N.B. This article started off as an email and addressed two problems at once. A leak from the rear gearbox seal is not related to a leak from the pinion seal. It is a simple matter to choose which part of the article applies.

There are two general types of gearbox seals. The British, European and some of the Japanese use seals with a small classy looking flexible materiel (silicone or some such) edging them. The Americans are just metal edged and they jam thing in metal into metal.

For all this the American seals lasts much longer. Those crazy cowboys!

So you can buy the original part for $35US and wait 'til it arrives, or, after you have removed the seal, you can take it to a gearbox place and the guy will find one that suits for $5US..

This repair will take about 2.0 hours depending on your luck, how quick you are and whether you are working alone.

First drain some of the gearbox oil...not all is necessary because the seal is above the bottom of the gearbox. Next drain all the differential oil because (though the shaft is above the bottom) old and new differential oils don't mix. Remove at least one car seat and the prop shaft cover. BTW, on my car, the trick is to see whether you can now access the rear of the bolts holding the propshaft UJ flange to the gearbox flange..the gearbox cover might be in the way. If it is, your choice is to remove the gearbox cover as well, or cut a small appropriate access hole in the gearbox cover.

After marking the propshaft and gearboxes flanges for a reference,  use keys (and a ratchet if you can),  remove these bolts.  In removing the flange, first test the torque with a torque wrench, start it low and adjust upward until you DON'T hear a click and don't tighten. Note the torque settings.

After you have removed the flange the large center bolt is visible and the torque on this should be tested as well before it is removed. NOW, with the correct socket, a ratchet and, if necessary, a pipe extension on the ratchet arm, remove the large bolt from the center of the rear gearbox flange. Remove the flange and voila...there is your rear seal. Pry it out and put it aside if you are on your way to the gearbox shop.

Depending on which type of replacement you chose, use gasket silicone or alternatively metal-on-metal-only silicone with the American style seal and align them carefully in the hole. Us techno-wizard types use a smooth ended 2x4 or make a board with a hole that touches the whole edge of the seal at once and then tap with another board until it is aligned properly and then then hammer the thing in solidly. The boards are made to allow a fit of the seals in evenly which is very very important.

Reassemble in the reverse order of diassembly torque the bolts to the values and markings you noted and made.

CHANGING YOUR DIFFERENTIAL (REAR PINION) SEAL (Plus 8 Salisbury)

Drain all the differential oil because (though the shaft is above the bottom of the differential) old and new differential oils don't mix. Angling and space will be an issue here and I suggest you remove at least the prop shaft cover.  You just may have to remove the prop shaft itself and if so see the top of this page in the section on replacing a gearbox rear seal OR you can sometimes remove the wooden backboard to allow for more room to move the propshaft.

To detach the propellor shaft flange from the differential, first marqge both flanges with a marker for reference. THE PROPELLOR SHAFT FLANGE AND THE DIFFERENTIAL FLANGE MUST BE BOLTED IN TTHE SAME POSITION. (See drive shaft vibration).  Then test the torque of the flange bolts with a torque wrench, start it low and adjust upward until you DON'T hear a click and don't tighten. Note the torque settings.

You can now move the prop shaft to the side and the large bolt holding the flange to the differential assembly is now visible. You must test its torque. (you will be surprised). This is the fun part. So  much so that I rented and brought an impact ratchet to the party. The rear flange is bolted on extremely tightly. If you can get it off with a ratchet with a pipe extension and a pipe wrench for bracing, more power to you but an impact ratchet will make it an easy job in a tight place. Once again, test the torque of the fitting and note the figure. After that huge nut is out, remove the flange and there is your other seal. This one will probably be metal on metal.

Remove the old seal, examine it to see where the problem was.. Then carefully align and position the new one with the appropriate silicone. On this side, (if memory serves)  I used  a pipe and wood buffer to tap the seal into place.

Re-assemble, (torquing to previously noted amounts) and aligning the marks on the propellor shaft. Then fill the differential., jack the back wheels, put on the prop shaft cover loosely to protect yourself and run the car to check for leaks. If none...complete the re-assembly and check agains at 20 miles, again at 100 and then at 1000. Now! Was that tough?

One other note, the cause of the leaks are important. If you have the elliptical rear shock system from the factory that may be the cause. See Rear Suspension Kit for why.

PLUS 4 (1959) GEARBOX LEAK
by John Sheally II

After pulling the gearbox on my 59 +4 to investigate a massive leak, I  found this fibre plug loose enough to spin in place and it seems that this  was the cause. Is this plug used as an oil seal it is in front of the  layshaft whichs seems to be drilled out for some sort of oil galley. Is it common for this fibre plug to cause such a huge leak?
 
That fibre plug can be the cause of a leak. It is designed to fit flush in the hole and be pressed tight when the two items are drawn together with bolting. It usually works because of the tight fit but I always put the
plug in place then seal it with high grade RTV l and let it sit overnight to dry before I bolt thing up thus no leak occurs.

That will take care of that but while you are there also take a look to see if you are getting oil leaking from your rear main seal or the rear main itself. Usually on a Plus-4 that is where your biggest leak comes from. The reason for this is that the rear main is inserted with a 1/4 inch felt seal on each and the felt just conducts oil through it forming a "STANDARD "TR" LEAK" out the bottom hole in the bell house onto the ground forming a puddle of oil where ever you go. This was corrected, in my case, by packing the rear main cap with strips of a cotten "T" shirt soaked in Indian Head Shellac. To do this torque the cap into place and proceed to push the strips into the groves on each side of the cap with a blunt punch until you can't get anymore of the material in to the groves leave about a 1/4 inch unfilled with the material and add a good sealer in the 1/4 inch such as high grade RTV and let it sit overnight to dry.

Put RTV on the back side of both halves of your rear main seal before you bolt it up also for a good seal there also. The rear main seal should be in place before the rear main cap is filled. Bolt your oil pan in place and enjoy a oil leak less Plus-4.

OIL SEAL DIMENSIONS FOR THE SALISBURY DIFFERENTIALS

3HA Salisbury oil seal is stamped as follows    2ha-019
int. dia (metal) approx.43mm
int. dia (skin) approx. 36mm
 
7HA Salisbury oil seal is stamped Autospin as 2871376-d3
int. dia (metal) approx 40mm
int. dia (skin) approx 31mm
 
The 7HA seal was introduced in 1961