Mark VIII Frequently Asked Questions
Transmission List of Categories
Where can I find detailed articles about the 4R70W transmission?
MN12 Performance.com Article
When my car shifts at part throttle, there is a shudder that feels like I'm driving over train tracks.
This is caused by the breakdown of the transmission fluid. The best fix for this is to completely flush the fluid out, replace it with Mercon V, and install a transmission cooler. While you're doing this, it is often a good idea for the 1-2 accumulator piston to be changed out, as well as a transmission filter change.
When my car shifts from First to Second, the shift is very abrupt and firm. Is this normal?
The 1-2 accumulator piston is a known weak point in the Mark VIII. The original design is flawed, and a TSB (Technical Service Bulletin) was issued by Ford. Continuing to drive the car with this will eventually cause damage to the transmission, so it is in your best interest to have it replaced, or do it yourself. Now is also a great time to have a transmission cooler installed, as well as flushing the system and refilling it with Mercon V. A paper describing the procedure, with part numbers, is available here: 1-2 Accumulator Paper
My car seems to vibrate beginning around 75-80 miles per hour. Is this normal?
Yes, the 94-98 Mark VIII has a two-piece driveshaft that is prone to vibration. Many members have had good experience changing to a one-piece driveshaft that is properly balanced. The 93 models have a one-piece driveshaft, and many do not exhibit the same vibration that the other models have. Some of our members have purchased aftermarket driveshafts from our vendors to correct this problem.
When driving on the highway, my car feels like it's shifting into Neutral, then it goes back into gear. What gives?
The MLPS (Manual Lever Position Sensor) may need replacement. This is what 'tells' the transmission what gear you have selected. When it fails, it may intermittently report the shifter is in Neutral, causing the symptoms above. It is sometimes referred to as a 'neutral safety switch'.
My mechanic said that I can only use Mercon III, not Mercon V in my transmission.
Mercon V is compatible with the transmission in the Mark VIII, and often provides better performance, as it is a synthetic blend.
I dropped my transmission pan, and found a yellow golf tee shaped thing in the pan. What is this?
This is nothing to be concerned about. It is simply a plug put inside the transmission during assembly to prevent foreign materials from getting inside before the car is assembled.
Can I swap a 5 speed transmission into my Mark VIII?
Theoretically, it can be done, but it would require fabrication, and more importantly, a lot of electronic sensors and engine management functions would have to be modified to make it work. It is NOT a cost effective upgrade, though anything can be done, if you have enough money for the project.
What's the "JMod" consist of and what will it do?
The JMod is a combination of modifications to the valve body and accumulator piston/springs that improves the shifting characteristics of the transmission. One of our members has posted a writeup of his experiences here:
Does my Mark VIII have a limited slip differential? (Posi)
All Mark VIII's were delivered with open rear ends. All 93-94, and 95-98 Base models were delivered with a 3.07 final drive ratio. 95-98 LSC models were delivered with a 3.27 final drive ratio.
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