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Discussion Starter · #1 ·
Hi guys, whats needed to step from a factory 4:11 setup in a 55p down to a 3:55 ratio?
Carrier has factory "shaped" tag indicating 4:11 - verified against serious RPMs at highway speed. Great fun around town, but want to step down.
Is it a straightforward swap or what? heard chatter about spacers and you "cant go down from 3:90 carrier" (whats that about?), etc.
alleviate the myths for a new dude. Thanks,Troy

'56 2dr post 210, m22, 350, flatblack
 

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I think I'd save the 4.11 drop out section and leave it as is if its in good shape and find a usable unit that needed to be rebuilt and have a new posi carrier and 3.55 gears built up. Or advertise around for a 1 for 1 trade but I'd want to hear the gears in a running car before swapping and showing no leakage aroung the pinion flange area

Also read this thread for more information

http://www.trifive.com/forums/showthread.php?t=3200

Regards, Robert
 

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some one will correct me if I'm wrong but I believe 3 series and 4 series carriers are different. I remember putting 4:11 gears on a 3 series carrier and we needed a spacer behind the ring gear. I don't believe you can put a 3 series on a 4 series..
 

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Send TriFive.com member DZAUTO (Tom Parsons) a private message. He is one of the foremost experts on 55-64 rear axles.
 

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Discussion Starter · #6 ·
Thanks everyone, ill keep watching this thread.
Suede - thats what i heard - you can put 4 series gears in a 3 series carrier, but not 3 series gears in a 4 carrier...(dammit, i want to know why, whos idea was that)
Ill pm the DZAUTO dude and get the what for, Again Thanks.
 

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Thanks everyone, ill keep watching this thread.
Suede - thats what i heard - you can put 4 series gears in a 3 series carrier, but not 3 series gears in a 4 carrier...(dammit, i want to know why, whos idea was that)
Ill pm the DZAUTO dude and get the what for, Again Thanks.
pinion size won't let it happen.
 

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This is from one of Toms (DZAUTO) post from ChevyTalk.


FIRST, you can ONLY use 4-series (and higher) gears on a 4-series posi unit. PERIOD! There is NO WAY to install 3-series gears on a 4-series posi unit. YES, a 3-series ring gear will physically bolt onto the 4-series flange, BUT IT WILL NOT SETUP BECAUSE THE RING GEAR WILL BE TO CLOSE TO THE PINION GEAR TO PERMIT PROPER ADJUSTMENT. The flange where the ring gear is bolted is CLOSER to the pinion gear on a 4-series posi unit than it is on a 3-series posi unit.
To install ANY 3-series ring gear on the posi, will require ONLY a 3-series posi. PERIOD.

ANY 4-series (and higher) ring gear can be bolted to a 3-series posi unit simply by installing a ring gear spacer between the 3-series ring gear and the flange. Longer bolts are then required. Also, SOME gear manufacturers make extra thick 4-series ring gears so that the 4-series gear can be used on a 3-series posi unit.

So, to summerize. You CANNOT, CANNOT, CANNOT use a 3-series ring gear on a 4-series posi. You can ONLY use 4-series gears on a 4-series posi.
To use 3-series gears, you MUST have a 3-series posi unit. BUT, you CAN use 4-series gears on a 3-series posi by using a spacer, OR, using extra thick 4-series ring gears.

Below is a side-by-side comparrison of a 3- and 4-series NON-posi differential (Posi units will be the same). Notice the difference in the position of the ring gear flange. The 3-series flange is further away from the pinion. This is necessary because 3-series pinion gears are thicker than 4-series pinion gears. Thus, a 3-series ring gear must be spaced further away from the pinion gear, and the 4-series posi WILL NOT ALLOW the ring gear to be spaced far enough away to permit adjustment.
 

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Discussion Starter · #11 ·
clear as mud

Thanks guys, I read it 3 times and now can dig it.
So, while i hunt for a decent 12bolt, i guess ill stuff some 29" tires under it for the highway.
The 4:11 is pristine, original & no whining or leakage. Maybe ill keep it around for future transmission options.
 
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