904 seems to be missing a gear and has high speed driveline vibration

[magnumdust]

Went racing today on my new magnum setup and had a frustrating time as all my hard work yeilded a 10mpg car that ran a best of 14.7 @ 91mph :wack:

On the first race i was beating a new camaro off the line and then the car just fell on its face at the top end. At about 80-90mph the car had a horrid driveline vibration. I'm not really sure what this could be. The U-joints are brand new

When i ran a 2nd pass i watched my speedo and found that the car was only shifting once during the entire quarter mile.

The car never revved over 4500rpm, so maybe its not going to 2nd gear? Is that even possible to lose a specific gear in an auto tranny?

The tranny linkage is stock 2 barrel 318 linkage. That prior to my ownership was installed incorrectly(on this tranny) and did not move unless the throttle was fully open. Its unknown how long the tranny was driven this way.

I'm positive it has 3rd as the highway rpms of 3k @ 65mph fit with my tire size and gear ratio.

 

[67Dart273]

First, I would NOT drive the car much into the "vibration zone." We can only imagine how bad the vibration is from your description.

Second, determine if the vibration is actually before/ after the engine / transmission.

Try bringing engine RPM up in neutral. If not vibration, jack the car up SAFELY in the rear and confirm it vibrates in gear.

Next, remove the rear tires and repeat

If the vibration is still there, try different gears

Try fairly high RPM with shifter in 1, then 2, finally drive

Last, remove the driveshaft and try different gears.

IF these tests point to the shaft itself, pull the U joints completely apart and inspect them, for bent/ damaged/ missing rollers, rust, lack of lube, missing/ improper installation of snap rings, etc

Also examine carefully how the joint fits the rear yoke saddles. It should fit fairly tight, with NO side/ side play

 

[magnumdust]

First, I would NOT drive the car much into the "vibration zone." We can only imagine how bad the vibration is from your description.

Second, determine if the vibration is actually before/ after the engine / transmission.

Try bringing engine RPM up in neutral. If not vibration, jack the car up SAFELY in the rear and confirm it vibrates in gear.

Next, remove the rear tires and repeat

If the vibration is still there, try different gears

Try fairly high RPM with shifter in 1, then 2, finally drive

Last, remove the driveshaft and try different gears.

IF these tests point to the shaft itself, pull the U joints completely apart and inspect them, for bent/ damaged/ missing rollers, rust, lack of lube, missing/ improper installation of snap rings, etc

Also examine carefully how the joint fits the rear yoke saddles. It should fit fairly tight, with NO side/ side play

yeah the car wasnt driven much into that "vibration zone". It was an all too familiar noise/feeling from when i had a u-joint break on the highway. I made 2 passes and babied the car home.

I'll check these things tomorrow morning.

 

[Supershafts]

You changed your original rear gear ratio, and changed joints ?

 

[magnumdust]

You changed your original rear gear ratio, and changed joints ?

The gears were changed a year or so ago w/o issue. U-joints were 2 months ago after the rear one let go on the highway.(last owner didnt install a needed clip). The new u-joints have *maybe* 100-150 miles on them including the 50 mile trip to the track.

 

[Supershafts]

So the gear ratio was changed a year ago too ____

But it was the last owners fault that the joint had no clip when the shaft was re-installed into the end yoke when the gear ratio was changed ? ? When you changed the joints it very well could be why its out of balance and when the joint broke on the highway if it wasn't rebalanced it surely is what your problem is.

That sounds very very odd to me to that the joint was re-installed in the end yoke at the time you had the gears done and no one noticed that, while they had 2 hands on it and tightening the straps ? ?..

Anyway whats the ratio now

 

[TrailBeast]

Chk your front band adjustment, and yes you can lose one gear in an auto.
My car shifted from first to third when I bought it, but lucky for me it was only way out of adjustment.
Once adjusted correctly, second gear was back.

 

[Divenut]

May want to make sure your driveshaft is balanced if you haven't already done so...Good luck getting her sorted out man.

Pat

 

[magnumdust]

I played with the car a little and now i'm a bit more confused. I havent done the driveshaft yet, but its "safe" presuming i'm at low speeds where the vibration isnt occuring.

For S&G's i tried to manually shift from 1st-2nd-3rd and wouldnt you know it, i have every gear that way, but on WOT it only shifted once and was a bit of a dog after 1st gear.

 

[OldmanRick]

I know there's probably about a 1% chance of this being your vibration problem, but my neighbor had a 70 Cuda, mainly a track car, 12s. He mentioned to me after a night at the strip that he started getting a vibration on the top end on his last two passes. A few weeks later late on a weekend night he says lets go make a few blasts so you can see what it feels like. Needless to say about 1/2 way through high gear it was so bad it scared the poop out of me. Then he says let me give one more try and i told him go ahead but i wont be in it.

Turns out he had cracked the pinion gear shaft/cluster in his sure grip.

 

[magnumdust]

I know there's probably about a 1% chance of this being your vibration problem, but my neighbor had a 70 Cuda, mainly a track car, 12s. He mentioned to me after a night at the strip that he started getting a vibration on the top end on his last two passes. A few weeks later late on a weekend night he says lets go make a few blasts so you can see what it feels like. Needless to say about 1/2 way through high gear it was so bad it scared the poop out of me. Then he says let me give one more try and i told him go ahead but i wont be in it.

Turns out he had cracked the pinion gear shaft/cluster in his sure grip.

well I sure hope that isnt the case. Hopefully this thursday i'll have my driveshaft out to the local shop to see if its out of balance. Then just kinda hope for the best until i get another track day. I don't know m
any places where i wanna try to get up to 90+

 

[Supershafts]

He cracked the pinion shaft and it didn't lock the wheels when he let off it ?

 

[OldmanRick]

He cracked the pinion shaft and it didn't lock the wheels when he let off it ?

Not with me in it and not that i know of. Surpisingly i didn't even hear any crazy noises from it, although the car was fairly loud. He had the driveshaft balanced and while it was at the shop he pulled the chunk and sent it out to upgrade from 4.57s to 5.13s and that was when it was found. I never actully saw the parts in question, had to take his word for it about the diagnosis.

 

[TrailBeast]

Sounds like it is skipping second and going right into third.
That would explain the doggieness after first.
Problem is, I'm not sure what to do about that.
Fishy68 might though.

Possibly a tighter governor spring?
A shift kit might do it also.

I played with the car a little and now i'm a bit more confused. I havent done the driveshaft yet, but its "safe" presuming i'm at low speeds where the vibration isnt occuring.

For S&G's i tried to manually shift from 1st-2nd-3rd and wouldnt you know it, i have every gear that way, but on WOT it only shifted once and was a bit of a dog after 1st gear.