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MG MGA - slight oil leak at rear seal with brake drum off

While waiting for new rear brake shoes and cylinder I've had the car just sitting up on jack stands with the drums off. I've noticed a bit of weeping oil coming from the area of the oil seal on each axel (see picture). Since there is no pressure on the seals with the drum off, not tightened, is this a "normal" situation?

- Ken

Ken Doris

Hard to see in the picture, but I presume you mean a slight oil leak at the paper gasket joint where the halfshaft flange meets the bearing hub. Very early cars, possibly the first six months of production or so, had only the paper gasket to seal this joint. Later cars also have a thin rubber O-ring installed in the face of the bearing hub before the paper gasket. This production change does not seem to be documented anywhere in factory records in SPL or CSM. That is, there is no official record of the early cars not having the O-ring. There is always a chance over 50+ years that one of the earlier hubs with no O-ring might find its way into a later car.

The O-ring was (obviously) added to prevent oil leak at this joint. The paper gasket was never deleted, presumably because its thickness makes up part of the dimension build-up controlling clamping of the wheel bearing outer race. Deleting the gasket would require a design change of the rotating bearing hub (different part number and multiple stocking of spare parts). If you have one of the early hubs with no O-ring, I recommend that you change it to the later style part.

For disc wheel cars, with wheel removed the brake drum is secured with two flat head screws, and also ultimately the wheel lug nuts. For wire wheel cars, with wheel removed the brake drum is secured with hex nuts and lock tabs. In either case, when brake drum is removed the halfshaft flange (or splined hub flange) is secured with only one flat head screw.

Very early cars with gasket only were notorious for a leak here. Later cars with the O-ring have an issue of difficulty tightening the single flat head screw enough to compress the O-ring sufficiently to close the paper gasket joint. There is an access hole in the brake drum that should be positioned in line with the single screw in the halfshaft flange, such that you can follow up and re-tighten the single screw after the brake drum is installed. I highly recommend you make a practice of doing this to make the single screw more secure to prevent oil leak when the brake drum is removed.
Barney Gaylord

Ken, I would say that would be normal as there is no holding pressure from the 4 hub/drum bolts. A small amount of oil is usually on the axle and can leak past the paper gasket if not held firmly with the 4 bolts. It will just need a clean up as you assemble.
Barry
Barry Gannon

The car is a MKII built in April of 1961 with disc wheels, so it must have the rubber O-ring. I'll be sure to tighten the single screw up as hard as possible and pull the drums and re-inspect after an initial trip or two.
Thanks!
- Ken
Ken Doris

"Later cars also have a thin rubber O-ring installed in the face of the bearing hub before the paper gasket. This production change does not seem to be documented anywhere in factory records in SPL or CSM. That is, there is no official record of the early cars not having the O-ring. "

Not true. Check the back (Sec H10, p H11/12) of Section H of WSM. Change introduced at axle 5225 WW, 3725 disc wheel. Don't ask me how to x-ref car & axle nos! (but they must be reasonably close to cars produced)
The seal ring does not appear in my only MGA SPL, an early 1500 one - which may be the first published one, no dates or revisions shown.

I have an index to CSM and SPL updates for Z Magnette, but not the actual papers referenced. However, generally these list all the cars the changes apply to, so my guess is that the corresponding MGA documents would show the same changes. CSM reference is only given as "H12", (about)the right page in the Z WSM; SPL reference is to "Parts List Amendment PMG122"

My Z Magnette WSM Sec H10, p H11, gives a little more info:
"A modified rear hub is fitted to later models from axle No.18835, incorporating an additional oil seal. The hub assembly has a groove machined in the4 face into which a rubber sealing ring is fitted as shown in Fig. H.8."
"The part number of the oil seal is ATB7229, but the part number of the hub remains unchanged."

Again, no idea how to x-ref axle to car, but it is clear that MGA & Z Mag have their own series. This change would be about mid production for Z, and before the May 1957 date of my Z SPL, since the new seal is listed.

Note that the drawing (not numbered) that accompanies these items shows ATB7229 as a rectangular section ring, not a O-ring. Thus is correct by my memory; I recall when we started getting O-rings in place of the correct rect. sec. ones, c 1968.

FRM
FR Millmore

Ah, this is true, just slipped my mind. I even have this note about the change point in one of my web pages, just didn't recall where the information was found.
http://mgaguru.com/mgtech/rearaxle/ra103.htm

There was no change of part number for the hub, which explains why it did not change in the SPL. But it is strange that the introduction point for the O-ring is not noted in the SPL, as earlier cars do not use the O-ring.

Now I'm curious on another point. The change you note from rectangular to round section O-rings around 1968 by coincidence coincides (approximately) with introduction of the tube-type rear axle in the MGB. So this may not be a production change, but is could be a change of factory supply for replacement parts. Does anyone have a copy of the MGB Service Parts List? If so, could you check to see if there was any note referring to change of this seal in the MGB banjo type rear axle?
Barney Gaylord

All very odd indeed.
The Z index shows the seal intro as PMG122, after the changes to LH threaded casing nut at CSM172/PMG84, and the new gasket at CSM246.
My 1500 SPL shows the nut change at car 10917DW, 11450WW, but does not show the seal ring at all.
I did just find a date on the back of the last page of this SPL, in VERY TINY print = "27/15 (94738) 6/56 - 5000", apparently one of 5000 copies printed.

I believe that the Service Memorandum or CSM, and SPL amendments (PMG***)are common to MGA & Z Mag.

Where's Dominic?

I recall that rectangular section seals in general sometimes were described on the part tags as "Lathe cut ring". Close inspection verified this - they were not moulded. Given the economic situation at the time, I can well imagine that the change to O-rings was a cost measure. Quite likely that the new parts carried the same number as the earlier ones, unless the seal was also used in a more critical application someplace in the empire.

Re another point: ATB7229 (1500) changes to ATB7354 for 1600 through MGB to -64 (where my reference book - BMC Fast Moving Parts - ends)

FRM
FR Millmore

This thread was discussed between 08/09/2011 and 09/09/2011

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