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Reverberation at 3k+ rpms


kev
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So this is an issue that I've had on this 88 automatic that I got running in the spring.  It has what I consider a 'wicked' reverberation from about 3000rpms and higher.   It doesn't vibrate the crap out of you, its more of a noise reverberation (it's loud).  It isn't speed specific, but rather rpm.   It peaks at around 3500rpms but does remain there for all rpms above.     I've checked all my mounts, etc and everything looks good.  My first thought is that I've eliminated the balance shafts but I've never experienced this on a conquest before, balance shafts or not.   Although, this is my first automatic where I removed the shafts.    Only other thing that I can think of is the torque converter.  Thoughts?   

Just some background:  Car was sitting in garages with the engine torn down to the block since 1997.  98k miles.   Fully rebuilt the engine over the winter and got it running in the early spring.   Transmission is untouched short of new fluid/filter.   Driveshaft hasn't been removed (by me at least).  Rear and axles had new axle seals and new fluid.   All mounts are original but verified they are not torn.  

30 years of driving these things and I still run into new issues that I haven't had prior!   

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Only thing I have seen is slight buzz in shifter near 3k with shafts deleted, is there a chance one or more of the rods have been replaced?   is the pilot bushing installed into rear of crank?  these are 2 possible causes,  I have seen rod weight differences between engines of close to 40 grams.    The pilot bushing will center the converter   much like a clutch pilot shaft bearing.

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The rods are original for sure and I reassembled them in the same positions they use to be, all facing the correct direction too.   There is no dowel in the crank, for the flexplate will not permit one.   But the correct sleeve is installed in the crank for flexplate alignment.   I went through my photos to confirm all of this. 

One thing that is interesting is the white paint on the flexplate.   I believe the torq converter has a white mark as well.  I honestly do not remember matching these two up upon engine installation.  My son was the one under the car at the time bolting the torq convertor.    I think this is a good place to start looking and it is pretty easy to check.   

 

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I had a chance to look into this over the weekend.  I pulled the inspection cover and removed the four bolts securing the torq conv to the flex plate.  I tried and tried to find white paint on the torq conv to use to clock it to the flex plate but I wasn't able to see anything, at least not with the light that I had.   So, I spun it 180 degrees from where I had it clocked and reassembled/torqued.   Took it for a drive and it is remarkably better...but it still has a reverberation.   I think this is the source of my issue but I'm still not sure I have it clocked in the correct position.  I will say that it is much more drivable now.  The reverberation that is there 'could' just be from the BSE.

Going back through my photos this morning, I found this picture of the torque converter.  One of the bolt holes is indeed painted white but I couldn't tell while under the car.  The color of the welded nut looked the same for all four.   But, in the photo, I noticed a white paint mark up higher.  It is on the same circle as the four round cutouts in the flexplate.  You can see the surface rust on the convertor where these were.   I should be able to see the white paint mark  if I rotate the engine about an 1/8 turn through these cutouts.   

I wish I would have looked this over in more detail before I went under the car but it isn't a hard job.  Jacking the car up and putting it on stands is the longest part.  But this time, I have a little more information and will get some better illumination.  

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Hmm, staring at my photos a bit more....

 

Here is the photo of the engine before installation.  The white mark on the flexplate is on the top.

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Now here is a photo of the engine compartment immediately before we put the engine in.  The white mark on the converter is on the bottom

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That tells me that I installed it originally 180 degrees out and, with what I did the past weekend, I should have it clocked correctly now.   

But, I'm known to beat a dead horse, and WILL be confirming this.   

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I never thought the converter would have to be clocked to the flexplate.  But obviously it does based on the improvement from what I did already.  I would have assumed they were balanced independently.   More reason to swap this car to a manual...which may be as early as this winter!  

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  • 3 weeks later...

As reinforcement to your diagnosis (though in a 5 speed) I had a 88 flywheel lightened, resurfaced and had the whole assembly balanced.  Was like butter when I installed. Years later I replaced the clutch and did not think about the balancing when I reinstalled a new clutch and pressure plate.  It then started vibrating in the transmission's shifter at 3000 rpm, though would go away at faster rpms  My car had the BSE kit on it when I bought it.  So I think you were right - there was a balance issue and by rotating corrected it.  Just live with it as the car is not driven frequently.

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1 hour ago, Paul87Quest said:

As reinforcement to your diagnosis (though in a 5 speed) I had a 88 flywheel lightened, resurfaced and had the whole assembly balanced.  Was like butter when I installed. Years later I replaced the clutch and did not think about the balancing when I reinstalled a new clutch and pressure plate.  It then started vibrating in the transmission's shifter at 3000 rpm, though would go away at faster rpms  My car had the BSE kit on it when I bought it.  So I think you were right - there was a balance issue and by rotating corrected it.  Just live with it as the car is not driven frequently.

I had my flywheel lightened, installed a stock Mitsubishi clutch and did a total engine rebuild that was zero balanced with a BSE kit and never experienced any hard vibration. But I did experience a slight vibration in the shifter knob accelerating at lower RPMS. You screw with these cars......You get what you get. Been dealing with  many different issues when doing modifications on these cars since 2002.

 

Bill

Edited by Caliber308
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