heminut
Well-Known Member
Mopar 8 3/4" (8.75) Ring and Pinion for 741, 742, or 489 case
8 3/4" ring and pinions for 741, 742, or 489 cases. Various ratios.
www.doctordiff.com
Students building a 1972 Plymouth Barracuda w/392 HEMI!
- Thread starter SpartanGarage
- Start date
www.doctordiff.com
SpartanGarage
Member
Is LSD desirable?
heminut
Well-Known Member
Yes, but not mandatory. There's one for sale right now on the forum;
FOR SALE - 3.23 Sure Grip
3.23 Sure Grip out of a Cuda. It worked, but I would clean and put new seals in. 489 case. Pics didn't upload, working on it!! $375.
www.forebodiesonly.com
It shouldn’t be too bad with what you have in there. You are within the range of Mopar recommended gears.
as stated by others .. the 2:76 will be "OK" and gas milage will be great. But you're going to be lacking that take off acceleration. 3:23 should be a happy middle ground. I have 3:91 behind a 440 - 6 pack and Tremec 5 speed (unknown specs). The tires keep wanting to roast off every time I drive it.
My wife is in love with purple so we're definitely in for a raffle ticket or two when they go on sale!
My wife is in love with purple so we're definitely in for a raffle ticket or two when they go on sale!
Mr Cuda
Well-Known Member
I would still reccommend 3.73 gears, with 3.55 at a minimum.
SpartanGarage
Member
There is a gentleman near me with 3.23 and suregrip. Spoke to the students today to get their input. Are you saying these 2 wont have much of a difference?
Xcudame
Well-Known Member
What a wonderful project! And welcome to FEBO from the desert! This will be a great learning experience for your students. You've come to the right site for any questions you might have as theses guys are awesome in their knowledge of all things Mopar and E-Body in particular! I have learned so much from this site that it's amazing!
If you can get the 3.23 gears at a really good price (say less than $500) and they're in good shape, they will be much better than the highway 2.76 gears!
If you can get the 3.23 gears at a really good price (say less than $500) and they're in good shape, they will be much better than the highway 2.76 gears!
Challenger RTA
Well-Known Member
Run the numbers. It's all a matter of personal preference from here. And sometimes what is available. The tire diameter has to be considered. Myself 3:23 or 3:55.
Vehicle Speed Gear Ratio Calculator & Formula Online Calculator Ultra
Transmission Calculator
Speed (km/h) = Engine RPM × Tire Diameter (mm) × π × 60 × Transmission Gear Ratio × Differential Gear Ratio × 1000000
Gear Ratio Calculator
Gear Ratio Calculator - Strange Engineering
Vehicle Speed Gear Ratio Calculator & Formula Online Calculator Ultra
Transmission Calculator
Speed (km/h) = Engine RPM × Tire Diameter (mm) × π × 60 × Transmission Gear Ratio × Differential Gear Ratio × 1000000
Gear Ratio Calculator
Gear Ratio Calculator - Strange Engineering
Last edited:
SpartanGarage
Member
Today students have the driveshaft installed however when you shift the transmission into 1st the yoke hits the shift shaft. My guess is the shaft is about 1 inch too long.
Todays lesson was bleeding hydraulic circuits. The Seniors were bleeding the clutch and the junior class bleed the brakes.
When they finished bleeding the clutch, it was a good thought process of why does this clunk and stop in 1st gear but when in 2nd and Reverse it rolls fine and when clutch is let out it engages?
Had a few minute conversation and put the car up in the air to find only in a rolled forward or back just a bit it would shift fine. then I was moving the car back and forth in 1st lightly for them to discover why its truly important to measure twice cut once! Speaking with SST about it. Not sure if it had anything to do with the car was on the lift and we measured with unloaded suspension and now measuring it with the car on the 4 post lift.
On another note the 392 HEMI fired up today. And of course there is a check engine light! haha. runs great! got to test the clutch and let it warm up a little bit. When we get a seat finished we shall back the car out and back in but not until the driveshaft gets sorted out. Then its off to the paint shop!
Todays lesson was bleeding hydraulic circuits. The Seniors were bleeding the clutch and the junior class bleed the brakes.
When they finished bleeding the clutch, it was a good thought process of why does this clunk and stop in 1st gear but when in 2nd and Reverse it rolls fine and when clutch is let out it engages?
Had a few minute conversation and put the car up in the air to find only in a rolled forward or back just a bit it would shift fine. then I was moving the car back and forth in 1st lightly for them to discover why its truly important to measure twice cut once! Speaking with SST about it. Not sure if it had anything to do with the car was on the lift and we measured with unloaded suspension and now measuring it with the car on the 4 post lift.
On another note the 392 HEMI fired up today. And of course there is a check engine light! haha. runs great! got to test the clutch and let it warm up a little bit. When we get a seat finished we shall back the car out and back in but not until the driveshaft gets sorted out. Then its off to the paint shop!
Litchkar
Well-Known Member
if it was my car, I would run 3.55 rear. Best to get 489 case, they have a larger pinion. I run a 3.23 with 15” tall tires, at 65 mph, you would be turning around 1,800 rpm. New challengers use 3.08 rears, but have 20” rims. Use this chart to calculate your rpm vs mph.
Spyder
Well-Known Member
I definitely will be buying tickets! Only thing I feel strongly needs to be changed is the gears. Good opportunity for the to learn how to set up a third member, and 2.76 is no fun at all. With that transmission, 3.73s would be my minimum, but I'd probably go 3.92s.
sixpactogo
Well-Known Member
It sounds like a great project. Thank you for reporting on it. I built my 68 Charger with a 6.1 Hemi and 545RFE Truck Transmission. Your Tremec gear ratio is not far off from mine. I use a 3.23 sure grip that works great for me but I don't race my car. I wanted some decent mileage so my car runs about 1700 RPMs in 5th gear giving me 20+ miles per gallon. Your 392 will deal ok with the 2.76 gear and a 30" tire but IMO the 3.23 gear would be better. 3.55 gears are great for a 4 speed car but are getting a little too low for that 392 5speed. The only thing I don't like about your part list is that GM fuel regulator/filter. They are supposed to regulate the fuel at 58psi but my 6.1 didn't like it at all. I ended up swapping it out for an adjustable regulator with a gauge. Maybe my regulator was just a bad one I am not sure. I never tested it. I am sure who ever wins that raffle will be a happy person. If I were 20 years younger I would be buying a ticket too. Good Luck with your project and your kids will be proud of their accomplishments and your help. Carry on Bro.
Spyder
Well-Known Member
I went from 2.76 open rear to a Dr. Diff 3.55 sure grip in my 440 Challenger. I'm currently thinking about/almost completely decided on going down from 28" to 26 or 27" tires for the rear because I now wish I had gone with 3.73s. 
Mine currently has 275 60R15's in back and 235s in front. It's due for tires before spring and I'm going to go down to 255 60R15s. I love the look of the big drag radials in back but it's just not doing quite what I want.
I love this project for the kids. My dad bought me a '63 Thunderbird when I was 14 or so and I got to work on it in high school auto shop. Got me started on a more expensive lifelong hobby than meth ever could have been!
Mine currently has 275 60R15's in back and 235s in front. It's due for tires before spring and I'm going to go down to 255 60R15s. I love the look of the big drag radials in back but it's just not doing quite what I want.
I love this project for the kids. My dad bought me a '63 Thunderbird when I was 14 or so and I got to work on it in high school auto shop. Got me started on a more expensive lifelong hobby than meth ever could have been!
SpartanGarage
Member
SpartanGarage
Member
Getting ready for prime then plum crazy!
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