PRELIMINARIES -

I've owned my 97 most of its life and with 138k miles it is a great runner. I've been through the typical V6 woes (front and top gaskets) and have kept it well maintained. Mechanically it is 100% and I suspect its going to rust out before it wears out.

I want to change the rear axle ratio and install a Detroit True Trac rear end. We're looking at getting a 4000# camper and the 3.08 ain't going to cut it. The DTT is getting put in since I'm going in there anyway. The truck is an automatic. Since the truck is for fun I'd like to go to a 3.90 or 4.10 rear end, but am willing to settle for a 3.55 to get the towing I need.

I want a smooth running truck but I don't care about speedo accuracy.

My mechanic can do the actual wrench work but does not have the capacity to do any chip re-programing. Looking at Hypertech's web page it appears the 97 & 98 4.2s have very limited re-programing capabilities. My mechanic says I might need to get a new ECM. He's not too proud to tell me he does not know for sure and directed me to our local Ford dealer. I made the call and really got no good answers, I got the feeling they didn't know or even care to help.

QUESTION -

Specifically has anyone here replaced the 3.08 in a 97 or 98 with a 4.10 (or any ratio)? What if any re-programing is required? Are there any components other than the what I'm replacing in the differential that need changing?

Can I expect to have a good running truck?

Thanks in advance for any assistance you can provide.

 

Well here's what I ended up doing...

I went to a 3.73 ratio (from 3.08) and added an Detroit True Trac limited slip. I bought a Jet Accu-speed calibrator to zero in the speedometer. With GPS I am within .5% accuracy.

The truck runs great! On two lane highways doing 55-60 I average 19+ MPG. On the expressway doing 75+ I average 15+ MPG. Thats just a 1 to 2 mpg penalty. Performance is like night and day. Feels like a my 98 4.6 V8. I should point out the mpg was a little better with the 4.6 but the V6 has 140k on it, the V8 was leased and had <36k on it when returned to FMCC.

I just picked up our new 4400# travel trailer and towed it 110 miles home. Keeping it locked out of od the truck had no problem maintaining speed (55-60) on some considerable mid Michigan hills.

I wish I had done this years ago! The tru trac works seamlessly - far better than the stock Ford LS I have had experience with previously. FYI - I did add a jumbo $40 trans cooler.

Dollar cost was $150 for Ring and Pinion, $120 for the complete rear axle bearing set, $400 for the Tru Trac, $170 for the Jet accuspeed, and $400 labor. Not cheap, but considering the only alternative was buying a used f150 V8 with limited slip, this project was very cost effective.

I have to believe that this is probably one of the best ways to get a big performance boost without sacrificing any reliability.

97dink