I have '78 El Camino that I swapped world class T5 from a firebird and a stock 3.73 rear end from a Monte Carlo SS.  I'm experiencing a bad vibration at 60 mph and above.  You can feel the vibration on the shifter and if you keep going faster you can see it on the rear view miror.  I also have a rattling sound from the trans in all gears.  Sorry for the length of this post, but it would do no good if I didn't list all the things I've tried and checked. I tried differant tires.  The output bushing in the trans isn't sloppy.  The motor mounts and trans mount are in good shape.  The U joints are new.  The u joint angles are within 1 degree of eachother.  Measuring a the yoke in the trans there is only half a thousanth of run out when you spin the drive shaft with the trans in nutral, so the mainshaft can't be bent.  I started with the origional drive shaft and got it shortened and balanced.  I tried to do an on car drive shaft balance with hose clamps to make up for inbalances in the rear yoke.  According to the balance tool I started with a 600 gram inbalance and got it down to around 60 grams with 5 hose clamps.  This made no percievable differance at all.  Under guidence of the shop that built my trans I had a new heavy wall 3" driveshaft made up.  They claimed that the stock drive shaft is thin and can't handle the increased rpm of the gears.  This made no differance.  I'm running out of things to check or try.  It seems as though the problem must be in the trans or rear end.  Could the rattle noise in the trans be related? The sound is most prevelent at a constant speed neither excelerating or slowing down.  You can hear it through the shifter.  It is amplified if you rest your hand on the shifter.  I had the trans rebuilt before I installed it It has new bearings syncros, cluster gear input shaft 1-2 slider 2nd gear and 3rd gear.  After that I had it torn down again.  The guy he had never heard one make a noise like that and the only thing he could find was 5'th gear had some play beteen the snap rings, so he shimmed that.  I reinstalled it with no change in the sound.  I've been plagued with these problems for about a year and can't seem to find the right answer.  Thanks for your help.  

I've been having the same problem with the T-5 I put in my vega for several years now. I've had it rebuilt, I've rebuilt the drive shaft and had it balanced, I've even had a new aluminum drive shaft made up with absolutely no luck. So this spring I am giving it the old heave ho and swapping in an automatic. GOOD LUCK!  

hmmm.... T5's in 87 thunderbird turbo coupes used a yoke that had damper ring on it...  probably for NVH...
should be able to be swapped onto any driveshaft if you could find one....

and have you checked the amount of plunge the yoke can still make into the tranny when the car is at ride height.. when the axle is hanging the shaft pulls out a little. when the car squats on the suspention it pushes in and may bottom out agenst the end of the output shaft.


a quick test is to find an oring that fits tight on the  outside of the yoke... push the yoke all the way in.. this pushes the Oring back to the max depth .. measure its location...  

grease on the yoke will stop the oring from rolling it will slide....

put the drive shaft in....  and slide the oring all the way up agenst the rear seal... then bottom out the suspention with a few friends...  jack it up and see what happens...

you can also do this on a muffler type drive on lift..  

If I remember right, I think I have about an inch of yoke sticking out from the rear seal of the trans.  I followed the instructions the drive shaft shop gave for arriving at the proper length and it came out to be 3" shorter than the shaft length was with the th350.  Which is the length difference of the two trannies.  This leads me to believe I arrived at the right drive shaft length.  I like your idea with the O ring.  It's probably worth a try.

Would using a dampener be just a bandaid to what ever the probem really is?

When I origionally took apart the trans the needle bearings under third gear were distroyed.  The plastic cage was melted.  The mainshaft didn't seem to have any damage.  I couldn't find a spec on diameter of the shaft to make sure it was OK, however the gear doesn't have any noticable play with the new bearing, so I assumed all is well.  How critical is this fit and when the mainshaft is spinning at high speeds and the gear is freewheeling could it be vibrating on the shaft?  This is the only questionable thing I can think of in assembly of the trans  

If I remember right, I think I have about an inch of yoke sticking out from the rear seal of the trans.  I followed the instructions the drive shaft shop gave for arriving at the proper length and it came out to be 3" shorter than the shaft length was with the th350.  Which is the length difference of the two trannies.  This leads me to believe I arrived at the right drive shaft length.  I like your idea with the O ring.  It's probably worth a try.

Would using a dampener be just a bandaid to what ever the probem really is?

When I origionally took apart the trans the needle bearings under third gear were distroyed.  The plastic cage was melted.  The mainshaft didn't seem to have any damage.  I couldn't find a spec on diameter of the shaft to make sure it was OK, however the gear doesn't have any noticable play with the new bearing, so I assumed all is well.  How critical is this fit and when the mainshaft is spinning at high speeds and the gear is freewheeling could it be vibrating on the shaft?  This is the only questionable thing I can think of in assembly of the trans  

if it is not the yoke too far in .... it will be pinion / joint angle problems..


what happens when you load the truck bed  and drive it with the tail dragging???

or .. and i know that you dont have them pump up the air shocks....


maybe slipping in some aluminum coil spring spacers under the springs for a test...  

I've measured the U joint angles and the front is less than one degree different from the rear.  If I understand how U joints work properly all you want is the trans output yoke to be parallel to the input yoke of the rear end. I tried a 1/8" shim under the trans just to see what would happen and it made the car undrivable. I also loosened all the rear suspention bolts and I found that you can get about 2 degrees of pinion angle adjustment in the rear suspention depending on where you tighten the bolts. The GM service manual suggested that one. The best I can get is about a one degree miss match.  Talking to guys I work with that set up stock cars, they say that they set their pinion angles at four degrees down and they don't have any vibrations even when coasting.  So one degree shouldn't be enough to worry about.

The car came with air shocks and I've tried it both jacked up and as low as it goes.

One spring seems to have sagged more than the other and the car sits a little lower on the left side.  I have new springs that I'm ready to install.  I doubt that would cause the problem.  I could be wrong?  You see lots of cars at the strip set up that way so they can launch straight.

The vibration can be felt when running the car on jackstands with the wheels removed and the drums bolted on, so I can try it without driving in tonight's snow storm.  

Well, the springs did nothing to correct the vibration or the ride height difference between the drivers and passenger sides of the car.  I'm not sure why the passenger side is about 1 1/4 inches higher the driver side or if this has anything to do with the vibration.

I was also thinking more about the U joint angles.  I've measured the angles on the vertical plane, but not the horizontal plane.  If the engine and trans are not parallel to the frame rails there would surely be a problem.  Also this would become more critical because the drive shaft is 3" shorter with the T5, making the angles greater.  I think this is the next thing I'm going to pursue.  

sounds like it is time to get it on a full sized rack... probably an alignment rack with a center lift so you can support the rear axle above the deck surface duplicating ride height.. and have someone bring it up to speed in the car while several professional mechanics look and listen underneigh...

i really dont like doing it on jackstands being under there with the driveshaft spinning... i have done it... i cannot reccomend it ... people have gotten wound up in the spinning drive shafts before...

getting it up on a proper rack and having several techs is the best way...

as for the angle in ride height...   what happens when you loosen the sway bar links... does the car level out...
hitting a huge pothole might put a bend into one...  

Sounds like you dont have enough driveshaft angle at ride height.Check your tranny mount too(even if its new)a bad mount will cause the vibration and racket you hear.The trans yoke may be worn out.GM srvice manuals call for putting axle grease on the trans splines and in the yoke on half and 3/4 ton pick ups that end up with the same problem you have.Solves the problem for about 10000 miles,then you gotta do it again.That T-5 trans puts the tail shaft higher up in relation to the original trans causing driveline vibration problems(unless you used a dedicated T-5 trans mount)for your application.That said you may still have a mis alignment problem between the drive shaft and diff.Play with the pinion angle some more(I feel you need more downward angle on the pinion)Make sure that rear end is tight too(bad pinion bearings?)Good luck,hope this helps you out.  

I had a vibration problem like yours - and to make a really long story short - solved it with new motor mounts.  One motor mount was bad, and because the motor was now low and offset it created a vibration just like what you describe.
Good luck.  

I tried swapping trans mounts.  The one I was using was solid rubber (presumably better) and the one I replaced it with was the hollow type.  The new one has elongated holes so I can adjust the alignment like I had wanted to try.  Moving the trans toward either side by a small amount only introduced a new vibration, just as shimming putting a shim under the trans mount had caused.  It seems that a U joint angle problem causes a vibration / noise at all speeds.  Can anyone confirm this?  That is what I have found when I change operating angles unfavorably.  

The motor mounts seem to be in good shape.  I tried putting my jack under the oil pan at light pressure and the car wanted to rise with very little tension taken up by the mounts.  Is this a fair test?  If the motor mounts were causing an alignment problem why would it be only at high speed?  Or could they be sloppy from side to side and with the torque of the engine at speed cause the misalignment?  

I replaced the motor mounts.  After they were out where I could really look at them they didn't look very good.  The passenger side was especially cracked and both were sloppy in the metal bracket.

Unfortunately the new mounts had no effect on the vibration.  

I've since tried swapping the rear end.  It still vibrates at the same drive shaft speed (the rear end has 2.73 gears).

I also tried adjustable upper control arms.  I tried all different angles, including how it's supposed to be with the trans U joint angle perfectly matching the U joint angle at the rear end, with no change in vibration.

The only thing left to try swapping is the trans itself.  Even though I tried running it up to the same speed with no drive shaft and it doesn't vibrate.  I don't know what else it could be.  

It sounds to me that the pinion is offset to the trans from side to side. You see the u-joint can only operate out of plane in one direction, if it tries in two the driveshaft will move in an oval pattern. If you have a dial indicator do a runout check on the rear of the driveshaft it shouldn't be more than a few thousands. If the runout is eccessive you'll need an adjustable panhard bar to bring it back. Let us know your result. Good luck