Mark VIII FAQs

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theterminator93

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North Ridgeville, OH
Vehicle Details
1997 Thunderbird 4.6, 1998 Mark VIII LSC
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I am considering the purchase of a Mark VIII. What should I look for?
As always, having a trusted mechanic go over the vehicle is a good idea, especially one familiar with the Mark VIII. This is a rare bear, though, so you may look for these Mark VIII specific trouble spots.
  • Leaking suspension. Check the vehicle after it's been sitting overnight. Is one corner or one end of the car completely down on the suspension?
  • Transmission shudder. On light acceleration, does the transmission 'shudder', as though you were driving over 'rumble strips' when shifting from 3rd to 4th gear? If so, this may indicate a failing torque converter (worst case scenario) or transmission fluid breakdown.
  • Brake vibration. The rotors are susceptible to warping, so this may be a 'bargaining chip'.
  • Driveshaft vibration. Try taking the car on a smooth road and run it up to 75-80 mph. If there is vibration, this may also be a 'bargaining chip'. Read below in Transmission for more information.
  • Startup rattle. The secondary cam tensioners are a known trouble spot. They will often rattle on the first few seconds after sitting overnight. Yet another 'bargaining chip'.
  • If you have chrome wheels, look under the center cap for bubbling in the chrome finish. This seems to affect the cars exposed to salted winter roads.
  • Check the rear swaybar, some members have reported cracked swaybars, due to corrosion in the hollow bar.
  • Climate control blend door. The blend door actuator for the 97/98 model years is known to break and leave you without control over how hot/cold the air gets.
  • The intake manifold runners (IMRCs) can get stuck due to lack of use over time. If the car falls flat on its face under hard acceleration over 3000 RPM, they may be stuck closed.
  • The headlights on the 1st generation easily overheat and burn on the inside. This produces a creamy white or even brown appearance at the back of the reflector. This is not common on the 2nd generation or 1st generation LSC models as both were equipped with cooler HIDs.

What are the differences between the First Generation (93-96) and Second Generation (97-98) models?
The exterior was treated to a 'makeover' in 97, with a new 'power dome' hood, different grille, front and rear fenders, trunklid, lighting improvements by way of HIDs on all models, neon taillight, LED turn signals and puddle lamps in the side mirrors. The message center offers more functions, such as the side view mirrors pointing down when in reverse. The steering wheel now has tilt/telescope functions, and is tied to the seating presets on the door. The lumbar support became mechanical, instead of an inflatable system. The intake tube is different, the 'beauty cover' over the engine was revised, and the interior was revised. The 2nd Gen cars also feature coil-on-plug type ignition, and the retractable rear radio mast was replaced with one embedded in the rear glass. Traction control went from an optional low-speed (under 35 mph) system to a standard all-speed system. The JBL stereo with CD player became standard on the 2nd Gen cars, the optional cellular (analog and non-upgradeable to digital) phone was integrated into the stereo and message center. Heated seats were offered as an option, and there was a passive anti-theft system with transponder-coded keys added. A digital odometer replaced the analog one with a revised instrument cluster, and a redundant PRNDL indicator added to the cluster as well.


What are the differences between a LSC model and a Base model?
The Luxury Sport Coupe (LSC) edition had perforated leather seats, true dual exhaust, different gearing, LSC badging, and on the 95-96 models, included HID headlights. Some chrome trim was also painted body color on the 2nd Gen cars, such as the grille. Suspension tuning (anti-roll bars, shock valving) was firmer on the LSC models as well. The LSC models were rated by Ford at 290 HP versus 280 HP for the base model, and have a 3.27 vs. 3.07 rear end gear. The speed limiting function of the powertrain module kicks in at about 124 mph, versus 130 mph on the Base model (due to the higher gearing and drive shaft speed).


What interior changes were made to the Mark VIII in its production run?
Sometime during the 94 model year, the center console changed from flat black to a woodgrain finish. In 95, the dash was remodeled to house a double DIN radio, instead of the single DIN and a revised climate control unit with more durable controls was introduced. In 1996, a rear center armrest was added. The 1997-98 models received some interior finish changes to include more woodgrain, a further revised climate control unit, a revised instrument cluster, different seats offering optional heating elements, different door panels and center console with retractable dual cup holders, a fully electronic tilt/telescoping steering wheel and soft "theater" lighting.


What different models of Mark VIII are there?
In 93, 94, and the first part of 95, there was only one model. Many warranty registration cards had the LSC nomenclature, though it was not labelled as such. Beginning in 1995, the LSC package was an option. There were a few limited-edition model runs, such as the 1996 Diamond Anniversary edition and 1998 Collector's Edition, which you can read more about here.
 
General Maintenance

My car is running very rough and/or stumbles off idle.
Spark plugs and wires often require replacement by the time your car reaches 60-70k miles. Copper plugs are recommended by many, but do require more frequent changes than [double] platinum plugs. When attempting to change the plugs, be sure to have a LONG socket extension (10" is a good start), as the plugs are DEEP in the heads. 2nd generation vehicles have COP ignition without wires - the COPs are known to fail as well, so they should be replaced periodically.


What kind of spark plugs should I use?
Several vendors recommend copper plugs for optimum performance. Motorcraft AWSF-12C (colder plugs), AWSF-32C (standard heat range) or Autolite 764 (standard heat range) are recommended, with the factory gap setting of 0.054". Double platinum plugs will provide 100,000 miles or greater of service life with a very minor performance expense.


Where's the fuel filter?
In the passenger side front fender well. The inner fender splash shield needs to come out to access it.


How do I change the air filter?
The air filter 'box' should have two bolts on top, then there are two bolts on the bottom which are difficult to see from the top. Once all four bolts are loosened, the box should come apart so you can replace the filter.


What kind of oil should I use?
Many club members use synthetics, such as Mobil 1, Valvoline or Amsoil. 5W-30 is the weight recommended by Ford.


What's the clattering noise I hear when I start my car? It goes away after a few seconds.
This is common on the Mark VIII and is caused by oil leakdown, causing the secondary cam tensioners to rattle until pressure builds up. The 'fix' from Ford costs over $1000 and requires serious disassembly of the front of the motor. Aside from the annoyance, if left alone damage is not typically likely. Installation of a pre-oiler will stop this, and anti-drainback oil filters (such as the Motorcraft FL-820s) help prevent this as well.


What kind of gas should I use?
Premium fuel of 91 octane or higher is recommended for the Mark VIII. The engine has a knock sensor that allows the use of regular fuels, but performance is negatively impacted due to reduced spark advance.


How do I refill the coolant system?
When the entire cooling system is drained and refilled, the following procedure should be used to ensure a complete fill without air bubbles.

NOTE: It is imperative the following procedure be adhered to. Failure to do so could result in damage to your engine.

1. Remove coolant reservoir pressure cap.​
2. Remove the engine coolant outlet tube fill plug on the engine.​
3. With the engine off and cool, add a 50/50 mixture of recommended cooling system fluid and water to the coolant outlet tube fill neck until the reservoir is full.​
NOTE: DO NOT FILL COOLANT SYSTEM THROUGH COOLANT RESERVOIR. COOLANT WILL NOT ENTER ENGINE, WHICH CAN LEAD TO ENGINE DAMAGE.​
NOTE: Avoid spilling coolant on the front end accessory drive belt, as this will allow the belt to slip and become noisy.​
4. Reinstall the pressure cap to the coolant reservoir.​
5. Continue filling at the engine coolant tube fill neck slowly while allowing air to escape.​
6. Reinstall the engine coolant tube fill plug when the system is full.​
7. Select maximum heater temperature and fan speed settings. Position control to discharge air at A/C vents in instrument panel.​
8. Start engine and allow to idle. While engine is idling, feel for hot air at A/C vents.​
NOTE: IF AIR DISCHARGE REMAINS COOL AND ENGINE TEMPERATURE GAUGE DOES NOT MOVE, SHUT ENGINE OFF IMMEDIATELY.​
This is an indication of low coolant level and/or air pockets in coolant system. Allow engine to cool and repeat the previous steps.​
9. Allow to idle until normal operating temperature is reached. Hot air should discharge from A/C vents. The engine temperature gauge should maintain a stabilized reading in the middle of the “NORMAL” range and the lower radiator hose should feel hot to the touch.​
10. Shut off the engine and allow to cool.​
11. After the engine cools down, recheck the engine coolant level. Fill reservoir to the COLD-FULL level as required.​
12. Check for leaks at the draincock, block plug and vent plug.​
13. Recheck the engine coolant level, using the recommended procedure, after one or two occasions of vehicle use. Fill to COLD-FULL level as required.​
 
Exhaust

What size tubing is stock?
2.25" tubing is used on all Mark VIII models.


What's this 'true dual' system on the LSC models?
The LSC exhaust goes from the manifold/pre-cats, into a dual in/dual out third catalytic converter, maintaining two separate pipes. It was worth 10 HP and 10 TQ, according to Ford.


Can I put headers on my car?
Yes, but it's not easy or cheap. Longtube headers show the greatest difference in horsepower and torque, but there are no readily available headers for our cars. They are typically custom built.


What upgrade options are there?
Many members have upgraded their exhausts from the front cats all the way to the back. Typically, a full dual exhaust, with either a H or X crossover installed near the front of the system, is installed with 2.5" tubing throughout the system. New mufflers are typically part of the equation as well.


Can I just replace the mufflers?

Sure, you can replace just the mufflers, for a different sound. It hasn't been proven to provide much difference in horsepower or torque, but many people are only looking to improve the sound of their car's exhaust.


What's the best muffler?
There is no 'best' muffler, only the one that meets YOUR particular needs. What some people may consider 'muscular and powerful sounding', others may find annoying and droning. The best flowing mufflers are typically those that have a 'straight through' design, such as Dynomax UltraFlo or Magnaflow mufflers. 'Turbo' mufflers typically have two 180 degree turns internally, and are often much more restrictive. Flowmaster mufflers have often been reported as creating a drone in the exhaust, particularly at highway speeds, but again, this is a personal preference.


Can I just cut off the mufflers and put in straight pipe?
Many of the people who have tried this have reported excessive droning and some low end torque loss. It is not typically recommended.


Why not just run two separate pipes all the way from the front to the back?
Using a crossover pipe with true dual exhausts has been shown to improve horsepower and torque throughout the powerband, due to the positive effects on exhaust scavenging. It also provides a more even exhaust note.


Will removing my third catalytic converter cause a Check Engine Light?
No.
 
Exterior/Lighting

My 1st Generation (93-96) low beams are about as effective as a candle in a hurricane. Are there any fixes?
This is probably the single biggest complaint for 1st Generation owners, caused by heat buildup from the halogen lamps literally burning all the reflective material off from the insides of the housings. The 95-96 LSC models were 'fixed' with the first domestic automaker's use of High Intensity Discharge lights, and these improve the situation tremendously. These can be retrofitted, but it is a completely new housing, and requires ballasts for the HID lamps. Otherwise, it is a straight bolt in, and will fit most 1st Generation cars with little or no modification. Used sets sometimes show up on the various auction sites as well, but as always, let the buyer beware.


My driver's side mirror is foggy or yellow. Is this normal?
This is a common complaint among owners of vehicles with the electrochromic auto-dimming mirror function. Essentially, the fluid has turned yellow or brown and the only 'fix' is to buy a replacement, or some have simply had a glass shop cut a 'plain' mirror to match the shape of the original.


My door handle fell off!
This is a fairly common occurrence, due to a combination of weak metal and a heavy door. Typical replacement, including painting the new handle to match, costs about $100, though some have managed to do it themselves for less, sourcing out only the painting.


My rear window has some odd bubbling in the gasket. Can I just replace the gasket?
Unfortunately, no. The gasket is bonded to the glass, so your best hope is to repair the existing gasket, as the glass is extremely expensive to replace (some estimates over $1500). Windshield molding adhesives, or some have recommended an adhesive from 3M that can be found at body shops, that is designed to adhere to plastics/metal/non-porous surfaces.


What are these LSC headlights that people keep talking about?
The 95-96 LSC option included HID headlamps, the first car produced by the Big Three domestic automakers with this technology. It can be distinguished by the clear front lenses.


How much does this HID replacement cost? Where can I buy them?
The MSRP of the HID housings, ballasts, and bulbs was about $1500 when they were still available. If you can find them on one of the various various auction sites, they are a direct swap as long as the ballasts and bulbs are included.


I have HID headlights, and one (or both) are not working.
The bulbs are no longer available from Ford. For 2nd Gen (97-98) cars, they have developed halogen replacements that include new housings. For the long term, this is the only solution. At the time of this writing (October 2008), there are a some used bulbs out there, but the longevity and availability of this as a solution is questionable at best. For 1st Gen (93-96) cars, the halogen housings of the non-LSC models can be retrofit.


Can I put halogen bulbs in my HID headlight housings?
The base, mounting system, connectors, and electrical specifications are far different, and the end result would be poor light output from your headlight housings. We do not recommend this.


How difficult is it to retrofit halogen headlights to my car originally equipped with HID bulbs?
Not very difficult for someone with basic mechanical skills. The housings are held in with three clips, and a little bit of re-wiring will need to be done, and the ballasts mounted securely to the car. Nothing beyond simple hand tools are required for the upgrade.


What about the Xenon-charged or blue HID bulbs?
INFORMATION ABOUT BLUE HEADLAMP BULBS:

Various companies and individuals are selling halogen bulbs that have a coating that makes them light up with a bluish color. There are lots of claims made for these bulbs, and lots of myth and misinformation surrounding the bulbs, their performance and their legality.

The output spectrum of halogen headlamp bulbs includes very little light in the blue spectrum range. These blue bulbs have a filter coating on them that allows only the blue spectrum through the filter. Because very little light is produced by a halogen bulb in this range in the first place, it is only this very small amount--a tiny fraction of the total amount of light produced by a halogen bulb filament--that ever reaches the road. This can be confirmed this with a good-quality non-chromosensitive light meter; even a very apparently-bright blue bulb actually throws very little light.

Recent tests by the US Department of Transportation's Office of Crash Avoidance Standards found that a standard-wattage 9004-type blue headlamp bulb reduced the road lighting ability of a standard headlamp by 67%, and increased glare for oncoming and preceding traffic by 33%.

This illustrates the difference between the signal image, which is what you see when you look at an illuminated light, and the emitted luminous flux, which is the light that is thrown from the bulb to illuminate surrounding items, either directly or via a reflector and/or lens.

Aside from the disadvantage of throwing less light onto the road, another aspect of blue light creates another road hazard when blue headlamp bulbs are used:

Blue is the shortest wavelength/highest frequency color of visible light, and, as such, scatters the most readily. This is why the sky is blue rather than any other color from the sun's white output spectrum. And, you may find it interesting to find a dark blue storefront sign or something else that's a dark, pure blue against a dark background in the absence of white light. From any appreciable distance, it's almost impossible for your eyes to see the blue lighted object as a sharply defined form...the edges blur significantly.

INFORMATION ABOUT HID BULBS:

Genuine arc-discharge (also called metal-halide HID) headlamps run with a bluish-white color temperature between 4300-5000K that reminds of the color of the electronic flash on your camera, because the same technology is at work (an electrical arc jumping through an atmosphere of Xenon gas). But despite the bluish appearance, this light is actually white with a discrete blue component. That is to say, the vast majority of the output light from an HID headlamp is a good, solid white that is closer to the white of the sun than most halogen bulbs' output spectrum can reach. And, in addition, there is a separate output spectrum of blue-green to blue-violet frequencies that is a byproduct of metal-halide lamps such as the HID lamps currently used in cars. That blue-green to blue-violet frequency band is "throwaway" light in an HID headlamp. The signal image of an automotive HID headlamp has a distinctly blue cast, but if you drive behind them you are struck by the very white characteristic of the light.

I FOUND BLUE-TINTED HALOGEN BULBS FOR SALE ONLINE. THE BULBS WERE ADVERTISED AS BEING DOT APPROVED. ARE THESE OK?

No. This marking is fraudulent because there is no such thing as "DOT approved". DOT does not "approve" products as the European regulatory body does.

THEN WHY ARE SO MANY MOTORISTS USING THE BLUE BULBS IF THEY'RE SO BAD?

There are several reasons I have learned by talking to users of these bulbs. Generally, they have been confused by marketing claims for the blue bulbs which falsely and incorrectly equates the blue bulbs' performance with the very expensive arc-discharge or LED headlamps found on top-line luxury cars. They have been led to believe that by replacing their car's proper headlamp bulbs with the blue-coated bulbs, their headlamps' performance will be increased. In fact, quite the opposite is true; their headlamps' performance is decreased by the use of blue bulbs.

The placebo effect is alive and well, however, and the motorist who pays $35 or more for a set of these bulbs often will continue to insist that his headlamps have been made "better". Some motorists have continued to insist that the blue bulbs' performance was better, even when the low emitted-light values are shown to them on a non-chromosensitive light meter in comparison to the readings from proper non-blue bulbs.

ARE BLUE BULBS THE SAME AS THESE "XENON" BULBS I HAVE SEEN FOR DIRECT REPLACEMENT OF REGULAR HALOGEN BULBS?

No. It is confusing, not only because of the explosion in recent years of all sorts of new products in the field of lighting and signalling, but also because some of the terms are being used to describe more than one product. For example, in the field of lighting, a "Xenon lamp" is a gas-discharge (or High Intensity Discharge)-sourced light, just like the light source in your camera's electronic flash. And we're seeing more and more such lights (under a plethora of brand names, which makes things even more confusing) on today's cars. BUT, we also have some companies using "Xenon" in their trade names for halogen bulbs that have a higher percentage of Xenon in their fill gas mix, and that gas is under higher pressure than normal halogen bulbs. And there is nothing preventing somebody from having high-Xenon-percentage halogen bulbs made with a blue-pass (or an anything-pass, for that matter) dichroic filter coating. The resultant mishmash of terms and technologies can be quite difficult to sort out.

The high-Xenon-percentage halogen bulbs are not a gimmick and not a scam - if they're not blue. All of the new bulb designs being produced for new headlamps, such as the new H7 bulb size, use this newly-tweaked, higher-pressure gas mix, and the results have been good, with the H7 achieving a higher luminous flux (amount of available usable light) from a given wattage than was achievable with halogen bulbs that used the old gas mix under the old lower pressure.

So after a few years' experience with H7s, the manufacturers have moved to update the older traditional bulb types with the new gas mix under the new, higher pressure. This increases the luminous flux of the bulb in a ready-made form factor that can be used in existing lamp assemblies.

This appearance of high-pressure/high-Xenon-percentage halogen bulbs is very comparable to the new-for-1979 halogen sealed beam headlamps that were available to replace the old-type non-halogen sealed beam headlamps. The shape, size, fit and electrical requirements didn't change, but the luminous flux did because of the replacement of the old inert gas fill with the new active halogen gas fill. A halogen gas fill allows the filament to run at a higher temperature without failing, increasing the luminous flux of a given-wattage filament. Likewise, the new high-Xenon-percentage/high-pressure gas fill that is beginning to appear in headlamp bulbs in traditional form factors offers a brightness improvement without damaging other performance characteristics of the lamp.
 
Suspension

Can the Mark VIII be lowered?
Yes, it's very simple. The directions for lowering the vehicle are available here.


My front end is 'sagging', that is, it drops all the way to the ground. What's wrong?
The most likely culprit is leaking bags. Over time, the air springs (bags) develop cracks in them that will leak at certain points. Once the crack is exposed, the bag will lose pressure, and your car will assume the 'slammed' position. The fix is to replace the air springs with new ones, or do a complete coil-spring conversion.


Can 2nd Generation (97-98) shocks and air bags be used on a 1st Generation Mark VIII?
Yes, all of the suspension components are interchangeable.


I get a clunking noise from the rear of my car when I drive over bumps.
This is often caused by worn shock mounts. Replacing the shock mounts with new ones often resolves this problem, and it's typically a good time to replace the shocks as well.


What are the differences between the 1st Generation rear shocks and the 2nd Generation rear shocks?
The 1st Generation vehicles had adjustable rear shocks with variable damping. There is an actuator on top of the shock that adjusts it for Firm or Soft, depending on the road speed and brake application. The 2nd Generation cars do not have this feature. They are interchangeable, if you wanted to put the 2nd Generation shocks (less expensive), they would fit, but you would lose the adjustable shock feature.


My rear swaybar/anti-roll bar is broken.
The hollow rear sway bar sometimes cracks due to corrosion, from what some have theorized is from exposure to road salt. Replacement bars can be ordered from www.addco.net in slightly larger diameters. The removal and replacement of the rear bar is pretty easy, the front one requires significantly more work, as the motor cradle has to be moved.


How to DISABLE check air ride message after coil conversion
Turn the air suspension switch in the trunk to OFF.
Remove the passenger front kick panel if you have trouble getting access to the wiring bundle behind the glove box.
Locate and cut the DARK GREEN wire with the LIGHT GREEN stripe or "tracer".
Leave the module connected and turn the suspension switch ON in the trunk.
 
Wheels and Tires

What were the stock wheel and tire sizes?
The Mark VIII, in all years and models, was delivered with 16x7 wheels, with 225/60VR16 tires. This applies to all of the different optional factory wheels as well.


What's the bolt pattern on the stock wheels?
5x4.25, with a 39 mm positive offset. Some people will call this a FWD wheel, since it has a positive offset.


What's the widest tire I can put on the factory wheel?
Some members have put a 255/50R16 on the factory rims, but whether or not it works seems to depend somewhat on the tire brand, model, and skill of the installer. 245/50R16 will fit more readily, though either way, they may not perform quite as well as a smaller tire, since the rule of thumb for tire/wheel sizing is rim width is greater than or equal to 80% of the section width of a tire. Using this formula, a tire with a 225 mm section width is about the biggest some people would recommend for a 7 inch wheel. The 245/50R16 is extremely close to the factory size tire in terms of circumference, but you can expect about a 3-5% difference in outside diameter, with the speedometer reading slightly higher than the actual speed. The 255/50R16 is even closer in diameter, sometime as little as half an inch difference in circumference. You can find a good tire sizing calculator here: Tire size calculator


If I put a 17 inch wheel on my car, what size(s) will fit?
Some members have put 17x8 or 17x9 (or 18" and larger) wheels on their cars and have not experienced problems with the tire rubbing on the fenderwells. Proper offset is crucial for this to be true. A 255/45R17, 245/50R17 or 245/45R17 tire will clear the fenders, on a wheel with proper offset. When moving to larger diameter/width wheels, always consult with a professional who is willing to stand behind their recommendations if you run into problems, especially with clearance, once the tires and wheels are on the car.


I have a vibration that feels like my tires are out of balance, but they were just balanced!
The Mark VIII is EXTREMELY sensitive to wheel imbalances. Be sure your dealer test drives your car to verify that there's no vibration from the tires/wheels before you leave the shop. Additionally, many users have found that by aligning the valve stem with the yellow painted stud, vibration is lessened. Some shops offer 'On-Car Balancing', which may also help reduce the vibration from wheels and tires. Many members have reported good results using the Hunter GSP9700 tire balancer.
 
Electrical

What's the code for the keypad on the driver's door?
This can typically be found on the trunk hinges, on a small white sticker. It is 5 digits long. It should also be affixed to the side of the remote/keyless entry module, found behind the trunk carpet on the driver's side.


My message center keeps telling me my door is ajar.
Spray some WD-40 into the door latch mechanism in the door itself. This will typically make the message go away for quite some time. If it reoccurs, simply spray some more WD-40 on the mechanism. I may take several applications and a few days for the problem to disappear completely, particularly if the door has been left unused for some time.


My 93-94 Mark VIII has cracked buttons on the Climate Control module. How do I fix this?
This is a common problem, caused by age and a poor hollow design of the original buttons. A climate control from a 95-96 model with thicker, more durable buttons can be used to replace this.


The heated seats are turned on, but either the bottom, back (or both) don't heat up.
This will happen if the heating element breaks. This is a relatively easy repair - remove the seat from the car and disassemble it completely (only basic hand tools are required), separating the foam seat bottom and back from the base. You can remove the leather seat cover completely, which is held on by velcro and plastic clips, from the bottom to access the heating element to solder the broken element segment together. Use kapton tape to insulate after repairing. To access the element for the seat back, you will need to have a helper hold open the leather seat cover as removing it is much more involved.
 
Transmission

Where can I find detailed articles about the 4R70W transmission?
Jerry's Thesis


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.


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?
YES! Read here for an article that outlines the process.


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. Read Jerry's Thesis for a detailed explanation of the process, and A-Train's writeups (part 1 and part 2) detailing the process.


Does my Mark VIII have a limited slip differential? ("Trac-Lok" or "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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