P38 Transmission Filter Service

 

 

Unfortunately the service procedure page for Classic Transmissions was overwritten at some point in the distant past and has not been located in the existing back up files. 

If you would like to submit a proper write up for the Classic model transmission service it would be greatly appreciated.



transpan
Introduction
Draining the Fluid and Removing the Pan
Removing the Filter
Installing the New Filter
Replacing the Pan and Refilling with Transmission Oil
Optional Removal of Chassis Cross Member
Parts Needed


Picture at Right:  Transmission oil pan on John's 4.0 looking rearwards.  See detailed description of duplicate image below left.



Introduction

Transmission service time comes around every 30,000 miles according to the official service schedule. At this time the transmission oil needs to be drained and refilled, and (less easily accomplished) the transmission oil filter needs to be replaced. Accessing the filter requires removal of the transmission oil pan. On the Classic this requires removal of the adjacent chassis cross member, requiring special tools and techniques, in addition to unbolting the exhaust downpipes at the manifold.  Fortunately the designers of the P38 managed to come up with a more sensible arrangement of underbody components, but the trans filter operation is still a bit of a challenge compared to most other routine maintenance operations. This page endeavors to ease the pain of the operation.

Draining the Fluid and Removing the Pan
The first order of business it draining the transmission oil from the drain plug at the bottom of the pan. A 17mm wrench is needed to remove the oil drain plug. Note the magnetic center of the plug which collects steel particles from the oil -- you should clean this before replacement.

After removing the plug and draining out the oil, you can replace the plug and remove the black transmission oil cooler return line (at top left in left hand image below) from the oil pan. A large Crescent wrench (bigger than 10 inch) will do the job. Be prepared for more oil to drip from this pipe after it is removed.

transpan

transpanoff

Transmission oil pan on author's 4.0 looking rearwards.  Black return pipe from transmission oil cooler enters oil pan at top center left. Forward drive shaft (prop shaft) at right.
Note tubular chassis crossmember at bottom of picture (mine is dented at lower left from hitting off-road obstacles). 

Similar view after removing transmission oil pan. Rags at top of image are to protect disconnected end of transmission oil cooler return line and stop it dripping. At center of image is the transmission oil filter with its oil intake pipe protruding down. Note screw at center holding this pipe in place -- this needs to be removed. Crossmember is below bottom of picture.


Next, the pan has to be removed. It is held in place by six 10mm bolts arranged around its edge (two of which are visible at top of picture above left). Most of them can easily be reached with a 10mm socket with medium extension, but the left rear bolt is in an awkward position and is much easier to access if you remove the chassis crossmember (see optional chassis crossmember removal section below).  However with a universal joint on the socket extension, or even a compact 10mm ring spanner (box wrench), this step can usually be avoided.

One other problem remains if the crossmember is not removed -- a large 15mm bolt at the center of it (see pictures below kindly supplied by Ron Beckett) prevents sufficient clearance to remove the pan once it is unbolted. Accordingly, it is best to remove this bolt as a preliminary to removing the six pan mounting bolts. Interestingly, as evident in the picture above left, this bolt is not present on my 1995 4.0SE, so there is no problem at all. (Readers please help here and tell us if the bolt is only there on the 4.6 due to the slightly different transmission used, or only on later models than mine). 

Bolt1

Bolt2


With clearance secured and the six mounting bolts removed, the pan can be moved forward and downwards to clear the chassis crossmember. The pan will still have some oil in the bottom of it, as the drain plug is cleverly designed not to be at the lowest point. Once the pan is off, oil will start dripping from all the exposed transmission parts, so keep your drain tray or container underneath.

Removing the Filter
At this point the shop manual says to remove the bolt holding the trans oil intake pipe (picture above right) and two bolts holding the filter in place (picture below left). It neglects to mention that these are actually long machine screws with Torx T-27 heads. They can be fairly tight but using a good Torx wrench on them will usually do the trick. Remove the single intake pipe bolt first. Then the spacer under the bolt head, and the bracket with the intake pipe can be pulled off.

transleft

transfiltoff.JPG

Another view (taken from left side of vehicle) of the filter in place, showing the two filter attachment bolts at upper left (Torx T27) and the trans oil intake pipe at right.
Oil line to transmission cooler is at left.

Rearward view of transmission underside after removing filter. At top right is filter outlet connection (see filter top photo below right)


Next the two other bolts holding the filter in place can be removed, and the filter will drop off. More oil spillage is bound to occur as you remove these three torx screws, as some oil will be left inside the filter and will spill out as it tilts down, so leave your oil collection pan in place under the vehicle.

Installing the New Filter

transfilbottom.JPG

transfiltop.JPG

New filter: Bottom view with intake at top right; new O-ring in place. Hole at lower right is for mounting bolt & spacer for curved inlet pipe (see above).

Top view of new filter. This side goes against the transmission underside. Outlet is shown at top right with new O-ring in place.


The new filter can now be prepared for installation by fitting the new O-rings that hopefully came with it to the inlet and outlet openings (see pictures above left and right). Lubricate the O-rings with new transmission oil.

The new filter is the offered up to the bottom of the transmission and bolted into place with the three torx bolts. First you can loosely install the two bolts near the filter  outlet (two holes at top right of image above right) and then you can loosely reinstall the curved intake tube, bracket and spacer. When everything is in place you can tighten up all three torx bolts.

Replacing the Pan and Refilling with Transmission Oil

The old rubber gasket should be removed from the perimeter of the pan and a new one (which hopefully came with your transmission filter kit) installed. Then the pan can be offered up to the underside of the transmission and bolted into place with the six 10mm bolts. Needless to say, during this process you should take steps not to get dirt from the vehicle underside into the pan -- this is easier said than done on a Range Rover like mine that has seen more dirt than pavement!

Making sure you replaced the drain plug, you can now refill the transmission with oil. It might not be obvious that the filler hole is simply the tube used for the transmission oil level dipstick! Just remove the dipstick, insert a funnel, and pour the oil in (ATF/Dexron III).

Here I ran into a snag as the driver's handbook and shop manual specify 9.7 litres capacity (about 10 US quarts) for all engines and years except 11 litres for the 94-98 4.6. For a refill this is a total work of fiction. The amount of old oil I drained out was only about 5 quarts. (Presumably the remainder stays in the torque converter and the transmission oil cooler circuit). There are dire warnings not to overfill the transmission, and there is only 0.25 quart between the upper and lower markers on the dipstick. So, you have to be pretty accurate in your guessing of how much to put in. The oil level has to be measured at idle with a cold engine, after shifting the tranny through the gamut of positions and back to Park.

I found about 5 and a half US quarts was the right amount for refilling the transmission on my 4.0 to the top of the markers on the dipstick; slightly more should be needed on a 4.6.

Optional Removal of Chassis Cross Member

Paul Bryant reports on doing the procedure on his 98 RR. To improve access he opted to remove the chassis crossmember, using a bottle jack purchased from a wrecker to spread the chassis rails. (He elected to use a mechanical jack as most hydraulic Jacks won't work if they are lying on their side). He was so successful, he came close to a head injury when the cross-member fell out from between the chassis rail! For more details on this routine procedure, see the Transmission Service section of the Classic RR Remedies Page.

Callan Campbell prefers to remove only the single 15mm bolt as described earlier, and reports "The only reason I tend to lower the crossmember or remove it is if I'm removing the transmission to replace the rear engine seals or to work on the cat. converter."

Parts Needed
The transmission filter, the two O-rings for the filter intake and outlet, and the pan gasket are usually sold as a kit, which also includes a new brass washer for the transmission oil drain plug.

 

 

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Page revised February 9, 2012