Diesel Engine Conversions Diesel Engine Swaps , 4bt Diesel and All Diesel Engine Conversion Related Discussions

Ford cummins tranny issues

  #11  
Old 11-05-2010 | 07:32 AM
prison's Avatar
Diesel Bomber
Joined: Oct 2010
Posts: 1,150
Likes: 29
From: Childress,TX
Default

i shoulda thought of that. now i'd be willing to bet your speedometer is off
 
  #12  
Old 11-17-2010 | 03:13 PM
12v swapper's Avatar
Diesel Fan
Joined: Nov 2009
Posts: 15
Likes: 2
From: arizona
Default

I'm not sure if ford used a transmission driven speedo or the electronic sensor in the rear diff like the later models. If its the electronic style then get a superlift truspeed module. It allowes you to set the speedo for different tires and gears. If its the mechanical style, then you will need to pull the driven gear and count teeth and look at the colors. different colors had different ratios for trans and diff options. You might still be able to get the speedo gears from ford or possibly a good tranny shop. Hope this helps.
 
  #13  
Old 11-18-2010 | 10:02 AM
DieselBurps's Avatar
Diesel Fan
Joined: Dec 2007
Posts: 27
Likes: 2
Default

FWIW - I'd want to get the rpms down a bit - I turn ~2000 rpm at 70 mph getting ~ 20 mpg on my 2500, although slowing down to ~1700 rpm nets me 24 mpg. Hopefully correcting your speedometer will show that you are going much faster than you think you are.
 
  #14  
Old 11-18-2010 | 12:19 PM
EasternAggie's Avatar
Diesel Bomber
Joined: Jul 2010
Posts: 2,139
Likes: 107
From: Broken Bow, Oklahoma
Default

With 35" tires, 3.55 gears, and running at 65mph in 5th gear (Diesel ZF5 has a .75 ratio), you should be turning 1661 rpms. Far cry from 2900 rpms.
 
  #15  
Old 11-24-2010 | 10:34 AM
12v swapper's Avatar
Diesel Fan
Joined: Nov 2009
Posts: 15
Likes: 2
From: arizona
Default

You actually need to measure the height of your tires. Very rarely are the tires true to the size printed on the sidewall. Most 35's are only about 33 1/2" to 34" tall. Then do the math. If I remember the formula correctly it should be mph x trans ratio x axle ratio x 336 divided by tire size. In 4th (direct) with 3.55 and 34's at 65 mph, you would be turnin about 2300 rpm. If you want to know what the rpms are for 5th(overdrive), just put that gear ratio in. The numbers wont lie but tachs and speedos often do! Good luck.
 
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
atreefunk
For Sale
1
04-13-2015 10:57 PM
metrickjb
24 Valve 2nd Gen Dodge Cummins 98.5-02
5
01-21-2015 04:16 AM
Trevlar11
12 Valve 2nd Gen Dodge Cummins 94-98
1
11-16-2014 01:59 PM
Diesel Bombers
Latest Automotive Industry News
0
11-04-2014 01:30 PM


Thread Tools
Search this Thread
Quick Reply: Ford cummins tranny issues



All times are GMT -5. The time now is 06:30 PM.