Engine vibration at certain RPM

[arnie93lx]

Reefbluegt, did you figure out the engine vibration? If not have you had the clutch/flywheel out recently? I know that flywheel dowels missing can cause a vibration because the pressure plate may not be centered perfectly. Check the flywheel for dowel pins if you haven't already. (it would do it with clutch in or out)

 

[ReefBlueGT]

Reefbluegt, did you figure out the engine vibration? If not have you had the clutch/flywheel out recently? I know that flywheel dowels missing can cause a vibration because the pressure plate may not be centered perfectly. Check the flywheel for dowel pins if you haven't already. (it would do it with clutch in or out)

Not yet. It seemed a little smoother today after I’d gone through and cleaned up the body grounds, and now that the air system is working properly.

Previous owner replaced clutch and flywheel almost 7 years ago. No idea the manufacturer or quality of parts used. Would have to take it somewhere to get it looked at.

 

[ThinBlue502]

How do your steering rack bushings look? Replaced mine a couple years back. I had to examine them very closely. They looked fine on the face, but had cracked and become very brittle behind the surface.

 

[ReefBlueGT]

Interesting update on this. Just got home from a drive and before pulling in, decided to really floor the gas and see how high I could rev the engine. Was responsive and smooth above the existing vibration around 1300 rpm. But once it got over 4000 to almost 5000, something growled and there was another brief vibration thudding through the column and dash. Wasn’t an exhaust growl, more like something mechanical grinding/vibrating deep inside the drivetrain somewhere. I replicated it a couple times. This was at a standstill just sitting in the street, in neutral, clutch not pushed in. @General karthief @arnie93lx what do you think about the above?

 

[arnie93lx]

It may be something clutch related but not positive. In neutral it is still spinning the input shaft on the tranny so could also be inside the tranny but not thinking that for sure. I'd jack it up, take the clutch cover off, see if you can see the clutch/dowel pins for the flywheel. If they are there then it is probably something deeper.

 

[ReefBlueGT]

It may be something clutch related but not positive. In neutral it is still spinning the input shaft on the tranny so could also be inside the tranny but not thinking that for sure. I'd jack it up, take the clutch cover off, see if you can see the clutch/dowel pins for the flywheel. If they are there then it is probably something deeper.

Definitely beyond my comfort/expertise level there, but I appreciate the quick feedback. Guess a trip to the mechanic will be in my future at some point. Thanks!

 

[General karthief]

I am in agreement, clutch or trans related.

 

[ReefBlueGT]

@arnie93lx & @General karthief thanks for the recommendation on this issue. Finally got it looked at this past week, mechanic looked at any other possible cause first, and then did recommend dropping the trans to take a look. He said the flywheel had a wobble, and it was also missing one of the dowel pins. Not a cheap fix, but so worth it. The engine sounds and feels almost like new while driving, and they also replaced the rear oil seal while up there, since that was leaking. There is still just the slightest flutter around the same RPM range, but not enough to shake the steering or even noticeable unless you're really looking for it. I guess just chalk that up to an old engine using 80s technology and engineering?

 

[limp]

I have a 93 GT vert, having this same problem; getting a strong vibration/shake through the steering column between 1300-1400 RPM. Occurs whether in gear, or not moving in neutral - clutch in, clutch out, doesn't matter. My car is basically stock, no crazy mods. Took it to a mechanic, the balancer was wobbling all over the place, so it was replaced, but did not fix the vibration. Then I noticed the radiator fan was cracked in several places. Replaced it and the thermal clutch just to be sure - engine runs much smoother and has more power now, but vibration at those RPM's is still present.

After taking it for a longer drive today and really focusing on how everything sounded and felt, determined the following: vibration is worse when the car is cold (live in So Cal, so not COLD, just when it hasn't been running awhile). By the time I got home and tried to make it shake again in neutral, it was nowhere near as strong, but still there. Also, the vibration is definitely traveling through the steering column - the steering wheel is shaking up and down, with some vibration getting transferred to the dash as well.. The engine itself and nothing I can see on it, is vibrating at all - I looked carefully while manually raising the throttle in the engine bay.

Lastly, I also ran KOEO/KOER and cylinder computer tests. All cylinders came back good, only EEC codes were 44/94, which I've gotten ever since I first pulled codes a couple years back. At some point when I have nothing else to do, I'll replace the crossover tube to see if those go away.

I am thinking the steering vibration has to be coming from the PS pump and/or PS rack. Both are original, and even though the car only has 77K miles on it, it's almost 30 years old now. Another factor is that there is a leak in the front of the engine compartment, approximately where the pump/steering rack are located. Lastly, the ride on the front end of the car has always been extremely harsh. Any little bump in the road sounds/feels like I'm driving over a steel beam. PO had lowered the front end a couple inches, I had the springs and struts replaced to OEM specs but no change in ride quality. The rear end of the car rides/feels as it should. There are subframe connectors and cross members from the PO. They are welded.

For background, I've had the car just over two years, I'm the third owner. This is my second Fox vert, having had an 86 5.0 LX back in the mid 90s which was 100% stock/original, so I'm familiar with how it should feel and act on the road.

I've searched and searched, and read many posts here. Unless there's something else I've missed, I'm ready to upgrade to a new SVE PS rack and also replace the PS pump with a remanufactured Motorcraft. Will have all hoses etc. replaced too just to make sure everything steering-related is new again.

Would appreciate any thoughts/feedback. Thanks!

Take off the PS belt and see if the vibration goes away...