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#1071431 - 07/25/21 01:15 AM Posi for my 87 SS  
Joined: Nov 2015
Posts: 7
BT87SS Offline
New Member
BT87SS  Offline
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Joined: Nov 2015
Posts: 7
Hillview Ky
Ok! I've been through a dozen posi trac discussions and none have given me the info I need . First off my all stock 87 SS doesn't have a posi. Second I have acquired one from a friend that didn't know he had one in his stash. Now it looks like the ring gear is smaller and the pinion is larger so I'm assuming it's a 2.29 Mine is a 3.73. Can someone tell me if I can put my 3.73 on the spool of the 2.29 or do I have to put a thicker 3.73 ring and pinion to make up the differencein the carrier height . Thanks !

Last edited by BT87SS; 07/25/21 03:14 AM.

87 SS,55 Belair
#1071432 - 07/25/21 02:12 AM Re: Posi for my 87 SS [Re: BT87SS]  
Joined: Jan 2000
Posts: 5,391
mmc427ss Offline
20+ Year
mmc427ss  Offline
20+ Year
Member

Joined: Jan 2000
Posts: 5,391
Pottstown, Pa
Count the teeth on the donor pinion, divide it into teeth on the donor ring gear, this will tell you the ratio. Most times the ratio is stamped on the side of the ring gear.
Typical the ring and pinion are sized for a certain carrier size. As in a 3 series carrier or 4 series. The thickness of the ring gear determines the series needed. Typically most carriers are 3 series. The 87 SS is a 3 series.
From what I see for the aftermarket carrriers the split is 3.23 and up go on a 3 series carrier.

I old days when you would put a 4.88 gear on a 3 series carrier a spacer was available to compensate for the difference. Don't know if that's possible with a 7 5/8" carrier.

So can't say that a ring gear in the low 2's ratio will fit a 3 carrier, or a 3.73 fits on a 2 series carrier.
Check that ring gear ratio on the donor ring and pinion first.
If you had both the old open carrier from the 87 and the new donor posi in hand you can measure the thickness of the flange the ring gear bolts on to. If they are both the same thickness the swap could precede. It's that thickness that determines carrier series to match ring gear thickness.
Bob

#1071433 - 07/25/21 02:28 AM Re: Posi for my 87 SS [Re: BT87SS]  
Joined: Jan 2000
Posts: 5,391
mmc427ss Offline
20+ Year
mmc427ss  Offline
20+ Year
Member

Joined: Jan 2000
Posts: 5,391
Pottstown, Pa
Here ya go, I just couldn't find his website a few minutes ago. Go to page 36 of this pdf catalog. Read the NOTE about carrier series/ring gear ratio.
https://tomsdifferentials.com/2011catalog/2017_Web_Catalog_Dec5.pdf

I've bought from Gary several times over the years. It was a good place to buy quality rear parts for a good price. And, they would talk to you.
Bob

#1071434 - 07/25/21 03:31 AM Re: Posi for my 87 SS [Re: BT87SS]  
Joined: Nov 2015
Posts: 7
BT87SS Offline
New Member
BT87SS  Offline
New Member

Joined: Nov 2015
Posts: 7
Hillview Ky
Ok ! Thanks so much for all the info. I saw where I could use the series 2 and use a thicker ring gear set with it. I changed my post after I saw the info I was looking for. Then you guys wrote your info and it made me feel a lot better about what I had. I didn't want a locker in there. I've heard a lot of bad things and tire wear. I think a limited slip is the way to go if you want to have fun and not break things.


87 SS,55 Belair
#1071437 - 07/26/21 01:08 AM Re: Posi for my 87 SS [Re: BT87SS]  
Joined: Dec 1999
Posts: 11,890
86ttop Offline
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86ttop  Offline
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Member

Joined: Dec 1999
Posts: 11,890
Brooksville, Fl
I didn't read all the above, but the short answer is no


Leo Paugh
It's not an attitude, it's just the way I am.
POW*MIA
You are not forgotten
If things improve with age, I must be approaching magnificent. thumbs
#1071456 - 07/28/21 11:45 PM Re: Posi for my 87 SS [Re: BT87SS]  
Joined: Nov 2015
Posts: 7
BT87SS Offline
New Member
BT87SS  Offline
New Member

Joined: Nov 2015
Posts: 7
Hillview Ky
Ok I went to Tom's Diffs and it says I can use a thick gear with
a series 2 housing to fit into my series 3 housing. Thanks you
mmc427ss!!


87 SS,55 Belair

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