8 3/4 3rd member swap vibration

[pamfan29]

I'm driving a 318/904 68 charger which originally had an open 2.76 741 housing which I switched out to a rebuilt 489 4.11 posi. My trouble is I'm getting a real bad vibration around 80-100 mph and it seems to be comming from the rear. I didnt think the angle of the driveshaft had changed with the new pumpkin but maybe it did and thats causing it. I don't know thats why I am asking you guys.

thanks


(p.s. tires are balanced and u-joints are replaced)

 

[70redbee]

Was this a used unit or newly rebuilt? Did you have it checked by a mechanic who is good on Mopar rears if used? It could be warn bearings in the rear or maybe even on the axles themselves. There are a lot of things that it could be and you will only find the problem with a process of elimination(sp) and inspecting each part seperatly. Give us all the info. you have since the swap so we can better help you. Good luck and keep us posted. OH by the way 100 mph is against the law...LOL

 

[1badgtx]

Could be the nut that holds the pinion gear is loose or the main pinion bearing is wore out..
Petty Blue 67 gTx

 

[Meep-Meep]

doing 80-100 MPH with 4.10's vs. 2.76's there will be a difference in output shaft RPM, so it's possible you might be seeing an existing problem that never showed up before. Perhaps a drive shaft issue?

 

[pamfan29]

Was this a used unit or newly rebuilt? Did you have it checked by a mechanic who is good on Mopar rears if used? It could be warn bearings in the rear or maybe even on the axles themselves. There are a lot of things that it could be and you will only find the problem with a process of elimination(sp) and inspecting each part seperatly. Give us all the info. you have since the swap so we can better help you. Good luck and keep us posted. OH by the way 100 mph is against the law...LOL

I bought it from a guy who claimed he was an expert on mopar rears and told he me completely rebuilt it... but when I told him about the vibration I never got a response. I checked out the pumpkin before I installed it and everything seemed to move freely without any noises it seems like if it was a bearing I'd feel the vibration at a low speed/RPM. I can tell you that before the installed the 489 I never had any vibration.

 

[Cranky]

Like Meep said, doing 100 mph, things like the drive shaft will be spinning much faster than it did when you had the 2.76 and doing 100 mph. The axles will be turning the same but everything else will be going nearly 50% faster than before. If everything feels good...no slop in the yoke etc and the drive shaft is bolted in right, I'd look at it's balance.

 

[lockerjesse]

(safety first).Often over looked. Remove the drive shaft from the differential yoke and look to the inside of the yoke where the U-joint cup c-clips ride up against the inner faces on either side, see if there is any c-clip impressions. If there is you need to replace the yoke because the drive shaft is not turning true.

 

[bigmanjbmopar]

What about axles, shouldn't he have upgraded the axles in this case? Also what about re balancing the drive shaft? Loose or old / wrong u joints often cause rattle. I have seen that first hand behind my friends cuda on the freeway not a pretty site.

 

[ilm65]

Assuming you changed the speedometer gear in the transmission, I'd agree with Meep and Cranky. And yes, there's no substitute for a well balanced drive shaft.

 

[pamfan29]

What about axles, shouldn't he have upgraded the axles in this case? .

Any Chance the vibration could be coming from a bad axel bearing?

 

[Cranky]

Any Chance the vibration could be coming from a bad axel bearing?

If an axle bearing was bad enough to cause a vibration, you would most likely hear the bearing too....and it most likely would be loud.