| Re: [GMCnet] Different models of P-30 master cylinders? [message #248381 is a reply to message #248379] |
Thu, 24 April 2014 15:38   |
James Hupy
Messages: 6806
Registered: May 2010
Karma:
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Senior Member |
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Tom, you are going to get a bunch of answers to your question. There are
more than 3. And, to complicate it further, if you have a bolt on
reservoir, there are several different ones there also. Where your brace
that steadies the booster/MC is located will affect push rod length as
well. From the info that you gave us, one could conclude that your pushrod
might be short. Remove the MC without taking the lines loose, pull it back
far enough to place some modelers clay on the outer end of the rod, then
reassemble without putting any pressure on the pedal. Then remove it again
and check the thickness of the clay. You should have 1/16" or so. Any more,
you need a longer rod. This is a S.W.A.G. method but is FAIRLY ACCURATE if
you are carefull. As with all things GMC, your results may vary.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
On Apr 24, 2014 1:25 PM, "Tom Whitton" <tomwhitton@bellsouth.net> wrote:
> Does anyone know if the following sent to me several years ago is still
> true? Are there still three different models of P-30 master cylinders and,
> the main reason for my question, do they all take the same length pushrod?
> There is quite a bit of travel on my brake pedal before the brakes engage
> and I want to reduce the travel if possible. The brakes are new and the
> rear drum shoes are adjusted tight. My brakes are excellent but I don't
> like the travel.
>
> (I think Emery Stora might have written this):
>
> "The are three different P-30 master cylinders. Two of them have a 1 1/4"
> bore and one has a 1 5/16" bore. I used the one with the 1 5/16" bore
> which is for a 1972-76 Chevrolet P-30 chassis which has 15" drums and 4"
> wide brake shoes. Carquest 20-1583 (rebuilt) or E84058 $122.43 (new).
> Price from year 2000. This one has about 10% more volume (or 10% less
> stroke for the same volume than the 1 1/4" bore on the other P-30 models.
>
> It will be necessary to make a pushrod that is 3 11/16" long. Use a steel
> rod of the same diameter as the original and round the end on a grinding
> wheel or adjustable pushrods can be purchased.
>
> Since the master cylinder is longer than the original it may be necessary
> to grind a reinforcing rib on the inside of the front fiberglass door the
> clear the bail on the master cylinder or washers can be placed between the
> hinge and the door to make the difference."
>
> I made my pushrod 3 11/16" long as suggested. I don't want to unbolt
> everything, including the vacuum pump and connections if there isn't a
> possibility of reducing the pedal travel. I will appreciate your thoughts.
>
> Thanks,
>
> Tom Whitton
> 26 foot updated GMC
> Paducah, KY
>
>
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