Brake Light/ Low power

[Ford_Iowa_Boy_7.3]

Hi everyone I was wondering if anyone knew why my 96 7.3 keeps keeps jumping around in voltage and the brake light also come on and the brakes are hard. I notice it the most at night when I have both the heater and my headlights on. I can still stop when the brake light comes on but its harder. Also to note no other light on the dash comes on besides the red brake light. Any help with this problem would be appreiciated!!

[madpogue]

Hard brake plus warning light means the vacuum pump. But it may not be the pump itself. If you're also having voltage/charging problems, the common thing between them is the belt. Either the belt is worn/damaged or the tensioner is no longer maintaining tension.

[Ford_Iowa_Boy_7.3]

Originally Posted by madpogue

Hard brake plus warning light means the vacuum pump. But it may not be the pump itself. If you're also having voltage/charging problems, the common thing between them is the belt. Either the belt is worn/damaged or the tensioner is no longer maintaining tension.

The vacuum pump doesnt look like its run off the belt, its on the back by the firewall.

[madpogue]

That's the brake booster, the thing that _consumes_ vacuum to provide power brakes. But diesel engines don't _produce_ vacuum, so it has to be pumped artificially. The pump is on the driver's side of the engine, below the A/C compressor.

[Ford_Iowa_Boy_7.3]

So the reason my voltage could be jumpin around is cuz the belt or tensioner are bad? and how would I test to see if the tensioner is bad?

[madpogue]

If you can push the belt and deflect it, and if you see the tensioner move as you do so, the spring is pretty-much shot.

[Ford_Iowa_Boy_7.3]

Alright I'll try that when i get off work. Thanks and I'll post what happens when I test it.

[Ford_Iowa_Boy_7.3]

Alright when i looked at the tensioner pulley its was movin around up and down alot. Does that mean its bad?

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[madpogue]

You mean the arm is swinging a lot? Or the pulley is loose on the arm? Not that it's a terribly important distinction; in either case, the tensioner is shot.

[Ford_Iowa_Boy_7.3]

The arm is swinging up and down alot. So you're sayin probably time for a new tensioner?