4L80E with a good controller would be the way to go. Not hard to do, and the benefits are massive. Not recommending any particular products, but here are an idea of prices. https://www.monstertransmission.com...e-Transmission-Fluid_p_5060.html#.Y1TlmHZBzIU https://www.usshift.com/pricing.shtml Other things are installation (no cost if you can do it yourself, the 4L80E is virtually a TH400 with overdrive added so will bolt pretty well straight up). And you will need to shorten the driveshaft a bit. You could pull it off for not much more than the Gear Vendor, and then have your old trans to sell and recoup some cash.....
First off, 1/0.78 = 1.28. A ratio of 0.78:1 represents 28% overdrive, not 22%. That's a fairly close ratio interval, as these things go, but: 1.28² = 1.638, which is close to typical automatic and wide-ratio manual ratio intervals (e.g. TH400's 2.48/1.48 = 1.676). That's why GV market their unit as a viable splitter. Yes, the GV unit is actually a Laycock de Normanville Type J overdrive; in fact the first ones were built out of old LdN stock. It runs at something like four times the operating pressure as the Type J, though, which accounts for its survival under serious torque. It appears that this depends only on the spring pressure in the internal hydraulic regulator, so presumably a Type J out of a Volvo or AMC can be similarly modified. I presume that the solenoid engagement arose in the original design out of the ergonomic convenience of a rocker switch on the gear lever, and the facility to lock the unit out when there is a possibility of damage, e.g. when engaging in reverse or at too low a speed. The low speed thing is due to the internal hydraulic pump being driven by the transmission output, and the low regulator pressure, but there are ways of overcoming that, e.g. an external hydraulic pressure reservoir, or a complete separate external pressure source. Likewise, there are other ways to ensure reverse lockout. I cannot see any reason this design cannot be controlled by hydraulics alone. It can certainly be done — but not with GV's blessing. I disapprove of the gatekeeping aspect of GV's business model. By all accounts they treat the members of their exclusive club very well; but they treat outsiders, like someone looking to buy a tailhousing adapter on its own, like crap. That's their perfect right, but subverting that sounds like a challenge to me. There is potential for 3D printing here.
The gear vendors comes with a computerized control system. I made my own control system for my Chevy II, which has a full manual valve body. It will only engage when the shifter is 3rd gear. I have the gv computer on the unit in my truck. I leave it in manual mode all the time, and usually engage od after I get up to about 55, when I know I wont need to slow down for a while the truck is a 59 Chevy with a mild big block, th400 and 3.54 gears. There are several ways to go. Swapping rear gears is easiest/cheapest way to drop rpm. The gv is a nice unit. The modern od automatics are good too, if you can get it set up right. I got one gv for free, and 1000 off the second, through my involvement with Drag Week. At full retail price, it's a tougher decision.
I have 1 in my 55 Chevy 355 4 spd and 3.70 rear and it works fine.Drops down to about 1800 or so at 65mph
I vote for the 2.76 8 3/4 pumpkin. The cheapest easiest route to see if it will work for you. Most of Chrysler's C Bodies from the late 60's to 1973 have the 2.76, some even SureGrips, and not to expensive. My OT Polara in my avatar has a smog 440 with 2.76's and 235/70-15 tires, no tach, but I could run down the Interstate at 90 mph all day long if I could get away with it.
I did the same thing years ago with the 9" in my 57 Ford because I wanted more highway gear. Took out the 3.55 and put a 2.73 in. It's much better on the highway, but it absolutely sucked the life out of the car off the line. An OD trans would have allowed me to keep those gears and still have a better ratio on the highway.
We put a Gear vendors in our model A truck in 2015 It's been on dragweek 7 times. And it gets driven daily . It's not so much about the gas saving$ (although it makes a HUGE difference ) but just makes the drive more comfortable, and quiet. it's a bunch easier on the motor too. IF it's about the cost difference, putting a late model transmission costs a bunch more, then you have to have a separate controller, lock up convertor, etc. The GV unit is more economical We have a 275 50-15 tire 3.70:1 gears. when you click overdrive on @ 3000 Rpms, it drops to about 2550. HUGE difference. One thing they push is you can have a 6 speed transmission by splitting the gears (like a dump truck I guess) but NOBODY ever does that shit, no sure why they even bring it up.. . The GV comes with a control box. just leave it on, it will function like any other o.d. transmission. it will shift into o.d. between 2nd-3rd gear, then 3rd comes, and it's magic. then at about 20 MPH it kicks out of o.d. then when you're at the track, just turn it off. no big deal.
I put one in my OT Plymouth, 440, 8 3/4 with 3.55's and it dropped the rpms back down into the 2.70 range. I love it.
I think if you put one of these in an RV or tow vehicle the ability to split shift would be a great advantage. Often 1 gear is too high to pull a hill and the next is too low, being able to grab one in between would be awesome.
Swapping to a 4L80E will be north of $4K if I buy decent parts from reputable suppliers, and my shopping list is probably incomplete. Thanks everyone for the thought-provoking responses. I'm going to overthink this for a while...
If I can get my hands on examples of the aluminum parts, I can render and clone them. The hardened steel parts would be a different story.
You might find the input/output shaft sizes are a bit different between the original British overdrives, and the Gear Vendors version....
@Johnboy34 The cheapest method [and forget about it , driving methods] is the change the rear-end from 3.55:1 to somewhere around 2.90:1 This gives a 20% higher gearing. AND Then to recover lost torque multiplication off the line, install a wide ratio gear-set into the TH400 You can get a 2.97 first [which is 20% lower than the stock 2.48] and 1.58 second [which is 6% lower than the stock 1.48 second] 1st gear off the line should almost be the same. [3.55 x 2.48 = 8.80:1] [ 2.90 x 2.97 = 8.61:1] https://www.speedwaymotors.com/TCI-229700-Planetary-TH400-w-2-97-1st-and-1-57-2,333592.html
or swap the gears, and put a blower on the engine. I had a mild blown 454, th400, no overdrive, and 2.75 gears in my 55 for a long time, it was a fun car to drive. When I wanted to go fast, I put in some 3.25 gears, and it was still fine for driving half way across the country.
I put a US Gear (Doug Nash) in my 65 Galaxie with a C6 and a 472 with 4.11 gears. And I drove it a bunch of times the 6 hours from my house to Detroit and back....I even have some install picks if you would like to see them. It does wine, and it is noticeable, its not a minor noise. you get used to it but you always know its there, Overall I was happy with it. They say you can "bump" the tunnel out enough for clearance but I ended up cutting the tunnel, again, I have pics if you want to see it.
The reason it whines ( I called them about it after I installed mine) was because of the way the gears are cut. Again, good unit, just noisy
The Doug Nash unit is outdated by today's standards, since a TKO600 or T56 are readily available on the aftermarket or secondary market, have better ratios, and are stronger than the Doug Nash unit. Not that there is anything inherently wrong with them, just that newer, better options are out there now. I get the impression the OP wants OD but would like to retain his good TH400.
A thought I had: rig a short-throw reverse-pattern shifter so that the action is sideways, with P to the left and D to the right. Then control the OD via a fore-aft lever mounted to that. The result is a 6-speed H-gate. It'd be simple enough to incorporate a guard which prevents the lever from moving aft into the OD position once it passes left of 1. Close intervals are a road-race thing. I find myself skipping 3rd a lot between traffic lights, but I use every ratio I've got on the twisties.
Ok, thanks! I would like to see the pictures of your install! I wonder if you have to cut out for the Gear Venders unit? Bones
It depends. As shown in the previous photo, they're long. If a car has an X-frame or an X-member, they just won't fit without major surgery. jack vines
We use GV units in a large percentage of our builds. Never a problem , we also save on shipping cause they're 2 blocks away
I put one in a friends car for him with a 400 horse sbc, saginaw 4-speed with a 3.42 rear and a 26" tire. It worked flawlessly and he beat the heck out of it regularly. He used to split gears so it turned a 4 speed into an 8 speed and really helped with acceleration as well as the final O.D. It was a very impressive unit to me.
A problem with the Doug Nash is the top of it sits 8" above the input/output and since it will be in the front seat area it may not work.
Depends on the car. In my 65 Galaxie I only had to raise a portion of the trans tunnel about2 inches. I had to raise the seat 1 inch which wasnt an issue
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