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Old 05-19-2017, 02:58 AM   #1
chiliman
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Default Checking rear ratio

How do you check rear ratio without taking rear end apart thanks Richard
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Old 05-19-2017, 05:44 AM   #2
phoenix5x
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Default Re: 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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Old 05-19-2017, 06:07 AM   #3
Tom Wesenberg
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Default Re: Checking rear ratio

You asked the same question yesterday and got an answer.
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Old 05-19-2017, 06:30 AM   #4
chiliman
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Default Re: Checking rear ratio

Sorry Tom couldn't find how do you do it in the car
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Old 05-19-2017, 06:41 AM   #5
SeaSlugs
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Default Re: Checking rear ratio

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.
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Old 05-19-2017, 08:35 AM   #6
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Default Re: Checking rear 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
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Old 05-19-2017, 09:12 AM   #7
BILL WILLIAMSON
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Default Re: Checking rear ratio

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'?)
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Old 05-19-2017, 09:40 AM   #8
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Default Re: Checking rear ratio

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.
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Old 05-19-2017, 11:12 AM   #9
Tom Wesenberg
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Default Re: Checking rear ratio

Jack up only one rear wheel, put the tranny 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.
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Old 09-19-2017, 08:56 AM   #10
old31
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Default Re: Checking rear 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.
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Old 09-19-2017, 09:07 AM   #11
Tom Wesenberg
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Default Re: Checking rear ratio

Yep, sounds like you have the 4.11 ring and pinion. I can trade you a 3.78 for it if you want.
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Old 09-19-2017, 09:43 AM   #12
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Default Re: Checking rear ratio

Thanks, I would really like to go lower. Anyone have any trades for a 3.54?

Last edited by old31; 09-19-2017 at 02:52 PM.
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Old 10-12-2017, 01:34 PM   #13
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Default Re: Checking rear ratio

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

Last edited by old31; 10-12-2017 at 03:43 PM.
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Old 10-12-2017, 11:06 PM   #14
Tom Wesenberg
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Default Re: Checking rear ratio

Quote:
Originally Posted by old31 View Post
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
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?
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Old 10-13-2017, 03:07 AM   #15
old31
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Default Re: Checking rear 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.
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Old 10-13-2017, 04:31 AM   #16
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Default Re: Checking rear ratio

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
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Old 10-13-2017, 07:33 AM   #17
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Default Re: Checking rear ratio

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.
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Old 10-13-2017, 11:53 AM   #18
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Default Re: Checking rear ratio

Attached document may be of help.

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File Type: pdf ring & pinion MAFCA.pdf (78.8 KB, 57 views)
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Old 10-14-2017, 04:50 AM   #19
old31
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Default Re: Checking rear ratio

Quote:
Originally Posted by Synchro909 View Post
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
Yes, but remember that I have the engine out of the car.
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Old 10-14-2017, 11:19 AM   #20
Delrayhuh
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Default Re: Checking rear ratio

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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