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Rear end change

Miccara

Miccara

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Currently running an 8.75, posi 3:90. Just too much for street (in my opinion). Tired of cruising at 50mph! I was going to drop in a 3:55 - but now I'm thinking 3:23. Thoughts guys?

Car is a 4 speed, 440. Pushing 475hp.
 
When from 3.23 to a 3.54 dana for years like the extra gear. 3000 at 68 mph with appox 26" tire. Sold the 3.54 dana and switched to 4.10, got old 5 miles later. Unless you do a lot of 75 to 80 mph cruising 3.55 is a good compromise . I don't do conversions kph .:canada:
 
Miccara said:
Currently running an 8.75, posi 3:90. Just too much for street (in my opinion). Tired of cruising at 50mph! I was going to drop in a 3:55 - but now I'm thinking 3:23. Thoughts guys?

Car is a 4 speed, 440. Pushing 475hp.
Click to expand...
Myself, I prefer tall gearing,,,,with 475 hp & 4 speed, the 3:23 would give some great legs, usable power for more than a straight line. Just the way I think.
 
going from the 3.90’s to 3.55, you’ll see a 12% reduction in rpm (or if you maintain the same RPM, you’ll see a 12% increase in cruising speed). 50mph becomes 56mph.

You’ll see a 17% difference going to 3.23’s. 50mph becomes 59 mph.

I run 4.10’s but never cruise the interstate. The few times I did it was pretty annoying, so I get it. If it were me, I’d do the 3.23’s then if the power seems down, maybe do something to boost the power a bit down the line.
 
The 3:23's will be just fine. You have plenty of torque with that 440 engine.
Plus any highway driving you do will be nicer.
 
If cruising is what you are looking for, 3.23s it is. If some of both and you don't drive the car every day, then go 3.55s. All about what you are trying to accomplish
 
With 3.55s in mine I'm over 3000rpm at 60mph. I'm always on the highway for at least the first 20 minutes so I'm thinking to swap it to my 3.23 nonSG.
 
Glenwood said:
With 3.55s in mine I'm over 3000rpm at 60mph. I'm always on the highway for at least the first 20 minutes so I'm thinking to swap it to my 3.23 nonSG.
Click to expand...

You must have a really short tire. I’m running 4.10’s with 30” tires and I’m at 3000 rpm at 60-62 mph or so.
 
I think I'm gonna go with the 3.23's. The car has plenty of power and it would be nice to do some highway driving to a few different cruise nights! Thanks your opinions helped me decide. It'll be nice to see a little more gas mileage too! ;)
 
A Guy on here(most likely has my old 68 post 440 Coronet now a pro-street)is running 4:56 with a 727 with a tailshaft mounted Gear Vendors OD. In OD His final drive reduces to 3:20.
 
Bladecutter said:
A Guy on here(most likely has my old 68 post 440 Coronet now a pro-street)is running 4:56 with a 727 with a tailshaft mounted Gear Vendors OD. In OD His final drive reduces to 3:20.
Click to expand...

I considered a few options OD unit being one. Tremec the other. Problem is being Canadian. Friggin' Tremec with instal kit would run me probably close to $7000 Canadian. Just too tall a price for me.
 
Was reading this article.. On converting a 727 to use the 46RH tailshaft It would be cheaper by far to do this type of conversion. https://www.hemmings.com/magazine/mus/2006/07/Chrysler-A-518-Overdrive-Transmission/1301453.html

Was looking into this but there seems to be some controversy as to if it actually will work. PACT transmissions sells a kit to do this conversion.

I swapped from a 3:91 55mph@ 4000 rpms to a 3:23 55mph@ 2500 rpms. Still not great but not nearly as bad. 27 inch tall cooper cobras.

Here is the article from PACT very informative and gives the correct info on how to do the swap. https://transmissioncenter.net/shop/727-to-518-transmission-swap-information/

Funny thing is I have all the stuff to do this. I have a 95 ram with a bad transmission. And the motorhome 727 One day I might try and do this. I've never worked in the internals of a transmission. Might be worth just dicking around with it.
 
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If the car is mainly for cruising, go with 2.76 or 2.94! I went to a 2.94 with a 70 383 Challenger and hiway mileage jumped from 12 to 16. Couldn't believe it but wasn't going for mileage but more to run the highways doing 80. :D Car still had plenty of off the line power too. If you want the best of both worlds, go with an OD trans or a Gear Vendors unit.
 
Miccara said:
I considered a few options OD unit being one. Tremec the other. Problem is being Canadian. Friggin' Tremec with instal kit would run me probably close to $7000 Canadian. Just too tall a price for me.
Click to expand...
Guy told me the New Gear Vendors unit was just over 2500.00
 
Yea that gear vendors unit is expensive. After re-reading some of that Hemmings article I think they are talking about A-518 and A-727 which are small block applications, couldn't get any information on the big block aspect of the swap.
 
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I'm putting 3.23's in mine to start with. I have a set of 2.94's on the shelf just in case I want to road trip more. I won't ever go lower than 3.55 in mine, I could care less about racing.
 
I have 293's in my 67.. Its a 440/torqueflite car... I still wish it had an overdrive in it for the freeway... No problem beating most of the cars from a red light if that's what you want to do..
As a kid I had an A12 super bee with 410 butt gears... I hated them and it made the car pretty worthless except for around town... I swore I would never have low gears like that again....

Car online pic.jpg
 
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