1968 350-2 : Gear suggestion

Discussion in 'Got gears?' started by 68 Skylark cust, Sep 15, 2020.

  1. 68 Skylark cust

    68 Skylark cust French Canadian Member

    Hello Buick fellows , I am questioning myself about changing my diff gear in my 68 Skylark

    It has the stock 350-2 engine with a ST300 (2 speed automatic tranny) . The car was born with a 2.56 rear gear with 14'' tires. Now change for 3.08 with 15'' tires over the years.

    I'm not racing the car but I'd like to give it a little "help" to spin the wheels here and there (lol) while cruising it .
    Wonder what would be a good compromise with performance gain, fuel millage .. and rev noise (I have no tach)

    I forgot to say (if it matters) that my Canadian built car has a Chevy 12 bolts diff from factory

    Thank you
  2. philbquick

    philbquick Founders Club Member

    Put a 3.42 rear with a 200R4 in it.
  3. BrianTrick

    BrianTrick Brian Trick

    Are you keeping the 2-speed in it?
  4. LARRY70GS

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

    With 2.56 gears, 60 MPH is around 2000 RPM. With 3.08's, 60 MPH will be 2400. Steeper gears multiply torque, but at the expense of RPM and gas mileage. Have you optimized your ignition timing? That may give you the added ummmph you want without a gear change.
    68 Skylark cust likes this.
  5. SpecialWagon65

    SpecialWagon65 Ted Nagel

    The GS350 cars of 68 and 69 were equipped with a 3.23:1 rear.
    That has worked well for me- wagon and 69 GS350 run well.
    68 Skylark cust likes this.
  6. monzaz

    monzaz Jim

    your choices are 3.07 3.31 3.42 3.55 3.73 3.90 4.10 4.56 and beyond.
    you will need another carrier unless you want to use a ring gear spacer kit...which we have done many times for 12 sec and slower cars to save customers some money. (YOU MUST buy a kit that has the longer bolts or it will fail.) Other than that we have tested the spacers to 11.50 car and slicks with out issues. 4000 pound car.
  7. 68 Skylark cust

    68 Skylark cust French Canadian Member

    Yes , I just need a little "extra" . Probably go with the GS-like 3.23

    No , I remember seen a post you made about that , am I right ? That may worth the look before doing anything else . What was the title of that post ?

    Thank you all
  8. LARRY70GS

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

    68 Skylark cust likes this.

    MEXICOYA Well-Known Member

    I too am looking for an increase in gears and recently had the stock 350 rebuilt and had the EFI Sniper installed. It currently has the stock transmission and rear end. I was told going with a th350 and rebuilding the rear end with posi and 3:42 gears will definitely give it pop at take off. Have you known someone that has your recommended upgrade or do you have it? I'd be interested in learning how much of an increase that gives the car and how much of a price range is costs. Thanks for your time.

    - Victor
  10. philbquick

    philbquick Founders Club Member

  11. LARRY70GS

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

    The last year for the ST300 was 1969, but the switch pitch ST300 was only until 1967. 1968-9 ST300 was a fixed pitch 2 speed.

    MEXICOYA Well-Known Member

    Hey there, sorry for the late response. Yeah, I was told it has the st300 by the shop that did the engine rebuild and efi install. I've been calling around to get a price on the rear, but every shop tells me they need to open it up to see whats inside. Sucks that I can't just get a quote for the work. I do get a price range but then told I may have to locate the parts myself.

    I honestly regret the efi upgrade because of all this extra work it needs to get the most out of the efi. It runs smooth and sounds great, as I also put a TA camshaft and the stage 1 intake.

    I have gone back and forth on whether to see it just cause the difficulty in finding parts- gets pretty frustrating.

    Well, we'll see the route i go. I definitely don't want to spend more money and then have a very difficult time recouping that if I do decide to sell.

    Maybe one day a Buick only shop will open up in the Bay Area....wishful thinking!
  13. philbquick

    philbquick Founders Club Member

    So does that make it a TH300? Did they still call it an ST300??
  14. philbquick

    philbquick Founders Club Member

    I'm pretty sure if you go from a ratio in the 2s to a ratio in the 3s the entire center section needs to change.

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