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Home » GMC » GMCnet » JC-4 Vacuum Pump?? (maybe you don't want to bet your life on it!)
JC-4 Vacuum Pump?? [message #323858] Wed, 13 September 2017 21:08 Go to next message
rjw   United States
Messages: 354
Registered: September 2005
Karma: 5
Senior Member
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.
Re: [GMCnet] JC-4 Vacuum Pump?? [message #323860 is a reply to message #323858] Wed, 13 September 2017 21:36 Go to previous messageGo to next message
k2gkk is currently offline  k2gkk   United States
Messages: 3979
Registered: November 2009
Karma: 7
Senior Member
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 on behalf of RJW
Sent: Wednesday, September 13, 2017 21:08
To: gmclist-AT-list-DOT-gmcnet-DOT-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

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Re: [GMCnet] JC-4 Vacuum Pump?? [message #323861 is a reply to message #323860] Wed, 13 September 2017 22:24 Go to previous messageGo to next message
Jerry Wheeler is currently offline  Jerry Wheeler   United States
Messages: 216
Registered: January 2013
Karma: 0
Senior Member
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
wrote:

> 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 on behalf of RJW mygmc-AT-palmbeachgmc-DOT-com>
> Sent: Wednesday, September 13, 2017 21:08
> To: gmclist-AT-list-DOT-gmcnet-DOT-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
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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Re: [GMCnet] JC-4 Vacuum Pump?? [message #323863 is a reply to message #323861] Thu, 14 September 2017 06:11 Go to previous messageGo to next message
rjw   United States
Messages: 354
Registered: September 2005
Karma: 5
Senior Member
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.
Re: [GMCnet] JC-4 Vacuum Pump?? [message #323864 is a reply to message #323860] Thu, 14 September 2017 07:18 Go to previous messageGo to next message
USAussie is currently offline  USAussie   United States
Messages: 15324
Registered: July 2007
Location: Sydney, Australia
Karma: 41
Senior Member
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=Cj0KCQjw0ejNBRCYARIs ACEBhD
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-bounces-AT-temp-DOT-gmcnet-DOT-org [mailto:gmclist-bounces-AT-temp-DOT-gmcnet-DOT-org] On Behalf Of Rob Mueller
Sent: Tuesday, July 15, 2014 8:39 AM
To: gmclist-AT-temp-DOT-gmcnet-DOT-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-bounces-AT-list-DOT-gmcnet-DOT-org] On Behalf Of Les Burt
Sent: Tuesday, March 14, 2017 7:49 AM
To: gmclist-AT-list-DOT-gmcnet-DOT-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



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Regards, Rob M. (USAussie) The Pedantic Mechanic Sydney, Australia '75 Avion - AUS - The Blue Streak TZE365V100428 '75 Avion - USA - Double Trouble TZE365V100426
Re: JC-4 Vacuum Pump?? [message #323865 is a reply to message #323858] Thu, 14 September 2017 07:33 Go to previous messageGo to next message
Larry is currently offline  Larry   United States
Messages: 1993
Registered: January 2004
Location: Menomonie, WI
Karma: 3
Senior Member
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 Smile
78 Royale w/500 Caddy
Menomonie, WI.
Re: JC-4 Vacuum Pump?? [message #323871 is a reply to message #323865] Thu, 14 September 2017 11:31 Go to previous messageGo to next message
Hal StClair   United States
Messages: 652
Registered: March 2013
Location: Rio Rancho NM
Karma: 10
Senior Member
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, Rio Rancho, NM
Re: JC-4 Vacuum Pump?? [message #323877 is a reply to message #323858] Thu, 14 September 2017 16:30 Go to previous messageGo to next message
larry.whisler is currently offline  larry.whisler   
Messages: 348
Registered: August 2005
Karma: 8
Senior Member
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

Re: JC-4 Vacuum Pump?? [message #323879 is a reply to message #323858] Thu, 14 September 2017 17:12 Go to previous messageGo to next message
Johnny Bridges is currently offline  Johnny Bridges   United States
Messages: 6180
Registered: May 2011
Location: Braselton ga
Karma: 30
Senior Member
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
Re: [GMCnet] JC-4 Vacuum Pump?? [message #323880 is a reply to message #323877] Thu, 14 September 2017 17:55 Go to previous messageGo to next message
Ken Henderson is currently offline  Ken Henderson   United States
Messages: 7216
Registered: March 2004
Location: Americus, GA
Karma: 40
Senior Member
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
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.
>
​...​
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
Re: [GMCnet] JC-4 Vacuum Pump?? [message #323893 is a reply to message #323880] Fri, 15 September 2017 00:32 Go to previous messageGo to next message
johnd01 is currently offline  johnd01   United States
Messages: 67
Registered: July 2017
Location: Sacrameot
Karma: 0
Member
Just for comparison what is nominal engine vacuum in a braking situation?

On Thu, Sep 14, 2017 at 3:55 PM, Ken Henderson
wrote:

> 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
> 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.
>>
> ​...​
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>



--

*John Phillips*
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Johnd01
Re: [GMCnet] JC-4 Vacuum Pump?? [message #323895 is a reply to message #323893] Fri, 15 September 2017 06:10 Go to previous message
Ken Henderson is currently offline  Ken Henderson   United States
Messages: 7216
Registered: March 2004
Location: Americus, GA
Karma: 40
Senior Member
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
wrote:

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