F53 – Servicing Differential (Dana S135)

Servicing the differential oil is fairly easy and straight forward. Ford recommends using 75w140 synthetic.  The Dana Service manual says to change the oil every 250,000 miles or 3 years..  These specs could easily apply to a service truck that travels 250,000 miles in a few years.  However,  My Southwind is lucky if it sees 7,500 miles in a year.

I suspect my differential hasn’t been serviced in 20 years. I don’t know the maintenance history, so I wanted to take a look at the oil and have piece of mind that the oil is good and the magnet plug is clean and the service has been performed..

The S135 differential requires 12 quarts.  When I checked the sources, 75w140 synthetic oil cost about $15 a quart (GULP), and I needed 12 quarts ($180).  At that price,  I was considering draining the oil, running it through a filter,  then reusing it if it looked OK..   However, after further research, I found  Lucas 75w140 Synthetic at Amazon for $42 a gallon, $126 total, so decided to replace the oil with new..

Vehicle Speed Sensor – A side note,  I’ve owned several Fords over the years and it seems like a common problem is the vehicle speed sensor on top of the differential. This is used for the anti-skid brakes, and is known to cause an ABS light when they get 15-20 years old. I suspect the sensor gets weak, and over the years accumulates some metal fuzz on the tip of the sensor that may desensitize it.  Rather that clean and re-use the 20 year old sensor, I’ll replace it.   A new sensor NTK part # AB1376, ($16).

While the speed sensor is removed, I’ll use the speed sensor mounting hole to fill the oil, its easier to pour it in the speed sensor hole than it is to pour or pump it into the fill hole.

DRAIN OIL

Before starting, I sprayed the top of the differential speed sensor area with PB Blaster to clean it and make it easier to remove the speed sensor..

Use a 1/2 inch breaker bar and remove the drain plug on the bottom of the differential.  3 gallons is going to drain out so make sure the catch pan is big enough. Inspect and clean the magnet on the end of the plug.  Mine had just a little fuzz on it.  The oil I drained out was 20 years old.  It was a little dark,  but I probably could have re-used it.

While the oil is draining,  I wiped the top of the differential and removed the speed sensor.  Remove the bolt, then gently twist the sensor back and forth to break it lose as you gently pull it out.

If you haven’t done so yet, now’s a good time to inspect the differential vent that’s located on the drivers side frame rail.  Make sure its pointed down, or what I did,  I relocated it a little higher and wire tied it to bundles up near the top of the left frame rail.  The vent hose on mine was brittle so I also replaced the short section of hose.

FILL OIL

The fill plug is on the back of the differential.  I removed it so I could tell when the differential was full. But instead of filling at the fill plug,  I used a funnel and poured the oil in at the top, using the speed sensor hole. It took just short of 3 gallons before I seen oil coming out the fill hole on the back.  Reinstall the fill plug.

Sensor hole – Make sure the inside of the sensor hole is coated with oil or grease. Put a little grease on the o-ring of the new speed sensor and wiggle it back and forth as you push it into the hole.  Install the bolt and electrical connector.

INSPECT SWAY BAR MOUNT BOLTS

While you’re under here,  look at the sway bar mount bolts on the axle to make sure they’re tight.  On newer models (2006 and up) these have a habit of falling out.  Remove the bolts,  then reinstall using blue locktite and torque to 65 ft-lbs.