Really loud rattle at idle after trans rebuild

[djheater]

Lost my torque converter on a trip to Memphis.
Had a rebuilt transmission put in and a external cooler and drove it back to Chicago.

About halfway into the trip I noticed a really loud rattle while idling in drive. It doesn't always happen but most of the time it does and there seems to be some relationship between the air conditioner nad the noise. I've noticed that turning off the AC can make the noise go away, though that may just be my imagination, I haven't nailed down the relationship, if any.

The noise is extrememly loud and clacking, but goes away as soon as you take your foot off the brake.

Made the trip fine, but that noise is very troubling.

Thoughts, ideas? I'm at work now, but can run tests when I get home or answer specific questions.

Thanks for any help.

 

[MiataNC]

Loose (or missing bolts) motor mount, bracket, etc. It sounds like a moving part shifting around and hitting something else when the motor is under load.

Pop the hood and have someone take a look at the engine while you are idling in gear. See how much it moves compared to idling in park, then look for areas where parts intersect that they shoudn't be.

 

[djheater]

I don't experience any rattling when I'm driving, just when idling. Would a mount\bracket issue cause that? I would think you'd hear some noise while driving too.

 

[LTC8K6]

The fans would mostly come on at idle and if you turn the A/C on. Are any of the fan blades possibly hitting something?

 

[Zenmervolt]

It may be as simple as a loose heat shield.

ZV

 

[djheater]

Originally posted by: LTC8K6
The fans would mostly come on at idle and if you turn the A/C on. Are any of the fan blades possibly hitting something?

Or they might have mismounted the fan when they put the external cooler on.

I'll check for the sound on a cold start with the AC and fan off... that's a good suggestion.

When I heard the noise on the trip, I opened the hood and couldn't place the noise... I didn't THINK it was coming from the fan, but I'll check that.

 

[djheater]

Originally posted by: Zenmervolt
It may be as simple as a loose heat shield.

ZV

I would LOVE it to be so simple, but I wouldn't think I'd only hear it at idle. Would I?

 

[alpineranger]

My parents had a caravan with major transmission problems and eventual failure due to excessive heat. From day 1, loaded with people or stuff or going up inclines the transmission would slip like crazy. I've got an intrepid with what is basically the same transmission and it fortunately came with a stock transmission cooler. No transmission problems at all.

As far as the sound, if you can stick your head around the car when it's running and making the sound (with parking brake on, put it in drive with ac on, or have someone else apply the brakes while you look), narrowing down where it's coming from would probably be the best thing. A lot of times these rattles must be provided with the right input frequencies. If you don't replicate the conditions well enough (at idle in drive with ac, the engine would probably be idling at a lower rpm than it would otherwise), it could be hard to recreate.

 

[SparkyJJO]

Originally posted by: djheater

Originally posted by: Zenmervolt
It may be as simple as a loose heat shield.

ZV

I would LOVE it to be so simple, but I wouldn't think I'd only hear it at idle. Would I?

You could. My car at idle and certain speeds rattles due to the heat shield somewhere being loose. It has to do with certain resonant vibration frequencies and such. Drives me nuts but I can't figure out exactly where it is rattling

 

[boomerang]

Originally posted by: alpineranger
As far as the sound, if you can stick your head around the car when it's running and making the sound (with parking brake on, put it in drive with ac on, or have someone else apply the brakes while you look), narrowing down where it's coming from would probably be the best thing. A lot of times these rattles must be provided with the right input frequencies. If you don't replicate the conditions well enough (at idle in drive with ac, the engine would probably be idling at a lower rpm than it would otherwise), it could be hard to recreate.

Great advice here IMO.