Vacuum hose connected to alternator?

Submitted: Wednesday, May 23, 2007 at 17:04
ThreadID: 45794 Views:8581 Replies:5 FollowUps:8
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Hi
just wondering, why does my friend's 86 troopy have a vacuum hose connected to the back of the alternator??
Rich
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Reply By: David N. - Wednesday, May 23, 2007 at 17:10

Wednesday, May 23, 2007 at 17:10
because there's a vacuum pump on the alternator.
Diesels have no vacuum, and therefore need a pump for supplying vacuum to the brake booster etc
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Follow Up By: Dicko2 - Wednesday, May 23, 2007 at 17:59

Wednesday, May 23, 2007 at 17:59
Why do diesels have no vacuum? If there was no vacuum how does the engine suck in the air required for combustion .. or is the intake manifold pressure just too high to be useable...
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Reply By: Wayne (NSW) - Wednesday, May 23, 2007 at 17:13

Wednesday, May 23, 2007 at 17:13
Rich,

On the 2H motor the vacuum for the power assisted brakes came from the alternator. This is common.

On the later 1HZ motor the vacuum comes from the a vacuum pump that is built into the motor.

Wayne
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Follow Up By: Member - Doug T (W.A) - Wednesday, May 23, 2007 at 17:55

Wednesday, May 23, 2007 at 17:55
............you sure now , your not tellin' furphies are you .....
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Follow Up By: Steve from Top End Explorer Tours - Wednesday, May 23, 2007 at 20:03

Wednesday, May 23, 2007 at 20:03
Doug he is spot on

Steve
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Follow Up By: Member - Doug T (W.A) - Wednesday, May 23, 2007 at 20:09

Wednesday, May 23, 2007 at 20:09
Steve
Ya silly bugger I know that , I own a Troopy with 1hz ,trouble is it's not with me at the moment, been away 2 days getting Transfer Case done up at Toyota
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Follow Up By: Member - Jiarna (NT) - Wednesday, May 23, 2007 at 23:30

Wednesday, May 23, 2007 at 23:30
Well, the 1HZ's vacuum pump is not actually built into the motor - it bolts on and uses the same drive as the power steering pump.

I once had a Peugeot 504 diesel, and it had a belt-driven vacuum pump that sounded like a helicopter rotor when it was running (just in case you were interested LOL)

On the vacuum in the inlet manifold, we used to have a Fordson Major tractor with a Perkins diesel engine which was vacuum controlled. A butterfly in the inlet manifold created vacuum which was sensed by the injector pump and fuel adjusted accordingly. So not all diesel engines have wide-open inlet manifolds. BTW the tractor didn't have vacuum brakes. If it had, the engine would have raced every time you put a foot on the brakes and decreased the vacuum in the manifold.

Cheers
John
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Reply By: ross - Wednesday, May 23, 2007 at 17:54

Wednesday, May 23, 2007 at 17:54
The diesel engines dont produce enough vaccum in the manifold like the petrol engines so they need a pump and store it it in a reservoir (under the brake booster).

If the engine cuts out on a big hill you can use the brakes once or twice before you run out of vaccum
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Follow Up By: Dicko2 - Wednesday, May 23, 2007 at 18:10

Wednesday, May 23, 2007 at 18:10
Ah ok so I guess this is because they don't rev as high...
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Reply By: samsgoneagain - Wednesday, May 23, 2007 at 19:59

Wednesday, May 23, 2007 at 19:59
why has a diesel got les vacuum ? it does the same thing as a petrol , sucks the air in , squirts the fuel and bang-oh ~! away she goes......... fishing hopefully
AnswerID: 241919

Follow Up By: disco1942 - Wednesday, May 23, 2007 at 21:07

Wednesday, May 23, 2007 at 21:07
The vacuum in the intake manifold of a petrol engine is the result of the cylinders sucking against the restriction caused by the butterfly throttle control in the carburettor. A diesel engine does not have any constriction like that so there is no vacuum.

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Follow Up By: disco1942 - Wednesday, May 23, 2007 at 21:09

Wednesday, May 23, 2007 at 21:09
Also most modern diesels have a turbo blowing pressure into the manifold.
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Reply By: GerryP - Wednesday, May 23, 2007 at 23:11

Wednesday, May 23, 2007 at 23:11
A petrol motor controls the revs by adjusting the air flow - as said previously, by using a butterfly valve in the air intake. Downstream of the butterfly will be under vacuum, particularly when decelerating as the butterfly is then closed, but the cylinders are still trying to pump air in.

A diesel motor is opposite in that it is controlled by adjusting the amount of fuel to the motor. The air intake is completely open with no butterfly or any other form of restriction, therefore, no vacuum.

A very basic explanation, but I think it gets the idea across.

Cheers
Gerry
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