what rear end ratio in my 68 427?

[Brandon T.]

It's a 68 427/390 4sp car.

I have looked at the pumpkin and all I can see is "67"

it's a late 67 build car it's dated D07.

The rear end still has the original red tag label so I assume it is a positraction right? also what ratios was available for this car? to my knowledge 3.08, 3.36.....and what else could this car have came with?

like I said all I can see on the bottom of the diff is "67". Can't make anything else out.

[Donald T.]

Re: what rear end ratio in my 68 427?

Brandon,

Even the rear end code may not be accurate. The rear could have been rebuilt with different gears. The best way to determine the ratio is to compare the drive shaft rotations to the wheel rotations. Put the car up on jack stands. Mark the driveshaft and one of the wheels. With the trans in neutral, turn the wheel and count the number of turns of the driveshaft compared to the wheel. That ratio will give you the rear end gear.

All big blocks came with posi and you can verify when you turn the rear wheels. All available ratios for 1968 were 3.08, 3.35, 3.55, 3.70, 4.11, 4.56.

[Rich G.]

Re: what rear end ratio in my 68 427?

FWIW, my 68 BB with 4:11 gears turns ABOUT 1000 RPM for every 20 MPH, in 4th, so 2000=40MPH APPROXIMATELY.

As previously stated, the right way to tell is to lift it and count the turns

Rich

[Jack C.]

Re: what rear end ratio in my 68 427?

My early Jan 68 427/400 has a 3:36 rear end. There should be about 6 alphanumeric characters before the number 67

[Wayne M.]

Re: what rear end ratio in my 68 427?

It's a 68 427/390 4sp car.
.... also what ratios was available for this car? to my knowledge 3.08, 3.36.....and what else could this car have came with?

Brandon -- My reading of an old power train chart says that the L36 could have come with anything from 2.73 thru 3.70 ratio, depending on manual vs. auto; air conditioning or not.

[Brandon T.]

Re: what rear end ratio in my 68 427?

thanks,

and yes I know you can lift the car and rotate it just was wondering what possible gears it came with.

if I want the ratio I can find that out easy. Like I said just wondering what options it could have as far as ratio.

[Wayne M.]

Re: what rear end ratio in my 68 427?

.... Like I said just wondering what options it could have as far as ratio.

Brandon -- your L36 (applies to tri-power L68 as well) would have had the following if automatic trans: 3.08, standard, whether A/C or not. Option Economy 2.73 (again, A/C or not) -- no other ratios for automatic trans.

If 4 speed, depends if close ratio or wide: for WIDE, the standard ratio was 3.08, whether A/C or not. No economy ratio, but what they called the "performance" ratio was 3.36 (again A/C or not). No other ratios available with L36 or L68 wide ratio.

If CLOSE ratio 4-spd, standard ratio was 3.36; economy was 3.08, performance was 3.55, and "special purpose" was 3.70; again no difference if A/C or not.

Hope this answers what your car COULD have had.

[Brandon T.]

Re: what rear end ratio in my 68 427?

Brandon -- your L36 (applies to tri-power L68 as well) would have had the following if automatic trans: 3.08, standard, whether A/C or not. Option Economy 2.73 (again, A/C or not) -- no other ratios for automatic trans.

If 4 speed, depends if close ratio or wide: for WIDE, the standard ratio was 3.08, whether A/C or not. No economy ratio, but what they called the "performance" ratio was 3.36 (again A/C or not). No other ratios available with L36 or L68 wide ratio.

If CLOSE ratio 4-spd, standard ratio was 3.36; economy was 3.08, performance was 3.55, and "special purpose" was 3.70; again no difference if A/C or not.

Hope this answers what your car COULD have had.

Thanks, thats exactly the info I was after. Not sure if it's a wide or close ratio. The trans is matching but it lacks that close/wide ratio letter identifier since it's a early 68 build car and they started putting that A or whatever the wide ratio code on them after the build of my car.

so it's hard to say which it has since wide/close really doesn't have anything to do with the throw of the shifter (used to think it did)

My GUESS would be it's a wide ratio and it doesn't seem all that low geared so probably 3.08.

I'll have to watch my rpm's and determine it that way when I get it back on the road.

thanks!

[Wayne M.]

Re: what rear end ratio in my 68 427?

....I'll have to watch my rpm's and determine it that way when I get it back on the road.

Correct; regardless of the final drive differential ratio, and at any speed, the clue is in the drop in RPM in shifting from 3rd to 4th. The rev's will drop by 1.46 times with wide ratio, but only 1.28 if close.

Example: in 3rd gear, establish a constant speed; tach reads (say) 2700 rpm. Shift to 4th, maintain or re-establish speed to same as before, note rpm's. If 2110, means close ratio; if 1850 rpm, it's a wide ratio.