The Stovebolt Site Forums The Shop Area Driveline rear end swap

I have a 51 3600 that i would like to change out the rear end so that i can drive at highways speeds. Would a 3100 rear end work well at highway speeds and would it line up to my current motor and transmission? Thanks for an help.

A 3100 and 3600 don’t share the same frame (different width and length) so the spring mounts won’t line up. The 3100 doesn’t have an intermediate u-joint like the 3600 does. Anything is possible but the amount of work involved would not be worth the result.

I have heard that there are 4:11 gear sets that could be swapped in the pumpkin. Maybe a fellow “Bolter” could verify this for us!

Like Plakt says. If you get the rear end or center section from a 67-72 3/4 ton truck with v-8 & auto trans. It is a bolt in swap. Most of those had 4:11 gears. They are pretty rare though.
George

Thanks Wrenchbender. My truck is a straight drive so would is still be looking for a rearend from a v8 auto trans?

V8 auto trans.

Ed

Not most, i believe all came with 4.11 with that specific drive option. Im sure the post police will confirm or deny the specific info. I got mine from a 72 c20 suburban with that exact setup

Very minor point here. I did the swap but I thought the gear ratio was 4.10 (41/10 teeth). A 4.11 would have 37/9 teeth, right? I didn't count the teeth but the ratio might be important when ordering parts for a rebuild. So it isn't a 4.10?

Edit: My copy of the "Chevrolet Pickup Red Book" says in 1972 (and earlier) C-10 1/2-tons had 4.11's and C-20 3/4-tons had 4.10's.
And the K-20 3/4-ton series came with 4.10 and 4.11! I'm getting confused.

WHoa!! All stop. Put the wrenches down, Pastor J. What these guys have forgotten to tell you is that there is a very comprehensive Tech Tip in our Tech Tip section of the web site that covers this very issue for your truck.

Do nothing further until you have read our Tech Tip on upgrading the ...n to achieve comfortable crusing speeds. It is a ridiculously simple, easy and effective upgrade you can do in a couple of hours.

Go read. Now.

As for the rest of you ... shame on you for sending him down possible/probably rabbit holes when you *knew* this tech tip existed.

A V-8 Ed??? Seriously??

John THANK YOU SO MUCH. i do have one follow up question. The rear end on this truck has been changed whats the easy why to discover what i have?

Also on the link you sent me said something about Tech tip for upgrading brakes. I searched hard but could not find one for 3600s, am i missing it?

You can jack up one wheel and count the revolutions of the drive shaft and get a pretty good idea (not exact) of what you have.

In order to do this, chock the front wheels, jack up one rear wheel, release the emergency brake and place the transmission in neutral. Mark the tire so you can count one revolution, then mark the drive shaft also so you can count the revolutions. With a helper, turn the driveshaft counting the revolutions, until the tire turns one complete turn.

Now to calculate the ratio, divide the revolutions of the driveshaft by two. As an example, if the driveshaft went around 8-1/4 times, divide 8.25 (converted to decimals) by 2 and you get 4.125. That would most likely be 4.11.

Disclaimer: If you have a posi-traction rear, you will need to jack up both wheels and you don’t need to divide it by 2. The actual revolutions of the drive shaft needed to turn the tire one turn, is the gear ratio.

If you need to know the exact ratio, you will have to pull the rear cover. Some gear sets have the ratio punched into the edge of the gear. If not, you can count the gear teeth and divide the larger number by the smaller number.

Pastor J -- No, that brake tech tip is still in someone's head waiting to be written ... But now that I have smacked them all on the hands with my ruler, that's not very likely to happen ... at least in my lifetime.

Ahem. Where were we? Ah yes. When you say that the rear end has been "changed" ... what do you mean? The whole axle carrier assembly has been changed? Just the gearing has been changed?

If the whole shebang has been replaced with something newer ... well, we'll need to see some pictures of it (front and back of the differential, as well as the lug pattern) to identify it and we can go from there. But first, follow Phak's instructions on determining the ratio -- that's the first step here -- determine the "as is" before formulating a plan for the "to be."

But if we may back up a bit here ... have you driven this truck yet? If it has a different rear end ... have you established that it is, in fact, "slow"? Just making sure we're aren't jumping to possibly erroneous conclusions here ...

John
Nattering Nabob of Reality

Go back on what Johns link it is correct. It tells you exactly what you need to find and complete the task.
Elmo.