Chevy Tri Five Forum banner
1 - 7 of 7 Posts

·
Registered
Joined
·
8,575 Posts
Discussion Starter · #1 ·
Hi and do I have a question that I could use a little help with. I am restoring a '56 Chev. that came with a 3.55 ring and pinion. This was a non-posi unit. I refused to pay the inflated prices for a posi unit at local meets/swaps. Instead, I opted to buy a new Eaton unit for less money. I brought the rear and posi unit to the installer along with a spacer ring. He tried to get the proper mesh/depth but said he couldn't. He suggested to contact Eaton because something didn't appear right. I did call them and spoke with an engineer/representative. Explained the problem and he asked about the rear.
I'm an older fellow and don't always hear the best. I do believe that he did say this posi unit wouldn't fit a '56 Chev. that came non-posi from the factory with 3.55 gears. Does this sound possible or maybe I didn't hear him right. Does anyone have any experiences witht his issue? I'm presently thinking about trying an Auburn unit. Again, any experiences with this unit? Thanx for anything you can offer, Carmine.
 

·
Registered
Joined
·
845 Posts
Hi and do I have a question that I could use a little help with. I am restoring a '56 Chev. that came with a 3.55 ring and pinion. This was a non-posi unit. I refused to pay the inflated prices for a posi unit at local meets/swaps. Instead, I opted to buy a new Eaton unit for less money. I brought the rear and posi unit to the installer along with a spacer ring. He tried to get the proper mesh/depth but said he couldn't. He suggested to contact Eaton because something didn't appear right. I did call them and spoke with an engineer/representative. Explained the problem and he asked about the rear.
I'm an older fellow and don't always hear the best. I do believe that he did say this posi unit wouldn't fit a '56 Chev. that came non-posi from the factory with 3.55 gears. Does this sound possible or maybe I didn't hear him right. Does anyone have any experiences witht his issue? I'm presently thinking about trying an Auburn unit. Again, any experiences with this unit? Thanx for anything you can offer, Carmine.
I believe you must have a posi hoghead. The non posi hogheads have a rib inside that interfere with the original posi units. But I have no experience with the Eaton units.
 

·
Administrator & Tech Articles
Joined
·
52,787 Posts
Carmine.....Your post reminded me of a post about posi conversions over at CT.....See link:http://www.chevytalk.org/fusionbb/s...08/post/1990268/hl/posi/fromsearch/1/#1990268

Here is what's important:Make dang sure the shop is familiar with the process of removing a portion of the gusset that is in 57-64 NON-posi cases which MUST be done to add a posi into a NON-posi case. And that portion of the gusset that is removed MUST be removed all the way back to the wall of the case.





 

·
Registered
Joined
·
845 Posts
Wow, Great Pictures Pops!!! But is it ok to cut the rib out of a non posi, will it hurt the hoghead case??:trytofly:
 

·
Registered
Joined
·
845 Posts
Does anyone know if grinding the rib out of a non posi case will hurt anything? Is this what alot builders do if they don't have a positrac hoghead:confused0006:??
 

·
Registered
Joined
·
559 Posts
Tom Parsons wrote a great article of the very installation you are asking about on the Corvette Forum for C-1's. Has pictures and step by step.
 

·
Registered
Joined
·
37,967 Posts
The problem is not the gusset, though it may need to be cut down.

The problem is that 55-56 ring gears are a bit thinner than 57-64 ring gears, and that the flange on the differential case is machined to accomodate this.

The Eaton differential, and the stock Dana differential, are machined to work with 57-up gears only.

You have two solutions:

1) Use a 57-up gear set.
2) Put a spacer between the ring gear and differential, and use longer bolts.

I think this has been documented here recently. Certainly it's been documented on Chevytalk.
 
1 - 7 of 7 Posts
Top