Checking rear ratio

Mark the input shaft and the rear axle at a starting point. Then spin the input shaft 3 complete revolutions. If your axle spins about 1/2 of the way around probably have a 3.54. Larger ratios you might have to reduce that fraction..not precise but gets ya an idea

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same thing as above but put the trans in 3rd gear jack up one wheel and turn the engine over 3 turns using the hand crank. 3rd gear is a 1:1 ratio.
 
1 to 1 so what woud I have a 378 354 411 the car csme from redloge out side of yellowstone the motor sounds really fast when running 45 what would a 411 be 1 to 1
 
Remember, with ONE wheel jacked up, the other wheel turns TWICE as FAST!!
In Auto Shop, even with cutaway rear ends, it took me a LONG time, to FIGGER thet one out????
It's because the AXLE gears have TWICE as many teeth as the SPIDER gears have! (Comprende'?)
Bill Dummy
 
Sounds like a break down in communication here.
If all else fails, remove the rearend drain plug and drain oil. Remove filler plug and using a modelers paint brush, mark one tooth on the ring gear with white paint. Rotate one tire and count the number of teeth on the ring gear. Caution,,,,,,back tires must be off the ground to rotate. Report back with your teeth count.
 
Jack up only one rear wheel, put the ****** in high gear. Mark the tire and ground, then hand crank the engine. If you have to crank the engine just a little over 4 full turns to make the tire turn exactly 2 revs, then you have a 4.11 rear end ratio.

If you have to crank the engine 3 and 3/4 turns for two tire revs, then you have the 3.78 ratio.
 
Am I correct that I have a 4.11?

I did this check yesterday.

4-1/8 crank turns equaled 2 tire revs AND at 60 MPH I am doing 3,200 RPM.
 
Thanks, I would really like to go lower. Anyone have any trades for a 3.54?
 
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I have the engine out of the car and ran this test to double check my rear end ratio.

What does this tell you that I have.

With the engine out I turned the left rear wheel 1 turn counter clockwise, with the trans in 3rd gear.

The input shaft turned 1 full turn + an additional up to 7/8’s of a turn, it stopped just about at 11 o’clock. So, not quite 2 turns.

With the wheel turned two times counterclockwise input shaft turns two and three-quarter turns
 
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old31 said:
I have the engine out of the car and ran this test to double check my rear end ratio.

What does this tell you that I have.

With the engine out I turned the left rear wheel 1 turn counter clockwise, with the trans in 3rd gear.

The input shaft turned 1 full turn + an additional up to 7/8’s of a turn, it stopped just about at 11 o’clock. So, not quite 2 turns.

With the wheel turned two times counterclockwise input shaft turns two and three-quarter turns
Click to expand...

Was the other wheel locked from any turning? If it didn't turn at all, then you have a 2.75 rear end ratio, but that can't be.
Are you sure it wasn't 3 and 3/4 turns, which is the standard 3.78 ratio?
 
I had the left rear wheel jacked up, the right rear was on the floor, and the trans was in 3rd.

Very possible that I miscounted, I will try again later today.
 
Here's the method I use:
Remove spark plugs
Jack RH rear wheel just clear of the ground and mark the tyre at 12 O'Clock ( I use a spirit level to get it as close as I can)
Set the hand brake so it is just dragging
Select 3rd gear and direct drive if you have an overdrive
Turn the engine exactly 2 turns.
Now, if the mark on the tyre stops at 11-12 O'clock, you have 4.11
12-1 O'clock, you have 3.78
1-2 O'clock, you have 3.54
 
Clamp a vise grip onto the end of the input shaft with the transmission in 3rd gear and rotate the rear wheel that way. Perhaps a bit more precise.
 
Synchro909 said:
Here's the method I use:
Remove spark plugs
Jack RH rear wheel just clear of the ground and mark the tyre at 12 O'Clock ( I use a spirit level to get it as close as I can)
Set the hand brake so it is just dragging
Select 3rd gear and direct drive if you have an overdrive
Turn the engine exactly 2 turns.
Now, if the mark on the tyre stops at 11-12 O'clock, you have 4.11
12-1 O'clock, you have 3.78
1-2 O'clock, you have 3.54
Click to expand...

Yes, but remember that I have the engine out of the car.
 
I find a very accurate way to achieve the rear end ratio is to put the trans in neutral so the input shaft does not turn. Remove the speedo cable from the dash and hang the cables end out of the r/s door. Jack up the r/r wheel and spin it one revolution, then report back how many revolutions the speedo cable spun.
 
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