Mike,

Not a chip question, but you are an F150 guru, so here goes...please check the following thread and let me know your advice/opinion. Thanks

https://www.f150online.com/f150board...ML/001180.html

 

Hi jj,

OK, so you want to go from your current 3.73 gearing to 4.10's, as I understand that other thread?

To recalibrate the speedometer & odometer for the 4.10 gear change, since yours is a 1998 model according to that thread, a NASTRUCK, you just need to install the correct reduction gear in the tailshaft of the transmission, and that will restore speedo & odo accuracy, and shift points as well in the automatic models.

Because yours is a 1998 or earlier, it's much easier being able to replace the reduction gear to recalibrate the speedometer, and doing that brings shift points right back into line automatically; as long as the speedo is accurate the ECU uses mph to determine it's shift points, so restoring speedo accuracy also automatically restore shift points as well.

Starting in the 1999 model year in these trucks, all of that must be done in a custom program in the ECU (powertrain computer), so it's more involved & more expensive for those owners.

Good luck!

------------------
Mike Troyer
Performance Products, Inc.
National Distributor of Superchips
(540) 862-9515
Email: mtroyer@compuserve.com
Performance Products F150Online Superchip ordering system: F150Online Superchip Ordering System
National F-150 Online Rally Event Organizer

 

So, I will not have any problems on the highway?

 

Mike,

Just read your answer to the post. I have a '98 Expy w/5.4 auto. I installed 265/70-16 in place of the stock 255/70-16's. Based on your info about the speed affecting the gear change, is my truck shifting at the proper time? I think it's about 3% off or so. Should I even bother with trueing the speedo?

Thanks,
ExpyGator

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Silver '98 Expy XLT,4X2,5.4, LLS,CD changer, 3.31 Regular axle, trailer tow, 3rd row seat

• Flowmaster Force II 3" Cat-Back
• K&N Filter w/elbow mod
• Edelbrock IAS Shocks
• Michelin LTX M&S 265/70R16 (blackwalls out)
• Soundstream,JBL, Bazooka
• Xenon Head Light Bulbs
• Removed Luggage Rack
• Replaced factory ant.with cell phone ant.
• Removed receiver hitch

 

Expy,

I believe Mike will agree with this, but I wouldn't worry too much about the change you've made. I also went from 255/70/16 to 265/70/16 in my 1998 Nascar F150 4x2. My truck has a 3.73:1 axle ratio. Not in the computer or with the speedo, but in the gears, I would need to go to a 3.8:1 ratio to make the adjustment. So you see, the change is negligible. You may be off less than 1mph. On a side note, how is 3.31 for such a big ride??? My truck is much lighter than yours and I want to go to a 4.10:1 for more power/torque.

JJ

 

Hi jj,

I'm not exactly sure what you mean when you say "so I will not have any problems on the highway"...............

Restoring the speedometer accuracy as I described before will bring the odometer & shift points back into line automatically. That will take care of any operational issues with regards to speedo accuracy & shift points from your gear ratio change. If that is what you mean, then yes, you'll be fine.



------------------
Mike Troyer
Performance Products, Inc.
National Distributor of Superchips
(540) 862-9515
Email: mtroyer@compuserve.com
Performance Products F150Online Superchip ordering system: F150Online Superchip Ordering System
National F-150 Online Rally Event Organizer

 

jj:

The 3.31's make it a pig out of the hole. As a trade off, I can floor it at 37mph and it drops to first gear. Quite satisfying for the occasional low speed pass. It turns 2000rpm @70mph and in mixed drivng I get 16-18.5 mpg. With the 30 gallon tank, I've gone 576 miles on one tank.
ExpyGator
ps: Thanks for clearing up the shift point question.

 

Hi ExpyGator,

Sorry I didn't get to your question sooner, I just missed it, oops!

With regards to your shift points, yes, they are going to be off and also softer too, with taller tires.

Now, the question is, is it off enough to affect driveability to the point that you need to do something about it? That's really up to you, and your impression of it's day-to-day driveability. A 3% error may or may not be tolerable to you.

When your speedometer is off, the ECU can no longer use mph to determine it's shift points like it should, and has to default over to using rpms instead; while that sounds ok on the surface, in the real world it doesn't work as well the way Ford has it set up. Again, how satisfactory this is currently is all up to you & how you feel about your overall driveability.

Also, your mpg figures etc. are going to be off, as your odometer is not reporting mileage correctly either, it has the same error as the speedometer so you can't calculate that correctly unless you factor in the difference from the tire size change to get the math right, so that you end up with a correct mpg number. You probably already know that, too.

All in all, a 3% error is not so bad, and you may find you're able to live with it ok, that's of course up to you. Those taller tires, combined with having only a 3.31 gear ratio, make it a dog in terms of acceleration, but then, you already know all that; if you can live with that, there is nothing else operationally saying you absolutely *have* to make any changes there, so if you are OK with it as is, then just enjoy it & have fun!

------------------
Mike Troyer
Performance Products, Inc.
National Distributor of Superchips
(540) 862-9515
Email: mtroyer@compuserve.com
Performance Products F150Online Superchip ordering system: F150Online Superchip Ordering System
National F-150 Online Rally Event Organizer

[This message has been edited by Superchips_Distributor (edited 06-28-2001).]