What is this rear end

Discussion in 'Got gears?' started by jmbarber, Jun 7, 2020.

  1. monzaz

    monzaz Jim

    Run a pattern before removing the 3.42 gears and take backlash reading. Then disassemble.
    Reassemble it in the other rear and see where you are. Jim
  2. jmbarber

    jmbarber Well-Known Member

    Right, the rusty one is the original with the 3.42. The gloss black one is the replacement, and most likely from a 70. They are both posi.

    I don't plan to try to make the swap myself. I have not ever done that work, so will get someone with the proper skills to make sure it is done corrrectly.

    Thanks for all the help. It went down paths and ended up at a different place than I thought, but since they are both the same all should end well.
  3. BrianTrick

    BrianTrick Brian Trick

    What exactly is wrong with the original 3:42 rearend? Is the housings badly pitted or damaged?
  4. jmbarber

    jmbarber Well-Known Member

    I had a rusty frame, and I found a replacement. That replacement frame was ready for a body, all set up with new brake and fuel lines, emergency brake, steering etc. The rear end was set up along with the brakes, so I left them as is and put my body on the new frame. The rear end was set up with something like 2.90 gears, and I don't like the way it drives with that gearing. There is nothing wrong with the original rear end, but it didn't make sense to switch out all that nice new equipment. So that is why I want to switch just the gearing so I have the proper gearing for the car, and get the original drivability back.
  5. monzaz

    monzaz Jim

    2.93 gear is a pretty good driving ratio in my opinion - overdrive I would do 3.42 and steeper. I do not like hanging around town and going slow on the freeway.
    My Monte SS has 3.55 and over dirve. I will never go back to a three speed auto or anything that is 1 to 1 final drive with out at least 3.08 or taller
    Wife's 67 convert Camaro is 2.73 with 350th very good combo for everything.... Not a drag race car. Does burn outs well as we have a 2000 stall . 327 with a 252 comp cam fun little cruiser drop top. 15 flat in the 1/4 mile. 90 mph on freeway easy all day long.

    Attached Files:

  6. Mark Demko

    Mark Demko Well-Known Member

    If the original 3.42 rear is good and all it needs is a cosmetic redo, I'd do that all day long as opposed to switching guts, at least you'll know when its all clean and new looking it'll work:D
  7. flh73

    flh73 Well-Known Member

    Agreed on drive ability with a three speed. My Stage car with original set up 3:64 three speed is great fun for zero to 80 blast but forget about trying to cruise down the hwy at 70mph not fun. drove a friends 69 455 swap 3:73 gear with a 200-R4 Wow what a ride all around... The one under construction is the original 3:08, i think this might be ok.

    I second redoing the entire original rear axle. Swapping hardware brakes etc. is more forgiving then the "guts" especially if the gears are not setup correctly $$$.

  8. BrianTrick

    BrianTrick Brian Trick

    I’d rather keep the guts in the matching housing if possible,especially if you have never setup a rearend,or have the specific tools to do so. You can take it completely apart and put it back together the same way. Swap all of the bearings/seals,and possibly have Jim freshen-up the posi unit. While the housing is apart,you can degrease the whole thing in & out,and have it blasted a powder-coated,or just blast,prime,paint.
    AND you can do all of this while your car is still together and rolling.
  9. jmbarber

    jmbarber Well-Known Member

    All good advice. The issue for me with the most likely 2.93 gearing is that it doesn't match up well with the Stage 1 BB transmission. In order to get it to shift into third at city speeds requires a spurt of gas, and then lift. It needs that pressure to shift, and it doesn't get it at city speeds. Left to itself it shifts between 35 and 40mph. Not good for 30 or 35mph speed limit areas.
    All this discussion has me considering learning to live with it, and storing the rear end to sell with the car if I decide to do that.
    FYI, I drove the car to the Woodward Ave Dream Cruise one year before all my recent work started, and it was not at all uncomfortable at highway speeds. Maybe the 3.42 is just high enough to get the revs down into a more comfortable cruising area.
    Having Jim refresh the axle might be an interesting exercise in transportation logistics.
    Thanks for all the input everyone.
  10. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Sounds to me like you need an adjustable vacuum modulator. You should be able to adjust the minimum shift points down some.
  11. monzaz

    monzaz Jim

    tHAT IS WEIRD. sounds like something is sticking in the valve body or also make certain you have enough fluid when hot as the shift will get delayed with low fluid.
  12. jmbarber

    jmbarber Well-Known Member

    I checked the fluid awhile ago before that whole frame switch, but will check it again to be sure it is full.
    I thought of another issue that is causing an issue. Because of the gearing change, the speedometer must be reading low. If I am staying with the current gearing I will have to figure out how to adjust that speedometer gear. I did this on an MG some years ago, but I'm sure this is a different set up.
  13. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    You can figure that out. You need three numbers. First, rear tire size/height. Second, rear gear ratio, and third, the number of teeth on the DRIVE gear. The DRIVE gear is on the transmission output shaft. You can see the DRIVE gear when you pull out the DRIVEN gear sleeve. It's a helical gear. If you get the back end of the car in the air, you can rotate the driveshaft with the trans in neutral and count the number of teeth. You mentioned the BB transmission. They usually have a 16 tooth DRIVE gear, but you should check anyway. Once you have those 3 numbers, plug them into this calculator , and figure what DRIVEN gear you need.

  14. Eric Keel

    Eric Keel Member

    I have a 68 Skylark. The motor is being rebuilt and changing to A 4barrell carb and changing the cam.
    The rear end is a 2.70.
    should I change it?
    What is the best gear ratio to go with?
    Where is the best place to get one?
    Not looking to do any racing
  15. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    The 68-70 Buick 8.2 10 bolt rear is the one that came stock in your 68 Skylark. There are no new gears made for that rear. You might as well leave it the way it is. Not every cam needs more gear. It depends on the cam. If you haven't committed to a machine shop, I would encourage you to hold off doing anything to the engine. You should do some research on this site before choosing how you want to rebuild. That is the best way to avoid making common mistakes and wasting your money.
  16. monzaz

    monzaz Jim

    Stay in the 260 - 270 advertised cam range and you can keep the ratio I like the 260 - 268 range for fun torque in any size motor 2000 stall to 2500 and you wil lrip any ratio rear on the street easy.
    DO NOT forget about ignition...SO important to have a GOOD ignition system. PERIOD!


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