8.2 rear gears change

Discussion in 'Got gears?' started by josehf34, Jul 3, 2018.

  1. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Pull the speedometer DRIVEN gear sleeve out of the transmission. Look in the hole and you will see the DRIVE gear on the output shaft. Count the number of teeth on the DRIVE gear. All you need is that number, the tire height, and gear ratio, and you can calculate what DRIVEN gear you need for speedometer accuracy.
     
  2. flynbuick

    flynbuick Guest

    It is a 70 model year Muncie built for a Buick in October 1969. The partial VIN is shown and can be compared to the vehicle.

    Just drive down the road and compare a GPS mph reading to the speedo in the car. My suspicion is that the car speedo will read low relative to the GPS.
     
  3. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    X2, with a 26.5" tire, 3.42 gears, you should be at 65 MPH @ 2800 RPM.
     
  4. josehf34

    josehf34 Well-Known Member

    That's not possible because the car is all matching numbers, even the number stamped in the tranny is the same as engine number and car last vin numbers

    Speedometer screws directly to the transmission but I think we can discard speedometer gear because I'm reading speed based on GPS due to my speedo isn't too much accurate, I think the speedo cable is wrong or something because needle bounces too much

    Honestly I'm not taking in mind the car speedo, just GPS speedo
     
    Last edited: Jul 4, 2018
  5. flynbuick

    flynbuick Guest

    Pull the center out and lube it with graphite.
     
  6. josehf34

    josehf34 Well-Known Member

    Tried again this morning and my readings were these all in 4th gear:
    33mph @1800-1900 RPM
    55mph @ 2900-3000 RPM

    PD: RPMs are calculated with stock dash tach and also an additional aftermarket tach
     
  7. josehf34

    josehf34 Well-Known Member

    I forgot something...

    I don't know if matters but my speedo is in km/h instead of mph, does it changes something inside the transmission? I think is a weird question but I'm running out of possibilities for this issue :confused:
     
  8. flynbuick

    flynbuick Guest

    Can you borrow a friend's GPS and double check your readings?
     
  9. josehf34

    josehf34 Well-Known Member

    I'm going to try again coming home from work with the cellphone GPS and post my results :)
     
  10. flynbuick

    flynbuick Guest

    The 4th gear ratio on your Muncie is 1 to 1. It should not matter.

    For 55 mph your car should have read 88.5 kilometers per hour.
     
  11. josehf34

    josehf34 Well-Known Member

    Guys sorry for my delayed response but I've been a lot busy with work and family stuff.

    These two weeks I've been constantly tracking my speed / RPM with GPS, cellphone GPS and even street speed radars and seems to be like most of the records are fine, at 60mph I'm doing about 3000 - 3200 RPM but one strange thing that I've noticed is that at 1500 RPM (in both tachs) I'm doing like 32mph which seems to be ok to 3.42 gears, so I've no explanation to differences at higher RPMs

    Anyway I feel like my gearing isn't too comfortable for speed, even at 45 mph is kind of weird hearing the engine revving and being passed by 4 cyl cars Like if I were parked, so I've been considering the possibility of installing an overdrive transmission. I've read that some companies were making OD gears for my muncie to convert it to a 1-2-3-OD transmission but I think those gears sets are over because I haven't found who sells them, another option could be to change the muncie for a Borgwarner T5 out of a Mustang (is relatively easy find that transmission where I live) but I don't know how many modifications must be done to allow it to work behind my 455 and using the stock clutch
     
    Last edited: Jul 15, 2018
  12. BrianTrick

    BrianTrick Brian Trick

    Is it possible that your clutch is slipping. That would put your rpms up higher,but it would also give you some signs,like a bunch of heat,smell of a burning clutch,etc.
     
  13. josehf34

    josehf34 Well-Known Member

    I've none of those symptoms and also my clutch is new, I know clutch isn't slipping because if I shift into 3rd or 4rd on a dead stop and release the clutch the engine stalls immediately instead of hesitate like a worn clutch usually do
     
  14. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    I can tell you that the stock tachometer is notoriously inaccurate, so if your other tach agrees with the stock tach, then it is also no good.

    With 26.5" tires, 3.42 gears, at 33 MPH is 336/26.5 X 3.42 X 33 = 1431 RPM

    ...................................................55 MPH is 336/26.5 X 3.42 X 55 = 2385 RPM

    If the clutch isn't slipping, something else is in error. The GPS should be accurate, that leaves the tachometers. What kind of tachometer is the aftermarket one?

    You can add a Gear Vendors Overdrive to a Muncie if you want.

    http://www.gearvendors.com/hrgm4sm.html
     
    Last edited: Jul 16, 2018
  15. josehf34

    josehf34 Well-Known Member

    The aftermarket one is a cheap $10 unit that I used sometimes during cams break in. About the GV OD I know is a good unit and can practically convert the 4spd muncie to a 8spd but it costs about the same price of a full swap to a more modern tranny
     
  16. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    You need a good tachometer. I believe that is where the error lies.
     
  17. josehf34

    josehf34 Well-Known Member

    I agree that a better Tach could improve the RPM reading but right now I'm on highway with the car and is just horrible :( at 65mph both tachs are reading a bit more than 3000RPM and the engine Sounds like it's Going to blow apart, Even at that speed if I release the throttle the car immediately feels like If I step on brakes so maybe tachs reading are not too far from what it really is
     
  18. flynbuick

    flynbuick Guest

    The feeling that you describe is normal and the way it is for many muscle cars. If you have mostly driven modern cars, it would be no shock that this might be your perception about a 3.42 rear gear ratio. Try switching to a 5 speed manual transmission.
     
  19. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Horrible? That is what cars with 3.73-3.90 gears cruise at. If you are so unhappy, then you have 2 choices. Change the rear, or change the transmission. What else do you want us to tell you?:)
     
  20. 72STAGE1

    72STAGE1 STAGE 1 & 2

    Don't change tranny's, change rear gears. 2:73's someone on here will probably give you a set for just the shipping.
     

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