Engine/Transmission (1994 - 1998) transmission speedo gear

[SPatyna]

Reg: gear change,------- Recentlly switched from 3:54 to 4:10 gears. Also switched from 245-75 16 to 265-75-16 tires. Does anyone know how many tooth speedo gear is necessary for this combination. I haul a 10,500 lb. fifth wheel and decided 4:10 would be to my advantage. Truck is 1994 2wd auto- I am original owner 70,000 mi. with BD#10 plate , no cat. low restriction muffler, huge K&n, no air box , with pyro/ trans temp/ boost/ ( autometer). Any Comments appreciated--- S. Patyna

 

[Vaughn MacKenzie]

Hi S. Patyna, I'm not sure if the '94s use a speedo gear or not, because it was sometime around that year Dodge started taking the signal for the speedometer from the ABS tone ring in the rear axle (1989 or so was the last year they used a mechanical drive cable, all later speedos are electric). If that's the case you'd have the PCM reflashed.

 

[surfbeetle]

VM is partially right, you still need to change the speedo gear for the pickup at the trans. I changed from a 4:10 to a 3:54 last year on the '95 and went to 265's on the tires. I told the shop doing the work to change the gear (after posting here) and they did. Check out the thread here with more info

http://tdr1.com/forums/showthread.php?t=148842



Good luck.

 

[Zombie069]

Reg: gear change,------- Recentlly switched from 3:54 to 4:10 gears. Also switched from 245-75 16 to 265-75-16 tires. Does anyone know how many tooth speedo gear is necessary for this combination. I haul a 10,500 lb. fifth wheel and decided 4:10 would be to my advantage. Truck is 1994 2wd auto- I am original owner 70,000 mi. with BD#10 plate , no cat. low restriction muffler, huge K&n, no air box , with pyro/ trans temp/ boost/ ( autometer). Any Comments appreciated--- S. Patyna

You wouldn't want to get rid of the 3. 54 components would you??

I want to get rid of my 4. 10's.



Thanks

Brad

 

[SPatyna]

speedo gear/ tire change

Thanks to all for input on this subject. I Got it straighened out with a simple formula, this might be helpful for some. New tire rev. per mile, divided by original tire rev/mi X original gear ratio= new effective gear ratio. Here's an eg: 265-75-16 =637rev/mi divide by 662rev/mi(245-75-16)=0. 962x3. 54(original gear ratio)=new effective ratio of 3. 40. This must be considered when changing tires or gears. In my case switching to 4. 10 using this formula my new effective ratio is 3. 95 as i have switched from 245"s to 265's=34 tooth speedo gear/ 30 tooth speedo gear for3. 54"s with 265's . I know it sounds complex but it is accurate. And Zombie069 , just curious why you want 3. 54's over 4. 10's considering your 20mpg, with 315's that's a tall tire, might be sluggish with 3. 54's. -------------SPatyna

 

[Zombie069]

I'd like to be able to cruise highway speeds at less than 2500rpm.

I don't think it'd be sluggish, there enough power there to make up for it.

I would really like to throw 3. 31 in it but have not found many of those used.



Brad



For the above formula, what's the most accurate method to determine the tires revs/mile???

 

[SPatyna]

Speedo Gear

Good-Day all: reg: Zombie069 Quest. about rev/mi. Go to google punch in tires (search). Michelen site / then search catalog for truck tires . , you'll find many sizes rev/mi. Also my 94CTD auto 265-75-16(4. 10) 70,000mi, original truck rev"s around 1750-1800 rpm @ 62mph(or100km/hr) since I am a canadian(metric up here). Remember my new "actual gear is 3. 95 due to taller tire so 2000rpm should give me around 65-70 mph in OD. I consider that plenty fast enough pulling a 10,500 LB. Arctic Fox Fth. Whl. -----Hope this helped------------SPatyna.