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Rear axles


I have to get a rear axle to move forward with my car and could use some guidance. I have narrowed it down to 3. It is either a S10 4x4 with what ever gear makes sense, S10 G80 (posi) or 72' Ford ltd open 9" with 2.73.

The bucket is a original steel 27' and I've been told to go for the 4x4 over 4x2 because they are 4-5" longer. I don't know what the length on G80's are and see mixed reviews on them in general. The Ford 9" is obviously a favorite for many but it's got a pretty tall gear and no lsd. At this stage I've got a lot of parts to buy so I'm leaning toward the GM because they are a dime a dozen and can be found in any gearing id like. Plus if I found a newer one it would have disc brakes already.
I've posted this info before, but its probably time to roll it out again. The S10 10bolt 7.5/7.625" rear end is a good choice for the light low to medium horsepower small block cars. If you're running a blower, turbo, nitrous, etc you will probably want to step up to a larger rear like a 9" or 12 bolt. Its pretty easy to find a good one if you are in an area with a few junkyards.

I'm running the wider blazer rear end in my '27. The standard S10 is too narrow. The narrow ones work well with the '23 T's with beds, as long as you have wider back wheels and/or a standard width front axle. Some front axles are a bit wider than others and you could have a front track wider than the back- not a good look in my opinion. We used the same on our '23 project as it is running a wider front axle and the rear tires are not overly wide. You want to make sure the track width on the back is at least as wide as the front. With a 48" wide front axle, you should be ok with an 54.5" S10 rear on a '23 with wider tires.

With that being said, here is info I have compiled and written as this subject as it comes up often - I suggest you print it and take it with you to the junkyard so you can get one with a gearset you want. I'm partial to the 3.42's if you do do not have an overdrive tranny and do any highway driving and 3.73's if you do have an overdrive trans.

S10/Sonoma 7.5/7.625 Rear Axle Info

Chevrolet S10/ GMC Sonoma rear axles are a great choice for small lightweight Hot Rods such as a T-Buckets or early roadsters. These rear ends were made for many years and are plentiful and inexpensive to buy in junkyards all over. Nearly every part is available as a replacement from all of the standard auto parts retailers.

Finding a good rear end for your project:

GM made millions of S10's and they are perhaps the most found vehicle in junkyards today. Finding a good one is not too difficult providing you have a junkyard or two near you. Before heading out to the boneyard, I would first figure out what width of axle you need, and what gear set you need.

S10 2WD's have a drum to drum mounting width of 54.5" which is perfect for a T-Bucket with larger back wheels. The Blazer and 4WD models have about 4.5-5" more overall width and works well for 26 and newer fender-less roadsters, and 23 style T's with narrower rear wheels.

Rear axle ratios can be found by looking at the sticker in the glove box that has the RPO codes on it. Try find an axle that has the ratio you want as it will be much cheaper and easier than buying one that needs a gear ratio swap. As for year of S10, I recommend finding one from the newer body style (1994 and newer) The newer brakes have a bolt-on wheel cylinder that is preferred over the earlier style that uses a ring retainer. Newer axles are usually in better shape and have less miles, so I'd always recommend finding one as new as you can. One last item to consider: There are a couple kinds of pinion yokes. You will want a standard yoke to accept the u-joint. A lot of these rearends had a yoke with a balancer. You can swap these out with the simpler style. While you're at it, get the matching driveshaft!


S10 2WD: 54.5" Mounting Surface to Mounting Surface

S10 Blazer: 59.5" Mounting Surface to Mounting Surface

S10 4WD: 59.5" Mounting Surface to Mounting Surface

Bolt Pattern

5x120 (5x4.75")

Lug thread: M12x1.5 (12mm)

Axle Tube Diameter:



Rear Drum Brakes changed in 1992. Drums, cylinders and backing plates do not interchange with earlier models (83-91). The later brakes are preferable due to the bolt on wheel cylinders over the earlier style with retaining ring clip.

Drums: 9.5"x2"

Wheel Cylinders 3/4" (W/Power Brakes).

Disc Brakes: Some newer models came with rear disc brakes. These can usually be picked up for the same price, however replacement parts may be more costly.

Ring Pinion / Spline Size:

7.5" Ring Gear / 26 Spline Axles 1983-1992

7.625 Ring Gear / 28 Spline Axles 1988+

Rear Axle Codes (RPO - Found on tag in glove box)

GU2= 2:73 ratio
GU4= 3:08 ratio
GU5= 3:23 ratio
GU6= 3:42 ratio
GT4= 3:73 ratio
GT5= 4:10 ratio
GQ1= Open Differential Rear Axle
G80= Positraction/Locking Rear Axle (usually is next to the ratio code on tag)

Carrier Breaks: 2:73-3.08 ; 3.23-4.10 (3.08 and lower will not fit in 3.23 and higher and vice-versa). New pinion/ring gear sets can be bought to interchange.

Seals & Bearings

Wheel Seal: Timken 8660S (83-91) 4739 (92-02)

Pinion Seal: Timken 8610

Axle Bearings: Timken 5707

*This information has been complied from varies sources as well as the authors own experience. Information is believed accurate, but not guaranteed.



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