Re: [AMC-list] Identify 65 AMC 20

[Frank Swygert <farna@xxxxxxx>]

Letters weren't stamped on the diff to identify rear axle ratio until 
1970 for the AMC 20, 1972 for the AMC 15. Double letters were usually 
used to indicate Twin-Grip. Twin-Grip got a different single letter code 
starting in 1977 (i.e.: B = 3.15 standard, P = 3.15 TG).

Prior to 1970 (72 for the 15) the gear ratio was indicated by a tag on 
one of the cover bolts with the number of teeth on the pinion and ring 
gear written as a fraction. 13/41 (or 13-41) indicated a 13 tooth pinion 
gear with a 41 tooth ring gear. Divide 41 by 13 and you get 3.15. 
Twin-Grip was indicated by a tag on the filler plug of the AMC 15. I 
don't know where the tag is attached on the 20. All the TSMs say "tag 
attached to the rear cover filler plug" even though we know there is no 
such plug on the AMC 20 axle. Chalk that one up to the editors who 
didn't know any better, and no one caught it throughout the 60s! There 
is a tag either on the filler plug  near the pinion shaft or a rear 
cover bolt.

The only problem with the tag on the filler plug is that it's probably 
gone if the axle lube has ever been changed. Many of the gear ratio tags 
are gone for the same reason, though I always put them back. If the tag 
is missing the rear cover has to come off to identify Twin-Grip. With 
the cover off if you can clearly see the spider gears through two large 
openings in the differential carrier you have a standard diff. If the 
gears are enclosed then you have a Twin-Grip. There will be 5-6 small 
openings off to one side to allow lube into the case.

--
Frank Swygert
Publisher, "American Motors Cars"
Magazine (AMC)
For all AMC enthusiasts
http://www.amc-mag.com
(free download available!)

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