Ok to start, I did do a search on this topic. However I am confused. First off, I have a 1998 F150 4.6L and all the power programers I have looked at (ie. Hypertech, superchip, etc.) all say that for my model the programmer will not correct my speedo for tires/gears. So I have been looking at aftermarket speedo cables. (I read the thread posted by built54, and was reading the responses on figuring out the ratio and adding or subracting teeth from the gear). However, two questions I have are; 1) will correcting my speedo also correct my odometer? and 2) I have talked to multiple part stores, including three Ford dealerships, and they say the speedo for my model is driven electronically, is this true and why wouldnt the power programers just correct it then? Thanks.

Roy

 

Yes correcting the speedometer will correct the odometer, The thing to change is the speedometer driven gear not the cable. And yes the speedometer is actually electronically operated by a VSS, a vehicle speed sensor. the difference is that in the 97-98 model year, this signal is not sent through the PCM and then modified and sent to the instrument cluster as happens in later years. So there is no way to change the programing to modify the signal. The only way to change the signal is mechanically.

 

Thank you, chucks bp, for explaining why the speedometer could not be corrected on 97-98 models. I had no idea they weren't "driven" by the PCM.

So, this "driven gear" is down on the sensor at the axle?

- Jack

 

Ya, like JandJ said thanks!


So, by mechanically you mean adding or taking off teeth of the driven gear? And how exactly is that done?

Also to repeat JandJ's question, is that gear located in the axle?

 

No actually it is either on the output shaft of the transmission or the output shaft of the transfer case if 4WD. It goes in the hole where the old speedometer cable would have been on a mechanical system. It is basically a pulse generator driven by the plastic gears, it generates a low voltage AC current that is translated into a speed reading for the systems in the truck.

 

I think I'm glad the PCM controls my speedometer!

- Jack

 

Ok, I think I understand how it works and where it is, but how do I go about mechanically changing it to correct my speedo? sorry if i sound like a broken record.

 

When I had my gears installed on my 97 I bought a 23 tooth speedo gear going from 3.55's to 4.10's but my gear guy installed it. I know it was underneath the front of the vehicle but as far as me installing it in the exact location I didn't. Got mine from brothersperformance.com a long time ago. Hope this adds another piece to the puzzle.

 

Ah I see, so I just buy a new speedo gear? Ya, it did add another piece, thanks. So next question, how do I know what tooth gear to go with? I went from 3.55's to 4.56's and stock tires to 35x12.50s....?

 

got bored and went on the website to make sure I wasn't giving false info yrs later. PITA to navigate that site also. 23 tooth speedo gear is the highest they make and I was also told the higher the tooth the more accurate. Not sure if that's true but it worked. BTW if you have a Chilton's manual it might be in there I think it was in mine but it took a bit of looking. Pretty easy to install from what my installer told me. Here is the link and Ford Racing makes these. http://www.brothersperformance.com/c...roducts_id/449

 

sweet, yea I checked my chilton manual, and oddly enough its saying that its located ontop of the rear axle housing? Tomorrow, Ill crawl under there and check. I did some math, and concluded that with the tires and gears I upgraded by 19%. So according to a formula from another thread, I times .19 x the number of teeth on my current speedo gear, and thats the amount of teeth I need to increase. Correct me if im wrong.

I also found this website, which includes a tire/gear/tooth chart, yet doesnt match with my math...?

check out this page. has a lot of info, including a tire/gear/speedo gear chart, and a speedo calculator.

http://www.transmissioncenter.net/sp...n_______va.htm

 

to anyone else searching for this topic, I also found this post which has a lot of info.

http://74.125.95.132/search?q=cache:...lnk&cd=1&gl=us

 

ok for anyone else in my situation, with a 1998 f150 and who has installed 4.56s gears, one has to get an in-line speed calibrator. Two that I have found are a SUPERLIFT truspeed (~$230) and a JET accuspeed (~$150). First I talked to multiple dealerships, all saying different things (go figure). One said that the speed sensor in the rear axle is the one controlling the speedo. Another said that it is all done electronically. And another told me to talk to a offroad garage or a speedoshop. I tried both, a few offroad shops told me a Programmer or tuner would work (no, not for my model and year). Then a speedo shop told me he would hafta use his machine ?? cost about $180 (not TOO bad, but would like to do it myself). And the guys, from brothersperfomance informed me that the 23 tooth gear they have, would only work up to 4.10s. and THEY were the ones to finally tell me about the INLine devices. (good guys over there, honest) So thats that. Thankfully they dont look all that difficult to install. I will let you know when i do it. Thanks again for all yall help.

 

Good info and nice job job tracking down your own leads with the info provided. Always nice to see people use the tools they're given.

 

hey chuck i live in charleroi as well you know of any pcm tuners? locally