I have a 98 12 valve and i recently put 305's on it... my speedometer is off about 10%. not a huge deal but what can you do to fix it? gear in tranny... etc. Im pretty new to all this so any help is appreciated...

 

Not sure on the 98 47re if they have the speedo gear in the tailshaft or get the signal from the diff. My 99 V10 gets it from the diff, my Indy with 46re from the tailshaft. If its in the tailshaft check the back drivers side on the side of the trans.(pic below)
3.55grs w/245/75/16 tires is a 32tooth gear IIRC, going to 3.90grs I put in a 35 tooth

What profile tires do you have & gears?

 

A 98 will require a tuner capable of tire size change, via the pcm. Like a Hypertech or SuperChips. BTW, the dealer can flash the pcm also for tire size. Some dealers are jerks and say it can't be done, but it is possible.

 

Uh a 12 valve is a diesel there Zman, gas tuners no worky.

Back off the meds a tad, mkay?

check and see of a bully dog or smarty tuner adjusts for tire size.

 

LOL, DOH! Skipped right over that part. However, I think Hypertech has a stand alone tire size/rear gear module. And actually I looked, and the max energy and Power Programmer III both are available for a diesel. As is a Superchips. Not knowing much about diesels, Hyper says L6 5.9 and SC says 5.9 24 valve. But I'd call them, maybe they work with a 12 valve too. But I don't see why the stand alone tire/gear module Hyper sells wouldn't work.

 

Theres an old post about doing it with a smarty and they decided it wouldnt work... no ecm in these... From what i've read there's a pcm but dunno if that is what runs the speedometer or not. Im pretty clueless when it comes to all this stuff. Never been around it much.

 

The PCM does run the speedo in a 98 whether it gets the signal from the tailshaft sensor or the rear abs sensor on the axle. Go to the Hypertech site and look at the tire/gear module I was talking about. And call your local Dodge Dealer.

 

Just take one Lortab out for your rotation every day and at the end of the week, mail them to me for proper disposal

 

So what litre is a 12 valve compared to a 24 ? So I know a little more about them. And, atleast for a 24 valve, the Hyper and the SC work. All you have to do is look on their sites.

And btw, I'm not on anything now or recently, but that will change Friday at 6 am. So, after a couple days when I can start posting again, I'll start being stupid again.LOL

 

Ok, so a 12 and 24 valve are both 5.9's. Since the Hypertech site does not distinguish between the two(like the SC site does) I'm willing to bet the Hyper will work on either one. Just a phone call and you'll know for sure.