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I as my name says have a 73 GTO & I run 3:73's in the rear end. I've had them in there for about 20+ years now. I bought my car new with 3:08's . Out on the road the 3:08's were great, you could get out & go & my top end was some where around 140-150. I don't really know as I've only went as fast as I could once with it & it got me a ticket in 1975 going back to my ship when I was late getting back. The cop was really great & we had a long talk & he & the other cop had a good laugh about it. I ended up getting a warning ticket out of it. A few years later I switched to a 4 speed & hated the 3:08's in it then. I installed the 3:73's in it a years later & I love those gears. I get around 16 MPG running about 60 MPH. If I step it up from there the mileage goes down but not enough to want to go o a lower gear set. With the 3:73's & the 4 speed I run , it's an M-22. It comes out of the hole great & I run mid 11's in the 1/4 so I will keep them. Those gears are the best thing I have ever done for the car. I am running a 462 with Eldo. alum. heads & a RA IV cam 1:65 rockers, performer RPM intake & a Q-jet. The pistons are SRP forged with Eagle H-beam rods. I have RA IV exhaust manifolds to. I've had several different combos of engines in my 73 over the years but so far this set up works the best for me.
 

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Wow, great thread. I just read the whole thing looking for the answer to this question - will a 8.2 BOP rear end from a 1967-1972 A-body bolt right up in my '64 A-body? I understand it's an inch wider, I was more concerned with the spring pads, control arm and shock mounts, etc. Thanks...
 

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Ended up with a '68 GM 8.2 with an Eaton 3.08 posi from JD Race and Restoration. Got a good deal and he did a great job with the pallet and wrapping. I was leaning toward the 3.23, but I have to say I love this 3.08 with the M20 now that I've put a few miles on it. I also got the sway bar and boxed control arm kit from Ames, Gas-adjust shocks and did the rest of the bushings while I had it apart, handles great now. Road trip tomorrow to stretch it out a little. I set aside the BOP 2.56 one-legger for future, uh, whatever.

Great thread, it was good to read everyone's stories before pulling the trigger.
 

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Discussion Starter · #127 ·
3.08 was the tallest gear Pontiac put behind a 4 speed. It will be decent off the line, and excellent at cruise, mid-range, and top end. For a car that's driven on today's $4 gas, you'll never regret it. Slightly less oomph than the 3.23 from a dead stop, but far superior at highway speeds, and better overall mpg. Your engine will use less gas, run cooler, and run longer. Great choice, IMO.
 

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I have run 3:55's in a 70 GTO and find it the best of both worlds. Its behind a stroked 474 CID motor. Behind the motor is a new autogear M-22. The car has been to North Carolina, and up to to Maine. Does about 3000rpm at 70mph. I was running a 750 Holly 4150, but found out replacing the carb with a AED 850HO carb the car breaths a lot easily and less restrictive that was noticeable. The gas mileage on the highway actually got better by a few points.
 

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gears for my goat

would a 3.23 auburn 10 bolt be a good differential for my 65? im talkin the high performance series 10 bolt. i have a 12 bolt now but i wanna swap out. just wondering if this is a good buy for street/strip riding
 

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would a 3.23 auburn 10 bolt be a good differential for my 65? im talkin the high performance series 10 bolt. i have a 12 bolt now but i wanna swap out. just wondering if this is a good buy for street/strip riding
It all depends on the hp level and transmission you have. 3.23 with an automatic and a stall converter can be a good street combo but not great for drag racing. What do you intend to use the car for ?
 

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Question. I have a 65' GTO, fully restored. It has the 389 with the factory 4 barrel and a 4 speed transmission. My problem is with the gearing. I don't know if it can be fixed in the tranny or the rear end. First gear is just WWWAAAAAAYYY to high. My 69 Camaro and 2013 Challenger will take off at idle when I ease out on the clutch. The goat will die if I don't give it the beans with the gas pedal. 2nd and 3rd are okay, and 4th is WWWAAAAAAAYYY to low. Like, no discernible difference between 3 and 4 gear. For example, if I am cruising down the highway at 55 MPH doing around 3000 RPM, and I shift into 4, it drops to about 2950 RPM. D I need to see about regearing the rear end or is this something that can be fixed with the transmission? Thanks.
 

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It sounds like the transmission is not an original. The rpm drop between gears on a Muncie is generally 500 rpm, with the exception of an M20 between 1st and 2nd is about 750 rpm.

If the rear gear ratio is 2.73-3.08 an M21 will give you a high ratio requiring slipping the clutch to get moving. The M20 was the standard trans from the factory with a 2.52 first gear ratio rather than the 2.20 of the M21.
 

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M22 is the same gear ratios as an M21 with the 2.20 1st gear. If your tach only drops 100-150 rpm with the 3-4 shift, your tach isn't accurate.

The M21/22 with highway gears in the rear will create the need to slip the clutch to get going. They were originally installed with axle ratios of 3.73 or deeper.
 

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Stuck a $50 (in 1985) wrecking yard 2.56 (open) rear axle in my 69 428/62 heads TH400 GTO convertible adding 235-75-15 tires (~28.5") before going on a road trip back then. Got about 17 mpg at 70-80 mph at 2200-2600 rpm. Never ran any quarters, but with the torque, it was good enough for me... would break tire loose from 35 mph punch, shift out of 1st around 60 and 2nd just over 90 (got speedo calibrated but never regeared). Took it up to 4000 rpm once, was going just over 125 mph and still accelerating at a decent rate - I was older then (than when racing the 70 455 down by the river in the 70s) and realized if the car flipped I'd be dead so backed off - it was a bit scary because with stock suspension the car didn't handle so good. Car ran very smooth. That engine blew (dropped valve) so will be building a stroker now - sure appreciate this site for all the knowledge here. I could never get traction but would be nice to try with the long legs - though seems something would give (rear axle, u-joints, ???). That car is 3553 lbs according to oldride.com (about 500 heavier than a coupe).

I still have the old rear axle (WH is 3.55 open?). When I got the car (for $1800 in '84) it was primer gray with a knocking rod and fairly loud exhaust - roommate dubbed it the Road Warrior. Drove a bit before teardown and while coming down a hill in Sunnyvale CA, in right lane of 3-lane road toward a red light, there was a 260Z and ~70 Camaro sitting in the two left lanes at a stoplight... I was a couple car lengths back when the light changed and it was obvious they were going to run each other... and not paying attention to me coming up from behind. I mashed the pedal at about 20 mph, took off like a blaring rocket, and blew past both - as I passed I looked over to see the Z guy's wide eyes and dropped jaw, and left both far behind... introduced them to Pontiac and I got hooked on acceleration. The 69 was much faster than the stock 70 (though I think the 70 GTO is one of the classiest looking cars of all time).
 

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Discussion Starter · #138 ·
This is probably buried somewhere in this thread, but I have had a 2.56 Safe-T-Track in my otherwise stock '67 GTO convertible with a TH400 for about the past 5-6 years. I removed and mothballed the oem 3.36 open diff. I also re-geared the speedo and calibrated it. I love it for the type of driving I do with the car, which is long road trips. 20-21 mpg at 75-80 mph, and shifts into 3rd gear at about 105-107 at WOT. If you are going 85-90, and floor it, it kicks down into passing gear and gets with the program. VERY long legs. That said, these cars kind of hit a wall at 130-135 MPH....the front end starts to lift, the steering gets very, very light, and it gets.....interesting. I've seen old non-aero drag cars flip at speed (thus spoilers and dams later on) and I have been to that 'edge'. Funny how well air dams and spoilers work, as well as aerodynamics.....went 145 MPH in a friend's '74 Firebird, and it was planted and solid at that speed....totally unlike my older GTO's.
 

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I too am running a 2.56 Safe-T-Track and enjoy it for the driving I do these days. I installed it in my '66 Goat-a-mino about three years ago to see what the driving/performance differences would be over the 3.23 Safe-T-Track. This car is my daily around town and to Home Depot hauler; see my forum home page for an album about it. The engine is a '66 Goat 389 with Tri-Power and trans is a TH-400 with an RV kit in it. The engine has plenty of torque to make this ratio work well in city driving and when cruising the highways/Interstates it has the grunt to pass easily. Gas mileage is somewhat improved over the 3.23. Performance wise you still feel good acceleration but it's not brutal or pushing you hard back into the seat, though still great for rocketing up the Interstate on-ramp. The one thing I will be changing, and am in the process of doing it now, is to put in a higher stall torque converter. With this engine and the stock TH-400 converter I'm not able to power-brake without stalling the engine, just cannot get into the bottom of the horsepower band. So for a little more grunt off the line, even if I still can't power-brake, I'm putting in a stock TH-350 converter which has a bit higher stall than the TH-400 and it has the same durability. My transmission guy said to do this and save $$ over an aftermarket converter, unless you want to go nuts on stall speed. I hope he's right, we'll see.
And 60sMotorhead... I liked your reminiscing on the 260Z and 70 Camaro, fun stuff! We all have stories of our Goats and yesterdays races, and my stories start in Dec of 1968 when I bought my first one - '64 Tri-Power, 4-spd, 3.23, Sunfire Red convertible. Gas-Tires-Oil cruising Speedway Blvd in Tucson on many an evening, won some and lost some... and it was fun, fun, fun! For several years I thought my car was fast (I had added a cam, headers, etc) but then a buddy of mine bought a very nice used '67 Goat off a corner car lot... it was an HO, 4-spd, 4.33 Safe-T-Track... he ate me alive, now I knew was fast was! His car became well known on Speedway and always won its races - a 426 Hemi Roadrunner managed a tie with him, short a fender length. Style wise I like the '67 best, love the grill with stacked headlights.
Cheers. Gary, in Tucson.
 

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My car has a 2.93 pegleg rear end and it came with 225/70 Relines.
It would break the tire loose and chirp going into second but they were too tall and were rubbing on the fenders.
I just put a set of 225/60-15 T/As on it and now it will light the tire and lay a decent strip going into second.
It also stops a lot better so tire diameter makes a huge difference.
I don't hot rod the car so this ratio is fine and I don't think it is worth the bucks for a posi.

Since I just bought the car I figured I should service the tranny and bought a filter from the local parts guy according to application 67 w/ TH-400.
When I pulled the pan the filter was wrong it had a long rectangular filter on the driver's side.
I was told this was the original tranny but the filter according to application is a 400 out of a Caddy.
Did they use Caddy trannys in '67 or has this one been replaced?
Fluid was very clean and bright red and nothing to speak of in the bottom of the pan.
 
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