Dieselsite External Transmission Filter Kit Installation

June 29, 2005
Written by: E. Long
Discuss this article in this forum thread


This "how to" article was performed on a 2000 Ford Excursion with the 7.3L Powerstroke Diesel and 4R100 transmission. At the time of this installation, I was getting more into towing larger loads (mainly a friend's boat). Tipping the scales with the boat, trailer, gas, and gear, 7,000+ lbs was more than I had towed before. Having already gone through one transmission at 87,000 miles, with 60K on my 2nd transmision, I was looking for anything/everything possible to prolong the life of the transmission.


The goal of this install is to prolong the life of the transmission by adding an external, replaceable transmission filter kit. I also opted for the filter gauge so I know for sure when the filter needs replacing. This gauge is much better than Ford's air filter gauge on the air box in your engine compartment (mine has yet to move). 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.

This install procedure vs. provided instructions

The instructions provided with the Dieselsite external transmission filter kit tell you to choose where you want the filter to be mounted on the frame in the first step. I wasn't able to tell specifically where along the frame they mounted theirs (in the pictures provided with the install instructions), so I left the actual drilling/mounting to be one of the last steps -- after I routed the braided lines. I made the mistake of drilling the holes and mounting the filter too soon anyway, and found myself having to relocate it by a couple inches so the braided lines could reach the filter.

Required Tools:

(1) 7/8" wrench
(1) 16mm wrench
(1) 11mm wrench
(1) 11mm socket (1/4" ratchet)
(1) drill
(1) 1/4" drill bit
(1) safety goggles
(1) allen wrench (for optional filter gauge)
teflon tape
(3) zip ties
(1) drain pan
2-3 quarts of transmission fluid
lots of rags

Products needed:

(1) Dieselsite filter gauge (optional)
(1) Dieselsite External Transmission Filter Kit

Parts Inventory:

The parts list is as follows:
(1) filter
(2) braided lines
(1) filter mount/assembly & bracket
(2) large brass fittings (to connect to the filter assembly)
(1) 90-degree fitting
(2) straight-through fittings

Time Requirements

2-3 hours


3 out of 10 (1 being easiest, 10 being hardest)

Where to Buy

This kit is available exclusively from Dieselsite.com. Click here for a direct link to the product.

Step 1: Disconnect rear transmission line

NOTE: All brass fittings MUST have teflon tape on them, otherwise you will have leaks!

1.) Locate the rear (return) line on the transmission.

2.) Position the drain pan underneath the general area. The instructions say a few teaspoons will leak out, but it ended up being much more for me. It just keep draining and draining and draining.

3.) Using double wrenches, use your 7/8" wrench on the nut on the transmission (to hold it in place) while you loosen the nut on the transmission line with your 16mm wrench. Position the 16mm wrench so you can pull down for best leverage -- careful, this one will probably leave a mark. You'll hit your forearm on the transmission cross member that's bolted from the frame.

4.) Carefully bend the transmission line out of your way like pictures so you can better control the draining of the fluid. Otherwise it will leak onto the cross member and run everywhere. I used a rag to also slow the draining of fluid.

Step 2: Install 90-degree fitting on the disconnected line

1.) Using your teflon tape, wrap approximately 2 layers of tape around the threads on the straight-through fitting.

2.) Thread the straight-through fitting into the 90-degree fitting finger tight (we will tighten these once the install is complete).

3.) Swap rags so you can dry off the fitting on the transmission line you disconnected in step #1.

4.) Wrap two layers of teflon tape around the transmission line fitting and thread the other end of the 90-degree fitting onto this line. Again, only finger tight. This part is still messy, so keep the rags and drain pan handy.

Step 3: Install first stainless steel hose

1.) Grab one of the stainless steel lines (they're both identical). Teflon tape the straight end.

2.) Thread the straight end into the 90-degree fitting on the disconnected transmission line.

3.) Reposition the transmission line back to its original location between the transmission and the exhaust shielding.

Step 4: Mount the filter bracket, install gauge & line

1.) My instructions vary at this point from Dieselsite's included instructions. Dieselsite's instructions say to route the braided line underneath the frame. The Excursion has a lot of exhaust shielding around the top of the exhaust pipe, so I opted to route the braided line towards the back of the vehicle (over the transmission cross member), and over the top of the exhaust shielding. This way, no debris from the road or while offroading can get hung up on a line that extends below the frame rail. Plus, it just seemed a lot easier to route it this way as well. You may opt for another method, just keep the lines clear of any direct contact with the exhaust pipe (see the final install pictures below for my mounting location).

2.) Hang the transmission filter assembly on one of the bolts sticking out of the frame rail underneath the passenger side. I temporarily hooked up the first braided line to the filter assembly to avoid any further transmission from draining. This also gives you a general sense of where you need to mount the filter assembly so the braided lines can reach.

3.) I used an existing hole on the frame rail for one of the bolts for the filter bracket. Using your 1/4" drill bit and drill, drill a hole to the left (towards the back of the vehicle). Be sure to wear safety goggles as small metal shavings will fall onto you while drilling.

Step 5: Install gauge

1.) If you do not have the gauge, skip to the next step. Put two layers of teflon tape around the gauge fitting.

Remove the plug on the top of the filter housing (with an allen wrench) and install the gauge. You can wrench this down until it's tight and the gauge is facing the right direction.

Step 6: Route lines & tighten all fittings

1.) Put two layers of teflon tape around all remaining fittings and lines.

2.) Route the 90-degree end of this hose up and over the exhaust shielding and framerail.

3.) Finger-tighten the large brass fitting to the filter assembly, the 90-degree fitting to the large brass fitting, and the straight-through fitting to the 90-degree fitting.

4.) Install this hose on the front of the housing marked "in" designated by the arrow on top of the housing (the arrow points in towards the housing/assembly). Finger-tighten the fittings.

5.) Install line with the 90-degree end onto the transmission fitting. Finger-tighten.

6.) Route the line up and over the exhaust shielding and frame rail.

7.) Finger-tighten the large brass fitting into the filter assembly, the remaining straight-through fitting into the large brass fitting, and the straight end of the braided line to the fitting on the filter assembly.

Step 7: Secure lines, install filter, and test!

1.) Tighten all fittings and flare connections. Use double-wrenches everywhere possible to ensure tight seals.

2.) Zip-tie one of the lines to the cross member (see photos).

3.) Inspect the lines and make sure they will not rub up against anything (like the exhaust).

4.) Put a dab of transmission fluid (from one of your pans) around the rubber seal on top of the filter. Install the filter. Hand-tighten just like you would an oil filter.

5.) Start your vehicle and run the transmission through the gears in order to check for leaks. Make sure all fittings are dry and you have no fluid on the floor while the vehicle is running. Verify the gauge works if you have one (it started out in the yellow area for me, then eventually fell back into the green area after running for a few minutes). If the install checks out, add a quart or two of transmission fluid (depending on how much drained out during the install). Test drive, check for leaks, and enjoy your new Dieselsite external transmission filter!


For me, the filter adds peace of mind. I know when to change the filter based on the gauge, and I know this filter does a much better job than the internal transmission filter. This install is very easy and I highly recommend it for all 4R100 vehicles. I want to extend the life of this transmission (so I don't have another 87K failure) and the filter is an excellent part of the equation.

Additional Questions or Comments?

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