10 bolt to 12 bolt

[troyb_78]

I have an 84 c10 with 3.08 geared open 10 bolt. I am running a new 350 crate motor rebuild 700r4 and 31x10.5 tires. I do most of my driving from 45 to 60 mph with the taller tires I feel like I am really not getting the most of the OD. I would like to go to 3.42 or 3.73 ratio. I have access to a 12bolt out of a late 70 truck with 3.42s in good shape. What I am wanting to know is what is involved in doing a 10 to 12 bolt conversion. I know the u joints are not going to match up and I have heard the 10 bolt drive shaft will be short. Is it worth messing with or should just go looking for a 10 bolt with a higher ratio. Any help of advise will appreciated...

[gchemist]

I did the same swap. The driveshaft is okay. All you need is a new U-joint for the axel. The 12 bolts have a smaller cap than 10 bolts. You need a u-joint with two small caps and two large caps.
Clean and paint the 12 bolt before installation.

[troyb_78]

You don't happen to have a part number for that U joint?

[troyb_78]

Also will the drum brakes off the 10 bolt up to the 12?

[gchemist]

Sorry I don't have the part number. If memory serves, Spicer 1(?)32 comes to mind. Ask for a 10 and 12 bolt u-joint. Then tell them to find one with the same caps on opposite sides.

[SBTork]

Originally Posted by troyb_78

Also will the drum brakes off the 10 bolt up to the 12?

ill second that question. Also, would it be ok to just run the 12 bolt brakes?, because the rear on the newer trucks have that odd brake option, and I think the master cylinder was different too.

[SBTork]

.....anyone........

[74 shortbed 406]

I swapped the drivetrain out of an 81 chevy(10 bolt front, 12 bolt rear) into an 87 chevy (10bolts front/rear) and had no problems with the brakes. I rebuilt the brakes on the axles and went

[1SlowShortwide]

I used part number Neapco 3-3130 it was about $35.

[ElGracho]

Originally Posted by SBTork

ill second that question. Also, would it be ok to just run the 12 bolt brakes?, because the rear on the newer trucks have that odd brake option, and I think the master cylinder was different too.

I did the swap on an 84 K10. I used the brakes off the 10 bolt. You could use either. They will both bolt to either axle and could very likely be the same.

The ujoint is a conversion joint. I know NAPA will have them in stock. I have the number somewhere but I have to find it.

[1SlowShortwide]

What was the "weird brake option"?

[SBTork]

Originally Posted by 1SlowShortwide

What was the "weird brake option"?

well, I know that the later model trucks like mine had two different brake options for the front and rear, I thought they took a different master cylinder but I guess I could be wrong. If it's been done, then it must be ok, but now I know. Thanks for the replies.