help with punkin swap

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trudysduster

trudysduster

FABO Gold Member
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I have a 8.75 489 case with 4:10 gears in my 76 Duster. I have a 489 case with 3:91 gears here in the garage to go in my 73 Duster. The 4:10 is a little too much for my cruisin so I want to put the 3:91 in it.The yoke on the 3:91 punkin is bigger than the yoke on the 4:10 punkin. I was going to just swap the yokes but the crush sleeve issue worries me. I have never replaced one before. Is this hard to do . Can someone tell me what is involved. I read somewhere that Rumblefish mentioned Lakewood makes a crossover u-joint for this. maybe that is a possibility. If so where do I find it. Wouldnt that cause a vibration being off balanced. your help is appreciated,Bill
 
yes they make a conversion u-joint. probably the easiest way to go. i have gotten them from napa in the past. don't remember the number for it though.

another problem with switching the yoke is the possibility of the spline count being different.
 
Bill,

I believe you mean a conversion u-joint. That would be the easiest way out. Spicer makes them. Many car parts stores carry them. If you can't find one at your local car parts store, try a local driveshaft shop.
 
if you do a conversion joint wouldnt that be off balanced. big one on one side and little on the other or would it be compensated for the difference.
 
The conversion U-joint works fine. The only thing is your not going to see much difference going from 4:10's to 3:91's. Your only talking a 150 rpm drop at 60 mph at best. IMO it isn't worth the work swapping them. JMHO
 
fishy68 said:
The conversion U-joint works fine. The only thing is your not going to see much difference going from 4:10's to 3:91's. Your only talking a 150 rpm drop at 60 mph at best. IMO it isn't worth the work swapping them. JMHO
Click to expand...

That's what I was going to say.
 
well,the biggest reason I am swapping these out is to try and find a vibration in the car. I have had the driveshaft balanced and that didnt fix it and I have a feeling that when my son changed the gears in the 4:10 he didnt do somethin right. I am goin to see if the vibration stops and if so I am going to take this 4:10 to the driveline shop and have them put my 3:55 gears back in and rebuild this rearend. Thanks guys for the info on this. It saved me a lot of trouble. Bill
 
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