transmission regearing

[motoreese]

Hello All,
I don't really know much about automatic transmissions, so here is my question.
I have an A727 Torqueflite transmission in my 69 Charger. I currently have 3:23 gears in my rear end but would like to upgrade to either 3:55's or 3:73's but don't want to destroy my already poor gas milage but would like to go onto the highway with out her screaming. I am at 2600 RPM @ 65 mph...can i get a different gear in my transmission to where 1st and 2nd are the same but 3rd is a little higher so I have better take off in 1st and 2nd with the new gears but put a higher 3rd gear for highway or do they not sell gear ratios like that?


Thank you for any positive assistance you can tell me, it would be appreciated!
Scott

[fy469rtse]

Scott ,

if you change diff gears , it going to go up in the rev's thus chewing more fuel,
have you thought about putting a shift kit in trans for better shifting, you could also put a bit more stall in convertor
but i would start with a shift kit and see if you like the change ,
1 step at a time

[myk]

Going from a 3.23 to a 3.55 isn't much of a difference.  If you're going to go through the trouble of changing your gears you need to take it all the way and at least go with the 3.73.  That would put your car screaming, but what can you do?  Short of installing some sort of over-drive device you have to choose one or the other, or a dissatisfying compromise between the two. 

Gas mileage?  Not in these cars, my friend; they're from another time and just weren't built that way...

[chargerbr549]

A couple of options, not sure if your running a small block or big block, if your running a small block you can use the 904 based auto trans from around 81 and newer that have the lower first and second gear 2.74/1.54/1.0. Obviously you would have to mess with driveshaft modifications. Or if you have the big block setup you can get a low gear setup from a few different transmission builders but they aren't cheap, that way you can keep from having to goto a lower gear in the rear.

[Mike DC]

The stock trannys didn't have a 3rd "gear".   The top gear was a 1:1 direct ratio going straight through the trans like it came in from the engine.  (The stock 4spds were the same way with the 4th gear, although the factory overdrive 4spds in the late 1970s were another story . . . )  So any kind of re-gearing the automatic trans would need to be the other direction - lowering the 1st & 2nd gears in the transmission and the 3rd ratio stays the same.  


As others have said, if you have a smallblock then this is easy.  The factory made a slightly lower-geared (the 1st and 2nd) version of the 904 trans around 1980-ish.  If you have a big block motor then this isn't so easy.  The only gearsets for the stock trans aren't cheap and you have to weigh it against the cost/benefit of a more traditional overdrive solution like a trans swap or a Gear Vendors OD.  


IMO none of the big block overdrive automatic solutions are really GOOD.  The Gear Vendors setups do fit under the car but they are several thousand bucks for only a minor reduction in highway RPMs.

If you are willing to cut the tunnel & crossmember on the car, then a later version of a torqueflite with the factory 4th gear could be installed.  

But it means work on the tranny to change the bellhousing (there is aftermarket stuff here),  and either cutting & fabricating the crossmember/tunnel area of the car to keep the rear U-joint where it belongs, or else lesser cutting and leaving the driveline angles compromised.  The 1980s/1990s 4spd automatic transmission simply does not fit under the stock '69 Charger's floor/crossmember as the factory built everything.

[John_Kunkel]

One way to manipulate the final drive ratio with a stock 727 is to install a low gearset in the trans. The low gearset has a 2.74-1 first gear ratio compared to the stock 2.45-1.

With a 3.73 rear axle ratio and the stock 2.45 first gear the overall first gear ratio is 9.14-1. With the lowgearset and a 3.23 rear end the overall first gear is 8.85-1 so there wouldn't be a huge performance loss in the lower gears.

Adding a lockup converter would lower the rpm in high gear.

[rt green]

did 4wd pickups come with the same gearset?

[John_Kunkel]

No factory 727 ever came with the low gearset, aftermarket only.

[Mytur Binsdirti]

Gas mileage?  Not in these cars, my friend; they're from another time and just weren't built that way...

Even at today's (previously) high prices, gas is still the cheapest thing that you can put in these old beaters.

[Mike DC]

Even at today's (previously) high prices, gas is still the cheapest thing that you can put in these old beaters.

I agree.

But spinning the motor more slowly is also worthwhile for helping it live longer and making the ride more pleasant.  IMO those things are worth more than the mileage itself for most old car projects.   

[John_Kunkel]

I agree, with all my modern cars having overdrive I nearly panic    when the tach hits 2000 rpm and it has nothing to do with gas mileage.

[c00nhunterjoe]

If you have a 60's car and are complaining about gas mileage, then sell it and drive a prius..... its 2 tons of car with 50 year old technology. Its not meant to get good gas mileage. Its meant to fry tires and make you smile.
2600 at 65? What tires are on the rear? Have you verified your speedometer with a gps?

[1974dodgecharger]

If you have a 60's car and are complaining about gas mileage, then sell it and drive a prius..... its 2 tons of car with 50 year old technology. Its not meant to get good gas mileage. Its meant to fry tires and make you smile.
2600 at 65? What tires are on the rear? Have you verified your speedometer with a gps?

I think he wants to do a less wear and tear setup on his engine vs MPG?  

I agree if its MPG that's the least and should none of your worries considering you have that car.  You can increase the wheel diameter by 2inchs and save 300 to 400rpm I do that with my car.  My stock magnums with tires I think were 24 diameter tires? I would spin 3k going 65 or 70 like you mentioned.  Once I creased tire size to 28inchs I can spin 3k going 77 now.......

or change that rear end.....

[500Jon]

Stay at 3.23 and rebuild the trans its probably slipping anyways.

Lock-up converter 1978ish (I think) must help the gasmiles but its a different trans as well.

If it gas miles you want go to a 360, its a torque monster lol!

Best wishes and Crude is down 30% so watch the pumps?

5J

[c00nhunterjoe]

If you have a 60's car and are complaining about gas mileage, then sell it and drive a prius..... its 2 tons of car with 50 year old technology. Its not meant to get good gas mileage. Its meant to fry tires and make you smile.
2600 at 65? What tires are on the rear? Have you verified your speedometer with a gps?

I think he wants to do a less wear and tear setup on his engine vs MPG?  

I agree if its MPG that's the least and should none of your worries considering you have that car.  You can increase the wheel diameter by 2inchs and save 300 to 400rpm I do that with my car.  My stock magnums with tires I think were 24 diameter tires? I would spin 3k going 65 or 70 like you mentioned.  Once I creased tire size to 28inchs I can spin 3k going 77 now.......

or change that rear end.....

The way i interpreted his post was:
-wants more "get up and go" then he has
-wants no decrease in gas mileage
-wants no increase in highway rpm.

Based on all of that, slap a bigblock in it and dont change the rear.

[Mike DC]

If it gas miles you want go to a 360, its a torque monster lol!

That has to be the first time I've ever heard anyone recommend a 360 for gas mileage. 

[1974dodgecharger]

seems he wants it all, LMAO 

If you have a 60's car and are complaining about gas mileage, then sell it and drive a prius..... its 2 tons of car with 50 year old technology. Its not meant to get good gas mileage. Its meant to fry tires and make you smile.
2600 at 65? What tires are on the rear? Have you verified your speedometer with a gps?

I think he wants to do a less wear and tear setup on his engine vs MPG?  

I agree if its MPG that's the least and should none of your worries considering you have that car.  You can increase the wheel diameter by 2inchs and save 300 to 400rpm I do that with my car.  My stock magnums with tires I think were 24 diameter tires? I would spin 3k going 65 or 70 like you mentioned.  Once I creased tire size to 28inchs I can spin 3k going 77 now.......

or change that rear end.....

The way i interpreted his post was:
-wants more "get up and go" then he has
-wants no decrease in gas mileage
-wants no increase in highway rpm.

Based on all of that, slap a bigblock in it and dont change the rear.

[c00nhunterjoe]

There is nothing wrong with wanting it all. Thats a good place to start. But you have to be realistic with your goals and understand that everything about it will be give and take. Take mine for example; i have a respectable high 12- low 13 second 383. It doesnt have the off idle tire shredding torque that the more tame 440's do, but it makes plenty of power midrange and top end with enough lowend grunt to get the car moving faster then most hondas and the majority of mustangs i stumble across. I traded 70 mph highway cruises for a badass 60' by changing my fear end to a set of 4.88's. I can still cruise at 55 comfortably for my engine build and that is plenty for the roads i cruise. Had i left 2.76's in mine, she would have been a total turd up to 40 mph and the fuel economy would not be drastic. I used to get roughly 14 mpg with the auto/3k converter and 2.76's. Now with the 4spd/4.88's im sitting around 11ish. When you look at that change in the big picture, i go about 48 miles less per tank then before, and costs roughly $10 per tank more to go the same distance now as it did with 2.76's. So for me, $10/fillup was a worthwhile trade to have a car that screams and is a blast to drive i stead of a turd that cruised at 70mph. I find backroads cruising ALOT more fun then highways.

[Kern Dog]

Lots of good advice here.
I had a Gear Vendors overdrive in my 70 Charger. The OD ratio is a .78 to one which isn't that great compared to the OD ratio in most newer cars. At the time I also had a high stall torque converter to match the camshaft in the engine. The car wasn't much fun to cruise. The whole reason for the GV OD was to get better fuel economy on long trips, yet the high stall converter made the car feel lazy below 3000 rpms. At 70 I'd be at or around 2600-2800 rpms with a 3.91 diff and 27 1/2" tires. The car felt lazy until I floored it, then it took off like a rocket.
I sold the gear vendors and went back to direct drive but have yet to switch to the 3.55 gears that are wainting on a shelf. MAN the engine screams on the freeway! Even though I consider the .78 ratio to be pretty meager, it did drop the RPMs several hundred at freeway speeds.
There are companies making a  bolt in overdrive for these cars but they are S P E N D Y !! A company bought the parts and tooling from Shafi Kiesler and started building the 4 speed OD auto based on the General Motors 700R4/ 4L60E transmission. The kits start at $4999 and go as high as $6500. The OD ratio in those transmissions is a much better .70 to one, reducing cruise RPMs by almost a third. TWO drawbacks to those transmissions that I see: ONE) Cost. That kind of money is an investment that may take a LONG time to balance out as compared to the savings in gas and engine wear and tear. If you drive 1500 miles per year, you are only saving a couple hundred a year in gas. TWO) The gear ratios of that trans have a wide spread. 3.06 for first and 1.62 for 2nd? Really? If you run it up in 1st and upshift, the RPM drop going into 2nd is so great that the engine may lug until getting back up into the rpm "sweet spot". 3rd ratio is 1 to 1. These transmissions were originally designed in the late 70s for 305 and 350 engines making around 200 HP. They require internal upgrades by the supplier to handle the 500 HP that many of our big blocks are making now.

[Mike DC]

   
The Gear Vendors deal is better suited to an auto trans with a lockup converter.  But if you have a trans new enough for a lockup converter then it probably already has overdrive. 

[John_Kunkel]

The gear ratios of that trans have a wide spread. 3.06 for first and 1.62 for 2nd? Really? If you run it up in 1st and upshift, the RPM drop going into 2nd is so great that the engine may lug until getting back up into the rpm "sweet spot".

One would think so but I've have two cars with the 700R4 and it's not really a big issue.

[Kern Dog]

I think the ratios of the 700 are fine for stock engines with a wider power band. I had an 84 Chevy truck for 9 years and also swapped a 700 R4 into a 76 Camaro I had. Both had nearly stock engines. In theory, it seems to me that a 2nd gear ratio closer to 1.8 or 1.9 might be better.

[Mike DC]

     
Yeah, the downside of a wide gear spread totally depends on the engine.  A high-revving race engine will hate it.  A workhorse torque motor in a pickup will hardly notice.

[c00nhunterjoe]

904's were 2.70 in 1st and 1.54 i. 2nd. That pretty much the same split as the 700r4 and nobody complains about the 904's. If memory serves me the later od's such as the 500 and 47rh style trans that alot of guys swap to are a 2.74ish 1st and 1.5 2nd.

[John_Kunkel]

The low gearset in the 904 is '80 and later only, same gear in the A500 OD. Swapping these gears into an earlier 904 helps the performance in some installations.

727-based transmissions only had one gearset.