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Discussion Starter #1
hi, i have a 67 gto with 3 speed t400 and 3.55 diff, all is fine but it does rev high when driving around town, and uses a fair bit of petrol too, petrol is not a big concern i dont drive it much, but when i do drive it would be much better if it cruised at lower revs, i have read about the gear vendor overdrive, and also a bit about more modern transmissions, i dont want to chop up the car to fit a trans, but if one can be fitted with minor mods that might be interesting, has anyone any ideas on trans or gear vendor overdrives, thanks
 

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In spite of what's said, Gear Vendor's requires floorpan mods to fit. That, and it's kind of clunky/truck like in shifting in and out of OD. Very, very strong, though. I agree with Eric: a modified/upgraded modern OD trans....probably a 200R4, as it is basically a bolt in deal.
 

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Discussion Starter #5
In spite of what's said, Gear Vendor's requires floorpan mods to fit. That, and it's kind of clunky/truck like in shifting in and out of OD. Very, very strong, though. I agree with Eric: a modified/upgraded modern OD trans....probably a 200R4, as it is basically a bolt in deal.
hmmm not keen on messing with car so floorpan mod puts me off, i might look into the 4l60e some say its the go....probably end up leaving car as is but if i really could find a perfect solution without issues it would be tempting...
 

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Discussion Starter #6
after lots of reading today i am now really confused, so many different opinions, the 200r4 seems very popular if built strong by someone who knows the box.....but then the electronic ones like 4l60e might be the go as they can be controlled better, or 4l80e, bugger too many options, i was leaning towards the gearvendor but now more towards the 200r4, but like the electronic box if it fits correctly, i'm going to email a few sellers and see whats on offer...
 

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Be careful of "marketing hype". Just about every OD solution is going to require at least some amount of modification to the floor pan and/or crossmember to fit, some more than others. The Gear Vendors unit is bullet-proof strong. You didn't mention anything about your engine combination, how much power/torque you're making, etc and that has a significant impact on what will "live" behind it. Yes, it's possible to build one of the "smaller" transmissions (700r4, 2004r) so it'll survive behind a strong Pontiac, but it's not easy/cheap --- and not everyone actually knows how to do it. Getting the job done right adds to the cost, of course. I'd recommend trying to find and talk with people who have cars similar to yours and who've actually added OD to their cars to find out what their real experience has been. That's a little more difficult and takes more time, but is worth the effort in the long run. Hitting all the "big" Pontiac forums and asking is a good start. Places like here, Pontiac Street Performance, Performance Years, Pontiac Zone... That approach can have its pitfalls too, on the larger forums you can run into folks who have "strong opinions" but little or no actual experience so you have to learn how to separate the wheat from the chaff, so to speak. No matter what anywone says, don't start down any particular road unless it makes logical sense to you.

Bear
 

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fiesta, seriously, the cheapest and easiest solution for you by far is to simply remove your rear end assembly (very easy job) and bolt in a rear end with a 3.08 or a 3.23 gear ratio. Entire, decent 3.08-3.23 8.2 ten bolt GTO rear ends can be had in the States for less than $500 if you shop around. Totally easy, totally reversible, NO mods. I pulled the original 3.36 rear end out of my '67 GTO 3-4 years ago and replaced it with a 2.56 rear end that was given to me. An afternoon job. I love it: the car now gets over 20MPG at 75-80mph, is quiet, and much more pleasurable to drive. So, if it were me, I'd mothball the 3.55 you have and find a 3.23-3.08 and bolt it in.
 

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Discussion Starter #9
Be careful of "marketing hype". Just about every OD solution is going to require at least some amount of modification to the floor pan and/or crossmember to fit, some more than others. The Gear Vendors unit is bullet-proof strong. You didn't mention anything about your engine combination, how much power/torque you're making, etc and that has a significant impact on what will "live" behind it. Yes, it's possible to build one of the "smaller" transmissions (700r4, 2004r) so it'll survive behind a strong Pontiac, but it's not easy/cheap --- and not everyone actually knows how to do it. Getting the job done right adds to the cost, of course. I'd recommend trying to find and talk with people who have cars similar to yours and who've actually added OD to their cars to find out what their real experience has been. That's a little more difficult and takes more time, but is worth the effort in the long run. Hitting all the "big" Pontiac forums and asking is a good start. Places like here, Pontiac Street Performance, Performance Years, Pontiac Zone... That approach can have its pitfalls too, on the larger forums you can run into folks who have "strong opinions" but little or no actual experience so you have to learn how to separate the wheat from the chaff, so to speak. No matter what anywone says, don't start down any particular road unless it makes logical sense to you.

Bear
hi bear....i have learnt with all the things i have done on car that many dont work out as advertized so i hear you, have not looked at pontiac street performance forum, overdrive would be nice but its not critical car is ok with 355, but i figure if i can overdrive it correctly with zero issues and it all works as expected then i would seriously consider it, also i dont want to mess with floor pan or any nasty mods, a beefed up 200r4 from possibly art carr sounds interesting he gave me all the info on parts needed for the tv cable, but still i'm not sure about it many have problems with the setup.....308 rear hmmm maybe ....
 

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Discussion Starter #10
fiesta, seriously, the cheapest and easiest solution for you by far is to simply remove your rear end assembly (very easy job) and bolt in a rear end with a 3.08 or a 3.23 gear ratio. Entire, decent 3.08-3.23 8.2 ten bolt GTO rear ends can be had in the States for less than $500 if you shop around. Totally easy, totally reversible, NO mods. I pulled the original 3.36 rear end out of my '67 GTO 3-4 years ago and replaced it with a 2.56 rear end that was given to me. An afternoon job. I love it: the car now gets over 20MPG at 75-80mph, is quiet, and much more pleasurable to drive. So, if it were me, I'd mothball the 3.55 you have and find a 3.23-3.08 and bolt it in.
gidday gt, yes my friend here who helps me thru the maze also suggested go a 308 chevy 12 bolt....i might just reconsider this option, really car is fine with 355 but now i have the pypes 2.5 inch system its a little louder in cabin, not bad but when car is cruising with revs up it just feel like i need another gear, really with the short drives i do i shouldnt worry but i'm the perfectionist so maybe a 308 rear, i will give it some more thought, obviously am concearned about off the line acceleration i'm not drag racing but i like a bit of fun now and then, do u think i would notice a big drop in acceleration from the 355 to 308 ....i already have 275/60/15 rear tires 28 inch tall i think, i didnt notiice any loss in acceleration when i put on taller tires, but 355 to 308 ?...thanks
 

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That "how much" question is subjective. Will you be able to tell a difference? Yes. Will it be "a lot"? Well, that depends on what you call "a lot". That is the one down-side of addressing your issue by changing the rear gear: you're trading off-the-line acceleration for better highway manners. Although, with that famous Pontiac bottom-end torque the difference may not be as drastic as you'd suspect. The only way to "have your cake and eat it too" is to go with some sort of overdrive system, and as you've already discovered, that path has its compromises as well. If not having to modify the car and also ease of installation are major concerns for you, then a rear gear ratio change is probably the best way to go. If both those concerns are more significant to you than, say, cost and originality, then another alternative would be to switch to an aftermarket Ford 9" axle that's custom made to fit your car. They're never-have-to-worry-about-it-again strong, and if you're willing to purchase more than one center section with different gear ratios then you have the option of running whatever gear ratio you want with just a couple hours of work. I have a Moser 9" in my car and I love it. For the moment however I do just have one center section :D

Bear
 

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Fiesta, it won't pull as hard from a dead stop. But it will pull much harder at 70mph and above. A perfect (and easy to find) compromise ratio is a 3.23. Doesn't sound like it, but a world of difference from a 3.55. BTDT, on a few GTO's. 3.23's will cruise very nicely at high speed, and still be a terror off the line. I gave up a lot off the line with my drastic change from 3.36 to 2.56, but when I'm cruising 90mph at 3000 rpm, or shifting into 3rd at 105mph, it manages to put a smile on my face. So: a bolt-in beefed up 200r4, or a bolt in 3.23 or 3.08 rear end. Your choice, but both choices are good ones.
 

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Discussion Starter #13
thanks for all the info on tranny thoughts but at this point i have decided to put the change on hold and stay original, still an idea but not urgent or really needed, but might revisit the idea later down the track....
 
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