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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Chevhughes on February 23, 2015, 07:57:27 am

Title: 1985 C20 rear end decode help please
Post by: Chevhughes on February 23, 2015, 07:57:27 am

I have a 1985 c20 from Calif. it has a 700r4 and stock 350. I am trying to figure out what rear end is in the truck, and having no luck in my search. Thank you in advance for any help. The axel tube is stamped BDB G0921 Thank you again. any oil recomendations for this rear end ?

Title: Re: 1985 C20 rear end decode help please
Post by: zieg85 on February 23, 2015, 07:59:46 am

Do you have the sticker in the glove box?

Title: Re: 1985 C20 rear end decode help please
Post by: Chevhughes on February 23, 2015, 08:01:12 am

Glove box sticker is tough to read unfortunately

Title: Re: 1985 C20 rear end decode help please
Post by: zieg85 on February 23, 2015, 08:05:36 am

I can not find any info on the numbers you posted

Title: Re: 1985 C20 rear end decode help please
Post by: zieg85 on February 23, 2015, 08:07:53 am

I re-read your post.  You more than likely have a corporate 14 bolt semi float rear end.  Post a picture with the hubcap off to confirm

Title: Re: 1985 C20 rear end decode help please
Post by: Chevhughes on February 23, 2015, 08:16:18 am

it is 14 bolt

Title: Re: 1985 C20 rear end decode help please
Post by: zieg85 on February 23, 2015, 08:21:15 am

14 bolt semi float or 14 bolt full float are your 2 stock choices.  The first has a 9.5 " ring gear and the brake drum goes over the axle like a car rear end.  The full float axle bolts to the drum.  Pictured is the 10.5" full float

Title: Re: 1985 C20 rear end decode help please
Post by: zieg85 on February 23, 2015, 08:31:42 am

Semi float

Title: Re: 1985 C20 rear end decode help please
Post by: Chevhughes on February 23, 2015, 08:36:34 am

i'm thinking semi thank you very much, any idea on gear ratio ?

Title: Re: 1985 C20 rear end decode help please
Post by: zieg85 on February 23, 2015, 09:15:24 am

Try and get it from your glovebox sticker.  The only way is to take the cover off and see the stamped numbers on the ring gear.  For example 41 10 would be a 4.10 ratio

Title: Re: 1985 C20 rear end decode help please
Post by: zieg85 on February 23, 2015, 09:17:33 am

on car rear ends that first letter "B" is supposed to be the gear ratio but I can't find info on the corporate 14 bolts to decode it ratio wise

Title: Re: 1985 C20 rear end decode help please
Post by: Chevhughes on February 25, 2015, 07:06:30 am

Thank you for the help zieg. any oil recommendations for this rear end ?

Title: Re: 1985 C20 rear end decode help please
Post by: zieg85 on February 25, 2015, 12:56:16 pm

The manual calls out for 80W-90 GL-5

Title: Re: 1985 C20 rear end decode help please
Post by: Chevhughes on February 25, 2015, 02:48:41 pm

you guys are the best..

Title: Re: 1985 C20 rear end decode help please
Post by: Chevhughes on February 26, 2015, 06:08:54 am

After looking closer at the glovebox door, I think it reads GU5 ?  I think that is 3:23 ? does that sound right with a 350, 700r4 and bone stock from cali ?

Title: Re: 1985 C20 rear end decode help please
Post by: zieg85 on February 26, 2015, 07:44:46 am

GU5 makes sense.  3.23 is the ratio for a semi-float 14 bolt