JMod for 4R70W

Posted on May 8, 2011


I am getting ready to dive into my 4R70W 2001 transmission to perform a very tasty modification.  I have always been fascinated by Auto Transmissions, Sun and planetary gears.  Here is a good video of a basic view of a 4 speed auto trans.

A “JMOD”, as it is called is a internal modification to the Ford 4R70W transmission, which was the brainchild of Fords lead designer on this trans, Jerry, now retired.

The concept is to speed up the shift process, which causes much less slipping to occur during a shift from first to 2nd, and 2nd to 3rd, and 3rd to 4th gear.

Ford programmed the transmission to have a nice cushy soft shift to satisfy their target market, but in doing so, it causes undue wear and hastens the failure of the bands.

This procedure differs from a “shift kit” which changes springs and raises line pressure…I would NEVER raise the line pressure in a 4R70W transmission.

The benefit to the hot rodder or someone interested in performance, is that once the JMOD is performed, the car shifts decisively, especially at higher throttle positions or WOT, even chirping the tires in the 1-2 shift and 2-3 shift.  (-:  A Win-Win

Here is a video of a Vic with a Jmod. listen to the firm crisp shifts from 1-2 and 2-3.

Here is a vid of a Vic without a Jmod, listen to the 1-2 shift and the 2-3 shift for comparison…The shift takes much longer than the previous Jmod’d video.

Much has been written about this procedure on the web, especially on and the TCCOA site..a treasure trove of information about the Vic and the 4R70W  (Panther platform and prior).

Basic theory, by opening up the existing drilled holes in the separator plate that flow Hydro fluid during the shift, (2,4,5,9,11) to a larger size (from .081 to .110) the shift is much firmer.

Also, by removing the bottom springs in both 1-2 and 2-3 servo packs, the shifts are firmed a little more.  I am optionally replacing the stock spring in the OD shift circuit from stock pn F872-7F201-AA to a F2VY-7F201-A  spring, the flabby OD shift will firm up as well.

These recommended Modifications come straight from the lead engineer who is retired from Ford, Jerry W.

A series of links here, however, it is likely that you will need to register on CVN to see this data.
The first one will show you how to do the OD spring upgrade (to a softer HiPerf spring)

Parts that are needed include:

Upper and lower separator plate gaskets, 1W7Z-7D100-AB, 1L3Z-7C155-AA

Optional High performance OD servo spring, F2VY-7F201-A  (firms up the 3-4 OD shift)

Trans filter FT105

Mercon5 Fluid, 10 qts

Pan Gasket optional

7/64 drill bit for hole 2,4,5,9,11  (for 1-2 and 2-3 shift firmness)

3/32 drill bit for hole 10, engages reverse a little faster

Dielectric grease for connectors

Carb or brake cleaner.

Also need Inch/LB torque wrench, snap ring pliers, deep well 10mm socket 1/4 drive, 8mm socket, pliers, drill, Oil drain pan, razor blade (to remove gaskets), jack stands or ramps, or a lift if you are lucky enough.

Basic steps, not inclusive:

Drop the trans pan, pull the filter, remove the wire harness, drop the Control Valve, remove 3 pacman disks, pull the separator plate off the CV, remove gaskets, drill the holes in the Separator plate, reassemble with new gaskets, set aside and pull the 1-2 servo lower spring, pull the 2-3 server lower spring, capture the OD band, remove the OD servo spring, replace with softer spring (pn above), install the CV, install the filter, install the pan, fill, road test.

6/3 Went to my local dealer and picked up the upper and lower separator plate gaskets, about $2 each, picked up the trans filter $30 and bought a HP spring for the OD servo…about $30

Come to find out, the HP spring 3-4 is no longer available but my dealership found one at a firm in Wisconsin that handles obsolete parts.

Performed the JMOD on Fathers day.   Nothing like a whole day working on a car eh?

Everything went as expected, except for a couple things, When I dropped the control valve, the OD snap ring and piston dropped out also.  This is not supposed to happen.  The snap ring must have came loose, or was incorrectly inserted during transmission assembly at the factory.

Luckily I had already decided to change the OD spring to the hiperf one, and researched how to handle the OD band situation, where it drops out of the way of the piston, if not wedged in place when the piston is removed.  Since my piston was removed without me first doing the wedging, I had to fish it back into position..not difficult but you have to know that it’s a problem, and how to fix it, and not try to learn this from under the car.

With the band in the wrong position, you would have no 4th gear.

To fix this situation, drop the pan, drop the control valve, drop the OD servo out of the bore… again.  feels like it takes 3 hands.

hand 1, push up on the band using the access hole next to the servo bore, work it over as far as you can towards the OD bore. I used my first finger to work it in the proper location.

hand2, using a smaller tool, screwdriver, put into the OD bore, up into the smaller hole and try to catch the edge of the band and pull it over the hole, working both hands so hand 1 can hold the band in place, via the access hole, while hand 2 removes the screwdriver from the BORE and reinserts the servo into the bore, making sure that the tip of the shaft on the servo assembly catches the edge of the band, then reaffix the snap ring to hold it in place.

Again, register on CVN and find this link from shows nice graphics about what you are trying to do here:

You may also find the images by googling crownvic and 30.jpg 31.jpg and 32.jpg

The other situation was when I was filling the trans back up afterwords.  I added 4 qts and started the car, ran through the gears, then added 2 more, showed full, but car wouldnt move…had to run through the gears, and patiently wait for the fluid to exit the pan to the internals, then add even more fluid.  Ended up adding 10 qts..then all was well.

Shifts are very firm and pleasant to an old  hotrodder!

Tire squawk in the 1-2 shift no problem….!

Want a JMOD sticker?…$5 right here:

The old site (RIP Matt), is mirrored here now:  for reference, not directly related to JMOD procedures.

Watch for updates..