[JC4 PUMP] [BOOSTER
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[HORROR STORIES] [ACCUMULATORS]
auxiliary vacuum booster pump
Today I had 3 conversations about the JC4 pump and how to use it
as the auxiliary vacuum source for our brake systems. I guess the
GMCMI news letter has created some interest, so I thought I would give
the link to the information on how to buy and use this pump for our
This pump is still available new and like the 119 pump, requires no
external components in our application. This link shows how it
fits into our application, vs, the other pumps available.
Here are pictures of a mounting of the JC4 pump using a
bracket made by the Car guy
here is a link to his products
Here are pictures of using the Electric wiper Modification from the
"Wiperguy" to mount the JC4 pump
Here is the wiper kit
Excellent price on ebay , $79 plus $13 freight
TIPS ON HOW TO FIND A JUNKYARD VACUUM PUMP
The main article shows the models of the cars that used these pumps,
but, they are still hard to locate in a Junk Yard. Look at the
following pictures, they show where the pumps are located and what they
look like. There are words on the pictures that show the
different types of pumps and how they are mounted. It is
importiant to look at the insides of the pump before you leave the
junkyard. The pictures show how this is done.
1: Look for a car with a transverse engine, an engine that is
across the car.
2 Look at the driver side front, under the hood for a
3 Look at the rear of the battery holder for two rubber vacuum
lines that run next to the fender.(see picture)
4 If these lines are there, a pump is located just below the
battery, in front of the wheel.
5 You have to remove the plastic wheel liner to see the pump.
6 You can check to see if the pump is good buy removing the cone
shaped cover over the diaphragm.
7 Use a small pair of vice grips to bend down the tabs.
Remove the cover and a spring will pop out.
8 Remove the diaphragm by pulling on the center pin.
9 Inspect the diaphragm, if there are no holes in it, the pump is
good and can be used.
10 Remove the pump and the bracket and when you get home, replace the
VACUUM PUMP REBUILD
Many of us have worried about using a Junk Yard Dog vacuum pump on our
GMCs', especially since only 1 in 10 of the pumps from the wrecking
yard have a working diaphragm and there are no repair parts
available. The diaphragm is clearly a weak link in this
pump. Manny Trovao has
provided us what appears to be an excellent solution to this problem.
The Cadilac car of this generation, had a different pump. This
pump does not have the features of the ones in the Xcars, Power boost
relay, Min runtime, check valve. However, they used a piston
rather than the diaphragm. This Piston will work in the Xcar
pump and seems to
be easier to find. They do go bad just as often so take them
apart and look carefully inside the piston at the 4 rubber
flapper valves. If these are out of place or have a hole in them,
move on to the next car. The pictures are in the group shown
WILL NOT SOLVE THESE PROBLEMS
HORROR STORIES OF LOST BRAKES
This is My Story
It was a dark and rainy night in Morro Bay Ca. In traffic I
turned up the street going away from the bay. As I reached the
top of the
hill, the front wheels lost traction and started to spin and
on the wet pavement. I jammed on the brakes, and the engine died
the gas ran to the rear of the tank. There were cars behind me honking,
engine would not start, it was dark, it was wet and I had to back down
hill about a block, stopping many times to make the cars behind me go
in the busy traffic...
The vacuum pump ran the whole time, and saved my bacon. It
me about 10 min. which seemed like 10 hours to get on the flat where
engine would run...... I would not have wanted to look for a switch in
dark in situations like this when I am in full panic with out
Hallelujah brother, let it run, let it run. gene
On the other hand several of us know of an owner whose coach ran
out of power attempting to climb a narrow, winding mountain road just
outside Albuquerque who would have given her 1st born child for a
brakesystem. The coach rolled back down the road to the first bad curve
afterwhich it ended up in a ravine. The tow company further destroyed
what thecrash itself didn't accomplish. Owners survived. David
Ken B story
I put a new gasoline selector valve on my coach and drove it down
the street. About 1.5 miles from home the engine quit. I
called my wife to bring the blazer and tow me back home. It
is rural here and I could not turn the coach around. She towed me
home which was about 5 miles around to total circle to get back.
We did it at about 15 mph. Try stopping the coach when being
towed without vacuum. I ended up using the emergency brake every
time we need to slow down or stop. It was not fun.
The next week a new found friend that I met here (even though he
picks on me at times) sent me a vacuum pump in the mail from west
coast. It got installed immediately. Do not leave
home without it. BTW the selector valve had a crack in it and it
was sucking air. KenB
Testing the newly installed distributor. Low on fuel, but
not that low. Head to my favorite test hill. Steep thing that.
can check for "ping" to get my advance set as best I can. Wife is
driving and I'm listening near the hatch as we go up the
hill. Did I mention it was steep?
Carb backfires once and then the engine dies. Turns out that
I was very low on fuel and the steep hill put all the fuel away from
The vacuum pump that I installed at Gene's urging started
humming. A nice sound.
I took over the helm and backed us down this hill to a flat
driveway about 1/8 mile down. Fired the coach up and drove to a
On the way down, I just HAD to see what would happen if I turned
off the pump. Since it was wired to the key, that was easy.
Took but a few pumps and there was no way I could slow the coach with
Once again silently thanked Gene for his insistance that I should
install the pump.
Yes, I could have set the parking brake and left the coach on the
Would I have tried to back it down, thinking I could do it?
Quite possibly. At the time I really wouldn't have known better
since I was pretty new to the rig.
Can't for the life of me figure out why there is such an aversion
to this mod. Fairly simple, takes up minimal space and works
Whatever. It saved my butt Kelvin
Regarding the power brake system, I was leaving my sons house in
my 77Kingsley at Big Bear Calif when I ran out of gas on the way down
the mountain. I had just gotten the coach and was trying to
out how the gauges worked, which I learned on this trip. Since it
was down hill Idecided to see how I made out going down since there was
absolutely no whereto get gas on the way down and I didn't want to call
my son and have himrescue me with a 5 gallon gas can. I drifted
11 miles into a little towncalled Mentone, right into a gas station and
within 10 feet of the gas pump.The station attendant and I pushed it
the other 10 feet so I could fill itup.
On the way down I had no power steering but I had brakes because I
have the aux vacuum pump out of an old gm car that most have
It was a little hairy on the tight turns but as long as I had brakes it
didn't bother me. I can't think of ever wanting to drive my coach
without that vacuum pump.Bob
I have a hydroboost on my Blazer that uses power steering
fluid. The accumulator is good for maybe two low speed stops
after the engine dies. I would never install one on my GMC.
I installed a Powermaster on my GMC and it has worked great for
the first 1000 miles or so. It is totally self contained and as
long as there is 12 vdc to it and the ignition switch is on I have
power brakes. I haven't made a panic stop, but it seems to
develop more stopping power with less pedal pressure than the vacuum
booster it replaced.
While I got mine from a junk yard and rebuilt it, Powermasters are
available from all the Auto Parts Houses and someone sells an adapter
to install them on GMC's. I used an adapter and Powermaster from
a '87 Chevy Stationwagon and had to shorten the actuator rod 1" and
enlarge the adapter mounting holes through the dash since the adapter
uses metric studs that are slightly larger than the 3/8" ones used with
the vacuum booster. Everything else was a direct bolt in. The
wiring for the vacuum pump is the same as the Powermaster wiring.
I just cut the leads to the vacuum pump and spliced them to the
Powermaster wires. Also I can remove the spacers I installed when
I installed a P-30 master cylinder. Jim
SENSITIZED BOOSTERS LEAK VACUUM
(Kills a Vacuum tank Idea)
Well, I might have known, Gene & Emery are RIGHT! Another of
those ASSumptions, or believing something heard!
I connected a vacuum gauge to the accessory port on my vacuum
reservoir. Cranked the engine and got 20"Hg. Shut the engine down
and waited about 3 minutes -- still had 20"Hg. Put my foot on the
brake. The vacuum dropped about 2"Hg immediately, then continued
to drop at about 0.5"Hg per second! Mind you, that's with the 4"x30"
reservoir! Without it the rate would be much higher.
Among the variations of the test I conducted was to run the engine, put
my foot on the brake, and turn the Cadillac suspension
compressor/vacuum pump on. The pump WAS able to hold 20"Hg vacuum
and to recover it if I cycled the brake.
With neither the engine nor the pump running, the pedal rose slowly,
almost imperceptibly, as the vacuum decreased. I was, frankly,
surprised on the first trial, to find that it had moved: I
thought my foot was at the same level as when I first applied the
brakes, until I released and reapplied the pedal and found that it went
down only a little way.
I'm disappointed and baffled by this situation. For all my power
brake driving years -- at least 50 of them -- I've thought the vacuum
was trapped with the pedal down and would hold the brakes indefinitely.
The need for the reservoir is now more acute than I had any idea --
that controlled leak means that the fabled 2-3 brake applications must
be quick, short ones because one long one will deplete the vacuum.
And "long" will be pretty short.
An electrically driven pump also makes even more sense than I realized
-- that's the only way to extend the boosted brake application time
beyond about 30 seconds! :-(
Unless all of us have defective boosters. KenH
To plumb in the pump, remove the vacuum line from the brake
booster and connect to the filter. The other side of the filter
goes to the pump exhaust. A new hose goes from the suction side
of the pump to the brake booster.
Installed this way, the engine sucks through the filter, through the
pump, to the booster. The only time the pump comes on is when the
vacuum is too low and then it helps the engine vacuum. If the
engine stops, (goes up to ambient air pressure) the pump provides all
of the vacuum. If the pump fails the engine provides all of the
Some owners plumb the pump Tee connected between the
engine and the booster, a check valve is needed between the Tee and the
engine. The pump will not be able to draw a vacuum in this
configuration if the
engine stops because the engine will bring the booster up to ambient
pressure. A check valve is necessary to block the engine. I
not recommend this configuration. Gene
The pump must be mounted with the rubber mount bracket on the
top. There are drain holes in the bottom of the pump that remove
any moisture that might have collected inside the pump. If the
pump is mounted
upside down, it will have a short life. Gene
Here is some information from Jeff Diamond
Here is the place to get the Acc power for the control of the pump
Pump Second Source
(NONE OF THESE SOURCES
We show these sources to indicate where we have
The vacuum pump I used is a complete unit including the pump, vacuum
switch, and resilient mounting bracket --- everything you need except a
Pump: MP (Master Power) Brakes ---(704)664-8866 Part
$269.95 plus $20.30 shipping from NC to OR. Mounts easily
firewall "box" by the steering post under LH access panel.
retail $10.60, Net $7.99.
BTW, in the process of checking out my vacuum pump installation I found
that I had a small leak in the original vacuum line to the
booster.....probably never would have found it until complete failure
had I not installed the pump.Gary
This is available here from the local AC/Delco dealer for around
$127..the pump# is AC215-119
The AC2723 number above is the Master Power number and I had the
AC/Delco dealer xref the Gm# 22034995.
I found the 4-connection connector at Pep BoysCBWood
Surely in NJ there are some AC/Delco dealers. The pump number
just as you mentioned. The list price is $197.36 and the
wholesale price is
127.33. Ask for the wholesale price. You want a new
pump. You may have to
go to a junk yard to get the mounting bracket and an electrical
it. I could not find a source for the electrical connector,
except for the
junkyard. JR Wheeler
Thank you for inquiring with Auto Parts West. The vacuum pup
will cost $125.68. The freight via UPS ground is $5.00. If
you wish to order please use the order form at www.autopartswest.com
Ron and Julie
I bought the connector and the pins from NAPA - the lock tab on the
connector is slightly offset - I didn't have time to send it back or
for one in the junkyard so I used a nylon cable-tie to hold it in.
I bought a new pump from a GM dealer, I think it was around $150, NAPA
wanted $200 ( we don't have an AC/Delco store out here, we're lucky to
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