81 Rearend Replacement Options
Thread Starter
Racer
Joined: Nov 2001
Posts: 478
Likes: 3
From: Huntsville AL
81 Rearend Replacement Options
Well I got the rearend out and one of the clutch retainers was broken/missing, one carrier bearing cracked, and pinion shims destroyed, looks like buba has been here also 
So need input from everyone on what is the best way to go from here. Don't think I want to go back with the weak 81 al housing so just looking for what my options would be to beef up the weak link. Looks like I will asking santa for a new rearend
www.angelfire.com/al/swhite7/temp.html
YBnormal...drive a vette
So need input from everyone on what is the best way to go from here. Don't think I want to go back with the weak 81 al housing so just looking for what my options would be to beef up the weak link. Looks like I will asking santa for a new rearend
www.angelfire.com/al/swhite7/temp.html
YBnormal...drive a vette
Melting Slicks
Joined: Mar 2006
Posts: 2,465
Likes: 0
From: Orange Park Fl
I run between 350-400 hp with my stock rear end with no problems. The '81 rear end's "problem" is that it is geared so high. If you want serious high performance, you will probably want lower rear gears (Google Tom's rear ends). God bless, Sensei
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
The only problem with your rear end is the seals went bad, and it ran dry, or your trailing arms were trash, putting undo side strain on the crush sleeves, or the strut bushings were bad, etc. Have it rebuilt properly with a better ratio, and you will never have to touch it again.As for gears, 3.08 is fine for TH-350C, or even 3.55. Definitely 3.55 or 3.73 for a TH-700R conversion.
Tech Contributor
Joined: Aug 1999
Posts: 15,176
Likes: 3,991
From: Connecticut, USA
sorry but I don't agree that the problem was from lack of oil or any of those other reasons. There are plenty of bad rear bearings out there but they are not causing the differential to fail.
These units are weaker, some have run them in front of HP engines but I sure wouldn't I believe the iron bolt up but I don't have a cover here. Dan would know or you can ship me your cover and I'll see how it matches up to one of the iron units I have here.
Go over to digitalcorvettes and there is another guy there with the same problem.
That's what I would so anyway. Build a nice HD unit and bolt it in.
Also I asked Tom one day about beefing up the 80-82 and he just said what I did- they're junk.
Sorry to be so blut but they are what they are.
These units are weaker, some have run them in front of HP engines but I sure wouldn't I believe the iron bolt up but I don't have a cover here. Dan would know or you can ship me your cover and I'll see how it matches up to one of the iron units I have here.
Go over to digitalcorvettes and there is another guy there with the same problem.
That's what I would so anyway. Build a nice HD unit and bolt it in.
Also I asked Tom one day about beefing up the 80-82 and he just said what I did- they're junk.
Sorry to be so blut but they are what they are.
Last edited by GTR1999; Dec 19, 2006 at 11:15 AM.
Race Director
Joined: Dec 1999
Posts: 16,945
Likes: 9
Yes, the earlier diff bolts up to the batwing. You will need a few additional items. You need the pinion mount bracket, the camber bracket and the straight camber rods. The original stuff doesn't fit anymore as it uses the doubled up flange of the lid & case and you loose half of that.
Burning Brakes
Joined: Jun 2004
Posts: 936
Likes: 0
From: Tulsa OK
Yes, the earlier diff bolts up to the batwing. You will need a few additional items. You need the pinion mount bracket, the camber bracket and the straight camber rods. The original stuff doesn't fit anymore as it uses the doubled up flange of the lid & case and you loose half of that.
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Premium Supporting Vendor
Joined: May 2000
Posts: 4,312
Likes: 70
From: Clearwater FL
Cast iron diffs do bolt up to aluminum batwings. Here is proof. TT is correct, you will need additional parts as well.
http://www.vansteel.com/photos/index...Thumbs&e=4&s=1
http://www.vansteel.com/photos/index...Thumbs&e=4&s=1
Race Director
Joined: Dec 1999
Posts: 16,945
Likes: 9
You don't need to alter the driveshaft, the only reason for the driveshaft length difference is because the earlier iron diff cars have a drive flange on the spindle, the later cars have just a yoke.
Dan, tha nks for those pics.. the drive flanges are only for the HD/12 bolt setup, if you use the standard stuff you do not have to notch the batwing like that.
Dan, tha nks for those pics.. the drive flanges are only for the HD/12 bolt setup, if you use the standard stuff you do not have to notch the batwing like that.
Thread Starter
Racer
Joined: Nov 2001
Posts: 478
Likes: 3
From: Huntsville AL
Thanks for the input, just a few more questions:
1. Since the carrier is not that bad, can the cracked carrier bearing cap be replaced without remachining (i.e. bolt in replacement)?
2. Will the 81 carrier fit the earlier, cast iron units or will I need to get a full up unit complete with the cast iron unit?
3. What year rearends should I look for that will mate up with the 81 batwing?
Thanks for all the input, guess I will have a lot of work to do while my TAs are sent out.
1. Since the carrier is not that bad, can the cracked carrier bearing cap be replaced without remachining (i.e. bolt in replacement)?
2. Will the 81 carrier fit the earlier, cast iron units or will I need to get a full up unit complete with the cast iron unit?
3. What year rearends should I look for that will mate up with the 81 batwing?
Thanks for all the input, guess I will have a lot of work to do while my TAs are sent out.
Race Director
Joined: Dec 1999
Posts: 16,945
Likes: 9
1: is one of those alu saddle caps broken? Just replace it, it'll probably be fine..as you will notice the mating surface of the case is not even machined but as cast!!! Or do you mean something else?
2: No, your diff is a dana 44 diff not an eaton and the carrier won't fir the earlier iron case, the later one also uses an offset planetary system and 1 stub axle is longer than the other. The eatons (cast iron stuff) use equal length stubs. You'll need the entire cast iron diff assembly sans cover.
3: all years mate up, 63-82. C4 stuff although similar looking won't bolt up, not even the C4 super Dana 44
2: No, your diff is a dana 44 diff not an eaton and the carrier won't fir the earlier iron case, the later one also uses an offset planetary system and 1 stub axle is longer than the other. The eatons (cast iron stuff) use equal length stubs. You'll need the entire cast iron diff assembly sans cover.
3: all years mate up, 63-82. C4 stuff although similar looking won't bolt up, not even the C4 super Dana 44
Tech Contributor
Joined: Aug 1999
Posts: 15,176
Likes: 3,991
From: Connecticut, USA
If you go with an iron unit then say with a 70-79 unit. The posi case's are better then the earlier one. The clutches are not too good though so you should expect to go through them.
however you can "help" it a little:
Tech Contributor
Joined: Aug 1999
Posts: 15,176
Likes: 3,991
From: Connecticut, USA
Marck is correct, those 65-69 square window eaton tend to crack more then the later ones plus they use 10-18 gears which are not too good. The 70-79's are better to use , just the clutches and ring gear bolts(76-79) are junk.
If you want to go over this, I can tell you what options/years I'd use.
If you want to go over this, I can tell you what options/years I'd use.
Heel & Toe
Joined: Dec 2005
Posts: 18
Likes: 0
Contact Gary Watson at this address www.corvetteperfection.com his rear conversion frm the dana to eaton is the best for the buck I am putting 640 HP through mine and not having a problem and was a great way to go. He is a fantastic guy and full of good ideas
Thread Starter
Racer
Joined: Nov 2001
Posts: 478
Likes: 3
From: Huntsville AL
Thanks for all the input guys, I have learned so much this week about my rearend 
To answer an earlier question, yes one of the carrier bearing caps was cracked completely into. I think buba had been there before 
, also found broken clutch retainer and pinion shims were deformed and several had worn away into almost nothing.
So I have learned:
I have a dana 44
I will need a late model iron case with a eaton carrier
And what clutches should I use, I understand there are carbon fiber out there are they any good?
So many decisions to make , guess I will start looking after the holidays for a replacement while my trailing arms are sent off and being redone.
Thanks for all the help and info
YBnormal...drive a vette
To answer an earlier question, yes one of the carrier bearing caps was cracked completely into. I think buba had been there before , also found broken clutch retainer and pinion shims were deformed and several had worn away into almost nothing. So I have learned:
I have a dana 44
I will need a late model iron case with a eaton carrier
And what clutches should I use, I understand there are carbon fiber out there are they any good?
So many decisions to make
, guess I will start looking after the holidays for a replacement while my trailing arms are sent off and being redone.Thanks for all the help and info
YBnormal...drive a vette
Safety Car
Joined: Nov 2005
Posts: 3,961
Likes: 573
From: Lompoc, CA. Santa Barbara County
I'm going the other way. I have a 79 with iron differential and steel crossmember. I am replacing the steel crossmember with an aluminum batwing, just to save the weight. Do I need to notch the batwing? I'm building brackets now, but I need help. Help may come after the new year. Thanks for the pictures Vansteel.
