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Discussion Starter #1
I'm getting ready to change out the rear end on my '69 and I'm torn between what gear ratio to go with. I'm looking at either a 3.50 or 3.70 third member from Speedway Motors, and I'm leaning towards the 3.70's. I swapped in an AOD out of a 92 gt a few years back just for this occasion, so I've got a .67 final drive. I'm running 24 wheels/tires, and it looks like I'd be turning about 2400 rpms at 70mph, which seems pretty reasonable. I'd just like a second opinion (maybe from someone who has done an AOD swap?) as to what gears you'd recommend, what you're running and how you like it? The car has a pretty mild 351w with just some basic bolt-ons and I don't ever plan on running more than 350-400hp when I do the motor. I mostly drive around town and to car shows, it's just a weekend toy not a daily driver. I doubt I'll ever take it out to the track or the strip, so I want something that will be fun to zip around town in without it thrashing the gears, but still able to drive down the highway at reasonable rpms to make it to a car show a few hours away. Thanks in advance.
 

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1st gear is just as important as OD. Calculate that as well. Too much and it might bark 2nd before crossing an intersection. Another complaint you might find is when it wants to go into OD, that low it might want to do it [email protected] cruise then its a dog unless you keep foot in it to hold the lower gear.
Even without knowing what the AOD has for ratios I'd pick the 3.50s. Why go 70 @2400 when you could be going 80?:cool:
 

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I currently have a 3.50 rear gear, AOD and 27" rear tire. If my 3.70 wasn't so damn noisy, I'd run them. Plan to set up my 3.89's to run.
 

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Discussion Starter #5
Appreciate the feedback everyone. Sounds like between the two, 3.70’s are the way to go then?
 

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BAl, what gears does your axle have now ? if you're cruising two hours to get there, I wouldn't choose either of those, especially with the extra short tires. How about 3.00 or 3.25s ? If you want more acelleration, swap in the wide ratio first instead of what you have now. ( 2.84 / 2.48 ) LSG
 

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I'd go minimum 3.70 but most likely 3.89. If It is never really going to see the highway, 4.10's would be a hell of a lot of fun.
 

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Discussion Starter #8
BAl, what gears does your axle have now ? if you're cruising two hours to get there, I wouldn't choose either of those, especially with the extra short tires. How about 3.00 or 3.25s ? If you want more acelleration, swap in the wide ratio first instead of what you have now. ( 2.84 / 2.48 ) LSG
I have 3.00 (I swore it was a 3.08, but I pulled the tag today and it says 3.00) gears right now and it’s a dog with the AOD. I don’t usually drive it on the highway, I just wanted to be able to if I need be. According to my calculations, I’m sitting at around 1970 rpms at 70 mph right now, and with the 3.70’s, I’ll be at about 2400. Seems like that should be okay for the occasional road trip...I hope. I’m probably more concerned with it barking through the gears too fast in town now, but then again, got a lot of guys saying they’d go with an even shorter gear with their AOD, so I guess we’ll see. I went ahead and ordered the 3.70 unit before their Black Friday sale ended, sure hope it suits my needs. If not, I have a good sob story for my wife when I tell her I really need those 16” magnum 500’s I’ve been wanting, lol.

Fun side note, this started off as a repair job on a leaky master cylinder. Of course I had to check out the brakes “while I was at it”. Then it became a rear disc swap...then a new third member while I had the whole thing torn down. Here I am $2k later because of a $40 master cylinder...it’s one heck of a slippery slope fellas. Thanks again for your help, guys.
 
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