VCCA Home Forums TECHNICAL - 1945 AND NEWER 1961-1964 Axle Performance Gain

Hello to all,

We are looking for guidance and ideas about performance expectations for increasing the rear axle ratio on a 1963 Impala SS. The current drivetrain is a 327 4 barrel with Powerglide transmission and a 3.36 rear axle.

Can anyone describe what we might expect in terms of acceleration if we increase the axle ratio to 3.70? Will it be noticeable or will the result simply be more engine noise and reduced gas mileage?

The core question is if a 107 increase in tor

Sorry. Hit submit too soon!

The core question is whether a 10% increase in torque at the wheels is worth the cost and effort.

Thanks for the ideas.

A 1963 Impala with a 250 HP 327 engine had a 3.08 axle ratio.
A 1963 Impala with s 300 HP 327 engine had a 3.36 ratio.
Amoung other things the 300 HP engine had a larger exhaust system and an aluminum Carter AFB carburetor.
The 300 HP with the 3.36 and Power glide really flew. The 250 HP with the 3,08 was just OK.
The 327 with P.G. had a 1.76 low gear ratio and the 283 had a 1.82 low gear ratio. That didn't help the low gear performance in a 327 PG and a 3.08 ratio other than it would not up-shift intil over 65 MPH.
Are you sure it is a 3.36?
A 3.70 would be a little extreme with th e 14" wheels but a 3.55 a better selection.....even a 3.36 would liven it up.
A Friend of mine bought a new 1963 with a 300 HP and PG. It could esaily out run his brothers 1959 Pontiac with a 300 HP 389 engine and 4 speed hydramatic.

Hi Gene,

As I expected your inputs are right on target.

I am not sure exactly which engine and rear axle are in the car. I cannot believe it is a 300 hp 327 with a 3.36. The car does not leave the line very hard. This car is the reason I made the post about finding ID numbers.

I agree with you that if it is a 3.08 rear the 3.55 would be more than enough change. That is a 15% increase which would definitely be noticeable.

I will be back in the Quad Cities later this week so can hopefully confirm exactly what we have.

Thanks for the guidance.

The timing may have been retarded for using 87 octane gas. If it were mine I would advance the timing to 10 degress at idle and see if that helps. It is a preimum fuel engine. I always thought the 327 PG with a 3.08 was a dog off the line....this is when they were new.

My new to me 63 Impala sedan 283 powerglide, according to the typed in information in the 1963 Chevrolet Owner Protection Plan booklet I found in the glove box, is equipped with a 3.55 posi rear axle.(AN104) I have yet to verify this by crawling under the car and reading the actual number, but I'll tell ya what, that thing gets it pretty darn good for a big car when you mat that thing. Shifts out of low at 55mph

A 1963 238 Impala with P.G. had a 3.36 ratio. A BelAir 283 PG had a 3.08.
The "mountain" or special purpose option was a 3.55. It was option #G96. Posi was option #G80.
The were two different options according to the 1963 Finger
Tip facts book.
The diff. stamped number for AN is Posi. with 3.55 ratio and metallic brakes.
It would be interesing to see how yours is stamped.
If it does have Posi. both wheels will turn in the same direction (by hand) with the wheels off the ground.

I will let you all know in a couple of days!

It is easier to identify a posi-unit then that. On the front side of the carrier on the driver side of the car there is a raised letter "P" in the casting about 1/4" wide and around 5" in overall length. I have found that the stamped codes on the pad can be rather difficult to read. If it were never out of the car there will be a disc under one of the nuts about the size of fifty cent piece, that will have particular notches in it to identify the ratio

You can determine the axle ratio of a vehicle that has a an open drive shaft, with relative accuracy, by doing the following:

Open Axle (non positraction ). Two people required
Transmission in neutral.
Raise one rear wheel . The opposite wheel must not be allowed to turn.
Place the raised wheel valve stem at the 6 o'clock position.
Mark the prop shaft and the transmission tail stock.
First person is to count the prop shaft revolutions while the second person turns
the rear wheel (slowly) ten complete revolutions.
The prop shaft revolution number count is then doubled.
Example: A 3.36:1 axle ratio should have a count of 16.8 prop shaft revolutions times 2 = 33.6. Since you turned the wheel
ten revolutions, move the decimal one positions to the left.


Positraction Axle: Two people required.
Transmission in neutral.
Raise both rear wheels.
Place the valve stem of one rear wheel at the 6 o”clock position.
Mark the prop shaft and transmission tail stock.
First person counts the prop shaft revolutions while the second person slowly
turns one rear wheel ten complete revolutions.
The prop shaft actual count should be the axle ratio.
Example: A. 3.36:1 axle ratio should have a count of 33.6 prop shaft
revolutions. Since the wheel was turned ten revolutions, move the decimal one positions to the left.

Why would you go to all that trouble? For a non-posi you only have to turn the wheel two revolutions and count the driveshaft turns. For a posi, one revolution will due and count the driveshaft turns. A little over 3 turns = 3.08. A little over 3-1/2 turns = 3.55, etc.

Verne

Drum roll please....... The number on the housing is pretty difficult to read, however after some cleanup it looks like an M to me, which makes it a 3.36. I confirmed this by counting driveshaft revolutions while turning the wheel one revolution. Once again Gene you are correct!

You're correct, but the more turns, the greater the accuracy. I did this type of thing for a living and more is better, especially when the boss asks, are you sure? Now I'm asking myself, why did I bother?

The 3.36 was a good choice for 1963 driving. That is the same number of engine reveloutions as a 1950 -1956 Power Glide with a 3.55.
My rather heavy (for a 1957) Nomad with a 4 barrel feels like a hot rod but compared to a modern car it feels like it is stuck in a lower gear on the highway. The gas mileage is acceptable.
The 195 HP 2 barrel 1963 283 was a good performing engine, all things considered.

THE STIFFER THE REAR GEAR SET, the more the motor is going to wind tight sounding at 3000 rpm with 3.55 gears on the highway. final 1--1 rear ratio.

If you run a large diameter tire 28--29.5" tall, that helps to kill the effect of the gears a little verses a 25--26 " tall tire .

Want to really feel the effect , slip in a set of 4.11 gears and you will think your driving a sewing machine. Performance, definitely you get a big seat of the pants feel from start thru mid range.

Oh did I mention that because the motor is working harder your gas mileage will suffer.

I just always used to jack the car up, put a piece of tape on the driveshaft joint pointing toward me, mark the tire at the top or the bottom and spin the tire one complete turn. 3 1/2 turns = roughly 3.50 and a very close number to the 3.55 factory gears.

All that spinning and math, really ???

mike

Hello to all,

Thanks for your information and ideas about the expected performance for this drivetrain. I was able to talk the owner through some basic troubleshooting to determine if everything was as it should be.

The result is that the current owner determined that the car had no kick-down linkage. Whoever did the engine and transmission rebuild for the previous owner never re-installed it.

He was able to locate parts and had them installed by a local transmission shop. He says that the difference is amazing.

So the rear axle ratio change is a low probability for now. The owner wants to drive the car for a few months to get used to the great improvement.

If properly adjusted the trans. will not up-shift when floored until 60 MPH and down shift into low when floored below 55 MPH.

There is an adjustment procedure for that link-down linkage in the shop manual (you do have one, don't you?).
If there is nothing wrong with the transmission itself, that proper adjustment will ensure it will operate as it should.

Verne

Thanks for the reminder. The shop that installed the linkage also adjusted it. Yes, we do have a shop manual as well as the assembly manual.

I plan to drive the car probably sometime in the next 2 weeks or so after I get back to the Quad Cities. Hopefully everything is functioning as it should be.