Intermittent vibration

[Suby Fan]

Originally Posted by dcarrb

David, I'd be surprised to find fault with a ball joint or tie-rod end. The car tracks well and has no tendancy to follow ridges or wander. Tread shows no obvious abnormal wear. In 20 years of driving Subys I've never had a suspension component replaced (unless you wanna count rear wheel bearings). In the Road Salt Belt that might be a different story.

Thanks again.

dcb

you are right about this even in my shop in the 2 years i have worked there the only suby suspention thing i ever did was my mom's ball joint at 190k.... but my inner tie rods did have a little play in them last i checked on my SVX

[Beav]

Their tire machines certainly do. They probably build their own vs. re-badging Corghis like everyone elsse seems to do.

I'll have to agree to disagree when it comes to alignment machines though.

[pylon500]

Getting back to the first post, I too have a similar situation.
While cruising on one of our expressways (max 110kph ~68mph!) I started to get a vibration, slowed down it went away.
When I accelerated, it came back, when I went faster (who me?!) it went away again.
Thinking I had lost a small balance weight and was getting a minor harmonic sinc vibration, I took car for a re-balance.
Next weekend, same drive, same speed the vibration came back!
It always seemed to occour around 2700 rpm, but cant be sure if lock-up was engaged or not?
I did notice that if I pulled back into 3rd (about 3800 rpm @ 110kph), the vibration disappeared.
Thinking now at steady cruise the ECU is trying to lean out and maybe I've got a dirty injector that starts to miss?
Any other ideas?
Arthur.

[Beav]

Highly doubtful. Wouldn't it be easier to feel a lean miss from a failing injector when the load is high, like during acceleration? Cruising at 60mph without a/c, etc. only requires 12-14 hp., roughly. Getting to 60mph requires considerably more.

Road speed steady + rpm change + vibration change = something ahead of the transmission out of balance. Proper testing involves a vibration detection device (such as a Sirometer, about $16 USD) an accurate rpm reading and measuring the diameter of each drive belt pulley. Go here for additional info: http://www.cochran48.com/nvhbuster/about.htm

[Sr240sx]

I had some problems on my 240's balancing, creating a shudder around 55 mph. Basic balancing fixed that, but i can't exactly swap the wheels around to test for that sort of thing, so i need to be careful. 18x8.5's in the front and 18x9.5's in the rear can cause some annoying issues. namely, no rotating...

How wide is the barrel on a stock svx wheel? i'm guessing about 8 inces, but i'm not sure.

[dcarrb]

Just in from having my tires re-balanced at a shop with a GSP9700 set-up, First Choice Fast Lube. Clean shop, no wait. Got the usual what-is-this-what's-with-the-windows-say-ya-feel-that-vibration-at-130? business. Making a run to Atlanta later in the week, so we'll see how the old gal does when I can let her stretch her legs a bit.

dcb

[dcarrb]

Well, having the wheels re-balanced definitely made a difference for the good at cruising speeds, but something's still occasionally upsetting the car. I paid more attention this time: The shudder happens primarily when the engine's pulling, but not hard. Stomp it for a 35-to-80 mph pass, no problem. Ease on the gas from 35-to-60 and she sh-sh-shakes passing thru 55. Sometimes. Same deal nearing the top of a long, gentle uphill grade at highway speed with the cruise set, only it's less pronounced at higher speed. Click-off the cruise to unburden the drivetrain and she settles-down, then immediately pick-up the throttle and all's good.

The guy who did the balancing said one of my wheels (now left-rear, I believe) was "just a little bit" untrue, and he found and removed a row of stick-on weights inside one of the wheels. Any damage to that wheel must predate my ownership, 'cos I haven't hit anything.

Oh, and I think the left-rear wheel bearing's trying to tell me something. Again.

I'm more curious than concerned; I mean, I drove 300+ miles yesterday and still have the fillings in my teeth, so I'm not about to go throwing lots of money at the car hoping to luck upon a culprit. But it would be cool to figure out what's causing this.


dcb

[Beav]

Vibrations that occur only while under power only come from several things: engine misfire, but that is more prevalent under heavy load. Torque convertor shudder at lock-up, but if you were at speed for a while it was probably already engaged. If you accerlerated hard enough for it to disengage, then re-engage you may have felt it, but it only lasts for a second or so. You'll just have to pay attention to whether or not it is in lock-up or not. The more common cause for power-applied vibration is worn/loose u-joints, worn inner cv joints (rare) and driveline angularity issues, which I know at least a number of SVXs have problems with, mine included. Some are worse than others, I have mine almost licked but I only piddle with it once or twice/year.

[dcarrb]

Originally Posted by Beav

Torque convertor shudder at lock-up, but if you were at speed for a while it was probably already engaged. If you accerlerated hard enough for it to disengage, then re-engage you may have felt it, but it only lasts for a second or so. You'll just have to pay attention to whether or not it is in lock-up or not.

I'm fairly certain the TC has been in lockup when this happens, definitely in instances with the cruise control set. Feels like an upshift, quick and without a hint of shudder. In this hilly country it's easy to tell by the tach when it's not locked.

Driveline angularity issues? As in, something somewhere's not straight, square or true?

Reckon I'll just keep poking around. Thanks again for the input.

dcb