Thread: 2nd prime
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Old 01-06-2012, 07:22 AM
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Quote:
Originally Posted by FrostKing View Post
Our truck transmissions are still a 40 yr old 3-speed automatic with two over-drives, hence the poor gear spacing.
Quote:
Originally Posted by TNC View Post
One other question, because I'm new to Dodge. I'm sure I could research this one, but the comment made here about this tranny being based on a 40 year old design...if that's true, does this mean this tranny is just a redesigned Torqueflite?




While the 545RFE came from the 45RFE and one could argue the 45RFE is based on the Torqueflight family with additional planetary gears, the gear spacing issue is has nothing to do with it since the 727 uses 2.45:1 in first, 1.45 in second, and 1.00 in third while the 545RFE uses:
  • 1st 3.00:1
  • 2nd 1.67:1
  • 2nd Prime 1.50:1
  • 3rd 1.00:1
  • 4th 0.75:1
  • 5th 0.67:1
(Note the similarity to the 700R4 ratios of 3.06, 1.63, 1.00, 0.70)

If you take 2nd Prime out of the upshift sequence, the gear spacing is just fine. The whole 2nd Prime gear came about simply as a taller passing gear to avoid downshifting all the way down to the 1.67 gear when you stomp on it on the highway. As you would likely be in an overdriven gear at the time, jumping all the way down into the traditional 2nd gear causes rpms to skyrocket - again, note the similarity to the 700R4.

2nd Prime was not originally intended as an upshift gear, it just morphed into one.
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Last edited by 2011lilred; 01-06-2012 at 07:32 AM. Reason: clarification
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