Crown Vic J Mod: Any Experience?

"Rusty Vandura - www.tinyurl.com/keepoppo" (rustyvandura) 01/14/2020 at 11:22 • Filed to: None

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From what I’ve read, it’s a very doable thing and, maybe no cost. Anything you wouldn’t mind sharing?

Pic: Unrelated, but seems like a Very Nice Price.

Snuze: Needs another Swede > Rusty Vandura - www.tinyurl.com/keepoppo 01/14/2020 at 11:45

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What is the J mod?

ShrimpHappens, née WJalopy > Snuze: Needs another Swede 01/14/2020 at 11:56

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Blunt roller in the dash?

vondon302 > Rusty Vandura - www.tinyurl.com/keepoppo 01/14/2020 at 12:04

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I did this to my old p71. It works as advertised but would I do it again? For a fun beater yeah I’d do it but for daily driving probably not. 

Rusty Vandura - www.tinyurl.com/keepoppo > Snuze: Needs another Swede 01/14/2020 at 12:06

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It’s a mod to the valve body of the transmission where you drill out some passage holes, allowing the fluid to flow through more quickly, build up pressure more quickly, shift more positively and soundly. Also, I think you can stiffen or loosen or even remove some springs. But primarily, I think it’s about drilling out some passages. From underneath the car.

Jason Spears > Rusty Vandura - www.tinyurl.com/keepoppo 01/14/2020 at 12:08

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No idea, but you led me to my favorite video of the day so far.

I’m enjoying the calm, deliberate process, clear explanation, and good camera and light work . It’s s o un-Youtube.

Rusty Vandura - www.tinyurl.com/keepoppo > vondon302 01/14/2020 at 12:09

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That’s the kind of feedback I’m looking for. Did it shift too harshly? Did you go to maximum size on the holes? Did you change out any springs?

Rusty Vandura - www.tinyurl.com/keepoppo > Jason Spears 01/14/2020 at 12:09

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And you have led me to something very helpful. Thank you for this!

Snuze: Needs another Swede > Rusty Vandura - www.tinyurl.com/keepoppo 01/14/2020 at 12:13

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Sounds like the DIY version of one of those shift kits you can buy from Summit Racing or whatnot.  Cool.  I say, for your beat Vic, go for it!

Rusty Vandura - www.tinyurl.com/keepoppo > Snuze: Needs another Swede 01/14/2020 at 12:21

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Hey: you calling my Vic beat ?

I’m going to call it B.D.A.R. (Battle Damage Assessment and Repair) That’s an actual thing in the Army.

Urambo Tauro > Rusty Vandura - www.tinyurl.com/keepoppo 01/14/2020 at 12:35

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I J-modded the 4R70W in my ’96 Thunderbird when I rebuilt the rest of the transmission. Good mod! Be honest about which setting you choose though. There’s no need to make it shift extra hard if you’re only feeding it stock power. I went with the “mild” (<300hp) setting on mine and couldn’t be more pleased with the result. Not only did it firm up the shifts just the right amount , but perhaps my favorite feature was how much more quickly it fills the servo to engage reverse. Before the mod, it used to take about one full second to engage after moving the shifter, but the J-mod shortened that wait time dramatically.

vondon302 > Rusty Vandura - www.tinyurl.com/keepoppo 01/14/2020 at 12:45

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Max size on the holes and no springs. It shifted HARD after it but my car had a ton of miles on it too. It’s basically a do it yourself shift kit. 

Rusty Vandura - www.tinyurl.com/keepoppo > Urambo Tauro 01/14/2020 at 14:19

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This reinforces my thinking perfectly. I realized there was a hole size choice and I was feeling inclined to go sort of medium with it. I read an internet where the guy was saying that the faster shift actually was good for the trans, since there were shorter, more positive clutch happenings and this reduced heat. Sounds reasonable to me. My gripe with Ford Transmissions has always been that you can eat a sandwich in the time it takes them to shift. There’s a 48-minute YouTube video of a guy performing a J-mod that is very relaxed and methodical. Without knowing how much of a PITA this project is, it strikes me that if you were too modest, or if you increased horsepower later, you could do it a second time and make the holes larger.

Any experience fooling with the rear ends?

Rusty Vandura - www.tinyurl.com/keepoppo > vondon302 01/14/2020 at 14:20

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I think I would be modest in choosing the drill bit size. You can always re-drill a hole larger... Did you remove some springs?

vondon302 > Rusty Vandura - www.tinyurl.com/keepoppo 01/14/2020 at 14:24

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I don’t think so, but it was years ago.

Rusty Vandura - www.tinyurl.com/keepoppo > vondon302 01/14/2020 at 14:50

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Can you lift up the car and perform the mod from underneath?

vondon302 > Rusty Vandura - www.tinyurl.com/keepoppo 01/14/2020 at 15:20

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If you can get the trans pan off you can do it. 

Urambo Tauro > Rusty Vandura - www.tinyurl.com/keepoppo 01/14/2020 at 18:49

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Yeah the J-mod is very worthwhile IMO. Developed by an ex-Ford engineer, from w hat I understand (J stands for Jerry) . I like to think that in an alternate universe, the mild settings would have probably have become the factory tune if Jerry had his way .

I believe y our car has a stock 8.8 axle , right? I actually do have a little experience with those, having rebuilt the one in my Mustang.

Urambo Tauro > vondon302 01/14/2020 at 19:03

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Max size on the holes and no springs. It shifted HARD

Y ikes! Yeah before modding my ’96 Thunderbird I ha d heard that it was really easy to get too enthusiastic with the tune, so I went with t he mild settings. Absolutely loved the results. The shifts were were f irm, clear, positive, and satisfying without being too harsh .

Rusty Vandura - www.tinyurl.com/keepoppo > Urambo Tauro 01/14/2020 at 19:34

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Can we discuss this further, por favor?

I am trying to develop an idea of how doable it is for someone to rebuild their own rear end. I am actually quite skilled with mechanic’s tools. And others’ tools...

Regarding J-mod, I haven’t had the chance yet, but I need to find a listing of the parameters, how big of holes to drill, spring rates, whatever. I don’t want my transmission to bang shift every time, so I’ll probably want to wind up somewhere in the middle.

And there’s final drive ratio...

Urambo Tauro > Rusty Vandura - www.tinyurl.com/keepoppo 01/14/2020 at 20:02

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Most of the rebuild is well within the average DIYer’s capability. But there are two main hurdles (both IMPORTANT) that come to mind that you’ll need to prepare for if you want it done right .

The first is preloading the pinion bearings. It’s not as simple as just tightening down the pinion nut “to spec”. You need to tighten it a little bit at a time until it reaches a certain amount of rotational resistance (as measured by a beam-style INCH-pound torque wrench, no clickers ) . An d i f you go too far tightening the nut , you’ll have to start all over again with a fresh crush sleeve.

The other hurdle is getting the gear mesh pattern right. I got really lucky with mine, not having to go through a bunch of trial-and-error shimming. This is probably due to my rebuild being preventative in nature , as well as the fact that I didn’t change the gears themselves . I was able to put it right back where it belonged with fresh bearings on the first try. If you’re planning to change gears, expect to spend some time shimming and re-shimming until it’s right.

I did the rebuild in my garage, with the axle still mounte d to the car, which was on jackstands. Crawling around underneath wasn’t pleasant (especially for tightening that pinion nut!) , but doable. Much easier i f you have access to a lift, of course .

Rusty Vandura - www.tinyurl.com/keepoppo > Urambo Tauro 01/14/2020 at 21:46

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Bet I can get some learning about this on YouTube.

Urambo Tauro > Rusty Vandura - www.tinyurl.com/keepoppo 01/15/2020 at 06:38

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TCCoA is/was also the go-to resource on J-mod info. But the site had a redesign last year , and I’m not sure how to find the tech articles there anymore. Fortunately, I do happen to have a lot of that stuff saved to disk if you need it.

vondon302 > Urambo Tauro 01/15/2020 at 06:53

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The kick down was fun tho.

It made winter driving especially sketchy. 

Rusty Vandura - www.tinyurl.com/keepoppo > Urambo Tauro 01/15/2020 at 10:10

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Yes, this. Looks like there’s an LSD 8.8 at 3.73:1 that is installed in Exploders and such and is readily available. With the J-mod, should perk the car up quite a bit. I was told that by flashing the ECU (?) one can out a tune on the 4.6 as well. Need to research.

Urambo Tauro > Rusty Vandura - www.tinyurl.com/keepoppo 01/15/2020 at 11:22

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I’m afraid ECU/PCM tuning is outside my wheelhouse, but I’m sure you’ll find plenty of options out there for the Mod motor.

Rusty Vandura - www.tinyurl.com/keepoppo > Urambo Tauro 01/15/2020 at 16:51

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Doing some more research. I have like ZERO experience fooling with automatic transmissions. So for the almost 40 years I’ve been owning and maintaining my automobiles, I have invariably had my automatic transmissions serviced by transmission shops. We have a first rate shop a mile from my house. So with this Vic tranny, aside from J-mod considerations, if I wind up keeping it any length of time, I’d have the trans serviced up at Keith’s. Turns out they install many shift reprogramming kits. So a service is in the range of $250. They would install a Transgo reprogramming kit for around $400. True, the J modification is technically free, but would take me some hours to carry out and I’d have to do much research. And the J-mod does not include the springs and things that come along with the Transgo reprogramming kit. I may just go that route.

Urambo Tauro > Rusty Vandura - www.tinyurl.com/keepoppo 01/15/2020 at 17:57

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I put a TransG o kit in that 41TE that I rebuilt a while back and posted about on Oppo. TransG o has a good rep utation for extending the life of the transmission and not just firming up shifts for the sake of performance . I wouldn’t hesitate to recommend them. I’m not familiar with the differences in hole sizes between the J- mod and TransGo’s 4R70W kit, but I don’t think you can go wrong either way. I just have a bit of a soft spot for the J-mod after hearing about being developed by a Ford engineer.

BTW, another good brand you may come across in your research is Sonnax . They make a lot of kits for addressing specific transmission weak points. I used one of their spiral l ock rings to replace a snap ring on my 4R70W that was starting to work its way out and had almost let loose.

Rusty Vandura - www.tinyurl.com/keepoppo > Urambo Tauro 01/15/2020 at 18:11

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When I compare the Great Unknown that this represents to $400 to have my shop do it, I don’t see a great deal of light between them. There’s a lengthy YouTube video I still have to watch about the J-mod before I make up my mind.

Urambo Tauro > Rusty Vandura - www.tinyurl.com/keepoppo 01/15/2020 at 18:22

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W hile you’re thinking about it, consider taking the opportunity to add a drain plug to the pan. I f you find yourself deciding to re-enlarge any of the holes in the separator plate after the initial tune, you can easily drain and capture the fluid for re-use.

Rusty Vandura - www.tinyurl.com/keepoppo > Urambo Tauro 01/15/2020 at 18:34

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Interesting thought. I have to watch that YouTube video next. 48 minutes long...