911 - Truck PUrchase Decision - Help with Noise...(thanks) - Ford Powerstroke Diesel Forum
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Old 03-12-2007, 09:35 PM
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911 - Truck PUrchase Decision - Help with Noise...(thanks)

I'm a newbie, about to buy first PSD.

Test drove a very nice 99 (with the pre 99.5 7.3 PSD), Auto Tranny.

Everything seemed GREAT but during the test drive, while exiting the freeway (like first 5 minutes of test drive), noticed a higher pitched noise (not turbo whine) kind of like an overtone to the natural noise of the diesel motor. VERY noticeable. I then crossed over the freeway and listened on the side of the road - seemed natural - so I asked the owner (very nice current owner - original owner etc).

Owner says that the noise is there until you accelerate above 35mph. So, I floor it, truck accelerates and sure enough, at 35mph, the motor quiets (loses the higher pitched overtone to the natural motor sound) but continues to sound like it's accelerating, turbo whine is there, etc, etc.

At the next offramp, the owner tells me to go ahead and let it slow gradually and we both listen for the noise, sure enough, at 35mph, the noise returns. (btw - all this happened while in O/D - didn't test it while NOT in O/D. Also, temp gauge showed it wasn't too cold - had warmed up by then).

Owner tells me it's always been there and it's supposed to be there. She calls it the engine "purring" like when it doesn't need any more power, it makes that noise. That doesn't make sense to me because when I step on it from a stop sign, I hear the turbo whine, the sound I'm worried about is also there, until 35mph, then poof, only the turbo sound.

Other than this, the truck is amazing...

More details:
- 1999 7.3
- ~80k miles
- ALL Stock truck mechanically
- 1" lift in front, 3" lift in rear - 315's.
- Auto Tranny

If ANYONE can please help me get a handle on this noise, then I can make a decision wisely.

THANKS in advance for the help - you guys are all amazing on this site!
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Old 03-12-2007, 10:53 PM
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I have heard that sound in other trucks as well, I just put it down to being the tc lockup at a set speed, did it feel like it went away as it shifted into third at normal driving speeds and acceleration? Because I think thats what i was experiencing.

Gord.
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Old 03-13-2007, 10:51 AM
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Yeah Gord - it did go away at 35mph - not sure if that coincided with a shift to 3rd, but possibly.

The more I've searched for other noises and what I've read in threads called the TC Lockup sound, etc, there definitely is a parallel.

So, is this a NORMAL sound then? Nothing I should be worried about?

(and, what the heck is a TC Lockup? I know it's the torque converter, but didn't realize it had some sort of locking functionality - any education there would be helpful as well)

thanks again for the help...
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Old 03-13-2007, 11:25 PM
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It is a fluid coupling between the motor and trans, something like a clutch, at idle and low speeds, the converter is unlocked to prevent stalling, as you start moving, it locks up, sometimes giving the impression of an extra gear. By locking, it stops the slippage between the plates in the converter and gives a solid 1 to 1 for the motor and trans. When you let off the gas, it releases the lock, and the mtr drops down in RPM to save fuel, and locks again when you give it fuel. Hope that helps out some.

Gord.
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Old 03-14-2007, 11:37 AM
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Thanks again Gord - this has to be it. This truck is gonna be mine soon...can't wait!
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Old 03-14-2007, 12:05 PM
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hahaha, Glad I could help you out man, make sure you let us know when you get it, so we can help you spend your money.

Gord.
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