The Stovebolt Site Forums The Shop Area Engine Shop GM 14 bolt - determining ratio

A friend has two different 3/4 or 1 ton GM 14 bolt differentials available. The first thing I did was get the numbers off the axle tubes, one has RHR G1542 and the other has KHN G0161. I did a lot of searching via google and on the bolt site and the only thing I could come up with is the RHR unit appears to be a 72 1-ton model with a 4.57 ratio.

I can find nothing when searching for the KHN model.

The next thing we did was to count revolutions. This is where things start to get screwy. One wheel was on the ground and the other wheel was in the air. For the diff with a 4.57 (RHR) when I turned the wheel one full revolution the pinion turned 2.125 revoltions. How that correlates to a 4.57 ratio is beyond me.

When I turned the wheel on the KHN diff one full revoltion the pinion turned 1.6 revoltions.

Can anyone explain to me how the information relates to diff ratios?

Thanks,

Brad

Hy bkahler, because one wheel was on the ground the differential was involved, so basically you need to double your readings to come close to the correct ratios, hope that helps.

Wrench, thanks for the info. Based on your description that would make the KHN unit something like a 3.2 or 3.4 ratio. Unfortunately that would be to high for my application. I'm looking for a 4.10 gearset.

Thanks,

Brad

2 X 2.125 = 4.250

But it is more accurate to count the pinion revolutions per two full turns of the wheel.

Geeze I just count the teeth on the pinion and the ring gear. If I am gonna buy a rear end I am gonna open the cover before I pay.

Baldy,

Your 4.250 is close to the 4.57 that the RHR is supposed to be. But to low for my application.

Toyvo,

I will be pulling the cover off any diff that I plan on buying but I'd sure like to have a good idea of what to expect before doing so. My friend probably wouldn't appreciate the mess I'd make pulling covers like that.

Brad

I have one of those. But you can't have it! It's under my 1-ton pickup and it's going to stay there.

For your 4.10, you will be looking at 41 teeth.

OldSub, where do you live..?....

truckernix, thanks for the tooth count. I'm going to call my friend and have him pull the cover possibly this weekend and see whats inside.

Thanks,

Brad

I'm 2,384 miles northwest from Jefferson. Its the black truck sitting out front. The neighbors have some big dogs. Just ignore them.

The gear ratio is base on the number of teeth on the ring gear/the number of teeth on the pinion gear, i.e. 41 ring gear teeth/10 pinion gear teeth = 4.10 gear ratio. With the cover off to check the ratio, also check the gears for a good mesh pattern. Additionally, check the gear oil for any sign of suspended shavings. Also, grab the backing plates and pull them in and out to check for excessive slop. A good deal on a 14-bolt with 4.10 ratio, can be be a bad deal if the rearend requires a new ring and pinion master setup. Good luck with your search and I hope this information is helpful.