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C6 transmission RPM

Tiny
IAN NORDMAN
  • MEMBER
  • 1987 FORD F-250
  • 150,000 MILES
I have an 87 f250 6.9 idi diesel with a 3 speed c6 transmission. Also has sterling rear end with 3.55 gear ratio. Does 2400 rpm going 55 mph seem normal with this transmission and gear ratio? It seems like it is winding engine pretty high and was wondering if this is a normal rpm for 55 mph. Any response would be greatly appreciated thank you.
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Monday, November 7th, 2011 AT 6:44 PM

3 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,645 POSTS
That sounds correct. Remember, there is no OD, so the gearing will have a difference at that speed.
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Monday, November 7th, 2011 AT 6:46 PM
Tiny
IAN NORDMAN
  • MEMBER
  • 6 POSTS
From what I have heard on internet with other owners of same to similer truck, 2,400 rpm at 55mph is correct if equipped with 4.10 gears with c6 transmission. I have double checked my diff gears and they are in fact 3.55. I have 235/85/16 tires which are stock and still manage 2400 rpm at 55 mph. Shouldnt rpm be more in the 2,000 rpm range? Any available info would be great thanks!
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Monday, November 7th, 2011 AT 10:39 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,645 POSTS
I would say it's fine. However, we'll let this post open to see if others respond.
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Monday, November 7th, 2011 AT 11:09 PM

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