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Differential Pinion Seal Replacement

6/24/00 -- Got a leak coming from the front end of your differential housing? Relax, you can repair it with the differential in place. You need a new pinion seal.

Exactly one day after I decided to accept the collective wisdom of others and never jack up the rear of the car by the differential housing again -- I noticed the leak. Argh...

I've had my Spitfire on jack stands a half a dozen times since acquiring it in January, 2000 and had been using the differential case to lift the rear end. I tried to be certain to position the jack on both halves of the differential housing to distribute the weight evenly along the main seal that splits the casing, but blew out the front pinion seal in the process, apparently. This was evidenced by a fairly pervasive leak right near where the drive shaft connects to the differential flange. Beneath that flange lies the pinion seal. Observe the messy oil surrounding this flange in the photos below...

Another lesson learned -- and thanks to the knowledgable Spitfire list members, a quick diagnosis of the problem when I asked my fellow enthusiasts for help.

The original seals are made of metal and either rubber or leather, apparently. I find it highly impressive that this seal took 33 years to go bad -- forced into early retirement by my amateur mistake. I wish that original equipment seals were still available, but I'm told that the all-rubber replacements are better. Ask me in another 33 years if I agree with that statement.

After consulting once again with the crew on the Spitfire e-mail list, and after borrowing a 7/8" socket from my next door neighbor for the pinion nut, I set out to replace the worn seal with a new rubber seal. The new seals are flat on one side and cupped on the other. The flat side faces out when installing.

To change the seal, you must remove the driveshaft, remove the pinion nut, flange and then the old seal.

Removing the driveshaft was fairly straightforward. I noticed that two of the bolts had self-locking nuts and two had regular nuts with lock washers. Strange. I just used two open 7/16ths wrenches to remove the driveshaft bolts. They were on good and tight but after a bit of wrestling I got them all off. I had the handbrake off and the car in neutral for this exercise, so I could easily rotate the driveshaft to access the bolts.

It became readily apparent that I'd need more clearance from the driveshaft in order to work and my recently installed exhaust pipe was in my way, preventing the drive shaft from dropping down far enough for me to get to the castellated 7/8" pinion nut. Loosening a couple of the exhaust mounts was all that was needed to gain the necessary clearance and the driveshaft dropped several inches further.

Believe it or not, getting the dang cotter pin out of the castellated nut was one of the more time consuming elements of this job. I've misplaced my needle nosed pliers, which would have made the removal a snap. Oh well, I got it out, just the same. Before attempting to loosen the pinion nut, I engaged the handbrake as tightly as I could get it. I was cautioned by Huw Upshall to make certain to count the number of turns it took to remove the pinion nut, otherwise I could seriously screw up the rear end when I put it back together. I only had limited movement with my ratchet wrench, so I counted the number of cranks on the handle it took to get it off the pinion shaft. I also noted that in my case, the nut was just resting on the third full thread of the shaft.

Getting the pinion nut loose took a breaker bar attached to the socket drive. Don't ask me how, but at some point, the socket wrench came loose and flew sideways towards me, nailing me on the top of my forehead. I've got a nice big, red bump there now. Ouch.

Once the pinion nut was off, I expected to simply pull the flange right off. Nothing doing. It wouldn't budge. Nobody forewarned me about this, so I'm happy to pass this on to you. I tried tapping the flange off with a hammer, prying it loose with a giant screwdriver, using a 15" pry bar, etc., all to no avail. One of the Spitfire list members suggested that I try and rent a three pronged gear puller. All I could find after calling a couple of auto parts stores were the two pronged variety. I figured that should work just fine. I paid six bucks for the puller, which seemed like a good price to me. The store had one out of the package so that's what they sold it for. I noticed that the end of the pinion shaft has an indentation to mate with the pointed end of the puller bolt, so obviously, Triumph designed the flange to fit super snugly and intended this type of tool be used to remove the flange from the shaft.

TIP: The day after I successfully completed this project, another helpful list member, John T. Blair of Virginia Beach, VA suggested returning the pinion nut to the shaft and tightening it until the tip of the pinion shaft is parallel with the top of the nut as a way to prevent the shaft from splitting from the stress that the puller puts on it. In retrospect, I really wish I would have known about this 'cheap insurance' device before I used the puller and will most certainly abide by this useful safety technique in the future.

In no time, I finally had the flange off that I had been wrestling with. Now, how to remove that pinion seal with the flat, metal ring that sat flush with the differential mounting bracket and concealed most of the seal underneath it! It seemed to be in very, very tightly. Several people warned that I'd have to destroy the old seal to get it out, but I still wasn't sure how...

Others suggested that I tap into the metal ring with sheet metal screws through wood, to give me more leverage to tap the hole thing out. This seemed like a lot more work than it needed to be -- having to destroy the old seal to remove it just didn't seem to make any sense... I was already several hours into this project and anxious to finish it, so I tried something that seemed more logical to my way of thinking. I simply reversed the jaws of the puller, so they were facing outward, then inserted them under the inside edges of the seal as far in (wide) as they could go and used the puller to extract the seal.

It took several turns of the puller bolt before I knew whether it would work, but then I saw the seal starting to move -- and a few minutes later, it popped out, totally intact and undamaged (except for the original tendency to leak!). The below photos show the front (outside) and rear (inside) of the old seal, respectively, in something very close to its' actual size. Though it's difficult to tell, both sides have metal rings, compressing the rubber seal between them.

I pressed the new seal in with the cupped inside (towards the pinion) bearing and the flat side outside (towards the driveshaft) and noted that the new rubber seal set about 1/8" further into the opening than the original seal it replaced. The outside diameter of the new seal fit nice and snug, however.

After carefully replacing the flange, I gently tapped it in as far as I could with a hammer on each of the four corners where the driveshaft mounts, then inserted the washer and castellated pinion nut, retightening as close as I could get to the original spec. Feeling satisfied, I re-inserted the cotter pin, set it and then reattached the drive shaft, adding two new lock washers to the bolts that didn't have them originally. All that was left was to reattach the muffler supports and top up the gearbox. I did lose some oil when removing the old seal, but not as much as I had feared.

The car was on jackstands an equal amount in the front and rear. I removed the rear end filler plug and proceeded to pump gear oil into the reservoir. Unfortunately, I didn't realize that the fill neck for the gear oil was forming a fairly tight seal with the opening. So when I removed the oil line to check the level, about a pint of gear oil came out and onto the garage floor. Ich. When it was finished draining to the plug level, I replaced the plug, tightened it down a reasonable amount, careful not to overdo it -- and lowered the car back to ground level.

I took the car for a test drive. The rear end is totally silent whether accelerating, decelerating or coasting in neutral. Upon returning home, I was also very pleased to find that it appears to be totally leak free.

I cleaned the oil spill with degreaser and kitty litter and felt the satisfaction that another problem has been resolved. Now, if I can just tackle the leaking engine oil (yeah, right), I should have it made.

Note: A very helpful list member wrote back to tell me that he believed that the new seal should have been flush with the mounting plate surface like the old one was, and pressing it further into the cavity may cause the rear end to still leak. Worried, I went back out with a flashlight and took another look at the rear end several hours later -- and the bone dry surface beneath it. At this point, I'm afraid that I'll have to respectfully disagree with this concern.

If it was important for the new rubber seal to fit flush with the cavity opening, then I would think that the new seals would have been manufactured a bit thicker, so that when inserted fully like the original, that flush surface would exist. Unless I see a leak develop in the next several weeks, I'm going to have to assume that I installed the seal correctly and that either method (flush or fully seated) is probably fine. I would think so long as the ouside edge of the seal (around the perimeter of the cavity) is in full contact with the cavity wall, then there should be no problems with my installation.

If I discover a new leak in the future, I'll be sure to mention it directly below these comments, but so far after driving the car through the entire gear range for 20 minutes and checking for a leak several hours later without a drop, I'm cautiously optimistic and reasonably confident that this project is complete.

A special thanks once more to the several members of the Spitfire list for their invaluable assistance.

Please. Always wear your seatbelt while driving -- and that goes double for your children if you have any.

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