Vibration at idle (only when in gear)

Huh? I'm stumped then...
The vibration is only at idle or just above idle when in gear. It's not like the whole car is vibrating or anything, but I can feel a slight vibration in the steering wheel. If I'm driving, and just barely pressing the accelerator, I can get a similar sensation. But if I step on the pedal it goes away.
This points me to 2 things... The supercharger under load, and the automatic transmission. When I did my belts a couple of weeks ago, I noticed I could turn the supercharger pulley back and forth with a bit of slop in it. Since the couplers are roughly $50 I'll start there. If I'm lucky, it will be the final bit of PM the car needed for another 100,000 miles. If it's not the cause of the vibration, the coupler still needed to be replaced anyway and I'll take the car to a local transmission shop.

Could a power steering pump be part of this equation? The reason I ask, is that I haven't looked it over yet. The lower part of my engine is still pretty grimey from when my intake manifolds were leaking before I replaced them. Back east, during my time in Pennsylvania, I remember a lot of shops offering an engine steaming service. It got all the crud off of your engine. I wonder if I can locate a shop like that here in Las Vegas? If not, I'll grab my roll of quarters and hit the DIY car wash, open the hood, and have at it.

Thanks guys!

VegasScott

albertj wrote:

sounded like dueling Japanese hibachi chefs whacking utensils on their griddles. A BIG racket. That's when I replaced it.

Albertj

BTW, I LOVED your analogy!!!

VegasScott

VegasScott wrote:

Huh? I'm stumped then...
The vibration is only at idle or just above idle when in gear. It's not like the whole car is vibrating or anything, but I can feel a slight vibration in the steering wheel. If I'm driving, and just barely pressing the accelerator, I can get a similar sensation. But if I step on the pedal it goes away.
This points me to 2 things... The supercharger under load, and the automatic transmission. When I did my belts a couple of weeks ago, I noticed I could turn the supercharger pulley back and forth with a bit of slop in it. Since the couplers are roughly $50 I'll start there. If I'm lucky, it will be the final bit of PM the car needed for another 100,000 miles. If it's not the cause of the vibration, the coupler still needed to be replaced anyway and I'll take the car to a local transmission shop.

Could a power steering pump be part of this equation? The reason I ask, is that I haven't looked it over yet. The lower part of my engine is still pretty grimey from when my intake manifolds were leaking before I replaced them. Back east, during my time in Pennsylvania, I remember a lot of shops offering an engine steaming service. It got all the crud off of your engine. I wonder if I can locate a shop like that here in Las Vegas? If not, I'll grab my roll of quarters and hit the DIY car wash, open the hood, and have at it.

Thanks guys!

VegasScott

I am still thinking motor/transmission mounts.

Albertj

I finally have some time to breathe this weekend! I'm going to replace the coupler in the supercharger tomorrow morning, which should help this out some, but I think Albert is on to something, so I found both the front and rear trans mounts from Anchor (3127 & 3065) for $89 from RockAuto delivered. For $89 bucks, I figured I can't go wrong!

The mounts will have to wait until next weekend because I just placed the order tonight. But the coupler goes in tomorrow. I'll have to look at the power steering pump area too, I suspect it maybe leaking... (By evidence in the driveway)

I'd also like to check my power antenna and see if it's even connected. (Never has gone up or down)

VegasScott

Okay plugs, wires, and supercharger coupler done! It runs even smoother and a lot of the vibration is gone, but...

DING! DING! DING! WE HAVE A WINNER! Albert is correct! The rear trans mount is badly weather checked and I was able to have a buddy shift the car into and out of gear with his foot on the brake. The engine is flopping back and forth a lot.

So next weekend, it should be back to idling like a new car! No vibrations!

How long of a job is it to replace the rear trans mount?

Thanks!

VegasScott

I have also a problem with a loud, rambling noise, especially when my 98 Riv is stopped and in gear. When the transmission is placed in neutral, the noise goes away. My local GM shop claims the noise is normal and is coming from the the supercharger. Well, they are half-right: After researching the Internet, I discovered that the cause of the vibration/noise is the coupler that connects the nose of the supercharger to the supercharger unit.
One of the websites' blog has the following comments relating the cause of the noise/vibration:
Between 70,000 and 120,000 miles the factory coupler will start to fail. The holes in the factory coupler become egg shaped and cause a rattling and banging noise you hear in your supercharger. Also the pulley is offset from the serpentine belt and places considerable stress on the bearings and seal. The result is a supercharger nose that will start making noise and end up failing. If you’re not sure where your noise is coming from, you can check by removing the supercharger belt then turn the pulley back and forth to see if it is sloppy. If it is your coupler is bad.
Another website describes how to replace the coupler:
[i]"A quick step by step video of how to replace the coupler in the nose shaft of the Eaton M90 Supercharger equipped on GM's 3.8L engines. The coupler fittings get loose over time and cause a terrible noise at idle which eventually leads to other issues including knock retard.
http://travelcaronline.com/BUICK/buick-3800-supercharger/"[/i]

I suspect that the cause of the 'vibration' cited by the OP may not be engine mounts, but instead may only be a bad coupler. At least, this is the case with our 98 Riviera

If its me you are refering to, I've replaced the coupler, and the motor mounts. I still have some vibration, but nothing compared to what it was.

VegasScott

The new mounts are likely more stiff than the old ones and trasmit more noise/vibration.

Time to revisit this old thread. My car still has a slight vibration after all the tune up parts, SC coupler, motor mounts and whatever I could think of thrown at it. I am certain my slight vibration is with the transmission. I'll attack just about anything on the car, but transmission work, I leave to the guys with the proper training, jigs, tools, and fixtures for the jobs at hand. I drawn the line at fluid and filter replacement on transmissions.

Of the national chain shops, who do you guys like best for trans work? There's an Aamco Transmission shop not far from my home. I was thinking about talking to them.

There's nothing wrong with the car. It shifts great and drives very nice. I'm just anal regarding my vehicles and can't stand this slight vibration at idle in gear!

VegasScott

I used AAMCO with mixed results. I thought they charged too much, but they also needed to take the unit out 2 more times to fix it right, so it was nice having the no-questions-asked warranty, even though it's only 12k miles.

So far I've got 85k on my trans after rebuild. Other than the TCC giving out, the car shifts and pulls strong.

I'd be 100% sure that vibration is transmission-related before you drop it for rebuilding. Have the techs tell you what they think.

VegasScott wrote:

Time to revisit this old thread. My car still has a slight vibration after all the tune up parts, SC coupler, motor mounts and whatever I could think of thrown at it. I am certain my slight vibration is with the transmission. I'll attack just about anything on the car, but transmission work, I leave to the guys with the proper training, jigs, tools, and fixtures for the jobs at hand. I drawn the line at fluid and filter replacement on transmissions.

Of the national chain shops, who do you guys like best for trans work? There's an Aamco Transmission shop not far from my home. I was thinking about talking to them.

There's nothing wrong with the car. It shifts great and drives very nice. I'm just anal regarding my vehicles and can't stand this slight vibration at idle in gear!

VegasScott

When I next get my transmission serviced, I am going to have a gM dealer do the work and have them connect the thing to t Tech II and adjust the pressure in the trans to factory specs. I think one thing that happens is some techs like to increase the line pressures in the transmissions. It makes the car quicker off the line but tends to push hard at idle while stopped - giving us this goofty vibration thing.

Both good posts fellas! Thank you.

VegasScott