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S10 Rear ends---Info by Ben

Discussion in 'T-Bucket Engine and Driveline Articles' started by T-Test, Jan 30, 2015.

  1. T-Test

    T-Test
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    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!


    Widths:

    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:

    2-5/8"


    Brakes

    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.

    Ben
     
  2. fletcherson

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    Thanks Ben! That is a good article with good info! I am sure it will help many guys out and save some homework. I will add only this piece of seemingly over simple info, if you are unsure how to tell the ratio, or the tag is missing, a piece of chalk or even a scratch will tell. Just mark the pinion and hub and count the turns, it is not exact, but will clue you in fast. Ie: 3-3/4 pinion turns to 1 hub would indicate a 3.73, etc... If both hubs turn the same direction, it is likely a posi, if they turn opposite or only one turns, it's open. If it is open, be sure to hold one hub in place while counting to get accurate info. This is not exact science, but will help narrow the search while crawling through the dirt. Happy hunting!
     
  3. Bowtie T

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    You can also call your local GM parts dept., give them the VIN # and they will tell you ratio and if it's a limited slip or open.
     
  4. T-Test

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    Indycars likes this.
  5. Indycars

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    If you know a little about MS Excel, you can edit some number and get different speeds and any tire size you like.

    Maybe you like to cruise at 60 mph or maybe its 75 or 80 mph, just edit the numbers. Maybe you have a 30.5 inch tires or your trans is an 200-4R and has an overdrive ratio of .67 , just edit the numbers.

    Need help, just ask!!!
     

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  6. DavidLee

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    There are 4000# LS1 fourth-gen Camaros running high 9s on stock 7.625s, there are 170-horse 305s breaking built 7.625s, they're inconsistent in their failures. But they're not vveak for vvhat they are. There are Bonneville LSR cars pushing 1500 horses through them, but they are traction-limited. There is strong evidence from the LS1 community that the 2 strongest ratios are 3.42:1 and 3.23:1, and genuine GM gears are the strongest. More than half of failures are the ring and pinion, but the cross shaft and its retaining bolt are also vveak.
    If you vvant to try big HP, add a load bolt set to 0.0010" from the edge of the ring gear, to reduce deflection, run a girdle vvith preload bolts, also to reduce deflection, run a solid spacer rather than a crush sleeve, never even consider Ratech's Smart Sleeve, run synthetic 75VV140 vvith Lucas additive, or Moroso's Climbing Gear Lube, and never ever shock-load the thing vvith traction. This means no neutral-slams, no clutch-dumps, no povvershifts, no shift-kits that bark the tires on VVOT 1-2 upshifts, and no trans-brakes.
    Stock GM 28-spline shafts are stronger than the R&P, aftermarket 26-spline shafts are also. The GM 3R / S44 U-Joint is too. No need for a 1350 yoke, dunno vvhy it even exists. All of the available aftermarket diffs are stronger than the R&P, except the Zexel Torsen used in '96-'02 28 SSs / Firehavvks.
    My '95 Z28 had an Auburn in it from GM, and vvay over 100K miles. It still made tvvin black stripes, especially after I did a 2400-stall torque converter. And it vvas great in the snovv. I liked it so much that I tried another one, also used, off Ebay, in my '91 Camaro RS. Same great results.
    The 4VVD S-10s are ~58.5 vvith drums, I knovv because I used one in my '83 RX-7. The Explorer drum assembly is 59.5-ish. The Ranger 8.8 came in 3 different vvidths, the first 2 years vvas the narrovvest.
     






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