When I slow down to a stop, when the rpm's gets to about 1000 it increases slightly and there is now a loud thump noise under the car below my seat. I assume this is related to downshifting from second to first. (My car is an automatic). The sudden jump in rpm's (maybe 100rpm) has been happening for years, but the thump is new. I did install a tune with my DiabloSport i3 not too long ago, otherwise nothing has changed. How do I troubleshoot this?

2005 V8, 140k miles.

 

could be the transmission mount

 

Ok. How might I troubleshoot that? Tighten those bolts?

 

Bump. Any other suggestions?

 

Remove the tune and see if anything changes. I agree with JJHoover, transmission mount or maybe a motor mount.

 

On an automatic? Motor mount is one guess but it could also be related to transmission fluid that needs to be replaced. It should be done every 30-40K miles. How many times has it been done with the 140K you have on the clock?

Do the visual inspection on the tranny mount but I would suggest also servicing the tranny fluid and filter.

The transmission is controlled by an electronic solenoid pack that is very sensitive to dirt. The thumping could be the pack is starting to stick from dirty fluid. Ignore it long enough and it will damage the transmission or require replacement of the pack at the very least from varnish and dirt build up in the pack.

 

Tranny fluid was done at 30k and 95k. Dealer inspected at 140k and told me "light reddish tint." Was gonna wait time 150k but could do it now.

I didn't see anything obvious at the mount, but not sure I'd know it if I saw it. Photos attached.

 

I'll add, sometimes putting it into reverse gives a major clunk noise. I understand there is normal play in the drivetrain, but sometimes it's abnormally loud. I read this could be related to the U-joint, which I think is integral to the driveshaft in the 2006s. Don't think it can be replaced easily on its own.

 

I would guess by all that black crap being thrown from your universal joint, It 'might' have gone bad or going bad. If that doesn't fix your problem it will be taking care of a future problem They are replaceable.

 

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