Rear axle gear ratio change
#1
Junior Member
Thread Starter
Rear axle gear ratio change
So I have a 1986 camaro with factory 2.72 open diff and I want to go up to 3.73s. Has anyone done this swap before and is willing to share their knowledge with me? Both the factory and donor differentials have drum brakes
#2
Supreme Member
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Re: Rear axle gear ratio change
If you have a donor thirdgen rear with 3.73s and both are drums, about the only thing you might have to worry about are the threads on the brake lines. If they're the same year, it'd be a bolt-in swap. The speedometer will be off about 15-20mph. To make it read correctly, you would change one or both of the gears in the trans tail shaft. Probably have to change the "sleeve" for the driven gear too, since they're different based on tooth counts.
An 86 Z28 with a 305 could be TPI or carbed. Carb shouldn't mind a bit to have 3.73 gears. TPI would probably get a little cranky about it, since 3.73 gears will push the RPMs high enough that the engine will rev out of TPIs "sweet spot" too quickly.
An 86 Z28 with a 305 could be TPI or carbed. Carb shouldn't mind a bit to have 3.73 gears. TPI would probably get a little cranky about it, since 3.73 gears will push the RPMs high enough that the engine will rev out of TPIs "sweet spot" too quickly.
#3
Senior Member
Re: Rear axle gear ratio change
you wont be able to put 373s in the rear end you have. I tried. the housing is too small. you will need a completely new rear end. I have a 305, 700r4, 273 open rear end and the shop said the largest gears that will fit that housing is 308s. I wasn't going to pay $600 for 308s so I left it 273s for now. I used an rpm calculator and I decided 355s are better.
#4
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Re: Rear axle gear ratio change
It's not the housing that's the problem with a higher gear ratio, it's the carrier. The actual differential that the ring gear bolts to. 3.08 and down use one size carrier, and up use a different one. They make higher gears that will bolt to a 2-series carrier, but it doesn't really matter if the entire axle assembly is being changed.
#5
Re: Rear axle gear ratio change
you wont be able to put 373s in the rear end you have. I tried. the housing is too small. you will need a completely new rear end. I have a 305, 700r4, 273 open rear end and the shop said the largest gears that will fit that housing is 308s. I wasn't going to pay $600 for 308s so I left it 273s for now. I used an rpm calculator and I decided 355s are better.
#6
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Car: 89 Firebird
Engine: 355 TBI
Transmission: 700R4
Axle/Gears: 10 Bolt.Posi-3.73s
Re: Rear axle gear ratio change
Did the exact same swap. Except I swapped the whole rear end out being it was a very low mileage piece. Both were drum brake it was a quick easy swap. My speedo is way off now and I have a VSS and buffer box to deal with on the 89 which is why I haven't changed it. Yours wont be bad you have the cable speedo you only have to change the speedo gears to correct yours. I have the correct speedo- drive gears if you want to go through with that later id be willing to let them go for what I have in them.
#7
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Re: Rear axle gear ratio change
When you go outside of the factory supported gear ratios, it's still just a matter of having the correct drive/driven gears. There are online calculators for figuring the number of teeth needed.
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#9
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Re: Rear axle gear ratio change
if you go to richmond gears website they make the 373 that fits in the #2 carriers now no need to switch the diff https://www.richmondgear.com/wp-cont...n1.pdf#page=27
#10
Junior Member
Thread Starter
Re: Rear axle gear ratio change
Thanks for the input guys! I forgot to mention that the donor diff is a factory posi with 2.72s as well
#11
Re: Rear axle gear ratio change
The factory limited slip slip differential will be an Auburn. There is a good chance that it is already worn out or close to it. If you want to give it a try then you can get the thick gears that fit the 2 series Auburn. If you don't want to take a chance on the Auburn then I'd recommend a complete kit with a new 3 series LSD, new gears and a USA Standard installation kit from Quick Performance. http://www.quickperformance.com/GM-7...t_p_20409.html
#12
Junior Member
Thread Starter
Re: Rear axle gear ratio change
I figured its about as worn out as mine or more. I am very limited on funds so i dont think I'll be able to buy a new diff. I'll probably take a chance with the 2 series. Thanks for the link to the parts!
Last edited by Red86SS; 01-20-2018 at 08:43 AM.
#13
Junior Member
Thread Starter
Re: Rear axle gear ratio change
Did the exact same swap. Except I swapped the whole rear end out being it was a very low mileage piece. Both were drum brake it was a quick easy swap. My speedo is way off now and I have a VSS and buffer box to deal with on the 89 which is why I haven't changed it. Yours wont be bad you have the cable speedo you only have to change the speedo gears to correct yours. I have the correct speedo- drive gears if you want to go through with that later id be willing to let them go for what I have in them.
#14
Supreme Member
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Re: Rear axle gear ratio change
Never throw good money after bad. If you can't afford to do something right, find a way to save the money and do it later.
3.73 gears with a worn out differential will make for a smoky passenger's rear tire. But if you're not getting traction, you're just burning rubber. Might just as well get a peg leg 6cyl rear and run it as is.
3.73 gears with a worn out differential will make for a smoky passenger's rear tire. But if you're not getting traction, you're just burning rubber. Might just as well get a peg leg 6cyl rear and run it as is.
#15
Senior Member
Re: Rear axle gear ratio change
It's not the housing that's the problem with a higher gear ratio, it's the carrier. The actual differential that the ring gear bolts to. 3.08 and down use one size carrier, and up use a different one. They make higher gears that will bolt to a 2-series carrier, but it doesn't really matter if the entire axle assembly is being changed.
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Engine: 305
Transmission: T5
Axle/Gears: 4:10
Re: Rear axle gear ratio change
https://www.thirdgen.org/forums/transmissions-drivetrain/750865-hesitation-4-10-gears.html
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Car: 89 Iroc, saved from scrapyard
Engine: 350 vortec w/stealth ram
Transmission: 85 corvette 700r4
Axle/Gears: 3.73 posi
Re: Rear axle gear ratio change
Did the exact same swap. Except I swapped the whole rear end out being it was a very low mileage piece. Both were drum brake it was a quick easy swap. My speedo is way off now and I have a VSS and buffer box to deal with on the 89 which is why I haven't changed it. Yours wont be bad you have the cable speedo you only have to change the speedo gears to correct yours. I have the correct speedo- drive gears if you want to go through with that later id be willing to let them go for what I have in them.
Thanks
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