Drive line vibrations

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Byron Gray

Byron Gray

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Belfair Washington
I just swapped rear gears in my car. 73 duster 360, 727 trans I took out a 741 case that were 3.23s and i put in a 489 case 3.73s. A rebuilt case with brand new ring and pinion and all new bearings.

When I went to put the drive shaft back in I realized the u-joint was to small for the 489 case and I found one from moog part number ( moog 347) that has the 2 different size ends combination u-joint I think it's called and it fit perfectly on the case.

Took the car for a curse around my neighborhood to start breaking in the gears my neighborhood loops around a lake so at 25-30mph the gears sounded fine no noise or vibrations let the gears cool down then I took it out on the main road. Everything sounded fine untill I was getting up to about 50mph then i felt a pretty strong vibration. Only happens when I get up around 50mph.

I have not checked my pinion or drive shaft angles yet i have a list of things to go over and check. But I'm wondering since I put in that u joint to fit the 489 case if it threw off the balance of the drive shaft. Any and all help, information and input is greatly appreciated.
 
IMO the combination spider you put in the rear U joint is not causing the vibration unless it is installed incorrectly. It should easy to find, good luck with it.
 
DesertRat said:
IMO the combination spider you put in the rear U joint is not causing the vibration unless it is installed incorrectly. It should easy to find, good luck with it.
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Its my first time using them so I wasn't sure. I will double check it is in correctly thank you.
 
Just because you get the clips on doesn't mean taht it's centered. And you have to rock it back and forth to make sure it isn't binding. You could put a dial indicator on it.
 
Byron Gray said:
It is the same drive shaft so I would have to shorten it is about my only option then.
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You will have to check the clearance at the front yoke to the trans tail housing with it in the car. Some setups had 1.5" to 2" of clearance up there to begin with. See if you have that rubber cone boot on the rear trans dust seal, or if it is just the flush fit seal without the dust boot. Good to have at least 1" clearance from the actual end of the transmission tail shaft, a little more is ok too. That sliding yoke shaft slips up in there quite a ways.
 
George Jets said:
You will have to check the clearance at the front yoke to the trans tail housing with it in the car. Some setups had 1.5" to 2" of clearance up there to begin with. See if you have that rubber cone boot on the rear trans dust seal, or if it is just the flush fit seal without the dust boot. Good to have at least 1" clearance from the actual end of the transmission tail shaft, a little more is ok too. That sliding yoke shaft slips up in there quite a ways.
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I'm sure it has the rubber dust seal and I will double check the clearance it has.
 
George Jett’s, I have never encountered what u r saying about the 489 being an inch longer than a 741. That would mean if u went the other way ur drive shaft would almost be too short. Never once. Kim
 
oldkimmer said:
George Jett’s, I have never encountered what u r saying about the 489 being an inch longer than a 741. That would mean if u went the other way ur drive shaft would almost be too short. Never once. Kim
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OK Kim, I will have to measure them here tomorrow on the 741 and the 489 chunks themselves. It will be easy to figure it out for sure.

Some guy on here was saying the 741s were shorter.

Was thinking that the 741s are lighter duty with the smaller pinion bearings it made sense. And the pinion parts don't swap to the 489 case.

There is 2" length difference between the 7 1/4 and 8 3/4 for the driveshaft lenghts, rightly so as they are total different rear axles. I have done these converstions.

Will check it out. Thanks
 
Back in the day we used to switch pumpkins every Friday night to be able to race Saturday and Sunday. Then change them back again Sunday night so we could drive to work all week. Never once had to change a shaft. Kim
 
oldkimmer said:
Back in the day we used to switch pumpkins every Friday night to be able to race Saturday and Sunday. Then change them back again Sunday night so we could drive to work all week. Never once had to change a shaft. Kim
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Great
 
oldkimmer said:
George Jett’s, I have never encountered what u r saying about the 489 being an inch longer than a 741. That would mean if u went the other way ur drive shaft would almost be too short. Never once. Kim
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You are right oldkimmer, 741 and 489 chunks measure the same. 10.25" from the banjo face to the back of the u-joint caps on the assembled gear center chunks.
 
Sorry I didnt see all the replies. I still have a small vibration I noticed I have a small dent in my drive shaft now. So I will take it to get balanced. Thanks all.
 
I am wiling to bet it is that Moog Combo joint at the rear yoke. I would get another one from a different supplier and put that in there making sure it is centered, seated properly, and that the cups fit the cross pins correctly and in the proper order. As 2 of the 4 cups are larger to go with the large yoke on the rear end. Not good to get them mixed up.
 
George Jets said:
I am wiling to bet it is that Moog Combo joint at the rear yoke. I would get another one from a different supplier and put that in there making sure it is centered, seated properly, and that the cups fit the cross pins correctly and in the proper order. As 2 of the 4 cups are larger to go with the large yoke on the rear end. Not good to get them mixed up.
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Ok will look for a different one and try that. Probably be cheaper then getting it balanced to.
 
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