Transmission or differential swap?

Discussion in 'Engine/Drivetrain' started by 77RN23, Sep 11, 2016.

  1. 77RN23

    77RN23 Member

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    I currently have 4 speed in my '77 and what I'm pretty sure is a 4.1 differential. I really want to lower the rpms when I'm going 60+. I've been researching on and off for a few months and am stuck on whether to swap the transmission or changing the differential ratio. Unfortunately, I've never done this before on an automobile, so I need some help or suggestions. For the record, this truck is just my fun weekend run about. No towing, no heavy loads.

    Option 1. Swap the transmission to a W58. I found a few at a junk yard. I see that I'll also need the bell housing and I may need to modify the cross brace and shifter position. What else? Is it as simple as getting the transmission, having it rebuilt and bolting it in? Will my existing clutch work?

    OR

    Option 2. My rear axle is already leaking a little fluid near the passenger side wheel. So, I'm going to pull it and have new seals pressed in. Why not just change the final gear ratio while it's out? I seen some suggestions going to a 3.42 or 3.08 gear ratio. Where can I find these gear sets? I can find sets larger than 4 for larger tires/offroading, but that's it.

    Thanks.
     
  2. Lowtide671

    Lowtide671 Enthusiast

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    The most economical way you be to find just the rear end out of a truck that was auto...
     
  3. jetas

    jetas Grand Toyotaholic

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    Trans
     
  4. Perkolator

    Perkolator Veteran

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    I would do both the trans and the gears

    In regards to the comment by Lowtide -- I dunno, every auto Toyota diff I've ever seen has been a lower ratio than the manual trans version - because auto trans robs power and needs lower gears to compensate. I could definitely be wrong though....
     
  5. 77RN23

    77RN23 Member

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    Last edited: Sep 13, 2016
  6. 77RN23

    77RN23 Member

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    Well, according to justdifferentials...
    "Pre 79 rear ends are different unfortunately. Your best bet is to find a 79 and newer rear axle and swap it into your truck as you'll have much greater gear and diff options at that point."
     
  7. jetas

    jetas Grand Toyotaholic

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    How are they different?
     
  8. 77RN23

    77RN23 Member

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  9. Tuhd The Troll

    Tuhd The Troll Veteran

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    That thread points out that the axle is wider, not the differential. But, an inch on either side would mean more poke, if you're into that sorta thing. I didn't know that pre-'79 differentials were different, either.

    Also, another vote for swap both. A w58 with a 3.7x or 3.4x differential will give you nice, streetably taller gears. It may rob you of some acceleration, depending on the condition of your engine. Honestly, I'd be going for the 3.4ish if you can find it. My W50 5-speed with a 3.7ish rear was still a little high at 70mph, which seems to be the standard cruising speed around Houston if it's not rush hour.

    Question, what RPM is the truck at when doing 60?
     
  10. 77RN23

    77RN23 Member

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    Will the differential fit my current axle OR will an entire axle from the 82 that I found fit my 77?

    Around 3300 rpms. I'd like to be around 3000 when going 65.

    I just noticed that you're in Houston. What part?
     
    Last edited: Sep 14, 2016
  11. Sang park

    Sang park Member

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    You also want to check if your drive shaft is flanged or slipe yoke if you're planning on swapping transmission. If it's flanged then you will need to get a drive shaft with a slip yoke.
     
  12. Tuhd The Troll

    Tuhd The Troll Veteran

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    Not 100% sure on either half of the question. I have a 3.42 sitting in my kitchen that could be compared to your stock pumpkin if you need. I'm no driveline specialist, just so you know. If you have an 8" or a 7.5" will determine what will and won't fit.

    Depending on tires, you should get down to within 2300-2500 rpm with a w58 and 3.42 gearing at 65. My crude math said something like 2600 at 70mph with my tires, etc, vs the 3000@70 i had before. Cruising will be nice for you

    North edge of Houston, nearly in Spring. A quick 45 minutes from Magnolia, depending on the vehicle. I have an extra bellhousing (among other parts you might need) that fits the w58 to a 20r/22r
     
  13. Cade01

    Cade01 Veteran

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    The G082 is an 8 inch diff, so the diff from any G code axle should fit, including 4wds
     

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