Home » Public Forums » GMCnet » [GMCnet] Disc brake project still in failure mode
| Re: [GMCnet] Disc brake project still in failure mode [message #282400 is a reply to message #282398] |
Sat, 18 July 2015 12:51   |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma:
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Senior Member |
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Neil,
Even if you have the PV2 combination valve installed, it should not cause
the rear pressure to be lower than the front. The metering valve works
just the opposite of that: The FRONT pressure is held off until the rear
reaches about 130 psi and continues to increase with the rear pressure
reaches about 400-600 psi. The rear pressure should track the MC pressure
all the way. I'm at a loss to explain what may be causing yours to not do
so. You may have to start at the MC and check the pressure at each
connection, in turn, from there to the caliper.
One thought: Don't just take measure the caliper pressure and immediately
take that as gospel. Rather, HOLD THE PEDAL DOWN for an extended period to
see if the pressure rises. It should come up immediately, but if it
doesn't and comes up slowly, you'll know you have a flow restriction
somewhere. If it NEVER comes up, I don't know what to tell you.
Ken H.
On Sat, Jul 18, 2015 at 1:09 PM, Neil Fonville wrote:
> 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.
>
> On 7/18/15, 11:57 AM, "Gmclist on behalf of A."
> wrote:
>
>> Neil Fonville wrote on Sat, 18 July 2015 11:28
>>> Update: Went out today and installed the pressure gauge on the Right
>>> Front Rear Caliper. Best pressure reading we saw was about 300 psi. So
>>> I
>>> installed the gauge at the MC and was getting 800-900psi. Reinstalled
>>> in the Right front rear caliper and bleed good. Best we got was 400psi.
>>> Is
>>> it the combination valve causing me a problem?
>>>
>>> I have replaced the valve with what I thought was a PV4 for Disc/Disc
>>> conversions. I did pick this up from a local shop with no markings or
>>> paperwork. I had the PV2 which I removed and replaced with this PV4.
>>> Did I get the wrong part or defective? Is the PV4 the best option?
>>>
>>> Thanks,
>>> Neil
>> Don't be offended, but are you sure you didn't measure the pressure to
>> the fronts when you had the gauge at the master cylinder?
>>
>> You need to read the pressure at EACH output at the master cylinder.
>> That'll tell more of the story.
>> --
>> '73 23' Sequoia For Sale
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>> Upper Alabama
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>> headed as "forward", you can call it progress.
>>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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