john_sc400

95 SC400.. Auto trans. 96k miles

I hear a growl sort of a whine when decelerating, especially at very low speeds as I am in the process of stopping. It sounds like it's right under the console. I've even thought that perhaps there is a sound seal like a boot that could be damaged, and that may be, but that's not all of it.

It seems to be louder at slow speeds and then totally quits when the car rolls to a stop. It changes pitch a little as the transmission downshifts. It's not as noticable when accelerating or crusing.

I also hear and can feel a clunk when I take my foot off the throttle at low speeds. (It may do it at high speeds, too, but I just can't feel/hear it.

Are the growl/whine and clunk related?

What could it be?

Thanks,

John

ChronoJ1

iTrader: (2)

When did you change your AT fluid?
Do you have slotted/drilled rotors?

john_sc400

Had the AT fluid changed when I bought it, about 2 months ago. Seems like it was making the noise before and the fluid change made no difference.

No slotted rotors. The clunk when I take my foot off the accelerator is defininitely in the driveline. Not a big clunk, but it feels like play in the drive shaft.

chrisman

hi john,, you describe the sound as a growl-- growls are most likely a bearing.. noises can be "transmitted" thru parts.. your driveshaft could transmit the sound from either the rear end or a support bearing..
there is a rear bearing in the trans that could be making the noise--but because of its enviroment-constant oil- i have never seen any fail.. now, that doesnt mean they cannot fail,, rather, that i believe it is unlikely..
the sc400 has a driveshaft center support bearing because of the 2 piece driveshaft.. that would be the first thing i would check, next, i would check the rear end.. but the pinion gear bearings tend to make noise either on deccel or accel-usually not both.. there are also the side case bearings in the diff that may be making the noise.. in any case,, you may need to get under and start checking.. always be carefull/safe when getting under a car ..

rdm20fan

John, the sounds your describing are almost the same as mine right before the rear end went out, and locked up.
I used to try and do brake-torques with the car, and this made the spider gears work much harder then they were made to.
Replacing the rear end wasn't that difficult, although it wasn't really easy.
The negitive is that when the rear end broke, it locked up, and broke the imput shaft, and sprag in the trans.
it made for a fairly costly, and pain in the *** repair.
Chris and I had to replace the carrier in the rearend, and I then had to pull the trans out twice, and caused chris to rebuild it twice.
Get it looked at.

john_sc400

Aaarrrgggghhh. Not good news.

On top of which, I'm leaking power steering fluid like crazy. Just started yesterday. It has been dry, but suddenly almost all the fluid leaked out. I think the hose went.

p.hase

i have exactly the same soft whining noise when stopping my car lets say from 5 mph to zero. 107.000 miles now. dont you think this small noise occures due to normal wear of the transmission system? i have replaced one liter of the AT-fluid. one drain. so there is much old fluid left. 8 liters.

john_sc400

I wouldn't actually call it a 'soft' whine. It's louder than soft.
Had it up on a rack this weekend and the trans mount looks good.
Had the fluid change about 2000 mi ago. It did it before then, too.
I've heard something about a center support bearing and want to learn more about that.

john_sc400

I did some testing today and it appears that the noise is loudest when the tranny is in first gear. It comes on the loudest when it downshifts as I'm slowing to a stop. The downshift clunks, too. If I shift into neutral when it has almost stopped and is making the most noise, then the noise quits.

So it is most likely a first gear issue.

What could that be?

Is there a separate pump for first gear?

Or maybe some bearings on the first gear shaft?

Sure would like to see an exploded drawing of the trans so I could make a better educated guess.

BTW- when I say first gear, I mean the lowest gear in an auto trans.

chrisman

hi john,, first gear does not have a seperate pump,, but if you are in first gear on the manual shifter-in low-- the trans does something called engine braking.. in other words there is more of a direct connection between the engine and the output .. so lets say you are going down hill, the engine will slow the car down--just like having a manual trans in first gear.. in D,, this does not happen..
all that being said,, it does not sound like a trans problem--but i may be wrong.. in your case,, i would take a good look at the rear end.. noice on deceleration is usually a pinnion bearing-the smaller front bearing..this may also be the reason for the clunk when fist shifting to drive..
i have not seen many failures in the rear end--but if it was run dry for a while,, or if severly abused,, it could be on its last leg.. anyway,, check out the differential,, and tell us whats up..

john_sc400

I've revised the reply to this with some new information. I've decided that that sound has to be coming from the trans. The reason is that the sound does continue, albeit at a lower level, when the car is stopped, but in gear. If I shift to neutral, it completely stops. Shift back into gear and it starts again, and again very quiet until I accelerate.
As reported before, it is at its loudest when slowing down as it downshifts into L when it is almost to a stop.
The noise is better described as a bearing noise, not a whine or growl. The best example can he heard with listening to, oh perhaps, the alternator through a piece of pvc pipe. (changed trans fluid 2k miles ago)

Secondary issue is the driveline play. Yes there is a little. The clunk I report is better defined as a clink. (Well, at least I know what I mean). Not loud, but definitely a small amount of play in the driveline somewhere. U-Joint? Is there a center bearing? Play in the ring and pinion? (seems like I had something like this repaired in a 91 LS400 I used to own)

The driveline is smooth. No vibrations. But there might just possibly be a harmonic around 50mph. Hard to be sure yet. Might have been the road.

I still wonder if there is a torn gasket/bushing/sound block or whatever on the cable for the shift linkage, but I can't tell. I need to see a diagram first to see what it is. If it's torn or missing I might be getting more sound through than normal.

(Irrelevant here, but in the midst of all this, I had to have the power steering high pressure hose and the rack and pinion rebuilt. Plus ordered a used driver's side hinge. But I still really like the car...)

tttp5

iTrader: (1)

so how did u end up taking care of the sound?

I think it is a transmission sound too because i too get that sound of the faint whirring when coming to a stop.

did u find out exactly what it is?

it seems like a lot of ppl have this sound, is it just because the SC is getting old and some of the sound insulation is wearing out?

john_sc400

Putting up with it for now.

The next thing I'm going to do is change the trans mount and inspect the 'center bearing' whatever that is,

Seems like too much play in the driveline, too, (clink sound on accel and decel) so I also need to look at u-joints and pinion play.

When the trans mount is off I can inspect the cable that connects the shift linkage to the trans. There is supposed to be a grommet where it passes through the floor pan. Perhaps it has fallen or rotted off, thereby passing more sound into the passenger compartment.

(current project is replacing driver's door hinge--it feels 'lumpy' when I open and close the door)

rdm20fan

I'll bet you $ it's the rear end.
It sounds exactly like mine. I could have sworen it was the trans, but it wasn't.
Your going to deal with it until it breaks, when it breaks it will destroy the rearend, and the trans.

ChronoJ1

iTrader: (2)

now that i've read further about the symptoms...it sound exactly like mine too.
Especially the play, clicking, deceleration, (but no whining)

rdm,
Are you absolutely sure its the rear end? Care to explain why? Thanks in advance.