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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Rear Drivelines, Drive Axles and Gearing => Topic started by: fbody on April 22, 2010, 02:24:36 pm

Title: axle codes to rear end ratio?
Post by: fbody on April 22, 2010, 02:24:36 pm
anyone have a link to axle codes.. i know it is stamped on the tube, but where is the link that shows the code and then what rear end ratio that is?  thanks
Title: Re: axle codes to rear end ratio?
Post by: fbody on April 22, 2010, 02:35:53 pm
side note, i did look at 73-87.com, those rpo codes do not go as far back as 73.

mine, 73 C20, 3/4 ton, 454.  14 bolt.
Title: Re: axle codes to rear end ratio?
Post by: zieg85 on April 22, 2010, 06:56:07 pm
Your only way to know for sure is to take the cover off and look what is stamped on the ring gear.  37 years have gone by and someone might have changed it out.  My $.02
Title: Re: axle codes to rear end ratio?
Post by: choptop on April 22, 2010, 07:48:39 pm
probably need to change the oil anyway. Ive pulled the cover on 3 of them in the last day or so, and they all showed cruddy oil with signs or water. (Milky)
Title: Re: axle codes to rear end ratio?
Post by: VileZambonie on April 22, 2010, 10:22:49 pm
http://www.chuckschevytruckpages.com/rpo_codes_1973-87.html
Title: Re: axle codes to rear end ratio?
Post by: fbody on April 22, 2010, 11:13:32 pm
true on the oil change.  yea, i was scraping all sides of the axle tubes looking or stamped number.. nothing!  oh well, will pull cover and check there.
Title: Re: axle codes to rear end ratio?
Post by: fbody on May 03, 2010, 08:44:43 pm
found it.  code FD.. now I cannot find a link with that code on it.  anyone have any ideas or a book?
Title: Re: axle codes to rear end ratio? TFD in a 14 bolt
Post by: fbody on May 03, 2010, 11:21:04 pm
well shoot, i scraped off more junk.. code is actually TFD
Title: Re: axle codes to rear end ratio?
Post by: The Lady In Red on May 04, 2010, 09:55:14 pm
Quote from: zieg85 on April 22, 2010, 06:56:07 pm
Your only way to know for sure is to take the cover off and look what is stamped on the ring gear.  37 years have gone by and someone might have changed it out.  My $.02


Zieg is right... only way to know for sure.  However FYI, these are the codes available for your truck in '73:

3.21  (OPT HC8)
3.23  (OPT GU5)
3.42  (OPT GU6)
3.73  (OPT GT4)
4.10  (OPT GT5)