Vacuum pump wiring help

[tyler]

On the coach I got a few weeks ago, the po installed a brake vacuum pump, but didn't quite finish. If someone has one of these, or is willing to look
at the following install manual in light of my question, that would be great.

http://ssbrakes.com/attachment/63196-Instruction%20Manual

On page 7 it summarizes the wiring needed for the four pins of the relay. My install has a "Y" not pictured in the manual on the wire from relay
terminal 1 to vacuum switch. One side goes to vacuum switch as shown, the other side goes up behind the dash, where there is a designated but not
connected switch. Can someone confirm that the vacuum switch functions by simply grounding the circuit, and this additional wire up to the dash should
function as a additional way to manually activate the pump if I just make it switch/connect to a ground behind the dash?

If my thinking is correct, the pump will always be energized to run based on the pressure switch calling for it, AND/OR if I throw the toggle in the
dash it will energize it to run as long as the switch is "on".

I think my preference is for the dash toggle to energize the whole assembly/circuit, and then the pump actually cycles based on demand from the
pressure switch. I would call this a master switch rather than a demand switch, but I am making up terms by logic than any common usage! If I
understand how the relay works in general, to accomplish this the switch would instead be wired between the constant or ignition switched (another
debate in my head) 12 volt source to terminal 2. Thoughts?
--
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC

 

[armand minnie]

I have that same vacuum pump and same documentation with a different brand name (Frenos Iruna Brakes from Spain). Yes, the vacuum switch does provide
a ground (via the Tee body) that activates the relay with their wiring arrangement. I don't know why you would need to override the vacuum switch
though because the way they have it plumbed and wired it will be running a lot on its own. I ended up doing what Dave Lenzi recommends and having the
vacuum switch (using his adjustable one) essentially measuring the vacuum inside of the booster (by disabling the normal check valve) and having the
pump itself on the other side of an inline check valve. His booster has two vacuum ports which make that a lot easier.
--
Armand Minnie
Marana, AZ
'76 Eleganza II TZE166V103202
http://www.minniebiz.com
http://www.gmcws.org

 

[tyler]

Cool, one question answered - the ground could be supplied through the vacuum sensing switch or the dash switch.

I read somewhere that the vacuum switch won't trigger until down to near 10 inches(?). Given that PO has pump plumbed to evacuate a three inch PVC
pipe about 2.5 feet long (reservoir), and that is what is actually plumbed to the booster, I don't think it would run as much as without the
reservoir.

But, your comment made me consider not using the vacuum switch at all - engine dies, burden is on me to throw the switch to activate relay and thus
the pump. I have the PVC reservoir, so should have three activations of brake pedal to remember to turn on electric pump!
I could test/verify operation by ear and foot when I start the coach each trip.

How long does your pump run to pull down and stop? (and maybe a guess with a reservoir)
--
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC

 

[armand minnie]

I don't know how long it takes but I will try to measure it. Dave Lenzi says (I listen to him) that boosters are made to operate at 16 inches or more
of vacuum. According to the guy I bought my vacuum pump from (on Ebay) that switch (same as yours) is set to 18-20 inches but no telling for sure
unless you measure it. Another factor is what is the range of the switch - Dave says about 2 inches between on and off so that it is not running
unnecessarily. The switch that came with my pump had a problem (Ebay guy replaced it) so I bought one of Dave's adjustable switches. He told me to
adjust it so it comes on at 16 and goes off at about 20. Dave says that as soon as the booster vacuum goes below 16 you lose braking power and at 2800
feet of altitude my engine will only produce 15 inches so he says I should just tolerate the pump running a lot around home. I think turning the pump
on manually only is not a good idea - when your brakes are not working is no time to be looking for switches and waiting for pumps.
--
Armand Minnie
Marana, AZ
'76 Eleganza II TZE166V103202
http://www.minniebiz.com
http://www.gmcws.org

 

[johnny]

I have ne of those on the 26' coach. Due to leaky lines, it runs fairly often. It is simply teed into the line going to the booster, with a check
valve on the manifold side. This will be modified as follows. I will build a vacuum reservoir out of PVC and clamop it to the back if the frontmost
crossmember. The reservoir will tee into the booster line. The pump will go directly to the reservoir, it jas an internal check valve. A check valve
will be lplaced between the manifold and the tee in the booster line. My 23' is assemble this way, using the pump out of a Buick Century (I think) I
got at the local men's mall. I need the connector for it, it isn't currently powered. Even unpowered, the reservoir is sufficient to stop the coach
frpom highway speeds with substantial braking left over, by actual trial. Consequently the plug for the pump has been low priority.It will be a part
of 'things needed' for the NO. I don't want to go dumpster diving in the rain.

--johnny

n.b NO = New Owner, who is due here tomorrow.
--
'76 23' transmode Norris upfit, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"The road goes on forever, and the party never ends" --Robert Earl Keen

 

[thomas phipps]

Do not use a switch to either engage or disengage the auxiliary vacuum system. Let the pressure switch do the work. After loosing vacuum and having no
brakes is not a good plan to go looking for a switch of any kind. There should be enough vacuum in the system to apply the brakes once. Stand on the
petal with both feet and push hard. No feathering allowed.
Semi-disclaimer: My GMC has the J4 pump installed and it just works. No fuss, no muss.
Tom, MS II
--
1975 GMC Avion
KA4CSG