Rear end gears
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Joined: Mar 2023
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Rear end gears
Hey guys, I just got off the phone with a major performance parts store. I was/am looking to put lower gears in it to put the new power to the ground better.
I was told with the 8.5 independent rear end there is only 2 options. 3.45 and 3.70 which I have. Does anyone know if there are any manufacturers that make shorter gears for this rear end?
I was told with the 8.5 independent rear end there is only 2 options. 3.45 and 3.70 which I have. Does anyone know if there are any manufacturers that make shorter gears for this rear end?
Tech Contributor
Joined: Aug 1999
Posts: 15,154
Likes: 3,959
From: Connecticut, USA
Ok.
First, you spoke with the wrong people. It helps if you know what you're selling but I guess that doesn't matter much anymore as long as you read off a pc.
Your iron diff, if original, has a 3 series case in it. The actual condition of your diff is a whole different story, but the 3 series case will accept 273-308-336-355-370-373-390-411-433-456 std and thick gears. The USA Made gears are gone today but you might find some NOS US Gear. Not all the ratios are available today and some have been gone for years, ie the 273's.
There are a lot of places reboxing gears and selling them but they come from Richmond-Yukon- Motive- all imported. I have used all 3 they setup but I still like US Gear better, NOTE- Do not confuse US Gear with US Standard Gear, they're not the same nor are they made in the USA.
New power is interesting, depending on what you have and plan on doing. A stock 79 diff has a good posi case and spiders, but has lousy clutches, ring gear bolts, and axles. Not checking it or correctly addressing it will result in failure over time. How fast that happens depends on you and the condition the diff is in.
First, you spoke with the wrong people. It helps if you know what you're selling but I guess that doesn't matter much anymore as long as you read off a pc.
Your iron diff, if original, has a 3 series case in it. The actual condition of your diff is a whole different story, but the 3 series case will accept 273-308-336-355-370-373-390-411-433-456 std and thick gears. The USA Made gears are gone today but you might find some NOS US Gear. Not all the ratios are available today and some have been gone for years, ie the 273's.
There are a lot of places reboxing gears and selling them but they come from Richmond-Yukon- Motive- all imported. I have used all 3 they setup but I still like US Gear better, NOTE- Do not confuse US Gear with US Standard Gear, they're not the same nor are they made in the USA.
New power is interesting, depending on what you have and plan on doing. A stock 79 diff has a good posi case and spiders, but has lousy clutches, ring gear bolts, and axles. Not checking it or correctly addressing it will result in failure over time. How fast that happens depends on you and the condition the diff is in.
Thread Starter
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Joined: Mar 2023
Posts: 61
Likes: 8
Wow, thanks so much. New power is a 383 stroker. Had to change from 4 speed to auto, because I wear a prosthetic on my left leg. So no clutch for me. The 3.70 gears are just way to tall for what I'm doing with the car. I plan to autocross it, hopefully later this year. Every inch of my car gets very good attention from my shop guys.
Thread Starter
Advanced
Joined: Mar 2023
Posts: 61
Likes: 8
Ok.
First, you spoke with the wrong people. It helps if you know what you're selling but I guess that doesn't matter much anymore as long as you read off a pc.
Your iron diff, if original, has a 3 series case in it. The actual condition of your diff is a whole different story, but the 3 series case will accept 273-308-336-355-370-373-390-411-433-456 std and thick gears. The USA Made gears are gone today but you might find some NOS US Gear. Not all the ratios are available today and some have been gone for years, ie the 273's.
There are a lot of places reboxing gears and selling them but they come from Richmond-Yukon- Motive- all imported. I have used all 3 they setup but I still like US Gear better, NOTE- Do not confuse US Gear with US Standard Gear, they're not the same nor are they made in the USA.
New power is interesting, depending on what you have and plan on doing. A stock 79 diff has a good posi case and spiders, but has lousy clutches, ring gear bolts, and axles. Not checking it or correctly addressing it will result in failure over time. How fast that happens depends on you and the condition the diff is in.
First, you spoke with the wrong people. It helps if you know what you're selling but I guess that doesn't matter much anymore as long as you read off a pc.
Your iron diff, if original, has a 3 series case in it. The actual condition of your diff is a whole different story, but the 3 series case will accept 273-308-336-355-370-373-390-411-433-456 std and thick gears. The USA Made gears are gone today but you might find some NOS US Gear. Not all the ratios are available today and some have been gone for years, ie the 273's.
There are a lot of places reboxing gears and selling them but they come from Richmond-Yukon- Motive- all imported. I have used all 3 they setup but I still like US Gear better, NOTE- Do not confuse US Gear with US Standard Gear, they're not the same nor are they made in the USA.
New power is interesting, depending on what you have and plan on doing. A stock 79 diff has a good posi case and spiders, but has lousy clutches, ring gear bolts, and axles. Not checking it or correctly addressing it will result in failure over time. How fast that happens depends on you and the condition the diff is in.
Tech Contributor
Joined: Aug 1999
Posts: 15,154
Likes: 3,959
From: Connecticut, USA
First we need to be speaking the same language in order to communicate.
The Housing is actually termed by GM as the carrier.
The posi inside the carrier is the case.
The carrier or housing is the same for either 3 or 4 series gears. 4 series gears from GM were a performance option with certain engine/trans combo's but by 79 the car was being faded away. I don't believe any 4 series gears were available then. The difference between the case is the thickness of the mounting flanges since the ring gear thickness changes with the ratio.
However, it is now 44 years later, who knows if you still have the original diff or if it has been rebuilt. The only sure way is to remove and check it or do a tire to pinon yoke rotation check.
