: Drive Train Hum & No Overdrive



Red Corvette
03-28-12, 08:26 AM
Looks like Iíll be doing a lot of work to my 98 STS this spring if I decide to fix it.
It has now lost overdrive completely and because of the hum while the car is in motion I believe the torque converter took a crap. The TCC solenoid was replaced when I did the head gaskets so I really donít suspect that to be the problem.

Am I on the right track here or is there something else I should be looking at as the culprit? Thanks!

Submariner409
03-28-12, 09:51 AM
"Overdrive" in these transmissions is 4th gear - at a ratio of 0.68:1. If you can accelerate moderately and feel the 1-2, 2-3, and 3-4 shift points, you have overdrive.

TCC is a viscous clutch in the torque converter which removes the last 300 or so rpm of stator/rotor slip above highway speeds of 41-43 mpg. it's a "economy" feature - and that term is a stretch of the imagination..............

The hum - in all gears ?? ......or in 4th only. Sounds more like it could be a piece of rotating equipment - axle, brake, bearing.........I'll defer on this one and wait for a member who has had a transmission '"hummer".

Ranger
03-28-12, 10:45 AM
:yeah:

Are you SURE it is the trans and not a wheel bearing?

Red Corvette
03-28-12, 12:03 PM
I originally thought bearing as will, but the hum doesn’t change doing S turns. I’ll still have to put it up in the air and check for play.
I do not feel or hear it go into 4th (overdrive) I don’t recall what the RPM’s were at 70 mph but now they are at 2,400 and that doesn’t seem right?

Aztec ETC ECS
03-28-12, 12:59 PM
2400 at 70 doesn't sound too high. I'll try mine later. When you're at 70, pull it down to 3 to make sure. The 4th band rips off the lug but not very often. As for the TC, they are usually quiet in park and make noise when put into gear, not moving. The chain sprocket bearings could make noise and will change with evey shift. Might make noise in park and go away in gear until you start moving.

CadillacLuke24
03-28-12, 02:36 PM
2400 at 70 is high. Normally with the cruise set at 69 my N* turns 1850-2000 RPM as regular as a sunrise. It does hit 2400....if I'm climbing a 6% grade.

Submariner409
03-28-12, 04:38 PM
Click on my username, open my profile. use the 2 albums - 6 pages - of pictures and illustrations to find the 2 speed/rpm tables we did last fall. They show where your 4T80E should run for both the VIN 9 and VIN Y drivetrains above 43 mph, TCC engaged.

2400 rpm at 70 in a STS is about right - 2300 is closer, but guessing a needles' width is speculation at best.........look at the suggested tables.

There's a fair bit of difference between the speed/rpm curves of 9 and Y, so be careful - compare apples to apples - all else is bum dope.

Ranger
03-28-12, 10:12 PM
2400 at 70 is high. Normally with the cruise set at 69 my N* turns 1850-2000 RPM as regular as a sunrise. It does hit 2400....if I'm climbing a 6% grade.
That is correct for an LD8 like you have in your Deville, but the OP has an L37 (STS). Actually you should be turning 1950-2000.

CadillacLuke24
03-28-12, 11:48 PM
My bad. :D I forgotted that the L37s have a higher final drive.

Red Corvette
03-30-12, 05:38 PM
I’ve confirmed the noise is not a bearing. The wheels didn’t move at all grabbing at 6 & 12 o’clock or 3 & 9.

With the front of the car off the ground I started it up and put it in gear and at idle only the left wheel would spin. The right only spun once I raised the rpm’s.

Also I can spin the wheels with it in park, should that happen?

Almost forgot I do have 4th gear.

Ranger
03-30-12, 09:04 PM
Also I can spin the wheels with it in park, should that happen?
No..

Red Corvette
03-31-12, 08:37 AM
No..

What causes this?

Ranger
03-31-12, 12:33 PM
I am far from a transmission expert, but when in park, the parking pawl locks the trans. Based on what you said, I would suspect your car will roll in park as it would in neutral and that would point to a broken parking pawl.

Red Corvette
03-31-12, 01:12 PM
I am far from a transmission expert, but when in park, the parking pawl locks the trans. Based on what you said, I would suspect your car will roll in park as it would in neutral and that would point to a broken parking pawl.

And the pawl is inside the trans corect? I guess I better start using the parking brake. :)

I just took the car to the store and while slightly turning the steering wheel right to left the noise does change. Is it possible that there may be a problem with the steering rack? The noise is clearly coming from the center area of the car not at a wheel.

Aztec ETC ECS
03-31-12, 02:17 PM
I’ve confirmed the noise is not a bearing. The wheels didn’t move at all grabbing at 6 & 12 o’clock or 3 & 9.
What exactly does this mean?


With the front of the car off the ground I started it up and put it in gear and at idle only the left wheel would spin. The right only spun once I raised the rpm’s.
Only one wheel may spin since there in no posi unit.


Also I can spin the wheels with it in park, should that happen?
With the front wheels raised, you SHOULD be able to turn the wheels by hand in Park. Turn one wheel forward and the other will turn backwards.


Almost forgot I do have 4th gear.
I figured that by the RPMs.

It's hard to help any further with your noise without hearing it. Backing plate? Brake wear sensors? Bad tires?
Does it get louder right to left. Right side wheel bearing can do that & telegraph through the car.
(And I am a transmission expert)

maeng9981
03-31-12, 03:38 PM
With the front wheels raised, you SHOULD be able to turn the wheels by hand in Park. Turn one wheel forward and the other will turn backwards.

:yeah: That will happen.

Red Corvette
03-31-12, 03:43 PM
The noise (HUM) I’m hearing gets faster and louder as you accelerate.

If it was a bad bearing you would think you would have play in the wheels grabbing at 6 & 12 but there is none.

It seems to be getting worse every time I drive the car.

I think my wife’s camera can record I’ll have to figure out how to put it on the site so it can be heard.

Aztec ETC ECS
03-31-12, 03:50 PM
You mean "ROCKING" play? I've seen noisy wheel bearings have no play & quiet ones have lots of play. That's no way to check it. Left turn louder, right bearing. Right turn louder, left bearing. (Usually) But I've even seen it the other way. (Rarely)

Ranger
03-31-12, 09:05 PM
With the front wheels raised, you SHOULD be able to turn the wheels by hand in Park. Turn one wheel forward and the other will turn backwards.

IN PARK? Guess I stand corrected.


And the pawl is inside the trans corect? I guess I better start using the parking brake.
Easy enough to check. Just put the car in park and see if you can push it.

Yes, it's internal. Just for reference it is Part #22, but it sounds like yours is fine based on what Aztec said.

http://www.genmotorinfo.com/images/383517752/12033898.png

Aztec ETC ECS
03-31-12, 09:53 PM
There was never any complaint of the car rolling away. The car probably would have been in someone's living room by now if that were the case. Based on my 25+ years experience, I say RF wheel bearing, could be RR but not likely and I'm saying this only from the evidence presented without driving it.