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AZgoatguy: Cool Goat-a-mino - didn't know Canadian cars have different grilles etc. About the 67 Goats (I like them too - the stacked headlights with the diamond pattern wire grille is classy)... We used to run between the rivers (St. Louis into Alton) around 1975. A big guy had a BEAUTIFUL red 67 with a black vinyl top (you could see that vinyl pattern when the light hit it from behind), except the front clip was primered. I asked if he bought it like that and he said no - it was perfect when he bought it from some old lady until he hit a telephone pole with it.... ouch - the older cars were fast but they didn't handle or stop too good. I was driving a 70 455 GTO TH400 then (tan metallic with tan vinyl top) - I usually won until some 340 Duster beat me - and later got beat by Frank Marzuco with his 69 SS 396 Chevelle (he said about my GTO, "I thought that thing was fast") - both those cars had 4-speeds. I was humbled... Not sure what the deal was - had GTO up to 132mph once, but it really wasn't that fast off the line. I didn't know much about tuning then, but seemed it just didn't have the punch of the 69 428... I think it was heavier and the engine had lower compression (just looked up - hardtop was 600 lbs heavier than a 69, but only about 100 heavier than my 69 convertible). Never remember it pinging, so maybe could have advanced timing more and run it with Sunoco 101 (and look what I just found... brings back memories - inet is cool)
Tom McMahon: Sunoco Blend-O-Matic Gas Pump
 

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to Geeteeohguy: yeah that is a weird feeling when it kicks down from a 90 punch - the car never seemed to stop accelerating... not super fast, but constant. I also felt the 69 lightening up around 120 - I was getting a weird feeling in my stomach (and brain) that "to keep doing is not a good idea..."never driven something with air dams, but they also made made improvements in handling between 70 and 74. Almost forgot - l must have had the top down when going that fast in the GTO... I still have my college car, a 68 Impala convertible (rustbucket that I paid $300 for in Kansas City in 1980 - 350K miles on it now, though it's parked in backyard - replaced all bolt on panels with those from a clean CA car that I paid $75 for around '85 [now thinking was a shame to tear that car apart]). Anyway, the top was pretty worn out in '85, but still kept rain out - when I hit about 90 on the highway with top up, I started hearing this sound (for some reason I thought of a lot of bats flapping their wings) and about 5 seconds later the top ripped off completely... I replaced it (myself) with a lifetime guarantee top from JC Whitney - it's getting old again, and I called them about 5 years ago and asked if they'd honor the guarantee. They said yes if I had the receipt, which I still do (they printed them in ink back then, not the disappearing thermal stuff so many use now). They don't sell lifetime tops anymore - are 5-year
 

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Darth - a little late with this reply, but my M20 is 2.54 1st, then 1.88 and 1.42 2nd and 3rd. I checked 'em with a dial indicator on the rear brake hub, just to see if the method worked. If I shift at 3,000 rpm it drops about 650 rpm from 1st to second, 550 rpm from 2nd to third and 900 rpm from 3rd to 4th.
 

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lemans 2 speed

hi y'all, I have read a ton on this site and it is beyond sweet. can I put 3.90 posi (that I have) in my super turbine 300 68 lemans? how uncomfortable will this be on the highway? what are the tallest gears I can use with a 2 speed?

Would I be better off putting in a th350 first to see what performance gains there are, if any? It's a dog off the line but really has great highway gear (2.78 probably - wasn't this standard for lemans?) or wait until after rear end is done to see if I need to swap the tranny?

Thanks, CJ
 

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Discussion Starter · #145 ·
A 3.90 rear gear will be terrible on the highway behind any transmission without an overdrive. You would be MUCH better off keeping your 2.78 gear and bolting in a TH350. Cheaper, and way better to drive. Your car will feel like you added 100 horsepower, literall. The ST300 has a 1.76 first gear, wheras the TH350 has something like a 2.75 first gear. HUGE difference in off the line punch. Both transmissions have a 1:1 final drive, so those 3.90's would have you cruising at 50-55mph at 3000 rpm. If you want a little more low end grunt after installing the TH350, you could install a rear end with 2.93-3.08-3.23 gears. You would lose speed on the top end, though. Also, in this day of expensive gas, the TH350 is a win-win with your current 2.78's: you'll get better gas mileage around town and great gas mileage on the open road. I installed 2.56 gears in the back of my '67 GTO convertible with a TH400 trans and stock engine, and it gets over 20mph at 75-80 mph. I drive the wheels off of it.
 

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I have a 67 GTO, 335 HP 400 with Turbo 400 dual-gate, bought it in my youth in 1981. The car has factory A/C and came with a 2.93 posi. A couple of years into owning it, I had a bad axle bearing and, wanting to make the car a little faster, a buddy and I replaced the 2.93 with a 3.36 posi from another '67 GTO. I am also running larger tires than stock (225-70-15). I still have the 2.93 gears and posi that came out of the car 30 years ago.

Since I don't race the car at this point, either on the street or the track, I was thinking about going back to the 2.93 posi. Would it really be worth it, or am I not going to notice that much difference in highway RPMs?

I ran across a calculator that considers the gears and the tires, and together estimates that I'm probably running a hair over 56 mph when the speedometer shows 60, so I am putting a few extra miles on the odometer running this way - and I've probably put 25K on the car since the swap. This is the calculator:

http://www.roversd1.nl/sd1web/wheelcalc.html

I don't have access to a shop, I have a garage and a decent array of tools, no helper, so I'm not sure that I'd try to do it myself, it's been a long time since I did the job! What would you do?

This calculator estimates that if I changed from the 3.36 to the 2.93 with the 225-70-15 tires, my RPMs at 70 mph would go from 2,884 to 2,515. Worth it?

http://www.wallaceracing.com/calc-gear-tire-rpm-mph.php
 

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Longs, Welcome! Would suggest swapping from the 3.36 to the 2.93, ESP if the 2.93 safe-t-track was in good shape when you previously pulled it out.

What follows can be done in under 2 1/2 hours on a flat driveway without airtools. Have done it many times. What matters is the brakes on the current 3.36 rear are in good shape.

Ready to go? Loosen the lugnuts slightly on the rear wheels, jack the rearend of the car up under the center of the r/e hsg and put good sized jack stands under the cars side framerails in front of the rear. Next, pull the lugnuts, and tires and wheels off. Next remove the drums off the currently installed rear (the 3.36 Pontiac 8.2).

Next, unbolt the axles, takes a 9/16" socket and go through the access hole in the axle flange. Remove all 4 nuts and slide the axles out. They should pop right out, you can bump the inside of the axle flange with a large pickle fork off the top of the brake shoes if thy are a little tight. Next, unbolt the lower shock mount from the housing with an 11/16" socket. Next, slide the backing plates out slightly off the t-bolts of the 3.36 rear. With a piece of coat hanger or string, hang the backing plates up so they don't drop too much. By going this route, you are keeping the rear brake lines intact, from backing plate to backing plate, and there will be no need to have to bleed the brakes.

Next, remove the small bolt that holds the brass junction block of the rear brake hose. Pry the small tabs up and let the steel brake lines loose. Both lines and backing plate should now be unattached from the 3.36 rear. Next, remove the nuts and lock washers from the ubolts holding the driveshaft to the pinion flange. Bump the ubolts out and pry the driveshaft forward. Carefully drop the rear of the driveshaft, keep the yoke forward, in the transmission, or you will have a mess.

Last, going to remove the four 3/4" headed long bolts and nuts that hold the rearend housing to the upper and lower control arms. I usually remove the bolts out of the back of the lower arms first, then unbolt and remove the upper bolts. Once you get this far, you can slowly let the assembled rearend housing down on the floorjack and pull the now loose rearend hsg at an angle toward the side of car. that way, you can hop the shocks out of the way.

On the 2.93 rear, remove the old drums (if so equipped), axles, and backing plates, pull the rear cover, and carefully inspect the teeth on the the ring and pinion. As long as the 2.93 rear hasn't been setting outside on the ground, it probably won't have drawn up moisture from the ground and created rust at one point on the ring and pinion. If no rust, you should be fine. With 1 3/4 qts of new 80-90 rearend grease and a small bottle of GM posi additive installed, you can reinstall the cover with a gasket, and button it up. With the old backing plate and old lines removed, the 2.93 rear can now carefully go onto the cup of the big floor jack. Going back in , your only obstacle is the shocks hanging down slightly. There is usually enough play in the upper shock rubber mounts that you can manipulate the shocks if they are in the way. Once you get the 2.93 rear up and bolted in, look at the axles from both rears, most likely each has the sealed axle bearings (no external seals). If the axles out of the 3.36 rear are same length as the ones out of the 2.93, and the sealed axle bearings were replaced on the 3.36 rears axles, previously, and they don't now have 50k miles on the replacement bearings, you can substitute the axles out of the 3.36 into the 2.93 rear.

Replace the steel lines under the tabs, then button everything up. Helps to have a buddy, or a son to hand tools, and help roll the rearend into place. Do this several times, and you can actually do it proficiently in under two hours.
 

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Pinion Head, Thanks for that detailed explanation. You must have misunderstood my question, though, as it sound like your instructions were for changing the entire rear, not just the ring/pinion/carrier, etc. When I changed these years ago, that's all I changed. The housing and the rest of the rear is still the original. I just swapped the innards within the pumpkin, so to speak.
 

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Longs, yes, missed that the original ring and pinion had been removed and rear was then set up with a set of GM 3.36's. quickly reading you post, read it like you had the 2.93 rear loose, but it had a bad axle bearing. How's that for reading comprehension ;)

Still see the swap back to the original 2.93's as the best solution.
If the original 2.93 pinion still has the original piñon shim under the large pinion bearing, the whole process is going to be sped up. The original pinion is going to be replaced into the original hsg, and with a minimum of a new crush sleeve, new 1 1/8" pinion nut and new pinion seal, with the right tools and a lot of care, the pinion can be replaced and pinion depth and pinion drag can be reestablished. of course, pinion bearings and races may need to be replaced, as well.

Once pinion depth and drag are correct, can move to setting backlash. A longtime GM differential builder should have a large selection of cast side shims and thin side shims. All of my cast side spares are organized by style, to .0005 in thickness, in freezer bags. This speeds up looking for the correct thickness cast side spacer, so, can get onto installing a GM service spacer and thin side shim on the other side. If you did save the two original cast side spacers, when he 2.93 gear and carrier was removed, that is going to help speed things up as well.

Good luck on this, I can go into more detail if needed. HD 8.5's & strengthened 12 bolts are what I mainly build today, but have gone through many Pontiac 8.2's along with all of oddball 10 bolt GM rears of the late '60's.
 

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Discussion Starter · #150 ·
A 2.93 rear ratio for a '67 GTO with TH400 is in my opinion the perfect ratio. A MUCH better street gear than a 3.36....excellent power mid range, and great top end and fuel mileage. You'll find that you drive the car a lot more, as it will use much less fuel, too. Go for it!
 

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A 2.93 rear ratio for a '67 GTO with TH400 is in my opinion the perfect ratio. A MUCH better street gear than a 3.36....excellent power mid range, and great top end and fuel mileage. You'll find that you drive the car a lot more, as it will use much less fuel, too. Go for it!
Run that in my 68 and love it . I could not agree more and still a blast to drive. Doug
 

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That's what I'm wishing was in mine. I already have the Moser 9" and 3.50's I'd love to hear details of your 4L80E conversion, how it's built, did you modify the shifter, trans tunnel mods, etc.

Bear

Baer,
I’d love to tell you more but I bought it that way. Where you located? Come on over and check it out. I do know it’s a TCI street fighter with a Saturday night special stall. Mark Williams driveshaft going to a Daytona Pinion with Detroit Locker 31 spline. Butler built 461, 550hp, 580 torque.
 

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Thanks guys, I've been having the same inner dilemma. The 65 originally had 3:90s like Rukees, but they are long gone several owners ago and now it has a wrong 1971 rear in it with 3:23s. So I am still looking for a 65 rear and thinking about what ratio to use with the 421. Geetoguy is right, we're not kids anymore and gas isn't .35 a gallon so 3:90s are out. I'm tossing up whether to go 3:55s or 3;73s. Anyone running 3:73s? Thoughts?
Mike
Mike....I’m running 3:31’s in my rear behind a Muncie RockCrusher 4 speed powered by a 65 421 police interceptor....I wouldn’t want it any other way !!!....I can get rubber in all 4 gears...125 in a quarter mile and that’s what she tops out at..in first and 2nd I can pull the front end off the ground 3 feet....wicked quick and love it!
Troy
 

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Hi. I'm posting a new thread because I didn't want to hijack another thread that this subject came up on: Gear ratios. I was bragging about my "racing" days, and gear ratios were mentioned. The following is some information that I have learned over the years, and the following opinions on gear choice are my opinions and nothing else. I am no engineer. I've run GTO's over the years with ratio's from 2.56:1 to 4.56:1. Stock early GTO's with stickshift usually came through with 3.55 gears, and aut0 cars had 3.36 gears standard. The 3.55 (4-Series) carrier could accomodate gears from 4.88 or so down to 3.36. The 3 series carriers could accomodate gears from 3.23 down to 2.51. I found that "back in the day", with cheap gas and road noise a fact of life, the 3.55 gears were okay.....the '66 tended to be running about 3200 rpm at 70mph....right in the power band. The speed limit was 55 at the time.Top end was ok. Low end was great. Good "all around" gear, back then. Now, 3200 rpm at 70 is too darn high. Too much noise, too much fuel, and with a big block Pontiac, uneeded. I ran a 3.90 gear in a '65 for a while. That car HATED the hiway. Top end was 107 mph, at redline. It would get there really quick, though. I changed out those 3.90's with a 3.36 gearset (the tallest gearset I could run in my 4 series carrier) back in 1990. Changed the car. Now, it loves 70 mph. It feels just about as strong out of the hole (Still can't hook up....tire smoke central), my fuel economy went way up, and my road noise went way down. I had another '65 with a 3.23 gear and a 4-speed, and the 3.23 is my FAVORITE gear ratio for these cars. It does everything well: accellerate, cruise, and top end. I drove a '65 with a 2.56 gear. GREAT top end, doggy as hell off the line. Too extreme. A friend had a 2.93 gear in his '67. The car would kick down into 2nd gear (turbo 400) at 85-90 mph. We smoked a 427 '65 Corvette on the hiway one day....he was running 4.11's and was done at around 105mph. The '67 would top 140 mph, I'm sure. Another friend had a 4.88 geared, dual quad 455 '66. We broke the wheel studs on the rear wheels getting on the freeway one day. He jumped on it, and there we were. The car would lay rubber when you got on it at 65mph., in 4th gear. Scary. cruising speed was 55 mph. Got about 8mpg at 55! My convertible '67 has the stock, 3.36 gearset. I wish it had a 3.23. It is a little busier at speed than I wish it was. I guess I'm getting old...I like running at 75 mph with minimum road noise and fuel consumption. Today, there's a lot of options with overdrives, lock-up converters, etc. If you want to modify your GTO and add a 700R4 trans, or add a 5 or 6 speed stick, you can run a 3.55 or 4.11 gear and STILL cruise at high speeds. If you're like me, and don't want to cut up your original old Goat, you have to choose what gear ratio best suits YOUR needs. For this guy, it's 3.23's.
Jeff
 

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I am about to put a posi 3:42 in my 64 lemans. Im running afour speed muncie and a bored out 327 double hump high compression heads that somebody cammed. Ill let you guys know if it ends up a dream or a nightmare. My carrier is made for c clip axles and i believe i have flanged axles in my car. Does anybody know if this will work or do i need to buy new c clip axles for the differential swap?
 
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