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Need a transmission pro's advice

Miccara

Miccara

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Brampton, Ontario
I replaced the entire rear end in my 69 RR with a 3:90 gear. Car is factory manual. Of course the 3:90 makes it pretty much un-drivable on the highway. I knew this would be the issue and I am prepared to go with an aftermarket 5 speed. What gear ratios 1st, 2nd, 3rd, 4rth, final (because I don't know tranny's at all), will keep the performance of the 3:90 (somewhat), but get me highway ability. If I could cruise at 2500ish at 60-65mph I'd be happy. I was looking at some Tremec transmissions... opinions on those would be appreciated, and, any other options???
 
All you do is closely match the gear ratio to the 833, from 1st to 4th. The 5th gear is overdrive, which would reduce your RPM's on the highway.
 
i run a gear vendor with 4:56 Gears and absolutely love it !!
 
Gotta figure your rpm at your expected highway cruise, and whether your engine build has enough torque to hold speed effortlessly at that rpm without lugging or detonation. Stick close to factory ratios for 1-4, and if your engine has decent low end torque, go way big on the overdrive ratio.
 
Gee a 3.90 with a 28" tire should be fine on the highway. If not go to a 3.23.
 
Try the various sites like Tremac or American Powertrain and see about there calculators for final drive feel and ratio/rpm reductions.

You can get an idea if you know the final drive ratio of the trans.
In example if it was a .69 OD ratio, just multiply that number by your rear gear.
3.91 X .69 = 2.6979
 
Miccara said:
55mph is about 3500rpm with my 440. Just too much for a relaxing drive up the hwy.
Click to expand...
3400 with 4:11 and 29.5 inch tires. Would a taller tire get you to the 3000 range?
My 383 does not like to do the hwy thing below 3200 so I am fine with the 3400 at 70.
 
mopar 3 B said:
3400 with 4:11 and 29.5 inch tires. Would a taller tire get you to the 3000 range?
My 383 does not like to do the hwy thing below 3200 so I am fine with the 3400 at 70.
Click to expand...

My tires are Redline 26" so yes, a taller tire will help some.
 
Miccara said:
My tires are Redline 26" so yes, a taller tire will help some.
Click to expand...
That's your Problem 26" Tires ?? No Way ! IMO 28" minimum, im running a 30" tire on 4:56 Gear runs Awesome on the HWY.
 
I have 28" tires & 4.10 gear. 65 on the highway is about 3200 rpm. Sure wish it was less.
 
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