EL CAMINO 78-81 vs 82-up rear ends

[jjjaffo]

Okay folks, forgive me for this question. Why is there a split in years for the 7.5" rear ends? Is it just the wheel studs are different or are some internals different too? Such as bearings? The reason I ask is I plan to upgrade the rear end in my 1980 Elky. Nice 350/350 drivetrain and want to do a 3.08 gear with 28 spline axles and posi unit. Anything I need to know?

 

[Streetbu]

Standard, and meteic wheel studs is the only difference that I know of. I've owned and worked on g-bodies since '94

 

[jjjaffo]

Standard, and meteic wheel studs is the only difference that I know of. I've owned and worked on g-bodies since '94

Interesting. I just read a post from 2020 that mentioned something about a pinion bearing being different. I'm hoping more people chime in and put this to rest so I can build this rear end. Right now the 2.56 gears are killing this poor thing.

 

[79 USA 1]

Interesting. I just read a post from 2020 that mentioned something about a pinion bearing being different. I'm hoping more people chime in and put this to rest so I can build this rear end. Right now the 2.56 gears are killing this poor thing.

Yes!
76-80 used a larger rear pinion bearing. Timken #89449 cone #89410 cup which has a 3.125 outer diameter
81 up uses the Timken #89249 Cone #89210 cup which has 3.00 outer diameter.

Also keep in mind that A/G bodys with the 7.5/7.625 rears were 26 spline axles but the aftermarket does support 28 spline sets as well 8.5 axle shafts from the Grand National and 442 will work. I believe they need about .030 taken off the C clip end for proper end play.
Carrier cases change for 3.08 down and 3.23 up. You can buy spacers or "Thick Gears" to use s 3.08 down case with taller gears.
Lastly the 7.5 and 7.625 is the same case, Just a ever so slightly wider (.125) ring gear.

Sorry for the long winded explanation
Hope this helps.

 

[jjjaffo]

Yes!
76-80 used a larger rear pinion bearing. Timken #89449 cone #89410 cup which has a 3.125 outer diameter
81 up uses the Timken #89249 Cone #89210 cup which has 3.00 outer diameter.

Also keep in mind that A/G bodys with the 7.5/7.625 rears were 26 spline axles but the aftermarket does support 28 spline sets as well 8.5 axle shafts from the Grand National and 442 will work. I believe they need about .030 taken off the C clip end for proper end play.
Carrier cases change for 3.08 down and 3.23 up. You can buy spacers or "Thick Gears" to use s 3.08 down case with taller gears.
Lastly the 7.5 and 7.625 is the same case, Just a ever so slightly wider (.125) ring gear.

Sorry for the long winded explanation
Hope this helps.

Thank you for the explanation. So, I need to get the 76-80 bearing kit. Then I can use a 7.5/7.625 posi unit with 28 spline side gears and my gear of choice without issue? I will get a series 2 carrier for the 3.08 gear set.

 

[79 USA 1]

Thank you for the explanation. So, I need to get the 76-80 bearing kit. Then I can use a 7.5/7.625 posi unit with 28 spline side gears and my gear of choice without issue? I will get a series 2 carrier for the 3.08 gear set.

Correct.
You will need the 28 spline axles. The 3.08 gear set will be fine with the 2 series carrier as that was the factory break point.
In my 79 Monte Carlo (Parts Car now) I ran a Detroit Locker with KA axles out of Toms Differentials. Great axles and people to work with.

Toms Differentials

Axles ring and Pinions kits, bearings+seals Differentials U Joints, yokes, pads tom's custom parts merchandise Are you a Jobber or Distributor? signup for discounts and SAVE $$$ Tom’s Differentials…

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[jjjaffo]

I have to ask a question about these 7.5" rears. The word is always steer clear of them for performance as they will not hold up. Is that stock only, or modified too? I ask this because all the complaints I read most people don't mention if the rear end was modified.
From my own personal experience 20yrs ago with an 84 Cutlass, with a 408 BBC and turbo 400, I quickly blew the hell out of two factory posi units and twisted 3 sets of factory axles. Back then I didn't know any better so I bought a beefy Auburn posi, Richmond 3.42 gears and 28 spline axles and complete installation kit. This rear end then took everything I threw at it including 13.3 1/4 mile passes. The trans had a nasty 1st to 2nd shift that was like getting hit with a bat. In 20yrs not a single problem with that rear end. When modified, at what power level will they fail?

 

[Streetbu]

When sticky tires are used and you can get traction, that's when the bad stuff happens.

 

[Kamloops cutlass]

Are you 100% sold on 3.08s ?
Still pretty lazy gear in my opinion
If you just putt around or do highway driving it’s fine but on the street 3.42s will feel more energetic
Just my $ 0.02 worth , I may be overcharging 😁

 

[jjjaffo]

Are you 100% sold on 3.08s ?
Still pretty lazy gear in my opinion
If you just putt around or do highway driving it’s fine but on the street 3.42s will feel more energetic
Just my $ 0.02 worth , I may be overcharging 😁

I actually had 3.42 gears in my 84 Cutlass. They were a really fun gear but I hated the rpms at highway speeds. Now, the engine didn't care but my ears did.
The 350 I have is a nice warmed over rebuild with plenty of power. Compared to the 2.56 gears, the 3.08 will be noticeable. I want the 3.08 for long drives on the interstates and a little bit of gas mileage. Plus I'm running the original 14 inch rally wheels on it.