[GMCnet] JC-4 Vacuum Pump??

[RJW]

While getting ready to leave for the Elkhart rally, I had a conversation with a well respected and reliable GMCer about vacuum pumps.

I had mentioned that I have installed in my coach the often recommended "JC-4 Vacuum Pump". He remarked that most of them were not very good at
providing an adequate backup vacuum (for braking) in the event of an engine failure. But, that's why we have them, for an adequate vacuum source to
give us brakes if the motor goes south and stops producing vacuum.

I decided to do a test to see how my brakes work without engine vacuum and how the JC-4 does as a backup. I have a 1/2 mile stretch of road near my
house with little traffic. I drove there in my GMC and started out going 30 MPH, put it in neutral and shut down the motor. I pressed the brake
pedal a few times to dump vacuum and then tried to stop. The result was not good and it was a good thing I didn't have to stop because I could not
stop.

I did it again, except this time after shutting the motor off I turned the ignition back on (to power the JC-4 pump). I did the same thing, dumped the
vacuum, but now I could hear the pump running when I pressed the brake pedal. I waited until it stopped and then I tried to stop the coach. The
result was there was a slight improvement over no vacuum, but not what I had expected. I was able to stop, but it seemed not much better than with no
vacuum. I repeated these tests several times with the same resulsts.

I would not want to be going down a mountain road with a toad and try to stop with the engine not running and relying on the JC-4.

My conclusion is that I am going to get rid of my JC-4 and go to something more robust.

Apparently, the problem with the JC-4 is that it shuts off before adequate (for our needs) vacuum is achieved. It might be possible to by pass the
internal pressure switch to something that would allow it to pump down to the vacuum that we need to stop. Then maybe it would be OK.

My advice for those that have JC-4 Vacuum Pumps is to try my test and see how comfortable you are with it as your emergency vacuum backup.



--
Richard
76 Palm Beach
SE Michigan
www.PalmBeachGMC.com


Coop Roller Cam 455, Howell TBI + EBL, 3.42 FD, Quadra Bag, Macerator, Manny Tranny etc.


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[D C _Mac_ Macdonald]

I wonder if anyone has done a similar test using the European Ford (Azure ?) vacuum port?


~~ ~ D C "Mac" Macdonald ~ ~~
~ ~ Amateur Radio - K2GKK ~ ~
~ ~ Since 30 November '53 ~ ~
~ ~ USAF and FAA, Retired ~ ~
~ Member GMCMI and Classics ~
~ ~ ~ Oklahoma City, OK ~ ~ ~
~~ ~ ~ "The Money Pit" ~ ~ ~~
~ ~ ~ ~ TZE166V101966 ~ ~ ~ ~
~ ~ ~ '76 ex-Palm Beach ~ ~ ~
~~ k2gkk + hotmail dot com ~~
~ www.gmcmhphotos.com/okclb ~
~~ Cellphone: 405-642-7337 ~~
______________
|[ ]~~~[][ ][]\
"--OO--[]---O-"

________________________________
From: Gmclist <gmclist...@list.gmcnet.org> on behalf of RJW <my...@palmbeachgmc.com>
Sent: Wednesday, September 13, 2017 21:08
To: gmc...@list.gmcnet.org
Subject: [GMCnet] JC-4 Vacuum Pump??

While getting ready to leave for the Elkhart rally, I had a conversation with a well respected and reliable GMCer about vacuum pumps.

I had mentioned that I have installed in my coach the often recommended "JC-4 Vacuum Pump". He remarked that most of them were not very good at providing an adequate backup vacuum (for braking) in the event of an engine failure. But, that's why we have them, for an adequate vacuum source to give us brakes if the motor goes south and stops producing vacuum.

I decided to do a test to see how my brakes work without engine vacuum and how the JC-4 does as a backup. I have a 1/2 mile stretch of road near my house with little traffic. I drove there in my GMC and started out going 30 MPH, put it in neutral and shut down the motor. I pressed the brake pedal a few times to dump vacuum and then tried to stop. The result was not good and it was a good thing I didn't have to stop because I could not stop.

I did it again, except this time after shutting the motor off I turned the ignition back on (to power the JC-4 pump). I did the same thing, dumped the vacuum, but now I could hear the pump running when I pressed the brake pedal. I waited until it stopped and then I tried to stop the coach. The result was there was a slight improvement over no vacuum, but not what I had expected. I was able to stop, but it seemed not much better than with no vacuum. I repeated these tests several times with the same results.

I would not want to be going down a mountain road with a toad and try to stop with the engine not running and relying on the JC-4.

My conclusion is that I am going to get rid of my JC-4 and go to something more robust.

Apparently, the problem with the JC-4 is that it shuts off before adequate (for our needs) vacuum is achieved. It might be possible to by pass the internal pressure switch to something that would allow it to pump down to the vacuum that we need to stop. Then maybe it would be OK.

My advice for those that have JC-4 Vacuum Pumps is to try my test and see how comfortable you are with it as your emergency vacuum backup.
--
Richard
76 Palm Beach
SE Michigan

www.PalmBeachGMC.com<http://www.PalmBeachGMC.com>

[Jerry Wheeler]

Why not do the test with the ignition left on?? Perhaps our coach will
stop with the pump running. If my motor dies, I would not turn off the
ignition switch; I would want to be able to steer the coach when rolling,
even if I did not have brakes. By the way, I have the Delco vacuum pump
that is not longer available, but I have not tested my brakes; I have my
vacuum pump wired to a separate source for 12v, not the ignition switch. I
probably should do the same test you did Richard.
JR Wheeler 78 Royale NC/OR

On Wed, Sep 13, 2017 at 10:36 PM, D C _Mac_ Macdonald <k2...@hotmail.com>
wrote:

[RJW]

Jerry Wheeler wrote on Wed, 13 September 2017 23:24

> Why not do the test with the ignition left on?? Perhaps our coach will
> stop with the pump running. If my motor dies, I would not turn off the
> ignition switch; I would want to be able to steer the coach when rolling,
> even if I did not have brakes. By the way, I have the Delco vacuum pump
> that is not longer available, but I have not tested my brakes; I have my
> vacuum pump wired to a separate source for 12v, not the ignition switch. I
> probably should do the same test you did Richard.
> JR Wheeler 78 Royale NC/OR

I tested with the ignition off, to see what happens without any vacuum. Also, with the ignition on, to see how helpful the JC-4 pump would be in the

event of an engine failure.

All this time I thought I was covered in the event I lost vacuum.

Previously I had a Delco pump and that worked. It fell apart and since there were no replacements available at the time I went to the JC-4.

--
Richard
76 Palm Beach
SE Michigan
www.PalmBeachGMC.com

Coop Roller Cam 455, Howell TBI + EBL, 3.42 FD, Quadra Bag, Macerator, Manny Tranny etc.

[Rob Mueller]

G'day,

Below you will find an email I posted regarding these pumps which I believe will allay anyone fears about the Azure vacuum pump
along with one from Les B.

Dave L did a demo of it at the Shawnee GMCMI Convention in conjunction with the GMC booster and it was amazing!

They are still available from Dorman P/N 904-814 unfortunately they ain't $115 any more! However, I ga-ron-tee this pump will out
perform anything else on the market. Take into consideration it was NOT a backup; it was the only vacuum source for braking in the
Azure!

Parts Geek: $270

Tiny URL: http://tinyurl.com/yd67vxnv

Full URL:

http://www.partsgeek.com/gbproducts/MC/96880-07204175.html?utm_content=MC&utm_term=2011-2012+Ford+F150+Vacuum+Pump+Dorman+904-814+11
-12+Ford+Vacuum+Pump&fp=pp&gbm=a&utm_source=google&utm_medium=ff&utm_campaign=PartsGeek+Google+Base&gclid=Cj0KCQjw0ejNBRCYARIsACEBhD
MJXd7M1Vub_JJNNZn-UymXHSV_MBXSF00I_mGgYjShlK39uLWkwhwaAtJwEALw_wcB&ad=47362750812


Summit: $295

Tiny URL: http://tinyurl.com/ycwhtfqc

Full URL:

https://www.summitracing.com/parts/rnb-904-814?seid=srese1&cm_mmc=pla-google-_-shopping-_-srese1-_-dorman&gclid=Cj0KCQjw0ejNBRCYARIs
ACEBhDOUFYu2r1XI7d0a6f9p9ngSRDZ_Afn10346Vg_vAai3Is1YONpWxJQaAmPaEALw_wcB

Oscaro: $302

Tiny URL: http://tinyurl.com/y73fnw2t

Full URL:

http://www.oscaroparts.com/dorman-vacuum-pump-904-814-20092795-5172-p?gclid=Cj0KCQjw0ejNBRCYARIsACEBhDOhetmRt90FGWXDzIZJzjSFu4KcevP9
FOl0ggALwyk1BzDNGILre90aAkWiEALw_wcB


-----Original Message-----
From: gmclist...@temp.gmcnet.org [mailto:gmclist...@temp.gmcnet.org] On Behalf Of Rob Mueller
Sent: Tuesday, July 15, 2014 8:39 AM
To: gmc...@temp.gmcnet.org
Subject: [GMCnet] SUPER Brake Booster Aux Vacuum Pump

G'day,

Here's a SUPER brake booster Aux Vacuum Pump for our GMC's

http://www.ebay.com/itm/Ford-Continental-Electric-Vacuum-Pump-12VDC-Ford-A426C-/370691272503

I purchased two of them and they really SUCK! ;-)

At $115 with free shipping they are a bargain compared to anything else out there. If you read the blurb you will note that they
were meant to go in an electric vehicle sold in Europe that has been discontinued (Ford Azure). That means they were the ONLY vacuum
source for the brake booster so they had to be designed to be ultra reliable. I took one of these suckers apart and found that the
internals are very simple and crank / connecting rods run on bearings!

Because they have dual diaphragms they suck a lot more than any other pump on the market.

Unfortunately you will have to come up with a mounting bracket as none are available commercially.

If you buy one you will note that the plastic 3/8" barb fitting has a little tab that fits in a slot on the pump that keeps it from
rotating, with a small Dremel tool you can remove the barb and the fitting will rotate 360 degrees.

More photos:

http://www.gmcmhphotos.com/photos/g6633-brake-booster-vacuum-pump.html

Regards,
Rob M.

-----Original Message-----
From: Gmclist [mailto:gmclist...@list.gmcnet.org] On Behalf Of Les Burt
Sent: Tuesday, March 14, 2017 7:49 AM
To: gmc...@list.gmcnet.org
Subject: Re: [GMCnet] Anybody installed a Delco 20804130 Vacuum Pump??

The ford vacuum pump ( aka Ford Azzure vacuum pump) that was listed on eBay a while back is still easily found. The early f150
ecoboost pick up uses the same pump. They were notorious for corrosion, so Ford revised the design and the latest version has a
black composite body. You can buy them here in Canada at the Ford dealer for just a bit over $200cad.

Les Burt
Montreal
'75 Eleganza 26'
The EWIP (Eternal Work In Progress)

Regards,
Rob M.
The Pedantic Mechanic
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808

[Larry]

I have the Ford (Azure ?) vacuum pump as a backup for vacuum brakes. I did test it on a seldom traveled road near my home. Traveling at 60mph, in
neutral with the key ON, engine off, as long as I do not pump the brakes rapidly, the pump keeps up with the vacuum needs for braking to a safe stop.
Handling the lac of power steering is another matter. I have a vacuum switch on the booster that I can adjust up to 25 in/vac. I have it set at 21
in/vac with a control switch on the arm rest to my left. I only turn it on when the engine is not running and I need vacuum to move the coach....like
when my motor went south and needed to back the coach off of the tilt bed of the wrecker. Also use it when launching my coach on to the elevating
ramps that I use for raising the coach to do maintaince. One foot on gas, the other one brake so I don't roll off the end of the ramp takes the vacuum
down to low numbers. Turn on the vacuum pump for instant brakes. Just what I do.
--
Larry
78 Royale w/500 Caddy
Menomonie, WI.

[Hal StClair]

I used the Ford pump as the only source of vacuum when I first did the Diesel swap(diesels make no vacuum). The pump seemed to work fine but one of
the downsides to using them is that they loose efficiently at high altitudes. We live at 5280' and quite often drive over 8000' where these pumps are
limited. I chose to build a hydro boost system which works well but also has it's own drawbacks during engine failures. Nothing out there is "perfect"
for every situation. It's best to find the balance you are comfortable with and go for it. Just my way of thinking.
Hal
--
1977 Royale 101348,

1977 Royale 101586, Diesel powered,

1975 Eleganza II, 101230

1974 Eagle Bus 45',w/slideout

[larry.whisler]

Richard,

When we were at Blaine's work rally, John Shotwell and I attached
a JC-4 vacuum pump to a vac gauge to check the amount of vacuum
of a brand new pump versus a used pump from the salvage yard.

Both pumps produced 8 psi vacuum based on their internal cutoff switch.

Someone was looking into altering the internal switch to achieve a higher
vacuum. I have no doubt that the JC4 pump could provide an adequate amount \
of vacuum if the switch could be overridden.

The problem my arise at high altitude where the pump would run continuously
because it cannot achieve the required vacuum to turn the unit off.



JMHO

larry

[Johnny Bridges via Gmclist]

Lemme suggest, instead of dropping a perfectly good albeit no very great volume pump, simply add a reservoir. II use about 3 feet of 4 inch PVC pipe
capped at each end strapped to the cross-member in front of the radiator using band clamps. Glue a couple of bayonet connectors into it, and be sure
to add a check valve. Onmy 23' coacg, good for three complete stops w/o engine assist.

--johnny

--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased

[Ken Henderson]

Pete Pappas, past SunShine Statesman & Dixielander, devised a way to
increase the cutoff pressure of the JC4. He sent me details at one time.
Unfortunately I can neither remember nor find the details. I do recall that
it involved adding something like a ballpoint pen spring and a small
machine screw. I never did it because I figured I'd prefer to bypass the
internal switch and add an external one -- which I never did because the
Azure pumps came along first.

Searching for that mod, I came across the link to Gene's brake postings.
Here it is for the enlightenment of newbies:

http://gmcmotorhome.info/addens.html

Ken H.

On Thu, Sep 14, 2017 at 5:30 PM, larry.whisler <larry....@hotmail.com>
wrote:

> ​...

>
> Someone was looking into altering the internal switch to achieve a higher
> vacuum. I have no doubt that the JC4 pump could provide an adequate
> amount \
> of vacuum if the switch could be overridden.
>

​...​

[John Phillips]

Just for comparison what is nominal engine vacuum in a braking situation?

On Thu, Sep 14, 2017 at 3:55 PM, Ken Henderson <hend...@bellsouth.net>
wrote:

--

*John Phillips*

[Ken Henderson]

Probably 25" Hg. Since the booster holds the highest vacuum it's seen
since the last brake application, it's conceivable that it could be as high
as 30" Hg. after a long off-throttle deceleration.

Ken H.

On Fri, Sep 15, 2017 at 1:32 AM, John Phillips <john.ph...@gmail.com>
wrote:

> Just for comparison what is nominal engine vacuum in a braking situation?
>

[slc]

The question was "Just for comparison what is nominal engine vacuum in a braking situation?"


I am pretty sure unless you are very good at being a mechanic, that you may wonder the same thing.

I read a message a time back where someone was taking readings and said with the vacuum pump
running, the system would hold 20lbs vacuum.

But he also suggested that pressing the brake pedal, with the engine not running, and holding the
pedal down, does not hold the psi, but the vacuum leaks off, ever so slowly. You will eventually,
and it seems in a short time lose any vacuum you have stored if you have no vac pump operational when
the engine dies.

food for thought.

Just what I read.
--
GatsbysCruise. \
74GMC260 Former Glacier Model style. \
Waukegan, Illinois \ Keep those MiniDiscs Spinning \ MY GREYHOUND IS FASTER THAN YOUR HONOR ROLL STUDENT \ WindowsXP-Win7-Win8.1-UBUNTU STUDIO -
UBUNTU VOYAGER - Berzin Auto Center

[Bruce Hislop]

I posted this about a year ago on the operation of the JC-4 vacuum pump. Its not a great pump, about 8-9" of vacuum is all you can expect from it.

I bypassed the internal circuitry so now it only acts as a vacuum pump. Then I wired it through a relay controlled by Dave Lenzi's vacuum switch
assembly. Best I can get is about 15" of vacuum. Not great but better than nothing.

http://www.gmcmhphotos.com/photos/data/6785/JC-4_vacuum_pump_operation.pdf

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that

[RJW]

RF_Burns wrote on Sun, 23 May 2021 14:45

> I posted this about a year ago on the operation of the JC-4 vacuum pump. Its not a great pump, about 8-9" of vacuum is all you can expect from
> it.
>
> I bypassed the internal circuitry so now it only acts as a vacuum pump. Then I wired it through a relay controlled by Dave Lenzi's vacuum switch
> assembly. Best I can get is about 15" of vacuum. Not great but better than nothing.
>
> http://www.gmcmhphotos.com/photos/data/6785/JC-4_vacuum_pump_operation.pdf

I might have kept my JC-4 pump had I known about the mod to use an external switch and some sort of reserve vacuum storage container. I thought a lot
about the possibility of losing brakes while I was driving down to Death Valley from California and was happy I had the upgrade over the JC-4 pump.
That trip caused me to decide to go with Dave Lenzi's disk brakes (I already had a 4-bag system). During the installation of the disk brakes I found
out that I had a badly leaking drum brake cylinder that may have contributed to my less than great brakes during that trip down to the valley.

--
Richard
76 Palm Beach
SE Michigan
www.PalmBeachGMC.com

Roller Cam 455, TBI+EBL, 3.42 FD, 4 Bag, Macerator, Lenzi (brakes, vacuum system, front end stuff), Manny Tranny, vacuum step, Tankless + OEM water
heaters.

[Bruce Hislop]

Richard,
Have you read DaveL's article in the Spring GMCMI magazine about the proportioning vales. If you have replaced your OEM with a brass proportioning
valve, you may have limited rear brake pressure.

The "Mod" of the JC-4 wasn't really a high tech "Mod". I believe the internal control circuitry pulled one side of the motor to ground through a
Power FET to turn it ON. I just moved wire on the switched side of the motor to the JC-4 ground pin and ran that pin through the relay to ground....
I'd have to look at it again to be sure.

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that

[RJW]

RF_Burns wrote on Sun, 23 May 2021 22:01

> Richard,
> Have you read DaveL's article in the Spring GMCMI magazine about the proportioning vales. If you have replaced your OEM with a brass
> proportioning valve, you may have limited rear brake pressure.
>
> The "Mod" of the JC-4 wasn't really a high tech "Mod". I believe the internal control circuitry pulled one side of the motor to ground through a
> Power FET to turn it ON. I just moved wire on the switched side of the motor to the JC-4 ground pin and ran that pin through the relay to
> ground.... I'd have to look at it again to be sure.

I never changed out my OEM valve to the often touted brass proportioning valve because I never got around to it. As it turned out, Dave showed me his
cutaways of various valves and explained what he had learned about them during a visit to his place in March. Consequently, I'm happy I never got
around to switching to a brass valve. I've never had better braking, since I installed his disk brakes, the newer 4-bag suspension, 80MM calipers in
the front and a still working OEM proportioning valve. However, I don't have a working parking brake.

--
Richard
76 Palm Beach
SE Michigan
www.PalmBeachGMC.com


Roller Cam 455, TBI+EBL, 3.42 FD, 4 Bag, Macerator, Lenzi (brakes, vacuum system, front end stuff), Manny Tranny, vacuum step, Tankless + OEM water
heaters.