I need smart guys to help with my bird...

[markd79ta]

Originally posted by N20LT4Bird
Mark, this sounds interesting, how do you know that the bushing is the prob if you have not fixed it yet?

There are no for sure(s), but I went through the diagnostic with a drive-line guy in his shop with the car on the rack. He was 99.9% sure as well as I concurred with another 99.9%. The car exhibited similar symptoms to a very minor degree at 110ish mph before the gear install. With the extra revolutions of the drive-shaft after the install, it just got a lot worse. Now if I fix it, and it still occurs, then I will feel really stupid

[N20LT4Bird]

Is it a vibration that just comes in all of the sudden at 4000 rpm or so under heavy load? I dont feel anything until I hit 3rd (a little) and then 4th (alot). I also dont feel it at high speeds in a high gear like 6th (probably becasue theres no load on it).

I just checked the play up and down on the yoke and I do have a little play, but its minimul. The only thing that is holding me back from jumping right in and changing it is the fact that the ratio in my rear did not change. But, maybe the fact that the slip yoke is sitting further in is just enough to disturb it.

[markd79ta]

Originally posted by N20LT4Bird
Is it a vibration that just comes in all of the sudden at 4000 rpm or so under heavy load? I dont feel anything until I hit 3rd (a little) and then 4th (alot). I also dont feel it at high speeds in a high gear like 6th (probably becasue theres no load on it).

This last part is kinda odd. The copper bushing wouldn't be that hard for you to install if you want to rule that out as a possibility. If your drive-line is good and you are concerned about a possible engine problem, maybe put it on a dyno so you can see what it is doing at 4,000rpm. My problem is progressive with both speed and RPM coupled together...it sounds as though this may not be the case with your car.

However, you are pushing out a lot more HP then I am, so the problems could mutate into something else. In other words, you may just have minimal play, but that may be enough given the output of your engine coupled with the 3.73s

[fastTa]

Originally posted by N20LT4Bird
The vibration is not noticeable if the car is in neutral. If I put my foot on the clutch and maintain the rpm, the vibration goes away.

Well this is a bit confusing I must admit. The first sentence would lead me to believe that it was originating in the motor since the motor was disengaged from the drivetrain and consequently and simultaneously the vibration stopped. However the second sentence would lead me to believe that it was NOT the motor because if you are maintaining the RPM and the vibration is not noticeable, then it likely is not an engine orginated vibration.

It sounds like the vibration is only developing under load on the drivetrain.

The layshaft and the output shaft (tailshaft) are always turning if your car is moving and even if the clutch is disengaged. The only part of the tranny that stops moving when you push in the clutch is the input shaft/gear.

I'm not sure if your input shaft bearing retainer is aluminum or steel, but I am betting on aluminum. As you know it is kinda hard to diagnose w/o feeling the vibration in person but if your input shaft bearing retainer is aluminum I would say that would be my best guess at your vibration.

Let us know what you find Sean!

[TraceZ]

Originally posted by fastTA

The only part of the tranny that stops moving when you push in the clutch is the input shaft/gear.

Assuming the car is moving....
Unless the transmission is in neutral, the input shaft is always spinning, regardless of clutch position.

[fastTa]

Originally posted by TraceZ
Assuming the car is moving....
Unless the transmission is in neutral, the input shaft is always spinning, regardless of clutch position.

You are right Tracy. Sometimes during my long winded attempts at diagnostic interventions, and coupled with my adult ADD , I get a little a head of myself!

To clarify, the input shaft and layshaft are always turning when the engine is running and the clutch is engaged. The output shaft is always turning if the car is moving.

Essentially the connecting point between the input shaft/layshaft and the output shaft (tailshaft), is the selector collar.

Back to the point, my bet is still on a worn or bad input shaft bearing retainer.

[N20LT4Bird]

Well, im taking the trip to syracuse tommorrow. My dad offered to look at it at his shop to help diagnose it, so hopefully I will have an answer soon.

[fastTa]

I'll keep my fingers crossed that it is nothing too costly.

[fastTa]

Sean I don't mean to change the subject but, other than the vibration problem how does the new setup seem to run?

[Joe 1320]

Originally posted by fastTA


Back to the point, my bet is still on a worn or bad input shaft bearing retainer.

That's my bet as well. Keep us posted, Sean.

[N20LT4Bird]

Originally posted by fastTA
Sean I don't mean to change the subject but, other than the vibration problem how does the new setup seem to run?

Its running great! I dont have any complaints with the rear. It was perfect for about a week and half, and then this vibration reared its ugly head. I immediately assumed I screwed something up in the rear, so I pulled it all apart and replaced all of the bearings. That was apparently dumb. The vibration is still there. So, its on to other stuff. I will check the input shaft bearing idea with my Dad. He'll drive it and probably figure it out right away

The lack of power I previously mentioned may be in my head?? I checked all of the wires yesterday and I had a few ugly looking ones, so I may change those next week. Hopefully its in my head.

[Injuneer]

Originally posted by N20LT4Bird
How much clearance should I have? The shaft definately goes in further than it used to......

Do you think this would vibrate only at high engine rpm's though? Wouldnt it be more of a speed related vibration?

With the car at normal ride height, there should be a minimum of 1/2" clearance between the driveshaft slider and the end of the output shaft. Unbolt the u-bolts from the u-joint, and slide the DS forward until it bottoms out. That's where you want 1/2". As HP goes up, that dimension needs to go up.... to a max of 1".

I don't know when or if this would make things vibrate, unless it has already bent the output shaft. I think that some people with the Moser 12-bolts, who don't check the clearance are seeing similar problems, based on posts I have read.

And... the only thing you have changed in your setup is the rear axle..... I would suspect the vibration is somehow related to that.

Fred

[N20LT4Bird]

Well, after our diag session this afternoon, we believe that I have two problems - one being the driveline vibration and the other - an engine power loss problem.

My father suspects that I have set the pinion depth incorrectly in the rear. Driveshaft slip joint looks good. The other possible is the input shaft bearing, but going with Fred's reasoning (the rear is the only recent change), im think im gonna reset the shims on the rear.

Now, my engine lacking power is a seperate issue. I thought I was dreaming it up, but my father confirmed it - its not pulling in the upper rpms. Normally, it pulls like a freight train at 4000 rpm and up. Now, it seems to kinda fall on its face. We did a fuel injector cleaning just in case, but we are suspecting a spark delivery issue. Its not like its missing at all, it just lacks power in the upper end.

What causes the "spark scatter" in the LT1's that you guys have talked about? I am thinking my wires need to be changed, but maybe something else?? Coil, module, opti (dont say opti )??

[wako29]

when was the last time you changed the opti?

[N20LT4Bird]

Ive owned it for almost 3 years and have never changed it. I dont want to either.