Jmod vs tune

[MinnesotaMM]

Okay from what I understand, doing the jmod tightens up the shifts and increases the life of the transmission. Does anyone have a detailed tutorial with lots of pictures? Or better yet a video link? Doesn't a tune do the same thing though? Increase pressure and tighten shift points + the shift schedule? Im trying to get a better understanding so that if I get the jmod done I get a tune according to what I need. Or if I even need to get the jmod done. Thanks!

[RacerX]

http://www.crownvic.net/tech/4R70Wnotes.pdf

Tune is a no-brainer. Everyone loves their first real tune. J-Mod you need some technical experience or someone that knows how to do it. J-Mod allows more fluid to move faster without having to raise line pressures to shift sooner causing the friction plates to engage sooner. This reduces wear and tear. Btw, don't ever hammer down into or out of fourth. It's an OD band and can distort/wear easy. Keep it out of od with a heavy foot.

[MinnesotaMM]

So do I need a tune made for the jmod if I get it done? When im gettin on it around 55 miles an hour I get a hesitation around 3,000-3,500 is that the od band? So just drive it with the od off when im givin it then?

[justbob]

OD off or you will slowly kill the trans. No, you don't need a tune for the Jmod. Although you would probably like to have one so you could dial back the line pressure. Another option is not removing the accumulator springs, but replacing them with lighter weight ones.


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[MinnesotaMM]

so should i just drive all the time with the od off then? n what do u think about a sct 9100?

[justbob]

I do. Until 50 or so.


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[justbob]

9100 junk

You will want a 3000 or 3015




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[Curless]

I never drive with od engauged until I reach cruising speed. I hate the shifting...I'm not tuned yet though :(

[stevengerard]

Btw, don't ever hammer down into or out of fourth. It's an OD band and can distort/wear easy. Keep it out of od with a heavy foot.

X2 I'm proof of that, I never hammered it with OD on except for a couple of times maybe. And when I got the parts back from my recent trans rebuild it was the OD band that was burned. Could have been the final straw as i was cruising at 78 when the seal gave but who knows.

But now that my trans has been built with heavey duty parts and the Jmod was done I think I need a new tune. The OD light has blinked on and off a few times and the trans guy says that's expected as the old tune doesn't understand the new pressure limits. Does that sound right?

[sailsmen]

I recall early on a number of MM trans failures were due to a clip popping off. I don't remember the details of what clip or where.

[Curless]

X2 I'm proof of that, I never hammered it with OD on except for a couple of times maybe. And when I got the parts back from my recent trans rebuild it was the OD band that was burned. Could have been the final straw as i was cruising at 78 when the seal gave but who knows.

But now that my trans has been built with heavey duty parts and the Jmod was done I think I need a new tune. The OD light has blinked on and off a few times and the trans guy says that's expected as the old tune doesn't understand the new pressure limits. Does that sound right?

Hmmm, not so sure about this...anyone with experience know...what code comes up?

[MinnesotaMM]

Great information thanks! Is anyone here from around mn and knows how to do a jmod? I'd like to get it done before I have to park it for winter.