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Rear diff ID

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Old Aug 8, 2015 | 02:45 PM
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1968SafariYellow's Avatar
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Default Rear diff ID

Hello all

I've been a lurker for a while as I have been fixing up a 1968 BB Coupe for my dad. Lots of great info on here, but i've hit a roadblock.

We took the body off and had it and the frame blasted. Once I got the frame back, I started looking around and decided to check the rear differential number in an attempt to identify it.

I can't find anything that matches my numbers and was hoping you all could help.

Drivers side casting: K187 (I assume 11/18/1967)
Passenger side casting: 8899143
Stamp on base: OK 334 (backwards)N 7E

Any ideas on that stamp?

Thanks
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Old Aug 8, 2015 | 03:21 PM
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Hi 68,
WELCOME! First Post!
The only listing I can find for an OK code is a 3.08 ratio differential used in 1978….. but the date doesn't work?!?
So?
Regards,
Alan
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Old Aug 8, 2015 | 03:34 PM
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1968SafariYellow's Avatar
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I spun the tires and counted the drive shaft revolutions and came up with 3 full turns which I believe is 3.08, so that is probably right. Thanks!

Any idea how that will drive with an m21 and l71? I am trying to make everything somewhat correct to what we believe it was originally. Seems like it should have a 4.11:1
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Old Aug 8, 2015 | 03:46 PM
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Originally Posted by 1968SafariYellow
I spun the tires and counted the drive shaft revolutions and came up with 3 full turns which I believe is 3.08, so that is probably right. Thanks!

Any idea how that will drive with an m21 and l71? I am trying to make everything somewhat correct to what we believe it was originally. Seems like it should have a 4.11:1
According to the book I have your casting date decodes as a letter for the month, one or two numbers for the day and one number for the year. Yours would be 11/18/77. The stamp on the bottom shows OK which is a 3.08:1 as Alan said and 334 indicates the day of the year for assembly.
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Old Aug 8, 2015 | 05:02 PM
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Hi 68,
I think most people would say that a 4:11 ratio would be fun for a little while but would wear out it's welcome pretty quickly with the L-71.
The 427 engines were available with the full range of ratios in 68 so anything would be 'possible' for your car…. only the tank sheet would indicate what was 'likely'.
Regards,
Alan
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Old Aug 8, 2015 | 06:46 PM
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Any idea how that will drive with an m21 and l71?
It'll be really nice on the freeway but 3.08 inst alot of gear when matched with a M21 so leaving from a stop will take a bit of clutch slip. My L36 has 3.70s and a M21 and its a bit revvy on the freeway but leaves pretty easy from a stop.
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