Wierd Tranny noise (4 speed auto with O/D)

[KnifeEdge_2K1]

ive noticed a wierd thing with my transmission, every once in a while when im at a stop light with my foot on the brake and still in gear the tranny/engine (cant tell) would make this duh duh duh duh noise which sounds kinda like a diesal or a tennisball bouncing up and down really fast, i hope its not pinging/knocking but i find that if i shift into neutral right away, the sound stops, when i shift back in gear it comes back. what's intresting is though that once i get my foot off the brakes the noise stops and the car pulls away like normal (a tad less pull then normal but this might be due to an incline or different surface friction)

ill try and record the noise on my pda if i ever get the chance but since this is unpredictable and my pda is not always on me it might take a while

the best way i can discribe it is it goes like

dig ga dig ga dig ga really fast, it only happens when idling in gear while stationary, it isnt the timing belt cuz my engine doesnt have one (its a chain) and the most logical conclusion ive come to is either something is loose on my a/c belt, fan belt (if i have one i dont know, too cold to check engine bay), or somehow the fluid in my torque converter suddenly all got flushed out and pieces of metal are smacking each other ...

the last scenario is pretty unlikely due to the fact ... torque converters dont have metal on metal contact points ... it is after all a fluid coupling

[johnnynumfiv]

First thing I thought of was the torque converter, could also be your serpentine belt or tensioner.

[MrVette83]

first thing i thought of was low torque converter fluid and it's slipping just a lil bit. If your noise increased with engine speed I would suggest the timing chain. I say this simply b/c at one time my Grand Am sounded like a diesel very badly, what happened was the tensioner for the timing chain had gone down(it was hydraulic) and it was allowing the chain to get some free play, thus smacking against the timing cover.

[KnifeEdge_2K1]

hmm there aint really a noise when im moving which is why i suspect the torque converter, my logic is if its any other part of the driveline noise would increase would speed

but johnny said something bout low torque converter fluid ... i dont see how that can create the noise cuz if there's less fluid wouldnt there be less resistance ... and less noise ??

[johnnynumfiv]

sometimes serpintine belt noise or tensioner noise doesn't increase with engine speed, I'm not to sure about the fluid level though, I dont have much experience with auto trannies, sorry.

[pimento]

"If a vehicle has a hard heavy vibration at idle that goes away as soon as the car starts driving, I look for a bad motor mount. The motor mounts are typically blocks of rubber that isolate the engine from the frame and body of the car. If worn, severely compressed, or eaten away by oil leaks, they may allow the engine to touch the frame at idle, transmitting the vibration. When you drive, the torque (twisting force) causes the engine to rise slightly and the vibration disappears. If your car vibrates a lot when idling with the transmission in drive, put it in reverse. If the vibration goes away you've got a bad mount. A motor mount can also split perfectly, with half the rubber staying on the frame and half with the engine. At idle it will still have the desired cushioning effect but step on the gas hard and the engine will leap up eight to twelve inches, causing a vibration, a clunk, and a tug on every vital hose and connection."

http://www.thecarconnection.com/index.asp?article=8152&sid=281&n=158

Bingo.

[baddabang]

"If a vehicle has a hard heavy vibration at idle that goes away as soon as the car starts driving, I look for a bad motor mount. The motor mounts are typically blocks of rubber that isolate the engine from the frame and body of the car. If worn, severely compressed, or eaten away by oil leaks, they may allow the engine to touch the frame at idle, transmitting the vibration. When you drive, the torque (twisting force) causes the engine to rise slightly and the vibration disappears. If your car vibrates a lot when idling with the transmission in drive, put it in reverse. If the vibration goes away you've got a bad mount. A motor mount can also split perfectly, with half the rubber staying on the frame and half with the engine. At idle it will still have the desired cushioning effect but step on the gas hard and the engine will leap up eight to twelve inches, causing a vibration, a clunk, and a tug on every vital hose and connection."

http://www.thecarconnection.com/index.asp?article=8152&sid=281&n=158

Bingo.


Not really, He is talking about a noise not a vibration.

Knife are you still driving a blazer?
Iv had plenty of problems with mine, The only transmition problem I had was about 6 months ago, When it would change gears the car would pull ahead quickly. And if it is a vibration like Pimento said, I would call it on bad U joints. I had to get those replaced too. :(

[KnifeEdge_2K1]

blazer?

[BjD]

I think Pimento may be onto something. If the mounts are broke some part of the engine/box may be hitting the body, we had a similar problem on my dad's old Peugeot. When in drive, and stationary, the turbine is locked, so there is more resistance on the pump, which I imagine would cause the engine to lean over a little. If the mounts are broke this may cause the engine to lean enough to hit something :) Its surprising how much movement there is in engine mount rubbers.
If the noise only occurs at idle when stopped it probably isnt the UJ's as they wouldn't be rotating.