Archived gear change and Speedometer

[surfbeetle]

My 95 is in the shop because the rear end went out. Once they change the rear end from a 4. 10 to a 3. 54, is there anything that has to be done to make sure that the speedometer still reads correct? I put this in the 911 because I want to get the answer asap so I can make sure the shop gets it taken care of before I pick up this week. Thanks.

 

[Nate]

Nope. It will work fine.

 

[macdaddy]

Nate is right that it will work fine, however it will be inaccurate.



Someone else chime in here but I think it will read slower than you are actually driving . I am not sure how you do the recalibrate, but I believe it is done through the trucks ECM. I remember you used to have to use what was called a "bypass" on the older cable driven set ups.



Mac

 

[Nate]

It will read the correct speed, unless 95 is a different setup then my 98. I haven't touched anything from when I had 3. 55s to now with 4. 10s and it reads just the same. This is verfied with my GPS as well.

 

[macdaddy]

Nate



Sorry the last gear swap I did was back in 85 went from 3:55's to 4:56's due to tire diameter.



From what you are saying is that the Dodge speedo's are self calibrating . I didn't know this



Mac

 

[redram]

It will NOT read accurate - you need to change the speedometer gear that is located in the tailstock of the transmission. 10 dollar part at the dealer.



In 98 - this became electronic but in 94-97 it uses a speedometer gear that generates electronic pulses - you'll need to get one callibrated for the 3. 55 which should have 31 teeth on it -

 

[Nate]

Ok... I thought maybe the older trucks would have something else. It's not hard to change the gear. Not even a 5 min job. My Jeep uses the same setup.

 

[K5IP]

It will work but read slower than you are actually going (. 16%)

4. 11-3. 54/3. 54=>16

i. e. 16%

You need to change the gear ratio by 16% to fix the errors in both speedometer and odometer.

You will not be able to get it exactly right, however the factory serviced manual does have a chart of available speedometer gear changes available. I think the "driven" gear has about 15 teeth. Assuming a 15 tooth gear, You need to go to fewer teeth and a one tooth change is:

(15-14/14)=. 07 or 7%. So, assuming you have a 15 tooth driven gear, you probably need a change to 13 (14% change, as close as you will get) tooth plastic gear on the end of the speedometer cable pickup. (it is actually an electronic pick up i. e. VSS)

Pull the speedometer cable, count the gear teeth, and calculate as above.

Rog

 

[surfbeetle]

Thanks for the replies. I called the gear shop and told them this info. I believe that they found a 30 tooth gear for it. I have 265's for the tire size, so 31 teeth would have been if I was still running 245s. I should be getting the truck back tomorrow. They told me that the spacers on the bearing were chewed up and that pieces of it were floating around inside and had damaged the seals and gears. Usually, they don't have any problems with Dana 80s, of course, mine had to be the one that had the problem. Oh well, what can you do? Thanks again.

 

[K5IP]

If you really have a 31 tooth plastic (driven) speedometer gear, you will need:



3. 54x31/4. 11=26. 7. Since you cant get a gear with 26. 7 teeth,



A twenty seven tooth gear is a close as you are goint to get.



It's within 1%, very close.



Rog

 

[dtygart]

Hi Surf

If you are still looking for gear and can't find one locally go to ricksontruck.com, tell them truck, trans, rear end and tires and they will sell you the right gear. Takes 3 mins to change.

david

 

[surfbeetle]

Thank you everyone for your responses, I got the truck back on Friday. Everything seems to be good. It is a little odd being able go faster than 85 mph. Now, the truck cruises at 70 mph at 2000 rpm. I drove it for 10 years with 4. 10's, it's almost like driving a different truck.

 

[Katmandu]

In 98 - this became electronic

How do 98+ get the Speedometer readings ??

.