differential gear ratio

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wild4679
Posts: 28
Joined: July 8th, 2017, 7:14 am
Body Type: 82B
Model Year: 1931

differential gear ratio

Post by wild4679 » September 7th, 2017, 9:50 pm

I've learned AA's came with different gear ratio's in the differential. The higher speed rear ends were stamped on the outside. How does one find these stamps? I have three complete rear ends and two of them have stamps on the right side. I have included a picture of one of them. At this writing, I can not read the stamp, but believe that with some elbow grease, I can interpret what is stamped.

Can someone help me learn if this is the gear ratio stamp and what it means? My goal is to install a rear end in my
31 to obtain the maximum comfortable highway speed.
Rear end stamps.JPG
Rear end stamps.JPG (900.96 KiB) Viewed 518 times

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Chris Haynes
Posts: 1913
Joined: September 7th, 2003, 5:18 pm
Body Type: 82A
Model Year: 1930
Location: North Hills, CA/ Pine Grove, CA

Re: differential gear ratio

Post by Chris Haynes » September 7th, 2017, 10:06 pm

Easiest way is to remove the speedometer drive from the drive-line. The ratio will be stamped on the gear.

wild4679
Posts: 28
Joined: July 8th, 2017, 7:14 am
Body Type: 82B
Model Year: 1931

Re: differential gear ratio

Post by wild4679 » September 8th, 2017, 6:50 am

Thanks Chris. Only one problem: the speedometer cables are gone. So not only do I need to know the gear ratios of the three rear ends so I can choose the two I will use (two trucks to rebuild), but I'm assuming I will need to know the ratios to order the correct speedometer cables.

Now what?

Bob C
Posts: 1080
Joined: April 24th, 2003, 11:50 am
Body Type: Mail truck, Stake tr
Model Year: 1931
Location: SO CAL

Re: differential gear ratio

Post by Bob C » September 8th, 2017, 8:42 am

Like Chris said you need to remove the driven speedometer gear from the torque tube not the speedometer cable.

Bob
driven-gear.jpg
driven-gear.jpg (61.04 KiB) Viewed 493 times

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1crosscut
Posts: 700
Joined: December 25th, 2010, 7:22 pm
Body Type: 82-A
Model Year: 1929
Location: Lincoln, NE

Re: differential gear ratio

Post by 1crosscut » September 8th, 2017, 11:16 am

Block one drum / wheel from turning. Mark the other drum / wheel. Clamp a vise grip to the end of the drive shaft and see how many turns it takes to rotate the marked wheel one full rotation. You can compute the gear ratio from that.
------------
Dave

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Farrell In Vancouver
Posts: 286
Joined: February 23rd, 2011, 6:52 am
Body Type: Deck
Model Year: 1931
Location: Vancouver BC Canada

Re: differential gear ratio

Post by Farrell In Vancouver » September 8th, 2017, 12:29 pm

You are looking for a tag on one of the diff bolts that reads 7-36 which should denote the 5.14 gear set for high speed.

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Chris Haynes
Posts: 1913
Joined: September 7th, 2003, 5:18 pm
Body Type: 82A
Model Year: 1930
Location: North Hills, CA/ Pine Grove, CA

Re: differential gear ratio

Post by Chris Haynes » September 8th, 2017, 2:59 pm

Farrell In Vancouver wrote:
September 8th, 2017, 12:29 pm
You are looking for a tag on one of the diff bolts that reads 7-36 which should denote the 5.14 gear set for high speed.
My Early 1930 has High Speed gears. But NO TAG on the rear axle. A tag is easily removed.

Hayslip
Posts: 174
Joined: February 26th, 2007, 6:20 am
Model Year: 1930

Re: differential gear ratio

Post by Hayslip » September 8th, 2017, 5:45 pm

The images on the housing as shown above are hallmarks and will tell the restorer NOTHING. They may refer to suppliers of housings or they may indicate batches of stampings in case of defects; a mystery yet to be solved. Obviously not all AA housings were made in the same casting mold; maybe they indicate which mold in case of a problem.
Hayslip

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Neil Wilson
Posts: 2481
Joined: February 5th, 2003, 9:42 pm
Body Type: 89-A
Model Year: 1930
Location: Boulder, CO
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Re: differential gear ratio

Post by Neil Wilson » September 8th, 2017, 8:12 pm

1crosscut wrote:
September 8th, 2017, 11:16 am
Block one drum / wheel from turning. Mark the other drum / wheel. Clamp a vise grip to the end of the drive shaft and see how many turns it takes to rotate the marked wheel one full rotation. You can compute the gear ratio from that.
FYI - You need to divide the number of drive shaft revolutions by 2 to determine the gear ratio.
Regards, Neil Wilson
______________________________________
neil@aafords.com - use this email for contact
www.aafords.com - AA information and photographs

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tiredtruckrestorer
Posts: 288
Joined: April 20th, 2003, 7:09 pm
Model Year: 1931
Location: Orwigsburg, PA

Re: differential gear ratio

Post by tiredtruckrestorer » September 8th, 2017, 8:15 pm

The lower triangle in the picture (although upside down to read the letters in it) is the Timken trademark. The big "T" down the middle is for Timken, the "D" and "A" on either side of it is for Detroit Axles, and the "CO" beneath it is for Company. Can tell what the other triangle means.

Keith

Stakebed
Posts: 1076
Joined: June 14th, 2007, 7:29 pm
Body Type: Grainbox
Model Year: 1929
Location: Illinois

Re: differential gear ratio

Post by Stakebed » September 8th, 2017, 10:16 pm

tiredtruckrestorer wrote:
September 8th, 2017, 8:15 pm
The lower triangle in the picture (although upside down to read the letters in it) is the Timken trademark. The big "T" down the middle is for Timken, the "D" and "A" on either side of it is for Detroit Axles, and the "CO" beneath it is for Company. Can tell what the other triangle means.

Keith
So since its timken logo embossed does that mean its one of those Canuck rearends? :mrgreen:

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tiredtruckrestorer
Posts: 288
Joined: April 20th, 2003, 7:09 pm
Model Year: 1931
Location: Orwigsburg, PA

Re: differential gear ratio

Post by tiredtruckrestorer » September 9th, 2017, 4:15 pm

No, the Canadian Timken rear is completely different than the '30-'31 "AA" Timken used in the trucks in the US.

Keith

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Chris Haynes
Posts: 1913
Joined: September 7th, 2003, 5:18 pm
Body Type: 82A
Model Year: 1930
Location: North Hills, CA/ Pine Grove, CA

Re: differential gear ratio

Post by Chris Haynes » September 10th, 2017, 10:01 am

Once again. Take a wrench and remove the speedometer drive. The gear ratio is stamped on it.

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