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Upgrade differential ratio

Tiny
94FLEETWOOD
  • MEMBER
  • 1994 CADILLAC FLEETWOOD
  • 115,000 MILES
Hi, I am planning on using my 94 Cadillac Fleetwood to tow a camper trailer. The diff. Ratio it has is at 2.56:1 (not the best towing ratio).
I plan on upgrading to a 2.93:1 (from a Brougham) to increase the towing capacity to 5000lbs. Will this affect the pcm? Is there a tuning that must be done to the chip?
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Monday, August 29th, 2011 AT 12:22 AM

4 Replies

Tiny
MHPAUTOS
  • MECHANIC
  • 31,937 POSTS
No change there is required, but with the different diff ratio you will get an inaccurate speedo reading, you may be able to change the speedo drive to one for a model with that ratio.
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Monday, August 29th, 2011 AT 2:03 AM
Tiny
94FLEETWOOD
  • MEMBER
  • 2 POSTS
Thanks for your input. The car has 235/75/15 tires on. Originally, it should run on 235/70/15. Would this slight difference in tire size compensate the speedo difference a little?
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Monday, August 29th, 2011 AT 2:08 AM
Tiny
CADIEMAN
  • MECHANIC
  • 3,544 POSTS
Their is about 4 to five gears with different teeth nunbers. Make sure you have a good tranny cooler and a heavy duty radiator if possable. Thanks for using 2carpros
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Monday, August 29th, 2011 AT 9:30 PM
Tiny
MHPAUTOS
  • MECHANIC
  • 31,937 POSTS
It is only the dia of the trye that will alter spedo readings, both are 15" so ther is no differance there.
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Monday, August 29th, 2011 AT 10:28 PM

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