[V8] Noise under load @ 1800 RPM

[Dave Saad]

Bingo.

If you are sitting in the car, with the brakes on, and in gear, and  
you give it some throttle, you are going to torque the motor. If the  
motor mounts are shot (likely) then something is going to clank.  
Usually it is the exhaust pipes but it just depends on how the motor  
moves under load.

Try your experiment in both forward and reverse gears.  It will  
probably be worse or different depending on which way the motor is  
trying to twist.

Again - the dead giveaway (beside the clanking) is to look at the  
torque stop up by the alternator. If it is broken, you have bad motor  
mounts.

Dave


On Mar 6, 2009, at 9:06 AM, Ingo Rautenberg wrote:

> Based on what you've said, it's gotta be motor mount(s).  Really.  I
> have yet to see the trans mounts fail.  The motor mount's give in
> relation to torque and I'm 95% sure that's your problem.  Otherwise
> you'd have something loose or broken with the exhaust in my
> experience -- but you say the exhaust checks out.  It deifinitely
> fits the "sounds like it's coming from the floorboard" description to
> me.
>
> Now I have had the bolt break that holds the rear diff at the back of
> the car, so that's one other place to look for a load-induced knock.
>
> -Ingo
>
> On Mar 5, 2009, at 9:17 PM, Seamus O'Carey wrote:
>
>> I've been trying to get to the bottom of this noise issue since I
>> bought the
>> car.  I thought maybe it was just a loose exhaust hanger, but I
>> just had it
>> checked out and the entire exhaust system is solid and all the  
>> hangers
>> intact.
>>
>> We did discover, though, that the noise comes on only under load
>> (whether
>> accelerating or while standing still with the car in gear) and very
>> suddenly
>> just before 1800 RPM, and goes away a little after 2k.  Inside the
>> car, it's
>> a loud grumble that you can feel through the seat/floorboard.  What
>> confounded us, however, is you can NOT hear the noise from outside
>> the car.
>> Not even a hint of it, even with the window open.
>>
>> The guy at the exhaust shop thought maybe it was coming from the
>> center
>> differential, just behind the transmission (even though he listened
>> to it
>> with a stethoscope and still couldn't hear anything).  He mentioned
>> something about how Subaru owners can pull a fuse that will disable
>> the
>> center differential in their cars, which would help them diagnose
>> something
>> like this.  Do we have something similar in the V8?
>>
>> Seamus
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