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What type of differental oil is required in 1955 Thunderbird

Discussion in '1955 - 1966 Classic Ford Thunderbird' started by doug7740, Apr 14, 2019 at 8:30 PM.

  1. I’m performing some springtime maintenance on my 1955 Thunderbird before the start of cruising season and since I have never changed the rear differential oil I was wondering what kind or brand of oil should I use?

    Referring to the service manual, it says that the rear differential requires 3½ pints of SAE 90 multipurpose gear lubricant. Since there is nothing wrong with the differential on my T-Bird, I don’t want to cause any problems by using the wrong type of oil.
    doug7740
    1955 Thunderbird Blue
     
    Tater Salad likes this.
  2. Great question Doug, I look forward to any responses. I have to change my rear end seal in the next few weeks and have been assuming regular gear oil shouldn't be an issue.
     
  3. Dale Leonard

    Dale Leonard Blown Valkyrie Rider Lifetime Donor

    Change it to a pure synthetic and it will run cooler and perform correctly.
     
    biddle likes this.
  4. biddle

    biddle Forum Moderator Staff Member

  5. Dale Leonard

    Dale Leonard Blown Valkyrie Rider Lifetime Donor

  6. CSPIDY

    CSPIDY Well-Known Member Lifetime Donor

    I don't usually trash talk products but Royal Purple is not a very good product from my personal experience. for the rear ends in our early birds a non synthetic 85-145 is best. this is advise was given to me by the drive line shop that worked my rear end this past winter. (this is all they work on)
    unless you are racing you car or using it as a daily driver, full synthetics add no value.
     
  7. biddle

    biddle Forum Moderator Staff Member

  8. Dale Leonard

    Dale Leonard Blown Valkyrie Rider Lifetime Donor

    Never had a problem with Royal Purple or synthetic in older differentials. Only had a problem if there was an existing problem that I did not know about, such as a worn bearing or seal ect:
     
  9. After reading everyone’s comments I became more confused on what kind of differential oil to use in my 1955 Thunderbird, so I asked Gil Baumgartner who is the CTCI Authenticity Chairman. Gil suggested that I use NAPN SAE 90W mineral gear oil, because it is as originally used in early Thunderbird transmissions and differentials.

    doug7740
    1955 Thunderbird Blue

    upload_2019-4-17_8-10-0.jpg
     
    Tater Salad likes this.
  10. CSPIDY

    CSPIDY Well-Known Member Lifetime Donor

    I’m using Napa mineral oil in mine,
     
  11. CSPIDY

    CSPIDY Well-Known Member Lifetime Donor

    Full synthetics will not harm your differential, I was told the only issue may be if you let your car sit for long periods of time the mineral base ooils will leave a beaver coating on the parts above the level of the oil and less likely to rust. I apologize if I added to the confusion.
     
  12. biddle

    biddle Forum Moderator Staff Member

    Use 65 year old technology because that was what was done originally? That's a terrible justification from a logical standpoint.
     
    randy d likes this.
  13. I decided to use what was called for because I was concerned that the synthetic lubricant would damage the old school bearings. Since Gil Baumgartner did not recommend a synthetic lubricant, I decided to go with what he recommended.

    doug7740
    1955 Thunderbird Blue
     
    CSPIDY and Tater Salad like this.
  14. fordrodsteven

    fordrodsteven Well-Known Member Gold Donor

    I personally will use anything that meets or exceeds spec of original type oil whether it is synthetic or not.
     
  15. biddle

    biddle Forum Moderator Staff Member

    The only concern I've ever heard about regarding synthetic oils is with motor oils. Old cars have sludge buildup in seals that actually are preventing leaks. Newer synthetic oils have detergents that could possibly reveal these leaks. How could a product that has less heat and friction and is more consistent than real oil cause damage? Synthetic oils are far superior.

    Here is a good blog on synthetic motor oils for classic cars- https://www.bellperformance.com/blog/synthetic-oils-in-classic-cars

    Screenshot_20190418-162729.jpg
     
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