Flex Plate Installed Backwards – Symptoms and Consequences

In the olden days, all vehicles came with a manual transmission. These vehicles use a flywheel, unlike the automatic ones that use a flex plate. Today, the vehicles using manual transmission have dwindled to less than 5% in the USA. The trend is the same across the world.

Knowing the difference between a manual and an auto transmission is important because you get to understand the day's topic. Is it possible to install a flex plate backward, and if this happens, what are the symptoms and consequences that follow?

What is a flex plate?

A flex plate can be said to be the metal disc located between the engine of your automatic transmission motor vehicle and the transmission system. It connects to the torque converter, which replaces the clutch in a manual transmission. The flex plate is attached to the vehicle's crankshaft, making it possible for it to transfer energy onto the torque converter.

The term flex is used in the flex plate because this component can flex across its main axis. To allow the plate to accommodate the torque converter's motion when the wheels' rotational speeds change, the plate can bend from side to side.

Unlike the manual transmission flywheel, which is thick and heavy, a flex plate is comparatively thinner and lighter. This is because the coupling action with the torque converter is much smoother than for the flywheel and the clutch. The flex plate comes with teeth at its edge that are used to couple it with the starter motor.

Installing a flex plate

First, installing a flex plate involves lifting heavy parts and a lot of expertise in the workings of a car's engine. It is not advisable to start the process if you are not sure how to go about it. If you are good and ready to install a flex plate on your vehicle, here are the tools you should have;

• Voltmeter
• Tools to remove and fasten fasteners
• Wire brush
• Flex plate turning tool
• Thread locking compound
• A floor jack

1) Remove the flex plate

Start by removing the old flex plate. Pay close attention to the kind of damage the plate has so that you can correct such issues before installing the new one. Such issues could be electrically or mechanically associated. It is imperative to correct the issues first to avoid the new plate from getting damaged like the one you are removing.

2) Prepare the surface before installing the new flex plate

Clean the crankshaft surface with a wire brush. Also, clean the threads to ensure that nothing is blocking the fasteners. When installing the new flex plate, ensure it sits properly against the crank. Make sure that the plate slides smoothly over the crankshaft pilot diameter.

3) Match the flex plate with the torque converter

The next step is to align the plate against the torque converter. Every flex plate is unique and specific to a certain car's make, model, and generation. The bolt pattern on the plate should therefore line up with that on the torque converter. The converter pads must be completely flat against the plate.

4) Fix the flex plate on the crankshaft

You can now fix the flex plate onto the crankshaft. This is done using the thread locker located on the crank bolts. The converter and the front pump must be of the required clearance. If the clearance looks bigger than required, use shims that are flat and consistent pad to pad. If, on the other hand, the clearance looks smaller, the machine increases the clearance. Serious failures can arise if this clearance is not done correctly. The clearance between the converter and the flex plate is about 1/8" for many cars.

5) Install the starter

After ensuring that the mechanical and electrical systems are working properly, it is time to connect the starter. The starter should only be engaged after the converter and the transmission has been installed.

How to avoid installing a flex plate backward

• Normally, a flex plate has a lip at the center. This lip is put there, so it becomes impossible to go against the crankshaft. The flex plate should only be flat against the converter. The size of the lip is usually 1/16 of an inch. You should, therefore, know that a flex plate has been installed backwards if it is flat against the crank. Moreover, the crank has a dowel pin that is used to index the flex plate.
• When installed, the balance weight of the flex plate should be towards the engine. The torque converter bolt pads are meant to face the converter. By ensuring that the converter bolt pads and the flex plate lip are facing in the right direction, you can never go wrong when installing a flex plate.
• You can also confirm whether the flex plate is installed wrongly by looking at the plate and making sure that the indents are facing the engine. The indentations should never face the torque converter.
• If you are having trouble bolting up the transmission when you install a new flex plate, then it is time to reevaluate the process again. It should not be difficult to slide the torque converter back into the transmission. There should be enough room to allow the converter to rotate without hitting the flex plate.
• In the case where the aftermarket flex plate is flat, you will need a long crank. On the other hand, you will need a spacer if the crank is short. This is to allow the flex plate to fit well. Care must be taken to ensure that the spacer is properly centered by the flex plate lip on the crankshaft.

What happens when you install a flex plate backwards?

It is possible to install a flex plate backwards. If this is done, there can be serious damage to not only the plate but also to the transmission and the engine. Here are some of the consequences you should expect;

Since the flex plate comes with a lip that should be towards the engine, if fixed backwards, the plate will likely be deformed when the crank bolts are getting torqued. This will then mean that you will be very lucky if you will not need to buy another flex plate to replace the damaged one.

For some engines, the engine is balanced on the bench. The engine balancing will be off if the flex plate is installed backwards. This will then translate to a whole lot of issues when the flex plate is connected to the torque converter.

The ring gear of the flex plate will be far off and won't engage with the starter when you install the plate backwards. The ring gear will also not disengage because it is too close. Ideally, the distance between the flex plate's ring gear and the starter's end should be around 0.1" with a variance allowance of 0.04". Because the flex plate turns many times, the ring gear will likely get ruined.

It has been reported that the transmission system and the gearbox were damaged because the flex plate was installed backwards. The good thing with the flex plate is that you will notice immediately if it has been installed backwards. When you engage the reverse and forward gear, the noise and the knocking sound should alert you early enough.

When the flex plate is damaged, then here are the symptoms

• The starter bogs down and will have difficulty turning
• When starting, the starter will make a whining sound
• The engine will run roughly
• There will be clunking, chirping, and grinding from the rear part of the engine when it is idling.
• There will be a knocking sound coming from the engine. This is especially the case when you shift into Drive or Reverse gear.
• There will be excessive vibrations in the car when driving at normal speeds.
• You will also notice a loss of power when driving at higher speeds.

It is important to note that a flex plate is a precision engine part, and cracking or warping will cause all manner of issues. Normally, a flex plate is replaced rather than repaired. This is because it is not expensive, but the work involved is extensive. Moreover, you wouldn't want to not be 100% sure of the reliability of such an essential engine component.

Conclusion

The flex plate of an automatic transmission vehicle is designed to be unique to the make and model of the car. It comes with indents and holes to help you install it without making an error. Moreover, the lip on the plate serves as the universal indicator that it should face towards the engine. For the EOM flex plates that are flat, you will need to have the right additional components and tools to help you install them.

To avoid making the mistake of installing a flex plate backwards, it is highly recommended that you let an expert do the job.