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Thread: rear end work

  1. Default rear end work

    Can anyone recommend a shop in Calgary that can change my rear end gear ratio without raping me in the process.?

    I have a 10 bolt someone that previously owned my car, had the gear center put an Auburn posi in with 3.55 gears. I put a 700R4 in the car but I'm not happy with it at highway speed. It has short 24.5 " tires and its about 2800 RPM at 100 km/hr. I do all highway with the car so I want to maybe put the 3.08 ratio back in to get the rpm down.

    Suggestions welcome.

  2. Default

    The gear center is quoting $1500 , to change the ring and pinion gear and he wants me to remove the axle from the car so he doesn't have a hot rod in the shop. That sounds like a lot of money to me and a pain in the ass. I think I can get a bigger tire under there that is 2 inch diameter bigger , which I can do for under $200 so I'm hoping it will buy me 200 rpm.

    I'm wishing now I went with a lock up torque convertor with the 700R4 . Its a 2400 stall and definitely seems looser which I don't think is helping me on the highway.

  3. Default

    This site has died . I wonder who is bothering to fund the web space ? Last one out turn off the lights.

  4. #4
    Join Date
    Oct 2005
    Location
    Alberta's Capital City
    Posts
    667

    Default

    Have you talked to Dario?

    As for RPM @ X MPH, if you PM me an email address, I can send you a crude spreadsheet I cobbled together, so that you can run the numbers with various axle ratios or tire diameters.....

    James

  5. Default

    I talked to Dario before I bought the car about doing a LS swap , but decided to just do a 700R4 conversion. He seems pretty swamped with work.

    I have run my tire size, rear axle ratio ect. through a bunch of RPM calculators but they all say I should be at 2100 RPM at 100 km/hr but I am at 2800. Its a non lock up 700R4 with a 2400 stall so I am wondering what my true overdrive ratio would be ?

    I doubt its the .7 to 1 that a lot of sites suggest.

  6. #6
    Join Date
    Oct 2005
    Location
    Alberta's Capital City
    Posts
    667

    Default

    First Example using 0.7 as trans OD ratio, & 2100 RPM

    Tire Diameter RPM Axle Ratio Trans Ratio MPH
    24.5 2100 3.55 0.70 61.620


    Second example using 1:1 trans ratio, @ 2800 RPM

    Tire Diameter RPM Axle Ratio Trans Ratio MPH
    24.5 2800 3.55 1.00 57.512

    So, it looks like your'e not any getting OD !

    and BTW, my crappy spreadsheet has a separate page to calculate the actual height of metric tires in inches

  7. Default

    It's definitely making the fourth shift , but without the lockup and the 2400 stall I think you are right, its not .7 to 1

    There was a turbo 350 in it before and I was doing over 3500 RPM at speed ( speedo gear was wrong so don't know exactly) so it's a big improvement. I think being used to modern cars is not helping where your doing 110 at 2000 rpm.

  8. Default

    Just a thought.....maybe I should hook up a second temporary tach and make sure mine isn't reading high.

  9. #9
    Join Date
    Oct 2005
    Location
    Alberta's Capital City
    Posts
    667

    Default

    Chances are pretty low that the tach is the issue. I would be more concerned with the ACTUAL height of your tires, AND the ACTUAL MPH/KPH vs the speed indicated by your speedo. If you've messed with tire height (vs stock) but haven't changed the gears on the trans/speedo cable, your indicated speed may be incorrect.
    As a check, you can probably find a free speedometer app that uses the GPS in your phone , would be good to verify the speedos output, and for comparing the factory speedo's numbers against your calculations of what your speed should be at any given RPM.....

    James

  10. #10
    Join Date
    Nov 2007
    Location
    Edmonton
    Posts
    792

    Default

    I can set up gears for you, but I'm located in Edmonton.

    If your diff is a common piece is it an option to swap out for another diff with factory installed 3.08 gears? Could be a cost conscious avenue if you're using an S10 or G body diff for example.

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