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Dieselsite Ford Transmission Filtration Systems

External Transmission Filter Kit for Automatic Transmissions and Ford 6 Speed Transmissions
Your Cost:
From $239.00 to $259.00
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Product Description


  • Most cars and light trucks are 5/16".
  • Most Pre-1997 E4OD's use a 5/16" line.
  • 1997 E4OD can be either 5/16" or 3/8" - you will have to check your truck for the correct line size. 
  • The 1999-2003 4R100 uses a 3/8" line.
  • The Ford 6-Speed Manual uses a 3/8" line.
  • The Ford 5 Speed Automatic 5R110 uses 1/2" Line.
  • If the flare nut takes a 1/2" wrench then your line size is 5/16". 
  • If the flare nut takes a 5/8" wrench then your line size is 3/8". 
  • If the flare nut takes a 3/4" wrench then your line size is 1/2". 

*Installation shown with optional pressure gauge.

Our kits are made with stainless braided high pressure hose and fittings that match the OEM connections. This allows for easier installation and quick removal should the need arise. There is no cutting or modifying needed of the OEM lines or connections when installing our unit.

Automatic transmissions have internal filters designed to capture only large particles. These filters are designed as a pickup to keep large particles from flowing through the transmission. These filters are on the suction side of the pump. Fine filtration in the pan is not an option for the transmission manufacturers due to the fact that transmission pumps should not be restricted. The only way to get fine filtration for a transmission is with an external transmission filter kit on the push side of the pump. The 4R100/E4OD and many other transmissions were never equipped with this type of external filter.  The Allison in the Chevy and many medium duty and heavy duty trucks come equipped from the factory with an external transmission filter. This is not a new idea in transmission maintenance and protection. 

The OEM filter location requires that you pull the pan to change or check the filter. With our kit you can simply spin on a new filter element. With the optional pressure gauge to monitor when you should change your filter, you can avoid unnecessary filter changes.

Manual Transmissions have no filter at all. This is an obvious problem as gear wear is floating around in the system causing even more wear. To run an external transmission filter on a manual transmission, the transmission would have to have a factory installed internal pump.  To our knowledge, the Ford 6-speed manual transmission is the only manual unit to have an internal pump.  Since pumps are installed in manual transmissions in order to run external coolers, the presence of a cooler on your vehicle would indicate that you have an internal pump in your manual transmission.  If so, you can order the kit with your corresponding line size and fabricate it to work on your vehicle.  OR, give us a call and we will see if we can figure it out for/with you.


How it works:  Our filter is on the "push" side of the pump.  This location allows for a filter with increased efficiency -- or smaller micron rating. Normally, dirty fluid is in the pan, and we assume the OEM filter catches the really big particles before it enters the valves and pump. After running through the transmission, it leaves as "dirty" fluid. This fluid will have clutch dust and other impurities which are all normal in any automatic transmission. This dirty fluid would be recirculated back to the pan.  With our kit you can catch dirty fluid BEFORE it makes it back to the pan. Keeping the fluid clean, keeps your valve body clean which keeps your transmission shift quality at its highest. After installation of our external kit the filter in the pan now acts simply as a pickup for the pump and virtually never needs changed.

Our unit has a bypass valve in the housing as an added safety feature. This internal bypass valve in the housing is set at 25 psi to allow some fluid to bypass the filter should the filter become restricted. In addition, if the filter becomes plugged, our unit will go into complete bypass mode and allow the full volume of fluid flow to bypass the filter and insure that your transmission always has returning fluid for lubrication.   With normal routine oil and filter changes and a properly operating transmission the full bypass mode should never occur.

Our filters have a micron rating of 22 microns. That is extremely fine filtration for a transmission. Pan filters have no real micron rating. Many are nothing but screens.

Our kit also acts as a "mini" cooler since it is detached from the transmission and the air flow over the filter element would help to dissipate a small amount of heat.


  • Protects your transmission in the case of a torque converter failure by catching the debris before it can make it back to the transmission. Before the installation of our Factory Tech Monsterbox, we personally lost 3 torque converters in one transmission and the transmission was still in perfect condition.
  • No need to drop the pan again for messy filter changes. Your OEM filter will only require changing every 100,000 miles or so.
  • The fluid in pan stays clean, protecting the transmission from debris.
  • The filter canister acts as a small transmission cooler.
  • The bypass valve design allows fluid flow even if the filter plugs with debris.
  • Allows the addition of a transmission filter pressure gauge to monitor the condition of the filter.
  • The spin on filter replacements are less expensive than the OEM style.


We are currently working on new models to fit different applications. Transmissions use different line connections, but luckily many use similar line sizes so our kit can fit multiple applications. Simply look at the return line(rear of the transmission) and see what size line you have.

  • Most cars and light trucks are 5/16".
  • Most Pre-1997 E4OD's use a 5/16" line.
  • 1997 E4OD can be either 5/16" or 3/8" - you will have to check your truck for the correct line size. 
  • The 1999-2003 4R100 uses a 3/8" line.
  • The Ford 6-Speed Manual uses a 3/8" line.
  • The Ford 5 Speed Automatic 5R110 uses 1/2" Line.


Question:  Will the installation of the DIESELSITE External Transmission Filter Kit cause any increase in flow restriction or loss of flow volume to the return into the transmission?

Answer: No. We built this unit with flow ratings specifically in mind. We tested them with clean and dirty filters and there was still more than the required flow specified by Ford. The required amount is 32 oz. in 15 seconds. Our filter unit flowed over 32 oz. in less than 10 seconds - even with TWO Tru-Cool aftermarket transmission coolers installed inline. Even fully plugged, our kit will allow full fluid flow.  You will never be without returning fluid to the transmission.


Question:  What makes this unit better than other transmission filters?

Answer: We have the only full flow system on the market with a built in bypass valve. This insures that should the filter plug with debris, fluid will still return to the transmission. A filter housing with a bypass valve is NOT the same as a bypass filter.   A bypass filter typically "samples" the fluid and filters only a small amount on each pass. As the filter gets dirtier, less will get sampled and more unfiltered oil returns to the pan. Our unit -- a housing with a bypass valve-- filters ALL the fluid on every pass when the filter is clean. Only when the filter becomes very dirty does it enter "bypass mode".  At that point it will act as a "sampling" type filter similar to the bypass filter.  

In short, if the filter is clean, all oil is returned to the pan clean. This benefit will most likely save a transmission should you lose a torque converter causing a large amount of debris to be sent downline. In this case, a "sampling" type unit will only catch a very small amount of the debris. Our unit will catch it all! The unit also has the ability to add a transmission filter pressure gauge to monitor the condition of the filter.

Another point to mention about the differences between a bypass filter and our bypass valve is that a bypass filter cannot be monitored by any gauge.  So, a dirty filter with no filtration capability remaining can actually never be detected.  Your only option is to change the filter at regular intervals and hope that it does not plug and go unnoticed. 

Another type of unit that we have seen being sold is a full flow unit WITHOUT a bypass valve.  These are the most common aftermarket kits because of cost factors.  These are also the most dangerous to be running.  When the filters are plugged, there is NO return fluid flow to the transmission and no way to allow for it.  Because is has no bypass valve you cannot monitor the filter's condition. You run a high risk of burning up the transmission from a dirty filter.

Lastly, the simple installation with OEM style connectors requires no cutting of your lines.


Question:  What is the micron rating of the OEM unit and why is yours a 22 micron element?

Answer: There isn't a rating on the OEM filter. If you had to rate it, according to Baldwin, it would be about 100 microns. It's basically a screen. 22 microns is smaller than the smallest clearance in the transmission.
We could definitely put a smaller micron filter on the housing, but the result would be less oil actually filtered in each pass as more fluid would pass through the bypass port because of increased resistance to flow through the filter. Because the 22 micron element was small enough to keep the system clean and allow all the fluid to be filtered in a single pass, it was the perfect choice.


Question:  I believe my manual transmission has an internal pump from the factory.  How can I tell if it does and will your kit work with my transmission?

Answer:  If you have an external cooler you must have an internal pump as that is how the fluid moves to the cooler and back.  If you aren't sure that you have an external cooler, look for the two external cooler lines typically on the passenger side of the transmission.  These lines will both head towards the radiator.  If you do have an internal pump, we can help you with the setup for your vehicle.  Our kit will work with any transmission that has an internal pump.  


Question:  How do I know what size lines I have?

Answer:  There are three very common sizes.  These are  5/16", 3/8" and 1/2".  An easy way to determine your line size is to find the flare nut at the end of your return cooler line that attaches to the transmission.  Follow the line from your cooler back to the transmission.  Using an open end wrench set determine what size wrench fits your flare nut. 

  • If the flare nut takes a 1/2" wrench then your line size is 5/16". 
  • If the flare nut takes a 5/8" wrench then your line size is 3/8". 
  • If the flare nut takes a 3/4" wrench then your line size is 1/2". 

This will generally work for all vehicles and applications.



Hey, guys and or gals!  

Just wanted to drop you a quick note here.  I purchased your dieselsite transmission filter kit with pressure gauge for my 02 diesel excursion.  I had to share this with you.  I installed your kit when my truck had 30K on it.  I had already done the initial tranny service right when I bought it, and converted to using Mobil syn atf fluid.  After reading about your product I decided to purchase the filter kit.  Well after driving a 100,000 miles.  It was time to drop the pan and change the internal filter.   To my shocked surprise the pan was just as clean as if I just serviced it yesterday!   And when I pulled the oem tranny filter out, I could not believe it.  The filter was not even dirty.  Amazing even after 100K of driving.  And there was zero debris in my pan. And the transmission shifts just as g ood now with 131,xxx as it did when I bought it.    

Im just stunned, that that little spin on filter is doing that good of a job.  You guys should be selling these to Ford.   

I also, purchased the coolant filter kit from you as well.  That one I was always leery about. But I read on several diesel post board about a coolant filter. And figured ah, what the heck, better have one.  Seeing the rate of water pumps going out.  But the curious george in me, decided to cut a old filter open.  Man you guys were spot on.  I could not believe the junk that was in there.  That's crazy.  So, for sure as you showed in the picture and your information was accurate 100%.  

 A happy customer !