Driveline Vibration

[philo_beddoe]

No, tires are new. Nothing in the wheels. In fact, it was there all the way to work this morning, even on hwy, but not as bad. Back to square one. I'm taking the weights out of the pass side. I'm going to start jacking sides up and stacking spacers, right side, left side...whatever. Depression is taking over.

[philo_beddoe]

Is there another style tranny mount i could try?

[SkinnyG]

One thing that confuses me with mine, is the inconsistentness of it.  If it was consistent, I would be quicker to blame a mechanical issue.  Driveshaft vibrations should ~always~ be there.

One area I've been starting to go down, is ignition timing.  Since I don't notice any vibration in 2nd (same road speed), I'm wondering if the advance at that point is maybe too much for the engine, and it's not happy, inducing a vibration.  I'll be trying some different advance springs over the next while to see.

[philo_beddoe]

One thing that confuses me with mine, is the inconsistentness of it.  If it was consistent, I would be quicker to blame a mechanical issue.  Driveshaft vibrations should ~always~ be there.

One area I've been starting to go down, is ignition timing.  Since I don't notice any vibration in 2nd (same road speed), I'm wondering if the advance at that point is maybe too much for the engine, and it's not happy, inducing a vibration.  I'll be trying some different advance springs over the next while to see.

I agree with your first paragraph 100%. Mine is not continuous or constant and that is what confuses me, if it were physical or mechanical and always present, i guess it be easier to pinpoint. Generally when active, it is an in and out pulsating drone. rrhummm---rrhummm---rrhummm... which fools me again, because that points to mechanical like something not level or balanced.

I'm going to keep messing with the tranny mount, and rule that out.

I know the basics on ignition timing, but i have no idea how it could relate to the kind of vibe i'm getting.  I dont get it in 2nd also, or under a relatively hard accell. Mine is at its worst when you let off on the pedal, crusing speed, but not taking foot off the pedal. If im doing say 55, and quickly drop in neutral, the vibe quickly dissapates.

[Rattler12]

Harmonic resonance from your exhaust setup........a buddy has that problem on his 40 Ford ........it'll make your head vibrate

[SkinnyG]

The harmonic possibility is one I have not chased.  I wanted to add braided flex joint to my exhaust (headers with traditional 3-bolt collectors), but my local shop cannot get 2-1/2" couplers.  Still looking around.   I could just run open headers, and see if I can notice any change underneath all that noise (the engine is quite snotty, so I'm sure I will love it, but I think everything will vibrate at that point....).

The cyclic vibration is throttle dependent too.  Somewhat temperature dependent.  Inconsistent on the road.

Too much ignition timing may make the engine try to fight against combustion sort of, and may make the engine more rough.  I recently dropped my vacuum advance limiter from 12° to 10°, but that didn't matter.  If I disconnect and plug the vacuum entirely, I would know for sure.

Hmmmm.... 2nd gear would have a significantly different amount of gas flow through the exhaust, which would move the gas flow out of the harmonic zone.  Hmmm......

[philo_beddoe]

Well, VileZambonie installed my crate 350, i had to slightly advance timing not long ago. My engine runs exactly how i want it. Perfect!

What would the vibration be like if you had  NO tranny mount? Continuous i assume. But not a pulsate in and out?

[philo_beddoe]

Well, I added one thick washer to the right bolt on the underside of the tranny mount under the crossmember and it was perhaps a little worse or the same. I tried to simulate weight on my pass side like the heavy guy I had in there the other day when I couldn't get it to vibrate. I think that was the wrong side,,so I tried the thick washer on the left side and,,,while cold, I took a test spin and the vibe was hard to detect, just like the other day. But that don't mean diddly-squat. No more getting hopes up, if the vibe is to a near minimal the next 48 hrs. then perhaps I'm on to something. Vile,,if you catch this...I know your the best of the best, but is it possible I could have a slight engine tilt? (not that I know anything about that), or should I try a better quality tranny mount. The one I have in there was $5.99.

Oh, and the only reason I didn't use the mounting bolts to the tranny is because I don't have a stinkin 15mm open end/box wrench. That's embarrassing.

[VileZambonie]

If you want to schedule an appointment let me know but tilting this way or that won't make a steady vibration that is speed dependent go away unless something is contacting or rubbing somewhere. If it's mechanical then the only way to eliminate it is to repair it. First thing is I would need to drive it and see what you are talking about.

[philo_beddoe]

Yeah, I agree. That's the tricky part, it'll probably be smooth like butter when you test drive.

[Irish_Alley]

park it at his place for a day then let him drive it

[philo_beddoe]

Irish, we may do that next week. Then again, this morning i took that test drive and wasnt bad.  We'll see how it is next week back and fourth to work.

[philo_beddoe]

Well today i drove to and fro all day. The vibe was there and never went away. When its doing it, i put my hand down on the hump and you can feel the normal humm of the engine/tranny, while your bottom side feels the pulsate drone vibe. Thus, im beginning to think its in the rear axle or diff somewhere. I have ruled out the tranny mount.

[philo_beddoe]

No new changes,  my vibe is always there now hot/cold,,to and fro. Vile Z, may take a look at it this weekend. He's the last hope for a truck that is near problem free. If he can fix it,,whoops,,i mean when he fixes it, a nice bodywork and paint is next. The vibe is only in the seat,,the culprit must lie somwhere between the rear wheels. Thats my theory.

[philo_beddoe]

I know i'm flip-flopping, but i had a passenger today, and the vibe was at a minimum. Just sayin. I cant make sense of it either.