Easy, that is an 8" rear. The easiest way to tell is you can get to the bottom nuts on the pumpkin with a ratchet and extension. The 9" bulges down there and the bottom nuts must be removed and replaced with a box end wrench. It has the drain fill plug in the back so it is an early version and correct.

 

The tag attached to the center section will tell you the ratio

 

Figure out what this tag says and report back. All the information on the tag.

 

Figure out what this tag says and report back. All the information on the tag.

You still need to verify what ever that tag says after 60 years though as that tag could have been off the original pumpkin and simply bolted back on with a pumpkin change or the tag came with the pumpkin that was changed, or it's original. The only way to know is to verify the information on the tag to what is actually there.

 

Read your tag, as others have mentioned.

On (what I assume is a conventional “open” rear axle) you can’t detect rear end ratio with the method you used.
With one tire on the ground,
mark the inside of the tire and a spot on the driveshaft with a paint marker. Now, rotate the suspended tire two revolutions and count the number of driveshaft turns. The reason to make two revolutions is the open differential actually rotates half as many times as a ‘posi,’ because of the design of the “open” gear operation.

 

Thanks for this tip GT

 

Ok. Thanks folks. I’ll jump back under tomorrow and see if I can decipher the tag details. My goal is really to see what it would take to make a subtle change to ratio both from a gas mileage perspective and from a noise perspective. I’m going to post a sister thread with some images of the current mufflers to see if I can do better there too.

 

1-1/2 rotations of the driveshaft to one wheel revolution on an open differential would indicate a 3.00:1 ratio which was the most common on a car with manual transmission. Mine, with 215/65R15's (26" diameter) runs just a hair under 3,000 rpm at 75 mph. A nice "song" at that speed.....

 

Thanks Bart. That is helpful. Is it worth considering changing gears to get the revs down a little. Or would I lose too much torque from a full stop. ( I know a 5 speed helps this issue but not sure 4K tranny switch makes sense for this car).

 

If you have a fixed engine fan, changing to a clutched fan will dramatically reduce engine noise.

 

Did switch to a clutch fan a couple years ago that’s a start. Thanks

 

@RudeMan , download a speedometer app on your phone to help determine speed.

I still use the app I downloaded years ago when calculating new cable gear.

 

Getting something besides Trush Turbo mufflers will also dramatically reduce engine noise.

 

standard ratios were C code 2.80 A code 3.00 k code 3.50-3.89-4.11

 

Ok. Novice here. So a C code 2.80 would presumably be lower RPM at the same speed. Right?

 

OK, finally had a min to wire brush the tag and snap a shot of the tag. Here it is.

 

The tag shows it's an open differential 3.00 ratio. If your car is not a GT it could be original but it was probably a special order.

 

Thanks Ronst. Not a GT. It just seemed like awfully high revs even at 55.

 

So then is reducing the RPM by a gear/ ratio swap to improve mileage and bring down the decibel level a little not a thing ?

 

Well, it's one way. I prefer having an overdrive and why my fastback has a T-5 transmission. In your case it sounds like you have crappy mufflers and changing your exhaust system would be the best approach.

 

3.00 was a very common gear ratio. I had it and changed to 3.50. The engine is not excessively noisy at any speed. And it still goes well over 100 mph with 3.50 gears. You can use simple math to compare RPM. If you want quiet, think about the exhaust. The tailpipe outlet location is also important. The further back the noise comes out, the better

 

For sure my mufflers will be swapped thanks. My tailpipes come through the rear valance.

 

3.00 = 2400 at 60
2.80 = 2200 at 60
3.25 = 2600 at 60
these are round numbers depending on your tire diameter.
you should still get at least 20mpg on the highway

 

@RudeMan

 

Well, I need to throw up some picks of my whole system including the headers and get advice. No point in having to do it twice.

 

Really appreciate all the replies members. Now that I’m relatively certain I have a 3.0 gear set, it seems like it makes sense to stay put for now and look for other ways to improve mileage and engine noise, ie better tuning, muffler choice etc. I can’t thank the forum enough for all the guidance. Best, RudeMan

 

Is it actually noisy or just higher rpms?

2.80 was stock on mine.
Changed to 3.25’s over ten years ago.

Sometimes I just stay in 4th (T5 transmission) especially around town.

4th is fine at highway speeds too.

5th is overdrive primarily for cruising.

 

consider changing 5th gear ratio.
I have a T5Z with 3.25 rear but i changed 5th gear to .80. 2000 rpm at 60 I can run 5th down to 45 on a flat road
It is a great combination

 

I had a car with an aftermarket market exhaust that "droned". When going fast enough, the drone went away. The muffler seemed to fill up with enough exhaust. Unfortualy, that speed was about 85 MPH.

 

That is correct.
This has always been a cruiser.
Can’t afford racing or concours. 😂

 

with the 3.35 first gear a 3.00 is going to be pretty peppy in first i dont think i would recommend any higher.