Ford flywheels and flexplates are apparently a very vexing topic for many people working on engine or transmission swaps like I was. As I researched the details for myself, it became very apparent that it's a confusing topic for many folks and that there are various sites out there that attempt to explain it. Since I had to read a bunch of sites to decipher things, I decided to start my own page to pull all this together in one place.

NOTE: This page is specific to Ford V8 stuff, and my work was on 302 and 5.0L engines. Extrapolating this information to anything beyond that should be done only after careful comparison of actual parts or other authoritative sources of information. Using the wrong flywheel or flexplate on your engine can - quite literally - destroy it due to excessive vibration, so use common sense and lots of care in selecting the flywheel to use.

Overview

As far as I can tell, there are two basic ways that the flywheels and flexplates differed - size (diameter and number of teeth) and the amount of imbalance that they contain (Many/most Ford V8 engines are externally balanced from the factory). The size matters because it determines the number of teeth on the flywheel and has to match the starter location that is cast into your transmission bellhousing. The amount of imbalance matters because the entire rotating assembly is balanced together, and externally balanced engines put part of the balance weight onto the harmonic balancer and onto the flywheel/flexplate. If you put a flywheel/flexplate with the wrong imbalance on your engine and run it, your main and rod bearings will take a serious pounding due to the vibrations and will likely give out in just a few miles of driving.

From my research so far, it seems that manual transmission applications (flywheels) and automatic transmission applications (flexplates) generally used the same sized pieces, and they will both be the same size, at least as far as the ring gear goes. For example, you can talk about a 164 tooth flywheel or flexplate - there does not appear to be unique sizing for automatic vs. manual setups. That's not to say that the automatic vs. manual transmission units were the same in any given year and model of car, just that they happen to be available with the same tooth count on the ring gear in various applications.

Details

The table below shows the nine different possibilities you have. It is important to note that not all of these combinations were ever used by the factory, so it is entirely possible you will need to get aftermarket parts to make your combination work. In addition to the two different imbalances used by the factory, there are also places that offer flywheels and flexplates with zero imbalance (also referred to as "internally balanced" on some sites) - these are used when building a custom motor. I mention it because that stuff is out there -  so be aware of it if you are working on a custom high performance motor that you do not know the entire history of. Also, the 148 tooth units are very rare and not even mentioned on many pages/sites I came across in my research. Apparently, they were only used in a few "small" vehicles like the V8 Mustang II installations. You may not be able to find this size flywheel/flexplate in the 50oz or "none" imbalance configurations, at least not easily. The others possibilities should all be readily available from either OEM or aftermarket sources. Reproduction flywheels for stock configurations are readily available - flywheels are considered a "wear" item and they do need to be replaced once in a while, so you can get them pretty easily it you look around a bit for them.

		Transmission Flywheel/Flexplate Requirement
		164 teeth	157 teeth	148 teeth
Engine imbalance	50oz	Possibility #1	Possibility #2	Possibility #3
	28oz	Possibility #4	Possibility #5	Possibility #6
	none	Possibility #7	Possibility #8	Possibility #9

To figure out what you need, start with your engine and find out what amount of imbalance you need. Then, figure out what size unit you require to match up with your transmission bellhousing. Now you know what flywheel or flexplate you need. Write down exactly what you need, and make sure you get the right unit. Research each item individually to make it easier on your brain, then when you get a clear answer on both of them, write it down for later reference, and use that information to select the right part for your needs.

Interesting Tidbits

Here are some Interesting and possibly useful tidbits of information I ran into while researching this.

• AOD transmissions used a 164 tooth flexplate.
• Mustang T5 transmissions used a 157 tooth flywheel and a 10.5" or 10" clutch disc.
• Ford light-duty trucks often used a 164 tooth flexplate and an 11" clutch disc, though some heavy-duty trucks used much larger clutches.
• C4 transmissions could have used any of the three tooth count flexplates depending on the bellhousing used. In original applications, it roughly corresponded to the "size" of the vehicle the transmission came in.
• C6 transmissions could have used either the 157 or 164 tooth flexplates, depending on which case it had. As with the C4, the size of the flexplate generally seemed to follow the size of the car it was used in.
• Ford changed the imbalance on the 302 (otherwise known as the 5.0L) engines in 1981. Some sources list this change as 1980 in a confusing way, but all of the reliable data I found said 1981 was the first year of the new 50oz imbalance motors. Thus, if your motor was built before 1981, then it's a 28oz imbalance motor. If it was build in 1981 or after, it's a 50oz imbalance motor. If you are not sure, use Google to find ways to check for sure what you have.
• Ford did not change the imbalance on the 351W (otherwise known as the 5.8L) engines - they stayed at a 28oz imbalance. This means that mixing a late model flywheel or flexplate between a 5.0L and 5.8L engine is a bad idea. The same goes for the harmonic balancers...
• If you are looking at custom/aftermarket parts, they may specify "internal" vs. "external" balance. Internal balance means there is zero imbalance in the flywheel or flexplate, and these should only be used on a custom motor that is internally balanced.
• Visual comparisons of the 164 and 157 and 148 tooth units should be very obvious as to which is which. If you have a known unit laying around, you can use it to compare against an unknown unit to see what it is.
• Once you know what to look for, you can easily tell the difference between 28oz and 50oz imbalance pieces by looking at the back side. The 50oz units will have a much larger weight on them. Comparing an unknown unit against a known unit is easy, and various websites have good side-by-side photos of the differences you can educate yourself. Use Google to find some samples and educate yourself if you want to be a good junkyard spotter.
• Starters can interchange between 164 and 157 tooth flywheels in many cases, but not all cases. Check the original application data for the transmission you are using to verify. Remember that the starter is bolted to the transmission bellhousing and not to the engine. For example, late model Mustangs (1986-1993, for example) used the same starter for manual transmission applications (157 tooth flywheel) and automatic transmission applications (164 tooth flexplate).
• You can change between the different balances, but it's expensive. You can do this if you are willing to have your motor re-balanced (which basically requires tearing it down like you would for a full rebuild) and you are willing to replace various parts (like the flywheel and harmonic balancer). It can be costly to re-balance the motor separately from a rebuild, but it can be done in some (most?) cases if needed. I'm only mentioning it because some folks are doing oddball/custom motor work or fitting a swap into an "unusual" body that dictates size requirements, and it's a possibility to keep in mind.

Pictures

157 tooth flywheel sitting on top of a 164 tooth flywheel - you can see the 164 tooth flywheel peeking out from behind the 157 tooth flywheel, showing the size difference.

164 tooth flywheel (left) and 157 tooth flywheel (right) - you can see the size difference if you look closely. You can also clearly see the clutch operating area on the smaller flywheel on the right. A bigger clutch means more holding power with less force, which is why you often see the larger 11" clutches and 164 tooth flywheels used in the trucks and larger cars, and the smaller 10" or 10.5" clutches and 157 tooth flywheels used in the smaller cars.

Rear of 164 tooth flywheel. Part # is E8TR-AA. This flywheel was removed from a 1989 F150 with a 5.0L and a 5-spd manual transmission and uses an 11-inch clutch. It is a 50-oz imbalance flywheel. Note the size of the imbalance weight in the upper left area of the flywheel. Because this flywheel is larger in diameter than the 157 tooth unit below, the weight has to be a bit smaller to achieve the same balancing effect.

Rear of 157 tooth flywheel. Part # is E1ZR-6360-AA. The writing on it claims it to be a late-model Mustang piece (unconfirmed as of yet), and it is a 50oz imbalance flywheel. I believe this flywheel uses a 10" or 10.5" clutch. Note the size of the imbalance weight in the upper left area of the flywheel. Because this flywheel is smaller in diameter than the 164 tooth unit above, the weight has to be a bit larger to achieve the same balancing effect.

Comments? Kudos? Got some parts you'd like to buy/sell/barter/swap? Nasty comments about my web page so far? You can email Mike or Debbie.

Page last updated 04/26/2008 11:41:08 PM