Robert G. Smits

66 GTO; Change Rear End Ratio vs Overdrive

Recommended Posts

66 GTO 389, 4 speed with 4.11 rear end ratio.  Would like to turn this into a better touring car.  Considering changing the rear end verses going to a Gear Vendor.  Thoughts and recommendations appreciated.  Looking for the best solution, not necessarily the cheapest.  Thanks

Share this post


Link to post
Share on other sites

Unless you buy a rear end assembly that's already been rebuilt and guaranteed, you will need to disassemble and check everything anyway.  Once you start unbolting things, you'll end up with a lot of "might as well" things you should do while it's apart.  I recommend just replacing the gear set and carefully inspecting everything, that way you'll know it's done to your standards and meets your requirements.  Is it a Safety-trac (posi) rear end?  I bet your 4:11 is a replacement gearset anyway.  My 67 is a 3:55 and that was special order.  Share a pic Bob, sounds like a great car.

Terry

GTO resized for forum.jpg

  • Like 2

Share this post


Link to post
Share on other sites

AC cars came with a 3.23 & is a reasonable touring gear. Or find a Trimec and save the fragile (small shaft) Muncie.

 

I have a 3.55 4 pinion in the Judge and keep looking for another gear at anything over 50.

Share this post


Link to post
Share on other sites

I will try to post a photo.  This is a nicely done (clone), 1500 miles since restoration and engine rebuild,  Headers and 2.5" exhaust with H pipe, 068 cam.  I found this one while looking for a real one and couldn't pass it up as I was looking for a driver with no interest in showing it.  Scheduled for Vintage Air this winter1349370237_66GTO.jpg.77d0e1a7d1e502e4dd5837fed6c0ff40.jpg

Edited by Robert G. Smits (see edit history)
  • Like 2

Share this post


Link to post
Share on other sites

I have the same experience as padgett.  I start looking for a higher gear around 45 and at 60 i'm no longer having fun.  Does anyone have any experience with a Gear Vendor in a muscle car?  Back in the 90's I towed all over the country towing a Classics using a 30 ft Airstream, 454 with RV cam, Banks headers and Gear Vendor.  I loved it

Share this post


Link to post
Share on other sites

I'm the original owner of this 69 H-O LeMans. In 1992 I built the car over for Grand Touring. ( brakes,suspension and steering modified, engine- a H-O 455 with a 068 cam. )  I run a 10 bolt 3.25 Safety Track. At 70MPH I'm at 3100-3200 RPM which is way high rpm for cruising. I also have a 2.56 ten bolt Safety Track and a 3.08 ten bolt Safety track. These rear ends were cheap to pick up at the local Pick You Part and relatively inexpensive to rebuild. Remember this; these BOP 10 bolt rear ends are different from the Chevrolet 10 & 12 Bolt types. They are stronger and have a larger diameter axle than the Chevy. Rear ends are easy to swap out in about twenty minutes. The LeMans while not built for drag racing runs a 12.37 @ 113mph with the 3.23, and still a respectable mid-low 14 second quarter mile with the 2.56 Posi. Times may be different but most people can't tell by the seat of the pants, in fact some people think the 2.56 is faster because just when they think it's wound out at 105MPH I shift to third gear. The gratifying part about the 2.56 is it's 24MPG car on the HYY. BTW the car weighs 4050

 p1020752.jpgp1020753.jpg

Edited by Pfeil (see edit history)
  • Like 1

Share this post


Link to post
Share on other sites

You realize you are heretical ? My 1972 tow wagon had a 3.07 "economy" axle. 3000 rpm at 70 was common then thanks to short 14" tires. What you really have is a resto-mod already.

 

Since my 3.55 is a 4 pinion posi, think I'll keep it but would like to swap in a five or six speed manual with a lot of OD in top. 2000 rpm at 70 is a sweet spot for a gas engine with lotsa torque.

Share this post


Link to post
Share on other sites

back in the day, some fool challanged me in my 1965 GTO. we came up to a stoplight and i nailed it. went about 50 feet before i came to a sudden stop. towed it to the shop and removed the diff cover to find all of the bolts in the 4:11 posi unit resembling poorly made pretzels. $100 bucks later, i had a tempest rear assembly with 3:06 gears in there.took all of an hour to do. i've done differential overhauls and they are only a little less painful than getting poked in the eye with a sharp stick. had some amazing top speed after that swap

Share this post


Link to post
Share on other sites

Thanks for all the replies.  Because of the 1st gear ratio I am afraid that a 2.56 to 3.06 ratio will require excessive clutch slippage off the line.  Would work much better with an automatic in my opinion.   Any thoughts on a Gear Vendor?

Share this post


Link to post
Share on other sites

After assembling a Corvair transaxle on the back of a trailer at the track (removed all synchros and made it a crash box, time was limited and spares lacking) any 10 or 12 bolt GM is a piece of cake, even a 4 pinion posi.

 

Most common sudden stop was the lockscrew in a 12 bolt shearing off.

 

ps you mean you have a close ratio Muncie - 2.20:1 1st ? That should be a large shaft. M21 (M22 was also close ratio but later. Was known as the "rock crusher" not so much for strength but the straight cut gear SOUNDED like it was crushing rocks. I'd still just go for a Tremec or Richmond with a long OD top.

Edited by padgett (see edit history)

Share this post


Link to post
Share on other sites
19 hours ago, padgett said:

You realize you are heretical ? My 1972 tow wagon had a 3.07 "economy" axle. 3000 rpm at 70 was common then thanks to short 14" tires. What you really have is a resto-mod already.

 

Since my 3.55 is a 4 pinion posi, think I'll keep it but would like to swap in a five or six speed manual with a lot of OD in top. 2000 rpm at 70 is a sweet spot for a gas engine with lotsa torque.

 

 It's not a resto mod. It's a street car that's been modified so that I can drive it on the track. They are known a Grand Touring cars. With just a few parts changes the car can pass as stock even though internals, especially steering and suspension,  most of which come right out of the GM parts bin anyway appear to be your every day Pontiac GTO, LeMans or Tempest parts. 

Edited by Pfeil (see edit history)

Share this post


Link to post
Share on other sites
4 hours ago, Robert G. Smits said:

Thanks for all the replies.  Because of the 1st gear ratio I am afraid that a 2.56 to 3.06 ratio will require excessive clutch slippage off the line.  Would work much better with an automatic in my opinion.   Any thoughts on a Gear Vendor?

 

If you would like to go with a 2.69- 2.93 rear, you can get yourself a wide ratio 4 speed. They are cheaper than the ever so in demand close ratio. The wide ratio has a deeper 1st.  and can easily be rebuilt. That would be the cheapest and fastest way to solve your problem.

Share this post


Link to post
Share on other sites

Guess I am confused, why not just get a five speed with .67 5th and be done with it.

 

Is this a good place to mention that back in the first fuel crisis a common conversion for a Goat was to add a BW OD to a Saginaw 4-speed, just needed to drill one hole.

  • Like 1

Share this post


Link to post
Share on other sites
5 minutes ago, padgett said:

Guess I am confused, why not just get a five speed with .67 5th and be done with it.

 

 

 I guess you are confused because you already said this in your first post.😉

Share this post


Link to post
Share on other sites
9 hours ago, Robert G. Smits said:

Thanks for all the replies.  Because of the 1st gear ratio I am afraid that a 2.56 to 3.06 ratio will require excessive clutch slippage off the line.  Would work much better with an automatic in my opinion.   Any thoughts on a Gear Vendor?

 

Bob,

 

Considering the torque and horsepower of your car, in my opinion neither the 2.56, nor the 3.06 would require excessive clutch slippage, and highway driving pleasure would be much improved. I cannot comment on the Gearvendor unit, but seriously considered it for the 1914 Buick before having Rempco make a 3.31 ring and pinion to replace the factory 4.08. The Buick never required sl;ipping the clutch, and is far, far less powerful than your "Goat". 😉

 

PS: with new differential gears there are far fewer parts to fail, and you can cruise those West Texas interstates with the big boys.

 

See you "down the road".

Share this post


Link to post
Share on other sites

OK fagedaboudit.

Share this post


Link to post
Share on other sites
45 minutes ago, Marty Roth said:

 

Bob,

 

Considering the torque and horsepower of your car, in my opinion neither the 2.56, nor the 3.06 would require excessive clutch slippage, and highway driving pleasure would be much improved. I cannot comment on the Gearvendor unit, but seriously considered it for the 1914 Buick before having Rempco make a 3.31 ring and pinion to replace the factory 4.08. The Buick never required sl;ipping the clutch, and is far, far less powerful than your "Goat". 😉

 

PS: with new differential gears there are far fewer parts to fail, and you can cruise those West Texas interstates with the big boys.

 

See you "down the road".

 

Uh Marty, it's "TIGER". And to a Pontiac guy "GOAT" has two meanings. 1. a derogatory word to a Pontiac owner. 2. Something a Tiger would probably eat.😉

65AdwGirltiger.jpgRelated image

1966 Pontiac 2+2 and GTO 2-page Ad, Tiger Scores Again!

Edited by Pfeil (see edit history)

Share this post


Link to post
Share on other sites
7 minutes ago, padgett said:

OK fagedaboudit.

You REALLY are confused.

Share this post


Link to post
Share on other sites
9 hours ago, Pfeil said:

 

Uh Marty, it's "TIGER". And to a Pontiac guy "GOAT" has two meanings. 1. a derogatory word to a Pontiac owner. 2. Something a Tiger would probably eat.😉

 

 

No disrespect intended,

I don't recall hearing that before.

I've had several Pontiacs - and an Oakland,

and my brother had an almost brand new 1964 GTO convertible-

389, Tri-Power, Fenton Mags, Wide Ovals,

it was silver with a black convertible top-

I was really disappointed when he sold it just before signing up with the Navy Band, and didn't offer it to me first.

Share this post


Link to post
Share on other sites

4:11 is awesome for drag racing and horrible for driving around in.   I was running factory 3:55 and that was fine around town but not great on the highway.

 

Swapping in the 15 inch wheels in back with oversized tires will help.

Edited by alsancle (see edit history)
  • Like 1

Share this post


Link to post
Share on other sites

GOAT vs Tiger?    As the proud owner of a 69 GTO 400/4 speed Vert in HS and College (I wanted the 66)  at well as a 68 we always referred to them as GOATs.   Have never heard anyone call them a Tiger.    Or do I misunderstand the conversation?

  • Like 1
  • Thanks 2

Share this post


Link to post
Share on other sites

Going to 15" wheels is about the equivalent of gearing up one gear set. Even if it is not intended to be a permanent arrangement it would give you a good idea of how you would like the next gear up. 

Share this post


Link to post
Share on other sites
1 hour ago, alsancle said:

GOAT vs Tiger?    As the proud owner of a 69 GTO 400/4 speed Vert in HS and College (I wanted the 66)  at well as a 68 we always referred to them as GOATs.   Have never heard anyone call them a Tiger.    Or do I misunderstand the conversation?

 

 In 1959 my dad placed a SO order on a very special 59 Catalina. 389 4 bolt main solid lifter Tri-Power hand built in the Pontiac toolroom to be raced in AS/A. This engine was one of the type of engines that was built for NASCAR teams and Drag racers. Later on I got my IHRA license at the age of 14 I raced the car in FS/A. I remember when the production 64 LeMans GTO's started showing up at the drag strip and street races. The term GOAT seemed to come from the MOPAR, but later all the opposition brand guys used it in verbal jousting about this new Pontiac. In this jousting of the new kid on the block ( the opposition) they switched the letters around to inexactly say GOAT. This was meant to rattle the GTO owner as in the old term "getting someone's goat". Unfortunately that moniker stuck with the GTO. For three years Pontiac advertising struggled with GTO Tiger theme to make sure it's nickname was the tiger. Uniroyal tire made special red line tires for the GTO and the tires were called TigerPaws. Later the term TIGER was applied to all Pontiac's which you can see in the last picture I posted with a GTO next to a Pontiac Catalina 2+2 

 

Just a FYI, The first time the word Tiger was ever mentioned was in a 1963 Pontiac Tempest add. In 1963 Pontiac re-cored the 389 engine to make it lighter, Pontiac also came out with a small bore version of the 389. The engine was called a 326. In 1963 the engine was really a 336, in 1964 it became a true 326. Anyroad this add for the Tempest had a picture in the middle of the street with a Tempest coming at you and one going away in the opposite direction. One of the Tempest had the 195.5 " ( half a 389-slant 4 engine) the other with a 336. The add said something like " can you tell which Tempest is the TIGER.

1963-Pontiac-Tempest-326-Can-You-Tell-Which-Is-The-Tiger-Original-Print-Ad-9x11-034

 

BTW this verbal jousting was not special to Pontiac guys. The nicknamed for FORD was " Found on the road Dead " and

"Fix Or Repair Daily".

Edited by Pfeil (see edit history)

Share this post


Link to post
Share on other sites

You learn something new everyday.   My HS days were 78-82  and Goat was never used a a pejorative.    The Tiger thing did not seem to stick.

Edited by alsancle (see edit history)
  • Like 1

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now