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post #1 of 5 (permalink) Old 01-28-2004, 07:38 AM Thread Starter
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j/mod q's

well i am thinking of doing the j/mod on my 97 xr7. the car has 111,000 miles on it. would you recomend doing this? or should i try to find a new or rebuilt 4r70w first and swap it in( of course doign the j/mod before install)? i know i need the frpp rear LSD differential as well. Thinking on 4.10's to go in, or will 3.73's be enough? the j mod looks somewhat intimidating. is it hard to do? or does it just look worse than it is? and any recomendations on torgue converters such as what rpm, lock up, non lock up? i figure before i work on the engine i should go ahead and do all the maintenance and upgrades to the drive train itself. also, i have heard some people have real hard shifts with the j/mod? is there a way to avoid this? i drive around 110 miles a day, so i want to improve shifting, but dont want earthshaking shifts while cruising around. is this a possible compromise? thanks for the help guys.
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post #2 of 5 (permalink) Old 01-29-2004, 05:38 PM Thread Starter
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post #3 of 5 (permalink) Old 01-29-2004, 05:40 PM
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J-Mod - Yes I would still do it! 111k isn't anything to worry about, and this will just add some life on to it most likely. You should'nt be too worried about doing the mod at all. Just do the seperator plate drilling, and the accumulator pistons. Forget about the OD/Reverse servos. Take your time, be careful, follow instructions.
You can have it shift as hard or soft as you'd like. I did the lowest mod to my trans, along with a spring upgrade, and leaving 2 springs out and I'm very happy with the way it shifted.

Torque Converters - The Mark VIII converter is a good budget mod for our cars. It's supposed to stall around 2,600-2,800 I believe. You will need a Mark VIII flexplate to use this as a mod. I ordered a '98 flexplate to use. Newer Mustangs use this same torque converter, though I would recommend you purchase it new.

If you want to spend more you can get a Morris or Pro-Torque for $350-400. A stall of around 3,000-3,200 would be a good thing.

You can also look into the PI Stallion multi-disc converter. You will have to shell out about $700-900 for this unit though.

You NEED a lock up converter!

Gears - Either gear is a good choice, and a good compromise would be 3.90's. It depends on what kind of car you're looking to build. If you drive 110 hwy miles everyday 4.10's probbaly wouldn't be very desirable. The FRPP diff. only comes with 3.73 gears as far as I know anyway.

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Last edited by BlackCat94; 01-29-2004 at 05:50 PM.
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post #4 of 5 (permalink) Old 01-29-2004, 05:50 PM
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Yes, do it. Use both a bottom and a top 1-2 accumulator spring and no 2-3 spring. Drill the holes to the mild specs. Don't bother with the od and reverse servos. These will make for a simple job.

Edit: beat me to it.
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post #5 of 5 (permalink) Old 01-29-2004, 06:09 PM
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the hardest j-mod shift just isnt that bad of a shift....its borerline racecar....but itll jar you.....but its not uncomfortable as you think....you want a mild gear change with no springs probably...prolly what your looking for.....if your pretty good with trannies in general the j-mod is quite easy......directions make it a little more difficult......but this also goes by how mechanically inclined you are...but basically if you follw the steps it isnt that bad.....the part that takes the most thinkin is drilling the holes......when you have the seperator plate out.....mark the holes with marker....then drill them.....so you dont mess up...theres a diagram in jerry's thesis

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