Adk46

Got everything buttoned up this morning and got out on a test drive. All went well (and the noise that led me to do this difficult job has gone away.) It's really quite something that the car stills runs after being so severely messed with by someone like me.

But there is a vibration between 2050 and 2200 RPM. In all gears? I should have explored that question better, but I think so.

Dwayne did something I didn't - mark the position of the rear flex plate relative to the torque converter so it could be re-installed the same way - important if they are jointly balanced. So, I had only a 33% chance of getting it right. I believe it will be easy to move them to another position (50% chance of success) and one more if necessary.

I put in a Constantine rebuilt TT, and added his clamp, too. I didn't unbolt the front flex plate. The half-shafts were unbolted, of course. I suppose that the wheels are now in a different position could be the cause, too. Oh - I put in new rear brake rotors. Damn - vibration problems are nasty.

Thoughts?

Chalkboss

Did you make sure to have clearance between the transmission mounts and cross member? If they touch you will feel a vibration. Happened to me.

Adk46

Ah - forgot to mention that I put in new transmission mounts, $OEM. (New engine mounts a few years ago.)

worf928

BRB-83-911SC

Curt - I hope it's as "simple" as re-indexing your rear flex plate. Not to scare you, but see my saga below regarding vibration after TT/gearbox R&R. Jump to post 50 for final resolution, after chasing down many rabbit holes. Bottom line, when the TT was out, the motor had shifted a bit on the motor mounts and taken a different set causing the motor mounts to make contact. I sincerely hope that is not the case here.

https://rennlist.com/forums/928-foru...n-puzzler.html

worf928

Adk46

I was not able to find the relevant section in the WSM, but there's a dime's thickness clearance on the side of one mount (I mean, between the transaxle and the vertical bearing surface of the mount). There's nearly a finger thickness of clearance above the cross member.

I found no shims on the mounts - maybe there should be now, given the above.

Everything was torqued properly according to my obsessive list-making.

My perception of this vibration is new, but it's not severe. After another test drive, I could tell I was getting used to it - almost. There is a bit of a "booming" sound to it mixing with the feeling. Naturally, I'm hypersensitive to anything funny after doing this big job.

Volvo mounts, installed three years ago, I think. That's an interesting correspondence, Brian. Might the vibration go away as the mounts return to their normal set?

BRB-83-911SC

I honestly can't say. However, I would caution that this was my experience, and may not be your issue. But, it may be worth a look at the motor mounts to see if there is any obvious contact (it was not obvious to us - until they were removed and you could see the witness marks). To note, I could feel the vibration through the body of the car, and almost a groaning sound at certain RPMs, and it was most obvious under load - which is totally understandable given there was metal on metal contact..

Do you notice the vibration when running the engine through the rev range while parked and in neutral? If not, I would keep looking aft of the bell housing. We were able to eventually isolate it to the engine causing the vibrations by essentially disconnecting everything rearward.

FredR

Curt,

Irrespective of what the cause of your issue is, your case in hand does beg the question as to what the protocol should be for engine support when the transmission/torque tube is removed. Sounds as though you innocently removed the transaxle and had no game plan for stabilising the engine whilst it was sat on what becomes a pivot. Not hard to visualise such might do no good whatsoever for the hydraulic mounts that are fickle enough when operated as intended. Sounds as though the motor could do to be stabilised with jacks prior to removal of the transaxle.

Never seen this specific aspect addressed previously but I a fair bet says it has been covered.

Adk46

Fred -

As I was studying the procedure, I had a "Wait a minute!" moment when I realized the engine would be left perched on its two mounts, free to tip forward or aft. I posted a question about this and I believe Stan told me not to worry, it wouldn't go far, but it might be worth checking ... I forget what, something aft. Indeed, the engine seemed not to move at all.

I recall a thread or two about how easy it is to slightly mis-align the engine mounts, enough to create contact, so previously OK mounts might become bad mounts if given the chance. I'll give mine a look-see. But wouldn't there be something like a clanking noise? My vibration feels smoothly sinusoidal, if you know what I mean.

I might just go ahead and re-position the flex-plate 120° tomorrow. Just need to open the lower access hole in the TC housing. I think.

Brian -

I'll scope out more details, but the vibration is most noticeable at light load, maybe only because there is not much going on that might mask my perception of it. On a scale of 0 to 10, where a vibration you can live with is a 3, this is a 4.

BRB-83-911SC

Curt - sounds like your issue may be different from what I experienced. Mine was such that it sounded/felt like it was causing damage - such that I didn't drive the car, except for testing, until it was resolved, and it came and went at 1200 RPM intervals. I think the metal on metal motor mount contact amplified (rather than absorbed) the inherent harmonic vibrations of the motor - enough to cause the interior trim to buzz.

Mrmerlin

I will guess that you have to turn the the rear flex plate one or two more times till it goes away Or gets worse
put a red dot on one of the the flywheel bolt areas then mark the bolt areas on the TC with a 1 2 3 ,
make a chart to describe the red dot to 1 to 2 then to 3
an engine with no TT attached to it will happily sit on the motor mounts without any other support.

Constantine

Hi Curt,

Vibrations in all gears at that specific RPM range would point to the motor's vibrations being transmitted through the body.

Would confirm health of the motor mounts and check for any contact with the body structure by the motor or exhaust.

Good luck with the hunt,
Constantine

Chalkboss

I also had a slight vibration resulting from the heat shields contacting the rear most attachment brackets for the rear belly pan, so check those too.

worf928