Electric vacuum pump issue

[Tinbasherdan]

Got ann electric vac pump kit for the defender as the Cummins doesn’t have a pump. Got it all installed today and it runs…… but won’t stop.

https://static.speedwaymotors.com/pdf/SSBC-Electric-Brake-Vacuum-Pump-Installation-Instructions.pdf

Wired as per the above, checked pressure switch for earth continuity, even bridged an earth direct, tested its operation and it breaks contact at 15inhg as per requirements.

Dead headed the switch with my finger to rule out an air leak, pump energises, reaches pressure and cuts very briefly (< 1 sec) then starts up again and won’t even attempt to cut. I’m leaning towards the relay being stuck but open to suggestions

 

[Erie Fred]

My Izusu truck had a small vacuum pump on the back of the alternator.
IIRC the dodge pick-ups with the Cummins had the same.

 

[sako243]

@Tinbasherdan do they have a proper wiring diagram for it? Following those instructions wasn't particularly clear to me, a simple diagram would be far easier to understand.

If it stops I'd hazard a guess the relay is working otherwise why would the motor stop? I'd carefully look at the coil side of the relay as it seems more likely that's not switching off properly.

 

[Tinbasherdan]

@Tinbasherdan do they have a proper wiring diagram for it? Following those instructions wasn't particularly clear to me, a simple diagram would be far easier to understand.

If it stops I'd hazard a guess the relay is working otherwise why would the motor stop? I'd carefully look at the coil side of the relay as it seems more likely that's not switching off properly.

It doesn’t stop, that’s the issue, can’t find a proper wiring diagram anywhere either

 

[jsf55]

CBS do a similar pump and relay set up, does the diagram help any ?

https://www.carbuilder.com/Attachment/DownloadFile?downloadId=40

 

[sako243]

It doesn’t stop, that’s the issue, can’t find a proper wiring diagram anywhere either

You said it stops briefly then resumes. I'm assuming the relay is to switch the motor power on and off via the pressure / vacuum switch? Therefore the relay does work.

I'd get a multimeter onto the switch and see what's happening with that when the pump switches on/off briefly.

 

[Tinbasherdan]

You said it stops briefly then resumes. I'm assuming the relay is to switch the motor power on and off via the pressure / vacuum switch? Therefore the relay does work.

I'd get a multimeter onto the switch and see what's happening with that when the pump switches on/off briefly.

For less than a second, not enough time for the motor to wind down.

 

[sako243]

Well what else is in the supply path of the motor then? Either you have a dodgy connection or the relay is interrupting the supply.

If the relay is interrupting the supply then you need to find out whether it's bring instructed to or whether it's doing it "randomly" (it won't be random but for some other reason, e.g. a dodgy connection).

Replace the pressure switch with a simple toggle switch - get your basics right. Can you turn on and off the pump via a relay. Once you've sorted that then it should simply be a case of swapping the toggle switch for the pressure switch.

You might need to confirm if the switch is normally open or normally closed.

 

[Tinbasherdan]

Well what else is in the supply path of the motor then? Either you have a dodgy connection or the relay is interrupting the supply.

If the relay is interrupting the supply then you need to find out whether it's bring instructed to or whether it's doing it "randomly" (it won't be random but for some other reason, e.g. a dodgy connection).

Replace the pressure switch with a simple toggle switch - get your basics right. Can you turn on and off the pump via a relay. Once you've sorted that then it should simply be a case of swapping the toggle switch for the pressure switch.

You might need to confirm if the switch is normally open or normally closed.

The relay is meant to interrupt the supply, it’s just not. The pressure switch breaks earth and de energises the relay which stops the pump, this is trying to de energise but not managing it

 

[Matrixx]

it is either the switch or the relay is faulty, you need to check the voltage on the switch then on the relay coil, and then on the contacts.

 

[sako243]

Can you draw a diagram of what you have wired up? You might even spot an issue as you draw it out.

 

[Hotstuff]

It’s not complicated enough to warrant a circuit diagram.

Can you post a photo of how you have connected your relay and identify the relay PIN numbers.

The relay is probably normally open and only switches to closed circuit when the coil circuit (terminals 1 & 3) is energised.
The coil circuit neutral is switched via the vacuum switch.

The pump motor is supplied from terminals 2 & 5 with the live supply looped from terminal 2.

If you ground the wire terminated to terminal 1 the motor should operate and terminals 2 & 5 should go from open circuit to closed circuit.

You could check continuity through the vacuum switch to check its operation. I don’t know if it’s looking for a negative or positive air pressure.

If the switch is functioning correctly then perhaps we need to be looking at what’s operating the vacuum switch. Leaky hose or bad hose connection?

Good luck.

 

[Tinbasherdan]

Sorted it. Wasn’t electrical at all! Check valve in pump head had some crud under it so was allowing pressure to bleed off back through the pump!

 

[Tinbasherdan]

Pump works but now the servo is leaking like a sieve. Never ends

 

[ranchero]

Pump works but now the servo is leaking like a sieve. Never ends

dump it and fit a hydroboost

 

[Tinbasherdan]

dump it and fit a hydroboost

Cheaper to buy another servo at 50 quid and get another 30 years use out of it!