My speedo is off....

[bdogg23]

well i was driving to cali with my dad and he was like lets just do 75mph the whole way there, no problem there. im driving behind him and look at my speedometer and is shows 65-70. so i call my dad on his cell phone and ask whats up? he says he's cruising at a steady 80mph. He says its my tires but i thought 235 was stock size, am i wrong or what? and can anyone tell me how to fix my speedometer?

 

[Alec]

If it is in fact a bit slow you should replace the speedo gear with one size smaller. I'd guess yours is a bit slow and your dads is a bit fast.

 

[bdogg23]

well the car my dad was driving was a rental so i dont know anything about it.

 

[X~FACTOR]

I say leave it as is so you'll rack up less mileage on your truck.

 

[Alec]

I'd test your truck with a GPS or at a speedo shop (pricey) or with a few other vehicles. Average the amount it's off with all the different vehicles when they read 70-75 and tell us what vehicles they were (different manufacturers have different tolerances for speedos, almost no one has a truly accurate speedo).

 

[Opera House]

Was everyone passing you?

My transfer case rear shaft seal has been leaking since I bought it over a year ago. Been meaning to do it. I even bought an $8 seal eight months ago. Just kept topping off the fluid. Finally decided to do it since I was going on a long vacation. Drive shaft removes with 12mm 12 point socket and the shaft flange takes a 30 mm or 1 3/16 socket. There is an O ring under the washer. Mine came out in one piece but you better be prepared if it doesn't. Seal surface needed just a little fine grit paper polishing in oil. With the shaft seal removed, I could see the pink speedometer gear.

Looked that up on the chart and it was a 19 tooth. The speedometer has always read 7-12 mph fast at all speeds, higher at lower speeds. Never bothered me that much but my better half is math challenged and she wouldn't drive till I got it fixed. Went to the dealer and got a red 21 tooth C4O-17271-A gear, $7.63 for the part. 70 mph X 19/21 = 63 mph. Dealer said the color was wine. What real mechanic knows about wine! Had to go a couple places to find it. They all saw the part number and asked me if I had an old Falcon from the 60's. Found the number from a chart here somewhere. Two wheel drive has different gears. Just remove the VSS on the transfer case and it just snaps in with a clip. I had wondered how they change the number of teeth on the same diameter gear, they sure get thin. These gears go from 16 to 21 so you can adjust for different axle and tire sizes.

Now my speedometer reads correct at 65. Still off at the lower speeds. My gas mileage instantly dropped 10% but I find I am driving fewer miles. One thing that has changed is that it shifts out of overdrive easier. I was pulling a trailer in the hills on a route I have traveled many times before. Weather conditions forced me to drive at 60 and the transmission did a lot of hunting in OD. Makes sense because the computer thought I was going 10% slower with a high load on the engine. Little mods can effect your transmission. Oh, and in 2500 miles she never drove one mile!