12 bolt carrier

[sg1747]

how do you know if you have a 3 or 4 series carrier.i have a 69 z with 373 and want to put 410 in.someone said you need a 4 for a 410 gear.

thanks

[396L35]

I think they sell a 4:10 for a 3 series, pick up a Jegs or Summit and check it out. Mark

[WILMASBOYL78]

Check the casting number on the carrier, if it's original probably 3 series...you can use a spacer to put 4 series gears on the 3 series carrier. If you need a GM 4 series Eaton unit...I have one.

wilma

[Dusk Blue Z]

US Gear http://www.usgear.com/us_strange.htm makes a thick 4.10 gear set to work on a 3 series carrier, part # is 01-888411X. Use that and you don't have mess with spacers or longer bolts. I agree with Mark, Jegs or Summit.

Mike

[SSRSBOB]

Using a spacer will sheer off the bolts under load.

Bob

[SSRSBOB]

Watch out for gear whine with aftermarket gears! Used GM are the best.

Bob

[Salvatore]

I just had a set of 4:56's put in my Z/28. Richmond gear from Jegs. No real whine at all. Its a matter of spending the time and getting the set up right. John, make sure you buy a 25 tooth trans gear for the speedo also.

[Musclecarkid]

Original GM 12 bolt 3 series carrier number xxx140. 4 series is xxx174.

[sg1747]

thanks everyone
john

[RichSchmidt]

Ring gear spacers dont shear the bolts I dont care what anybody says.I ran 5.13's with a spacer on my 12 bolt in a high 9 second car.The car weighed about 3500# and twisted the stock axles almost 90 degrees{thankfully they had C-clip eliminators on them},but never broke the ring gear bolts or the gears.The right bolts will have a shank that goes entirely through the spacer.

As for gear whine,the primary reason for gear whine is because aftermarket gears with over a 4,10:1 ratio must be set up with a different wear pattern then what most old timers learned from back in the day.In the case of Richmond gears,most gear with 3.90 and lower ration are called 39 or 49 series gears and can be set up with a tradtional pattern of centering the drive and coast pattern on the ring gear tooth.
Most 4.10 and higher ratios are 69 series gears and require that you use the pattern that is shown on the instructions with the gears.If you attempt to center the drive pattern,the coast pattern will run off the end of the tooth and cause horrible whine.Richmond designs them this way because the moving the pinion further into the mesh improves strength which is critical on high powered car with low pinion tooth count.So whoever sets up the gears needs to read the instructions.

BTW,the cutoff for 12 bolt ratios is 3.90,so you will either need the correct thicker ring gear set,or a spacer to keep your current carrier.Be carful first and check what gears you have now since aftermarket gear sets where also available to put some 3's gears onto 4 series carriers,so if you have aftermarket gears then check which carrier you have.Good luck.