Guest Jabo Posted September 15, 2008 Share Posted September 15, 2008 Hi, I'm a new member of the club but have owned my 72 since it was new. Glad to be onboard!! I've restored it back as close to original as I know how and recently refreshed the 350 to 383. My transmission is the original, I think a 350, and has a shift kit added and functions well. I'd like to be able to drive farther to shows and would love to have one more gear for better mileage. After reading several notes on the forum, I'm sure I don't need anything for the super powerful engines of the modified world. Hopefully there are those who have made transmission changes for the same reasons I want to. What is the simpleist way to get to a better gearing solution? Also what are the pitfalls of connecting such a transmission to a console shift? I don't know what gear I have at the differental but it's what ever came in the car. Thanks in advance for any advice. Jabo Quote Link to comment Share on other sites More sharing options...
stangeba Posted September 15, 2008 Share Posted September 15, 2008 Jabo, Welcome! So you are the original owner, cool. Someday I would also like to switch to an overdrive transmission for the lower engine speed and lower first gear ratio. My THM350 is original and shifts perfectly but is starting to leak again (149,000 miles now) The people here will be able to help you. Good luck, Bruce Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted September 16, 2008 Share Posted September 16, 2008 first WELCOME knowing what your rear axle ratio would be helpful, I think a 700R4 would work good for your application I am almost positive that they make a kit for the factory floor shifter to work with the 700R4 Quote Link to comment Share on other sites More sharing options...
Guest Jabo Posted September 16, 2008 Share Posted September 16, 2008 Thanks for the reply Sam, I'll see if I can determine the rear gear ratio. Do you know if the 700R4 is the same length and that the driveshaft will connect back up without alterations? Where'd you get the neat bowtie signature? Jabo Quote Link to comment Share on other sites More sharing options...
Guest Jabo Posted September 16, 2008 Share Posted September 16, 2008 Thanks for the Welcome Bruce, I wanted one badly in 70 and 71 but had to wait till 72 to get mine. Young family and new house, you know! Love the picture of you and your car. How is that created and included in you messages? My car has 190K plus now and is on it's second engine rebuild. The tranny was rebuilt and a shift kit added about 90K ago. See leaks a little too. Jabo Quote Link to comment Share on other sites More sharing options...
502ci Posted September 16, 2008 Share Posted September 16, 2008 I'll see if I can determine the rear gear ratio. Do you know if the 700R4 is the same length and that the driveshaft will connect back up without alterations? Quickest and easiest way is to jack both rear tires off the ground, put the car in neutral, mark the driveshaft with chalk or something, rotate one of the rear tires one full turn while counting how many times the driveshaft has rotated...if it rotates 2 and 3/4 times it is a 2.73...3 and 1/3 times it is a 3.31...and so on. I'm pretty sure any of the overdrive tranny's are gonna need a shorter driveshaft. Bill Quote Link to comment Share on other sites More sharing options...
monte70car Posted September 16, 2008 Share Posted September 16, 2008 yes as sam said there are kits to make the factory floor shift to work with an over drive trans. my ride has a level 2 bowtie overdrive 700r4 trans which is behind a 404 big block with 390hp. rear gear is a stock 2.73 with a power trax unit in it. the kit gives you a new dent plate and lenes, which are the only parts to change out. as for the trans you do more the trans cross member back, and some people had to cut the drive shaft down 3". there is a post that shows how long the drive shaft needs to be. for me i didnt have to cut any thing off the shaft. what kills a 700r4 is alot of heat. if you are thinking about a 700r4 talk to bowtie overdrive www.700r4.com. they also have a 200r4 and a 4l80e trans. the 200r4 is evenly geared where the 700 has a deep first gear. Quote Link to comment Share on other sites More sharing options...
kc8oye Posted September 16, 2008 Share Posted September 16, 2008 I have a 700r4 in my car and it's fantastic. But your rear gear ratio has a lot to do with it. if you have 3.08's or 2.73's I wouldn't recomend an over drive trans as you will be turning the engine at too low of an RPM and while it won't really _hurt_ anything, it may make your mileage worse, and the car will drive awful. I purposely chose the 700r4 because of it's extra low 1st gear, which really helps launch the 4000lb monte :> with my transmission in over drive with the torque converter 'locked' (I just use a switch on the dash) and my 3.55 gears in the back, with 27" tall rear tires (255/60-15) I turn 2200 rpm @ 70mph. depending on how mild your engine is, you could problaby run it lower, like around 1800 rpm, but I wouldn't try to go any less then that! i think I had to cut my driveshaft down by 6" (had a machine shop do it for me) the 700r4 worked fine with my factory column shifter, but I've since installed a Hurst Pro-Matic 2 ratchet shifter on the floor :> if you have a QuadraJet carb, the 700r4's "TV Cable" (similar to a 350's kickdown cable, yet different) will hook up just fine and work, if you use an Eddelbrock or Holley carb, you will need to get the correct kickdown lever to bolt on, and the correct cable support brackets. (holley has both of them available to fit their 4150 and 4160 carbs, the street avenger series is a real PITA in this department) Quote Link to comment Share on other sites More sharing options...
footballubet Posted September 16, 2008 Share Posted September 16, 2008 First off Welcome to the Madness! I have a 700r4 in my 71 with 3.73 gears The swap was not that painful. The driveshaft does need to be shortened about 3 inches. I had to move the crossmember back and drill the back two holes in the frame.You can get the shifter plate for the console at Shiftworks , comes with the detent and PRND plate. The only thing else is the TV cable hook up at the carb. Summit or Jeg's carries the brackets for different carbs. You can go several ways on the wiring of the lock-up. I installed a spring kit in mine and it locks up at 52 mph, and eliminates any wiring to the trans. There has been some bashing of the 700r4 in recent posts, but the guy that rebuilds the tranies for my garage said they are a good unit. So far, he's been right. Good luck in whatever you decide. Quote Link to comment Share on other sites More sharing options...
stangeba Posted September 16, 2008 Share Posted September 16, 2008 Jabo, To add a picture to your signiture, follow this: How to add a picture to your sig. Bruce Quote Link to comment Share on other sites More sharing options...
680HPStroker Posted September 16, 2008 Share Posted September 16, 2008 It's pretty much all been covered here already, but I'll put in a plug for rear gear ratio's. Anything below a 3.55 gear won't be worth the effort of installing an overdrive. If it were me I'd install an Eaton series 3 posi unit and set of Richmond 3.73 gears in the rear prior to installing an overdrive tranny. I'm still very biased and prefer a PROPERLY BUILT 700R4, but you can save little weight and use a PROPERLY BUILT 200R4. Make sure you buy a custom torque converter vise an off the shelf unit. If it were me I'd install a manual lock-up switch to delay lock-up until you want it. Finally you will have to relocate your crossmember further back and shorten your drive shaft unless you buy a custom made one. That way you can go back to a turbo 350 if you choose. There are several companies that make floor shift adapter kits for your swap. Make sure you choose a shop who specializes in overdrive swaps and builds performance units that have a reputation of holding up under severe duty conditions. Quote Link to comment Share on other sites More sharing options...
kc8oye Posted September 17, 2008 Share Posted September 17, 2008 The actual physics of the swap are amazingly simple. the 700r4 bolts in with no mods to the floor pan or cross member, you just move it back like 680hp says. the 700r4 uses the same driveshaft yoke as the TH350, so you just have it shortened, and you are ready to go. STrange Engineering has good prices on good driveshafts too.. it's worth upgrading to 1350 series ujoints just because I can't speak to the FACTORY floor shift units as my car never had one. my column shift stuff fit just fine, then I put in the aftermarket floor shifter that was designed for the 700r4. I agree with 680hp on the torque converter lock up, put a switch on the dash, but wire it thru the brake pedal switch, you will need to swap your brake light switch at the pedal for one out of a car from the 80's that had both switches. (I used one from an 89 olds cutlass cierra) I only lock the converter up when I'm on the freeway, or making long drives on the surface roads. Quote Link to comment Share on other sites More sharing options...
Guest Jabo Posted September 17, 2008 Share Posted September 17, 2008 Great advice and detailed info. Thanks to you, 680HP and the others for your experience. Jabo Quote Link to comment Share on other sites More sharing options...
Guest Jabo Posted September 19, 2008 Share Posted September 19, 2008 Bill, First of all thanks for trying to help me figure out my rear gear ratio. I hesitate sending this for fear of showing my ignorance but that's how we learn. When I jack both wheels off the ground, with the tranny in netrual,neither wheel will turn the driveshaft. I guess I need positrac for that maybe? Anyway when I put one wheel back on the ground and turn the other one the driveshaft turns one revolution with 3/4 revolation of the wheel. Is there anyway to figure the ratio from that? Jabo Quote Link to comment Share on other sites More sharing options...
Shadow Gray SS Posted September 19, 2008 Share Posted September 19, 2008 Did you try turning both rear wheels when it was on the stands? Quote Link to comment Share on other sites More sharing options...
Grease Posted September 19, 2008 Share Posted September 19, 2008 Leave one wheel on the ground and rotate the other 2 turns while counting the driveshaft revolutions . Quote Link to comment Share on other sites More sharing options...
Guest Jabo Posted September 19, 2008 Share Posted September 19, 2008 Jake, No, didn't try that but will. Thanks, Jabo Quote Link to comment Share on other sites More sharing options...
Guest Jabo Posted September 19, 2008 Share Posted September 19, 2008 Grease, Thanks, I should have figured that out!! Jabo Quote Link to comment Share on other sites More sharing options...
Phil Posted September 20, 2008 Share Posted September 20, 2008 Should be 2.56 gear. Quote Link to comment Share on other sites More sharing options...
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