Troubling engine noise on acceleration and reverse braking

[eburrows]

This is a wierd one: A loud, high pitched, metalic banging sound from the front, left, lower side of the engine, when I'm accelerating forward, braking in reverse, or stopped on a steep incline (like ramps).

I've already ruled out:

• Cats (removed Y-pipe, banged, shook, nothing.)
• Exhaust heat shields (All solid and/or re-welded)
• Rotating anciliaries (removed belt)
• Engine mounts (swapped QT ones for rubber)
• Brakes
• Exhaust manifold/header bolts

I've yet to swap spark plugs, but given the acceleration/incline thing, it seems unlikely. It sounds like it may be coming from inside the engine...

Any ideas?

 

[ChrismonDA]

Stop driving it. Get it towed to someone and have it diagnosed.

 

[kennith]

I agree. Deadline the vehicle until it's properly diagnosed.

Cheers,

Kennith

 

[cdansan]

Mine made a metallic banging rubbing sound when one of the caliper bolts fell out.
The caliper would rotate around the remaining bolt and hit and rub the wheel in reverse.
Then bang into the caliper bracket and rub the rotor going forward.

From in the cab I thought it was in the engine bay.

Dan

 

[p m]

Mine made a metallic banging rubbing sound when one of the caliper bolts fell out.
The caliper would rotate around the remaining bolt and hit and rub the wheel in reverse.
Then bang into the caliper bracket and rub the rotor going forward.

This is easy to rule in/out: does the sound happen when you are _moving_, or you are stopped?

 

[riceybean]

Mine made a metallic banging rubbing sound when one of the caliper bolts fell out.
The caliper would rotate around the remaining bolt and hit and rub the wheel in reverse.
Then bang into the caliper bracket and rub the rotor going forward.

From in the cab I thought it was in the engine bay.

Dan

My 96 did this too.

 

[eburrows]

This is easy to rule in/out: does the sound happen when you are _moving_, or you are stopped?

Both. It makes the sound when I accelerate forward from a stop, or when I brake while moving in reverse. It also makes the sound when stopped, if I'm on a significant incline (like ramps under the front wheels).

It does not make the sound when I'm stopped on level ground, with the engine idling.

 

[p m]

If it makes the same sound when the truck is stopped, brakes are out of the equation.
The first thing I'd be looking at are the flexplate-to-torque converter bolts.

 

[eburrows]

Thanks pm, I was wondering about that too. I looked through the front and bottom inspection ports, but couldn't see any cracking (I've destroyed a flex plate in this truck before), and I couldn't see the bolts at all. I'll take another look, and if I can't get in there to check the bolts, I'll take it to my mechanic.

 

[p m]

Also, if there's significant endplay in the crankshaft, the tabs on the flexplate may come into contact with the CkPS, eventually bending its tip. It may or may not result in a CEL - sometimes it works for a while like that.

 

[eburrows]

Yep, it was the flex plate. It had several small cracks near the inner radius.

I had worn out a flex plate on this truck before, and it sounded and behaved very differently, sounding a lot like a failing front prop shaft actually.

Thanks for the benefit of your experience pm.