What's my 72 Blazer Rear Diff?

[gsta86]

So, got Diamond back from the engine shop, everything is good to go on that front. Builder said RPMs way to high for freeway driving, around 3200rpm last I drive it. He said, rear diff feels like it's probably 4.11 gears, and recommended I drop down to 3.55gears. This I am trying to make this a short distance daily driver, (16miles round trip @ 65 ) how can I figure out at home what gearing I have? Any way to do this w/o pulling diff cover? We're the 4.11 stock? He also recommended that putting a 700r trans would def solve the problem and be the best overall solution. Please and thank you for dropping your 2 pennies into my piggy bank.

 

[PenguinLTZ]

Should be 3.73 stock.

Get the numbers that are stamped on the end of the pinion shaft. You may have to pull the u-joint, but that 12 bolt has 2 sets of numbers stamped right on the end of it, behind the ujoint.

You should be able to clean it off with a tooth brush and read them, but pulling those u-bolt straps and getting the u-joint out is really easy.

Get those 2 sets of numbers and divide = ratio

 

[gsta86]

Should be 3.73 stock.

Get the numbers that are stamped on the end of the pinion shaft. You may have to pull the u-joint, but that 12 bolt has 2 sets of numbers stamped right on the end of it, behind the ujoint.

You should be able to clean it off with a tooth brush and read them, but pulling those u-bolt straps and getting the u-joint out is really easy.

Get those 2 sets of numbers and divide = ratio

Too easy! As long as the numbers are there. I've noticed yellow paint marker on diff parts, pretty sure one of the previous owners swapped some parts. Thank you!

 

[gsta86]

Not being able to sleep w/o checking. I investigated my rear end, no ID tags,and didnt see any numbers that I could divide and make since. But! Checking the right where the driveshaft connects w/rear trans....call me dumb, but that's the u joint right? Any who, I found a gearing number 4.39, maybe could be 4.89, but that seems very very low. Thoughts?

 

[gsta86]

So, pulled the diff cover and the stamped numbers are 41-11 = 3.73 gears. I'm going to try and post some pix of all the numbers stamped everywhere just to give a better idea of my confusion. The front is a Dana 44.

 

[dirtyoldman]

While not ideal road gears they're not that bad.What size tires you running,larger diameter would help.


That being said,3200 is a bit high for freeway speeds.

 

[gsta86]

While not ideal road gears they're not that bad.What size tires you running,larger diameter would help.


That being said,3200 is a bit high for freeway speeds.

I've got 35" BFG KM2 on it. Ran it today for first time since I got it back. Took it up the Strand, cruised between 2k/2500rpm and I seemed to be at freeway speeds. Speedometer don't work so can't say for sure. Seat of the pants feel, and pacing a car in front of me.

New problem. Tinkering w/my gauges to try and make em work, ended up having 2 wires touch, cold/hot. Truck immediately shutoff there was some smoke. Now it won't start. It'll crank and crank, but won't turn, What'd I burn out? Got the battery on the charger hoping that's all it needs. Merry Christmas!

 

[PenguinLTZ]

So, pulled the diff cover and the stamped numbers are 41-11 = 3.73 gears. I'm going to try and post some pix of all the numbers stamped everywhere just to give a better idea of my confusion. The front is a Dana 44.

That is what I figured.

Just how freakin' fast are you going to turn 3200 with 35's?

Something is wrong there, sunshine

 

[dirtyoldman]

While not ideal road gears they're not that bad.What size tires you running,larger diameter would help.


That being said,3200 is a bit high for freeway speeds.

I've got 35" BFG KM2 on it. Ran it today for first time since I got it back. Took it up the Strand, cruised between 2k/2500rpm and I seemed to be at freeway speeds. Speedometer don't work so can't say for sure. Seat of the pants feel, and pacing a car in front of me.

New problem. Tinkering w/my gauges to try and make em work, ended up having 2 wires touch, cold/hot. Truck immediately shutoff there was some smoke. Now it won't start. It'll crank and crank, but won't turn, What'd I burn out? Got the battery on the charger hoping that's all it needs. Merry Christmas!

You might have fried the ignition switch,or look for a fusible link under the dash or out on the firewall

You might have fried the wire going from the starter to the ignition switch.

Get under the Blazer and check the wires connected to the starter solenoid,follow them back to the ignition switch.Hell the starter solenoid might even be fried

Have you checked all the fuses?


BTW,I love my KM2s

 

[gsta86]

While not ideal road gears they're not that bad.What size tires you running,larger diameter would help.


That being said,3200 is a bit high for freeway speeds.

I've got 35" BFG KM2 on it. Ran it today for first time since I got it back. Took it up the Strand, cruised between 2k/2500rpm and I seemed to be at freeway speeds. Speedometer don't work so can't say for sure. Seat of the pants feel, and pacing a car in front of me.

New problem. Tinkering w/my gauges to try and make em work, ended up having 2 wires touch, cold/hot. Truck immediately shutoff there was some smoke. Now it won't start. It'll crank and crank, but won't turn, What'd I burn out? Got the battery on the charger hoping that's all it needs. Merry Christmas!

You might have fried the ignition switch,or look for a fusible link under the dash or out on the firewall

You might have fried the wire going from the starter to the ignition switch.

Get under the Blazer and check the wires connected to the starter solenoid,follow them back to the ignition switch.Hell the starter solenoid might even be fried

Have you checked all the fuses?


BTW,I love my KM2s

Been doing research on msd website. Got a couple trouble shooting plans to do later today. Tried the first one just now, didn't get any spark. From the coil wife. Need to trace that red wire like you said though. From the looks of things,previous owner didn't run ignition box direct to battery like instructions highly suggest. The wiring in this thing is horrid.