1972 ring and pinion ratio question

[BCOWANWHEELS]

I have a 1972 c10 that came from gm with a 350 cu in engine and th350 trans. Could somebody tell me what the ring and pinion ratio is ? All help is appreciated as the tag on my diff is gone and i dont want to open it up as it has synthetic oil in it and its big $$$ for that oil.thanks
bob

[zeldman]

I have only owned one '72. It was a 350/350 like yours and it had a 3:08 rear gear.

[72Thunder]

I own a '72 C10 and same thing, tag is gone on mine but I had just opened up my rear end to do a complete rebuild and the ratio came to a 3:07. Pretty sure that was the more common ratio for those trucks with the 350/350 combo from what I've gathered. Hope this helps.

[Zeroman]

The Gear ratio code will be stamped on the top of the passenger side axle tube towards the top.
It might be difficult to see, and you might have to clean off years of dirt, rust, etc.
It is usually a three digit alphabetic code.
I do not have the list to decode, but I am sure there is someone on this board that can decode it for you.
Oh, and this code is only good if your Ring and Pinion are the originals.
Good luck.

[BCOWANWHEELS]

I have to re gear my speedometer and they specifically ask r&p ratio. some say 3:07 and some say 3:08. i,ve always assumed all gm 12 bolts were 3:08 when a auto was factory.unless ordered differently like performance or towing package etc. ???????????????

[Bobs68gmc]

Cant you just "clock " the R&P to the driveshaft?

Jack the rear so a tire off the ground. Mark the driveshaft and the rearend. Turn the tire 2 revolutions counting the number of times the driveshaft turns. The fractional values are a guesstimate, but if it only goes a couple inches past 3 then i would say 3.08, half way around 3.55, 3/4 would be 3.73.

This might not be precise enough for what your looking for , but it should get you in the ballpark. My 68 3/4 ton could have been 4.11, 4.56, or 5.14. When it went past 5 turns (checking it twice) i could only laugh.. and realized it was 5.14.


Edit- just reread your post of you wondering if either 3.07 or 3.08, that would call for documentation.Sorry, I retract my earlier statement.

[BCOWANWHEELS]

thanks i know the "old"school method of counting revs. i just want to get my speedo as close to right on as possible. my truck is lowered 5/7 and it goes thru hanger bearings about every 10 months even with a slip yoke drive shaft so I,am going to install a long tail out of a bop and not have a hanger bearing anymore. i didnt lower my truck it was that way before i got it. i,am also planning on a front mount flip for the trailing arms to correct the pinion angle and while i,am there drill the x-member for pass thru exhaust.

[69chevytrucker]

still have option sticker in glove box it will tell you look up rpo codes off it
other then that if 12 bolt 99% sure it will be 3.08 all the ones i messed with were

[67c10rustbuket]

If you check the "power team chart" thread by SStim it shows the original as assembled combos. The standard rear gear for 1972, C10, 350 V8, TH trans, was 3.07 with optional gears 3.73 or 4.11. If it were either "optional" gears (other than standard) it would be printed on the SPID. If its not on the spid it was the standard gear. So if no one ever changed it and it is original it is a 3.07 gear. This info is year/model/engine specific, Example: in '68 the standard gear with a 3ott and 327 V8 was 3.73.

Power team chart thread: http://67-72chevytrucks.com/vboard/s...d.php?t=575942 Check it out, lots of great info there.

[LockDoc]

Originally Posted by Zeroman

The Gear ratio code will be stamped on the top of the passenger side axle tube towards the top.
It might be difficult to see, and you might have to clean off years of dirt, rust, etc.
It is usually a three digit alphabetic code.
I do not have the list to decode, but I am sure there is someone on this board that can decode it for you.
Oh, and this code is only good if your Ring and Pinion are the originals.
Good luck.

Here is a link to the charts I posted a couple of years ago....

http://67-72chevytrucks.com/vboard/s...d.php?t=578793

LockDoc

[BCOWANWHEELS]

thanks fellas,i,ll check the glove box door code.

[leddzepp]

3.07 is a truck gear. 3.08 is a car gear.