Defender 300 tdi vacuum pump

[shack]

Hi all,
I've recently removed the original style vacuum pump from my defender, I've fitted an electric vac pump and vacuum switch, it all works fine except it keeps frying relays,I think it is because just as it achieves the required vacuum it cycles on and off several times rather quickly before it finally turns off, until of course you use the brakes and the whole process starts again, has anyone else tried this? If so have you had success ?

Cheers James

[Red90]

Get a reservoir to prevent it from cycling too quickly.

[bee utey]

If the relay is being fried fit a suppressor capacitor across the motor, like off an ignition coil or a condenser out of a points distributor.

[shack]

Ok,I can understand what the extra reservoir would do, but what would a capacitor do? I'm not fully aware of their function, the problem I think is that when vacuum is nearly reached, the unit runs on several times which causes the relay to cycle too many times and probably burns the contacts

[bee utey]

Ok,I can understand what the extra reservoir would do, but what would a capacitor do? I'm not fully aware of their function, the problem I think is that when vacuum is nearly reached, the unit runs on several times which causes the relay to cycle too many times and probably burns the contacts

Distributor points open and close a million times with a capacitor attached, but burn out in minutes when that capacitor fails. A capacitor acts like a low resistance to very sharply changing voltages so only a very faint spark will appear at the relay points. Motors like ignition coils contain strong magnetic fields when turned on, and suddenly disconnecting the power means the magnetic field collapses and the only way for its energy to dissipate is a high voltage arc at the points. Put in a capacitor and the high voltage is massively reduced as it acts as a short term conductor. The terms "capacitor" and "condenser" are more or less interchangeable.

[shack]

Ok thanks for that, will give it a go pronto....

Cheers James

[shack]

So I've done the condenser trick, and haven't fried another relay yet, so thanks for that advice bee utey, now the vacuum switch is playing up, it will be fine for a couple of days, then the switch will simply fail to reset when vacuum drops, as though it's stuck,a tap with a screw driver fixes it but as it's under the bonnet this is inconvenient to do while in town in traffic and draws unnecessary attention towards anther land rover, are the switches a bad idea or have I just got a dodgy one?

[bee utey]

Being a Defender you could rig up a long wire cable and spring so that you could whack the switch from inside the cab...

...or buy a new switch, they can't be all that dear. Early RRC EFI systems ran a vacuum switch (for decel injector cutoff) down the back of the inlet manifold, they seemed to last for years.

[shack]

No they are not that dear, most under $100, it's just that I was looking for a cost effective ( not cheap) method too improve the vac pump situation, have probably spent the best part of $400 already and it is still playing up, so another hundred and I could have bought two standard aftermarket jobs, if I knew another hundred bucks would cure it I'd go for it, but it's basically a hundred dollars too find out, and then if it doesn't work,I get too start again.....

Where is the line in the sand?

I may have already reached it...

[bee utey]

Of course it's possible that your relay coil needs suppression too. Most modern relays have a small diagram on the side and you look for a small additional symbol across the coil, either a diode or a resistor in most cases. Cheap relays have nothing. Example: