
Neil Fonville
Messages: 68
Registered: May 2014
Karma: 0
|
Member |
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I have confirmed I have the rear port on the P30 connected to the rear
brakes. Tested pressure again. Got 800 rising to 900 when holding on the
rear MC port. 500 steady at the rear output of the combination valve.
Did not have parts to test at the input of the valve.
Neil
On 7/19/15, 4:06 PM, "Gmclist on behalf of A."
wrote:
> Neil Fonville wrote on Sun, 19 July 2015 15:34
>> I'm going out later today to visually confirm the rear port of the MC
>> is plumbed to the read port of the combining valve. I'm fairly certain
>> it
>> is but I'm going to double check.
> Every possible next step hinges on that determination.
>
> The combination valve for disk brakes is not really a valve at all. It is
> a junction/distribution point with a differential switch. If there was no
> requirement for the differential switch, it could be replaced with a
> splice for the rears and a tee for the fronts. Not much to go wrong that
> can
> cause a pressure differential inside it. Same for the steel lines. If the
> line is 800 pounds at the master cylinder and 500 pounds coming out of the
> "valve", this is a head scratcher.
> --
> '73 23' Sequoia For Sale
> '73 23' CanyonLands For Sale
> Upper Alabama
> On "marriage equality": Once you define the direction that society is
> headed as "forward", you can call it progress.
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
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1975 GMC II
Allen, TX
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| Re: [GMCnet] Disc brake project still in failure mode [message #282520 is a reply to message #282516] |
Sun, 19 July 2015 18:29 |
Neil Fonville
Messages: 68
Registered: May 2014
Karma: 0
|
Member |
|
|
I sure hope that pay dirt comes soon. I doubt it¹s the line. I will
inspect it next but could be next weekend before time allows.
Thanks again.
Neil
On 7/19/15, 6:11 PM, "Gmclist on behalf of A."
wrote:
> Neil Fonville wrote on Sun, 19 July 2015 17:58
>> I have confirmed I have the rear port on the P30 connected to the rear
>> brakes. Tested pressure again. Got 800 rising to 900 when holding on
>> the
>> rear MC port. 500 steady at the rear output of the combination valve.
>> Did not have parts to test at the input of the valve.
>>
>> Neil
> You are within a couple shovels of paydirt. You got a 300 - 400 PSI drop
> between the master cylinder and the output of the combination valve. I
> don't
> know or care how that can even be possible. But you need to figure out
> which component has the evil in it - the line or the valve. Disconnect
> the line
> between the master cylinder and the combination valve and verify there
> isn't anything in it that would restrict flow. Then do the same between
> the
> input and output of the combination valve. Might need to replace the
> combination valve. Reassemble, bleed the rears one last time, and drive
> it.
> --
> '73 23' Sequoia For Sale
> '73 23' CanyonLands For Sale
> Upper Alabama
> On "marriage equality": Once you define the direction that society is
> headed as "forward", you can call it progress.
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
_______________________________________________
GMCnet mailing list
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1975 GMC II
Allen, TX
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