Drive line vibration

[ottawamerc]

Hi Guys

I have been chasing down this vibration in my car for some time now and some of you have mentioned that the drive line angles could cause this issue. I didnt really suspect that to be an option due to keeping a mainly stock drive train, now saying that I know 71 Chargers didnt come with 9 1/4's but hey they fit. I checked the specs on them from my 8 1/4 original and I was sure they were the same except I needed the shorter drive shaft. Now today I took the time and crawled under my car and ya the rear u joint doesnt really look well lined up So does a 9 1/4 C body diff fit in other than its 1.5" overall wider at the tires, are the angles ok???

Just wondering and looking for input

Thanks

Scott

[ottawamerc]

:UPDATE:

I bought an angle finder today and I rechecked the angles here's my findings---- trans is down 2* driveshaft down 4* diff is down 2*  So what I can figure is the front u-joint angle is 2* and the rear angle is 6* definatly seems out of wack. What do you think? Also I measured my drive shaft and it is DAMN forgot the measurment but I think it was 50 3/4" I'll reconfirm. Oh and its a 440 with a 727, 9 1/4 axle.

Thanks
Scott

[ottawamerc]

Ok so if I have this right the differential should go up 3-4* So what I tried today was make some shims out of steel that bumped up the diff 1-2* guessing and I took it for a test run and its better for sure. So I should get some 4* shims I guess?

Scott

[elacruze]

The important thing is that the front and rear u-joints have the same driveshaft angle, that is total included angle. It doesn't matter if the angle is up or down, as long as it's equal.

[MSRacing89]

The important thing is that the front and rear u-joints have the same driveshaft angle, that is total included angle. It doesn't matter if the angle is up or down, as long as it's equal.

'

Not necessarily...remember is trans is going downhill 2º. 

Is your rear yoke higher then your trans yoke?

If not then you are on the right track......generally try to the working angles under 3º.  Your rear was at 6º, and for leaf spring cars under normal driving conditions the working angle of 2º to 3º is ok.  For high HP apps you can go as much as 6 or 7.

[elacruze]

The important thing is that the front and rear u-joints have the same driveshaft angle, that is total included angle. It doesn't matter if the angle is up or down, as long as it's equal.

'

Not necessarily...remember is trans is going downhill 2º. 

Is your rear yoke higher then your trans yoke?

If not then you are on the right track......generally try to the working angles under 3º.  Your rear was at 6º, and for leaf spring cars under normal driving conditions the working angle of 2º to 3º is ok.  For high HP apps you can go as much as 6 or 7.

Doesn't matter. My trans yoke is 2* down and is lower than my axle yoke. But the trans and pinion centerlines are parallel. It doesn't matter the orientation of the parts, as long as the input and output are in parallel planes.

[375instroke]

Have you checked the tailshaft bushing?

[ottawamerc]

Have you checked the tailshaft bushing?

This is my next trip to the shop, cause when I was installing the new shims on the axles I noticed that the rear seal on the tail shaft is leaking and oil was leaking in other places also. There has allways been IMHO too much play since the rebuild

Scott

[ottawamerc]

Damn this alignment thing I crawled under the car just now and took some more measurments and today I got the transmission at 1* down, drive shaft 3* down and the diff at 5* up So now I guess I need to remove the 4* spacers I installed and I would be back to even.

Scott

[MSRacing89]

Damn this alignment thing I crawled under the car just now and took some more measurments and today I got the transmission at 1* down, drive shaft 3* down and the diff at 5* up So now I guess I need to remove the 4* spacers I installed and I would be back to even.

Scott

Be careful with that.  When you do that you will changed your front working angle by pushing the pinion down.  If you get over 3º working angle, could be issues.  See if you can get the pinion nose down about 1º and see where that puts your working angles. 

[ottawamerc]

See post..
http://www.dodgecharger.com/forum/index.php/topic,102445.0.html

Scott

[6spd68]

Another thing to consider with driveline vibration is the drive shaft itself.  If you've thrown a balancer weight, or twisted it with too much torque, that'll cause it as well.  Have had that happen with my T-bird (440HP 347cu Stroker) twice.  Easy way to see that is to have the car on a hoist in gear, go up to like 30 and watch how the diff moves around (we ended up popping jack stands on both ends of the axel and sure enough, bouncy bouncy)

Once I'd swapped out the shaft, no more issue!  Just sucked that in the process, I mangled my T-5's tailstock...

I know this may not have been your issue, but it's definitely worth mentioning for someone else's future reference