Cars shaking and vibrating

[finkous]

I’m almost at my wits end, so I’ve come to back to the forums for help…

I have an 81 malibu wagon and I’ve developed a shake/vibration. I’ve done a lot of work to the car over the yrs but since I installed a new 2004R trans and new posi rearend, the car now shakes at 50-65 mph (for the US friends😉). The strange thing as it doesn’t do it all the time. Comes and goes in between stopping and going again. In my quest to find the problem I’ve balanced tires, bought brand new tires and rims, new driveshaft with new unjoints and balanced, new steering box, I’ve checked ball joints, steering linkages etc multiple times.

I’m open to suggestions at this point.

 

[stew86MCSS396]

The assumption would be that you changed the cross member with the TH-2004r and perhaps driveshaft angles aren't optimum???

 

[airboatgreg]

With it not doing it all the time that indicates that something is changing. Do you feel it in the steering wheel or seat of your pants? Does it do it if you run in a lower gear, Do you have a locking torque converter? If you do will it do it with the TCC disengaged?

 

[rfpowerdude]

^^^^^
Check to see if the angles of the output yoke at the trans and input yoke to the rear (phasing) are the same when sitting level on the suspension. And also in a straight line...

 

[olskool]

^^^^^
Check to see if the angles of the output yoke at the trans and input yoke to the rear (phasing) are the same when sitting level on the suspension. And also in a straight line...

is it at light throttle? does it feel like you are running over a railroad track or the cuts at the edge of the road? i am thinking it may be your torque converter clutch. although 50-65 is high to feel the clutch, that problem usually occurs at around 45-50 mph, the next time it does it hold your right foot on the gas and let it happen and take your left foot and very gently touch the brake at the same time and see if it stops. if it stops then the clutch in your T/C is chattering. if this is the case google "shutter fix" lube guard sells it, put a tube in the dip stick tube, if the converter is good the shutter will be gone. but this may not be your problem.

 

[oldsofb]

Tremec has an app that has a driveline checker within it. It uses you phone as a level to check the angles.

Hutch

 

[86LK]

what happens if you slap the old diff back in the rear? does the problem go away? did you do anything else to the rear axle while you were in there?

 

[Rt Jam]

Do you know how to check driveshaft angles?

When it's vibrating, shift to a lower gear and note the change.

Do you have access to a wheel dyno? This can confirm it's coming from drivewheels end of car.

Jack up car and check tires for runout.