Opinions Wanted: Overdrive Transmission Swap Options

[70_440-6Cuda]

In getting opinions about rear end gear ratios I opened another can of worms and am down the road of transmission swaps.

Looking for a swap that can be done without any modifications to the chassis / body, something bolt in. 

I looked at the Silver Sport option and like the idea a lot, would make the car way more drivable, but pretty pricy at $6700 all in.
https://www.shiftsst.com/mopar/c233

Also looking into the 518 / 46RE (my understanding is the difference being electronic control)

Found this vacuum kit for the lock up  / OD.  Problem there is I may have an issue with vacuum with the cam I choose. plus I am assuming much better control with electronic
https://transmissioncenter.net/shop/patc-727-to-518-46rh-conversion-kit-click-here-for-727-to-46rh-swap-wiring-diagram/

Looking for feedback on what others have done.  Seems like there are a few options like going with a complete kit, or buying a crossmember and piecing it together yourself

Am I correct in assuming that hydraulic vs. electronic control will have the same shift pattern / quality, and the control will only affect the OD?  I will be planning on either buying the transmission newly built for my application, or sourcing one and having it rebuilt for my application

[Katfish]

Here's a link to some of the info lost from the other website.
This covers maybe the 1st half.

https://www.diyauto.com/manufacturers/plymouth/generations/barracuda-gen3/diys/727-to-a518-swap-a-novice-guide-by-360fish

It would be more work with BB, there are solutions where the 518 housing is cut, and the BB bell bolts up.

I put together a nice solution for automatically controlling the OD and LU so you aren't flipping switches.

I've been driving mine for 10yrs and absolutely love it!

[Katfish]

Gear Vendors is another option a lot of people use.

[Mr Cuda]

 Once you start modifiying, it never ends. First the bellhousing, and case cut. Then a 518/46 with a dana is going to make for a really short driveshaft.
 So a lowered ride height is going to be a challenge for u joint angle as the slip spline will be farther back and lower.
 You weren't thinking of keeping the 4.10's and crutching it with o.d.were you?
 Large cam? Hope its a roller. Check with your engine builder on lowest run speed for your flat tappet cam spec.
 With all that torque, skip the 3.54, and get a 3.31 dana gear set.
 No o.d. required.
 I'm running 3.54 with a 4spd and 27" tires. I've never considered freeway rpm to be high.
 Automatic probably adds 100-150 rpms over stick at some speeds, depending on converter. Factory high stall needs to run at 2600 to prevent converter flash, which will build heat and cook the trans.
 Or you can do a standard 727 lockup.
Just need a 75? (forget what first year is) big block lockup case and maybe an aftermarket stall lockup converter. Then your cruise rpm matches a manual.
 

 
 

[Cudajason]

Once you start modifiying, it never ends.
 
 

But that is the fun part!

[chargerdon]

on my 74 Chally with 360sb 408 stroker and Lunati 703 cam i put in the A518 46RH and i love it !!  To control both overdrive and lockup torque converter i installed 2 toggle switches onto the console.   Of note it that i am still running with 14" (25" diameter) tires and 3.23 sure grip.   The torque converter is a 2000 lockup stall.

First, discovered that you can simply leave the toggle switch for overdrive on all the time !   If you do the tranny will start in 1st, shift normally to second, and then into 3rd.  All NORMAL except the shift to overdrive then also takes place about 2 seconds after 3rd.   I rarely engage the lockup on the torque converter except at highway (60 mph plus speed) and you MUST turn off before coming to a stop !! 

With this combination 70mph and in OD i run around 2,600 RPM...nice and quiet and then with lockup engaged it drops another 300 down to 2250.   

Some day ill install a 50psi transmission oil pressure switch for the lockup torque converter so that i dont have to worry about remembering to turn it off before coming to a stop.   Engine vacuum isnt used, it simply screws into the oil pressure diagnostic port on the tranny and should hit 50 psi at about 50mph.

[Katfish]

For your situation, GV would be the least intrusive.

https://gearvendors.com/hrdodge3s.html

[70_440-6Cuda]

Oh man!! Lots of great info!  As for the modifying part, I agree it is the fun part.  I tend to get an idea in my head and then MUST find a way to engineer a solution, especially when it is a challenge.

For a little more info, I don't have engine specs yet, but here is what was discussed:
Stock bottom end balanced / blueprinted, aluminum heads, aftermarket 6 pack intake (port matched/polished), mad ignition, factory carbs set up for application, hydraulic roller cam, roller rockers. Cam selection is up to the builder, I just asked for a nasty idle with lots of lope because who doesn't love that sound?  I will also be running the 15" steel wheels and stock height tires; which I realize will be the limiting factor of all the power and torque, so maybe a set of drag radials to swap on and off.

I was thinking of going 4.10, or more likely 3.73, with the OD - I like the idea of 2600 rpm cruising speeds- just so much more enjoyable

@Katfish what was your solution to get away from the switches?

[Katfish]

Switches work, but I wanted a better solution.
The problem is not shifting into OD, it's downshifting that can be an issue.  During a panic stop, or even just normal stopping, you forget to flip the switches back and the car lugs.





Completely automatic, wanted my daughter to be able to drive it.
The control module automatically turns on/off the overdrive and lock-up for the transmission.

The 518 (46RH) is hydraulically controlled and uses 2 servos to enable the OD and LU.
The 3-pin connector on the transmission supplies the control voltages.
The center pin always has 12V power connected.  The 2 outer pins are switched grounds.  The front pin is the OD ground, the rear pin is the LU ground.

The module works according to the following sequence.
1) The 12V toggle switch supplies voltage to the relays and transmission center pin.
2) When the hydraulic pressure trips (50mph/adjustable) the pressure switch, ground is supplied to the vacuum switch.  When speed is below 50mph, hydraulic switch opens, disabling OD.
3) When there is enough vacuum, the vacuum switch closes, providing  the OD relay ground.  Under heavy acceleration, vacuum drops, opens switch, OD is disabled.
4) When OD relay has ground and 12V, it waits 10sec, then supplies 12V to the LU relay and ground to the transmission OD pin, enabling OD.
5) Now the LU relay has 12V, it's already grounded.  It waits the 10 sec programmable delay then provides ground to the transmission LU pin. So lock up doesn't occur until OD has been enabled and on for 10sec.
6) The programmable delays for both relays fix the situation when speed is fluctuating around 50mph.  This would normally cause the OD to kick on/off, the 10 sec (programmable) delay stops this from happening.

Flipped the washer pump bracket and it makes a perfect cradle.

[Brads70]

Katfish that's pretty darn impressive. Electronics are not my strength.  I bet you could market a kit and do well at it.

[70_440-6Cuda]

@Katfish what rear gearing and tires are you running and are you mated to a small block?  You mentioned the challenge with a big block - can you elaborate?.

Has anyone used the gear vendors kit?  Seems like a very easy solution.
My car was originally a 4.10 gear ratio - anyone running that set up and with what tires?  Disadvantages?  I am struggling to make a decision on rear gear ratio - I do not plan on tracking the car ever, but also long distance drives are probably not going to happen - car will be used for local shows, around town stoplight to stoplight burnouts and general local nonsense

I had a Shelby Cobra replica with 3.73s, a Tremec 5 speed  and 15" rear tires (I forget the size but would be similar considering the limited choices) and that seemed just about right

I will definitely overdrive, just not sure which one yet - I am now down the rabbit hole of tire selection - I originally though Polygalas as they just look so damn good - but the lack of performance kills it for me so i need to find an alternative

[Katfish]

I have a Dana with 3.73s
Rear tire is 275/40/18
Take a look here for the BB mod needed for the 518
https://board.moparts.org/ubbthreads/ubbthreads.php/posts/35994.html

[70_440-6Cuda]

Man, that seems just about right -

Anyone running 3.54 rear gears and how do they like them, would love not to spend an extra $450 to swap out what I have

@Brads70 I was doing some homework and saw your post that you swapped in 4.10s - just wondering why you decided on 4.10 and how the drivability is?

I am leaning towards keeping the 3.54s that I have, especially with the 440 having tons of torque to begin with

[Brads70]

Man, that seems just about right -

Anyone running 3.54 rear gears and how do they like them, would love not to spend an extra $450 to swap out what I have

@Brads70 I was doing some homework and saw your post that you swapped in 4.10s - just wondering why you decided on 4.10 and how the drivability is?

I am leaning towards keeping the 3.54s that I have, especially with the 440 having tons of torque to begin with

I find it perfect with my combo. Reason I swapped from 3:54-4:10 is with my engine combo it lugged at hwy speed. I had to drive at 80 MPH to avoid lugging. With the A41 first gear it launches really hard. I like that!    Fuel economy did drop a little with this swap but who builds these cars for fuel economy. Went from 18 to 15 if I remember correctly.

[dodj]

I am leaning towards keeping the 3.54s that I have, especially with the 440 having tons of torque to begin with

I'm wondering what kind of torque the 518 is capable of handling?