1979 C3 rear gear
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1979 C3 rear gear
Hello,
I am currently in the process of swapping a 1999 LS1/ 4L60E trans in to my 1979 C3. I sent my PCM out to get tuned and one of the questions is my “rear gear”. How could I tell my rear gear?
Thank you
I am currently in the process of swapping a 1999 LS1/ 4L60E trans in to my 1979 C3. I sent my PCM out to get tuned and one of the questions is my “rear gear”. How could I tell my rear gear?
Thank you
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From: Virginia
Since there is a chance your rear differential could have been rebuilt with different gears, the most definitive way to check is this:
Raise the rear of the car on jackstands. Have a helper place a mark or piece of tape on the driveshaft. Turn the rear wheel while your assistant counts the driveshaft revolutions. In my 79, this was 3.5 turns, so 3.55:1 gears. In my 80, it was just over 3 turns, so 3.07 gears.
Raise the rear of the car on jackstands. Have a helper place a mark or piece of tape on the driveshaft. Turn the rear wheel while your assistant counts the driveshaft revolutions. In my 79, this was 3.5 turns, so 3.55:1 gears. In my 80, it was just over 3 turns, so 3.07 gears.
Thread Starter
Advanced
Joined: Oct 2017
Posts: 60
Likes: 6
Since there is a chance your rear differential could have been rebuilt with different gears, the most definitive way to check is this:
Raise the rear of the car on jackstands. Have a helper place a mark or piece of tape on the driveshaft. Turn the rear wheel while your assistant counts the driveshaft revolutions. In my 79, this was 3.5 turns, so 3.55:1 gears. In my 80, it was just over 3 turns, so 3.07 gears.
Raise the rear of the car on jackstands. Have a helper place a mark or piece of tape on the driveshaft. Turn the rear wheel while your assistant counts the driveshaft revolutions. In my 79, this was 3.5 turns, so 3.55:1 gears. In my 80, it was just over 3 turns, so 3.07 gears.
Thanks
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Race Director
Joined: Mar 2017
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From: Virginia
One possibility is that you have a 2.72:1 gear (or 2.87:1), though those ratios only ever came in the aluminum Dana differential, and only in 81 and 82, but a PO could have swapped them out.
These cars have positractiton differentials, so I didn't think to ask before, but which way was your other rear wheel turning at the time? Mine turn together, but if your other wheel is bound or sticking, it may have changed your readings.
Last edited by Bikespace; Apr 18, 2020 at 07:31 PM.
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That's what I counted, too.
One possibility is that you have a 2.72:1 gear (or 2.87:1), though those ratios only ever came in the aluminum Dana differential, and only in 81 and 82, but a PO could have swapped them out.
These cars have positractiton differentials, so I didn't think to ask before, but which way was your other rear wheel turning at the time? Mine turn together, but if your other wheel is bound or sticking, it may have changed your readings.
One possibility is that you have a 2.72:1 gear (or 2.87:1), though those ratios only ever came in the aluminum Dana differential, and only in 81 and 82, but a PO could have swapped them out.
These cars have positractiton differentials, so I didn't think to ask before, but which way was your other rear wheel turning at the time? Mine turn together, but if your other wheel is bound or sticking, it may have changed your readings.
Race Director
Joined: Mar 2017
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From: Virginia
As it should. So 2.72 gears, I s'pose (possibly 2.87). At least that's my best guess.
Do you recall what RPMs you had at a certain speed on the highway? 60 MPH would have been just a hair over 2000 RPM.
https://spicerparts.com/calculators/...rpm-calculator
Do you recall what RPMs you had at a certain speed on the highway? 60 MPH would have been just a hair over 2000 RPM.
https://spicerparts.com/calculators/...rpm-calculator
Thread Starter
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Joined: Oct 2017
Posts: 60
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As it should. So 2.72 gears, I s'pose (possibly 2.87). At least that's my best guess.
Do you recall what RPMs you had at a certain speed on the highway? 60 MPH would have been just a hair over 2000 RPM.
https://spicerparts.com/calculators/...rpm-calculator
Do you recall what RPMs you had at a certain speed on the highway? 60 MPH would have been just a hair over 2000 RPM.
https://spicerparts.com/calculators/...rpm-calculator
Thank you