Vibration around 55 mph - Driveshaft out of balance?

[Guest]

Ok...here's one for you REALLLLLY big time experts out there...

(rocketraider r u there??)

After I had my new 3.73 gears put in (went from 3.08 to 3.73 so the driveshaft will spin faster at lower speeds.....) and new u joints put in I noticed an annoying vibration around 50-60 mph. I had not noticed it before and just thought it was a wheel which tossed a weight.

I went through several incarnations with my other garage trying to lick this vibration including 2 new tires and swapping all 4 rims (decided to buy SSII wheels so i wasn't mad at the rims purchase...)

Bottom line - after 2 new tires, 4 rims and much annoyance it didn't stop the vibrations. BUT today I did find out my rear end was now losing fluid (slightly) after only like 60 miles on new gears. They suggested to call the guy who did them and get the seal replaced at the pinion yoke in fornt of diff. housing. I called to make an appt for next week with the tranny place and asked the guy also about the vibration....he insists it is tires or suspension....

My friend at my car parts place suggested (after telling him this story today) I rotate the driveshaft 180 degrees and reinstall it and see it the vibration changed. I did this and it is less pronounced and the speed range at which it happens is a tighter "bracket". I.e. 55-57 mph instead of 50-60.

So is it safe to say my driveshaft is out of balance? Would this cause fuild to seep around a new pinion yoke seal? I am wondering if the guy who did my gears may have knocked a weight off or banged it or something or just the u joints being different.....

The guy who did my rear gears insisted up and down I don't need to balance the driveshaft and it is not the cause of the problem and it has to be tires or suspension. He is going to take back the car and deal with the leaking diff. seal....

What do you think guys? Am I barking up the wrong tree or am I on base here?

I need to go argue with the tranny guy I am thinking...

Thanks in advance!

[Guest]

HELLO, MY NAME IS FRANK.. IS YOUR CAR AN AUTO OR MANUAL TRANSMISSION? DID YOU CHECK THE TRANS MOUNT?? DID IT START "AFTER" THE GEARS WERE REPLACED?? NO OTHER WORK WAS DONE AT THE TIME? DID HE REPLACE THE BEARINGS AND TORQUE THE PINION NUT PROPERLY?? WERE THE U-JOINTS PERFECTLY INSTALLED? IF YOU GIVE SOME MORE SPECIFIC DETAILS , WE CAN GET THIS FIGURED OUT FOR YOU.. IF YOU WANT, GIVE ME A RING AT 208- 720-5480, I'LL TALK YOU THROUGH IT.. GOOD LUCK FRANK..

[Guest stude8]

I have been through drive shaft vibration on a 1978 Chrysler and found that there is a prescribed "Maxium" angle from the CL of the output shaft on trans to the slope the shaft makes going back the the pinion flange. If your rear springs are sagged a little bit you could be right on the verge of too much run out. You can also try rotating the U-joint at 90 degree intervals rather than just a flip of 180 degrees, sort fine tune it.

I also have heard of success putting large hose clamps around the shaft body and chalk a mark so you can turn the screw (Weight) section one way or the other to get the perfect balance.

OR you can take it to a drive shaft shop and get it balanced. They will probably want to make a new shaft tube and weld it in their lathe to get it dead nuts on.

Don't know what make we are talking about but I have heard horror stories about 1970's GM cars with double wall shafts and injected rubber insulators between the walls that dry out and you can never get them to balance when the inner core shifts around every revolution. Good luck.

[Guest]

Ok....more details per franks post.

1) Just left the car at the tranny shop. Balancing the tube is $30. I told him to do it and go from there. He promised the rest beyond the $30 labor is on their dime (since they did the gears....and didn't realize it wasn't right)on getting this right.

2) Car is a 1972 olds cutlass

3) Auto th350 tranny

4) corporate posi rear end. 10 bolt 8.5 inch gear

5) spings are old - but I have air shocks which take up the difference. I tried the car at low fill and high fill on the air shocks

I still would like to have ideas and anything i need to "check that they did" so when I hear back form these guys tomorrow I don't get screwed or have them not deal.

Frank- I'll try to call you later or tomorrow. I am not near a phone now. (long story - dropped car off and am waiting at library for the wife to pick me up)

thanks guys. I sooo appreciate having these forums to get help and ideas.

[Al Smeraldo]

I once had a bad bushing in the transmission output housing where the driveshaft front yoke tube fits. This caused a similar vibration to what you described. Al

[Guest]

I replaced the driveshaft now and did the bushign and seal at the tailshaft housing on tranny. The vibe is 99% gone now. Last thing I need to do is swap out that rear yoke. I think it is warped cause it has a weight on it and the lip looks nicked.

Wow driveline problems can be a pain! Lets see $100 for two tires; $200 on rims; $40 to balance driveshaft; $220 to then replace it since it was not 100%; $10 worth of misc bushings/seals; and $120 for a rear yoke & labor for the swap

Nearly $1000 later I am back in business and have super stock wheels now at least.

[Guest]

One more thing - here's a .jpg of that back yoke with a weight on it.