Submitted by BlackiceLSC
Visit the Lincoln Mark VIII Forum for more info

The following is a “How To” of how to perform a 1-2 shift accumulator piston and spring assembly replacement and 2-3 shift accumulator assembly replacement as well as the legendary “JMOD” to your Lincoln Mark VIII transmission.

The jmod is a modification to the 4r70w valve body. That being your automatic transmission. It involves removing certain springs and drilling bigger holes in the seperator plate allowing fluid to move more quickly making shifts faster and firmer. This reduces the heat that the stock settings create because of more friction due to the longer delay which makes the stock settings shift soft and slow. I had it done to my car along with an sct tune and tranny cooler and let me tell u it makes the auto a WHOLE lot more fun. Shifts as fast as a manual. I have beaten cars that should have taken me due to the fact they messed up shifting and my auto shifted hard and fast as the right time everytime! This is a highly recommended modification.

Parts You Will Need
  • New style 1-2 shift accumulator assembly with new upper and lower springs
  • New style piston and retainer
  • New style 2-3 shift accumulator, new spring, and retainer
  • New separator plate gaskets (2) ’96-later transmission oil pan with deep sump pocket, and filter/gasket
  • Finally, 12 qts. Mercon V transmission fluid


Removing the Stock 4R70W Accumulator
  1. Drain the transmission
  2. Remove the rubber plug in the bottom of the bell housing
  3. Rotate the motor by turning the crankshaft bolt on the front of the motor, until you see the torque converter drain plug through the access hole
  4. Then remove all the transmission pan bolts, and remove the pan – there will be fluid left in the pan, so caution must be used.

Next, remove the old filter from the transmission


Don’t forget to remove the magnet stuck in the old pan —- Carefully un-plug the 4 electrical connectors from the transmission


Next, remove the 25 bolts attaching the valve body to the transmission. Before you can remove the separator plate from the valve body, you must remove the three round covers, and one small bolt in the corner. Be sure you note how these covers come off so you can be sure they go back on the valve body when you are finished with the separator plate modification.


Now you will need to remove the old gaskets from the separator plate. Use a sharp putty knife, or gasket scraper. Be absolutely sure you remove ALL traces of the old gaskets from the separator plate

There is a small filter element located inside the bottom of the transmission case. Be sure not to lose this filter. I took pictures to show what it looks like, and where it goes, in case it should fall out


Now remove the old 1-2 shift accumulator assembly from the transmission. The 1-2 shift accumulator is located inside the round cylinder cavity on the forward, driver’s side of the bottom of the transmission case. In the photo you will see 4 round covers in the bottom of the case. The 1-2 shift accumulator is in the hole located in the top right of the photo


The next thing you want to do is to compress the 1-2 accumulator assembly by use of a large C-clamp. There is a flat-ledge location on the upper side of the transmission case to lock the C-clamp on while you compress the 1-2 accumulator by tightening the C-clamp. You will then need a good pair of C-clip pliers to remove the snap-ring that holds the 1-2 shift accumulator retainer in place


Once you remove the snap-ring, simply loosen the C-clamp, and let the 1-2 accumulator retainer come out. The entire 1-2 accumulator assembly should come right out with the retainer. Once it is all out of the cylinder bore, inspect the cylinder for damage/wear. If it looks clear, simply wipe the cylinder with a piece of scotch-brite and a clean cloth. The picture shows the entire 1-2 accumulator assembly removed, including the broken lower spring.

Installation of the New 4R70W 1-2 Shift Accumulator
Install the new 1-2 accumulator assembly with the new springs, and lubricate them slightly with a small amount of clean Mercon V fluid. I elected to leave the bottom spring out to firm up the 1-2 shifts. Push the entire assembly, including the retainer, up into the cylinder bore. You may need to use one hand to hold the assembly up high enough to re-install the snap-ring.

This is where a lot of people stop. In the case of my vehicle, I decided to replace the 2-3 shift accumulator assembly as well since the valve body was out. Unfortunately, I do not have any photos of this procedure but I will describe it for you. It is actually a lot easier to replace the 2-3 shift accumulator assembly.

The 2-3 accumulator is located in the opposite, rear corner of the transmission case. Simply grab the retainer with needle-nose pliers, and pull it down. Then, by putting pressure with your fingers on the inside wall of the 2-3 accumulator piston, pull downward, and it will come out. There is only 1 spring in the 2-3 accumulator assembly. It goes into the top of the piston. With a small amount of clean Mercon V fluid, slightly lubricate the new piston, and insert it back into the cylinder bore. I left the new spring out to firm up the 2-3 shift. Then, bend the three tabs on the new retainer outward to hold it inside the cylinder. It should “snap” into place. That’s it!

The “JMOD” on the Lincoln Mark VIII 4R70W Transmission
Now back to the separator plate. In this case, I am performing what is known as the “JMOD” to my transmission. This modification was published by one of Ford Motor’s Master Transmission engineers named “Jerry”. I will fill you in more on this at the end of the article.

What the “JMOD” entails in simple terms is the modification of the valve body separator plate to improve fluid pressure to critical components in a more efficient way by boring out some of the holes in the separator plate. This is highly recommended on ANY automatic transmission that is going to be subject to horsepower increases, or mild to moderate rear differential gear changes. To learn more about this modification, click HERE. After you have performed the “JMOD” to the separator plate, be sure there are no burrs from the drilling. Install the new separator plate gaskets, and the rest of the valve body as it came apart.

Here is a photo of another small filter that is hidden in the main valve body. I am pointing these out so you can keep an eye on them, and make sure they are in their proper location prior to re-assembly


It is now time to re-install the valve body. Be sure that you align the linkage assembly with the shaft on the driver’s side of the valve body. A common occurrence is to end up with the linkage out of position. Below is a picture of such a mistake


I re-installed the valve body without aligning the shift linkage with the shaft. Notice in the center of the photo the jagged bracket, or “Rooster” has a pin that aligns with the horizontal shaft traveling front to rear. In the photo, you can see how the pin is lined up with the center of the shaft. It should be toward the front of the shaft, between the two retainers. I discovered this AFTER installing the pan, and 10 qts of fluid. I had to remove the pan and the valve body to correct this error!

It is now time to double check the proper torque of the valve body bolts (see the article from the link earlier for proper torque specs). Then plug in all the electrical connectors, and wipe clean the gasket surface for the new pan. Install your new filter, and DON’T FORGET to place the magnet into the new pan. Install the new pan, and tighten the bolts to the proper torque specs

Here is the complete package


Now refill the transmission with about 10 qts of Mercon V fluid, check the level. It should hold 12 quarts total. Do not over fill. Here is a picture of the left over parts


You’re done! Now go test drive the car. Your “JMOD” transmission upgrade to your Lincoln Mark VIII is finished.

I spent a total of about $150.00 in parts, and about 4 hours labor. I had the luxury of using a lift at “Big Johnson’s Auto Repair” in Santa Rosa. I also had the help of John Schmidt. aka JOHNAEC, a well known icon on the Lincoln and Thunderbird websites. This job would not have gone near as smoothly as it did without John’s help. He supplied all the literature from the TCCOA website, Jerry’s thesis, as well as the specialty tools required (drill bits, torque wrench, C-clamp, snap-ring pliers), not to mention his handiwork when it comes to messy jobs.

As you recall, I elected to leave the lower spring out of the 1-2 shift accumulator assembly for “firmer” shifts. Well after a few days of driving the car, I was concerned that the 1-2 shifts were TOO firm. The “JMOD” did exactly what it is supposed to do. It made the shifts very quick with no noticeable slippage. But since I left the lower spring out of the 1-2, the shifts became a lot firmer than I had anticipated. So much firmer that I was concerned that perhaps it would cause un-wanted driveline damage. U-joints, half-shafts, CV joints, or worse, internal transmission components. After all, I had performed all the work to ensure longevity of the transmission, not to destroy it.

Well, today I decided to get back under the car, drop the pan, and install the lower spring in the 1-2 shift accumulator assembly.

I am very pleased with the end result. The my Lincoln Mark VIII shifts exactly the way I wanted it to. It now shifts firm enough at W.O.T. (wide open throttle) that it easily “chirps” the tires. But during normal driving, the shifts are quick and firm, but not so firm that I am worried about anything sustaining damage. The perfect combination of performance, comfort, and efficiency. The “JMOD” is a complete success.

If anyone is considering eliminating the lower 1-2 spring with a “JMOD” upgrade, be prepared. The shifts are very harsh. You will easily break the rear tires loose during heavy acceleration. This is what a lot of people are looking for. Just be sure your driveline is up to snuff to handle the extreme change in shift performance.

I was looking for something I have never had before. I wanted sharp shifts, with no slippage between gears. I wanted to “chirp” my tires under heavy acceleration. I wanted to have shifts that were not extreme, but close to normal during every day driving. I wanted all this without worrying about excessive wear to the internal components of the transmission, or the driveline components.

The “JMOD” gave me everything I wanted, and more. You should expect perfection. I had no idea my Lincoln Mark VIII would be so much more fun to drive!

How To Video
I happened to come across a how to Video a member of TOCCA and produced.

This video will take you step by step thru the Jmod Process. I hope it helps!