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MG TD TF 1500 - Leaking gearbox drain plug

My gearbox drain plug continues to leak. I replaced the washer with a new one and tightened it as much as I dare, but I still get the drip. I'm not too impressed with the fit of the washer. It does not seem to center when the drain plug is installed. Almost like the ID is too big around the threads and the OD too small for the drain plug size. Short of using a thread sealer, had anyone else had the same leaking issue? If so, how did you stop the leaking?

Jim
Jim Rice

Have you tried a Dowty washer?


PJ Jennings

Hi Paul:

No...I've not. Interesting design. Where might I find one that would fit the drain hole plug? Are they available commercially?
Jim Rice

This is somewhere in the archives. Originally, there was a round wire spring "clip" that fit in the recess of the threads up against the flat sealing part of the plug. This centered the washer. I have never seen that part available however. The Dowty washer should work if you can find one in that size. Try Amazon or Summit Racing. Amazon has sets with many sizes for $25. George
George Butz III

Thanks George:

Yeah...it seemed that something was missing. The thin washer just flops about in the recess under the plug and does not create a proper seal.
Jim Rice

You can make the spring out of a piece of copper wire. But before going through that, make sure both the plug and gearbox mating surfaces are perfect. Gently dress with a fine file if necessary. That usually solves any drips for me, along with a new crush washer.
Steve Simmons

Jim,
For gearbox filler and drain use 30.81 x 38.10 x 2.47mm Dowty washers. The same washer also fits the brake master cylinder cap. If you can't source them, I can supply them.

Regards
Declan
Declan Burns

Declan,

From my research those dimensions are 7/8”BSP?

I see those on EBay.

Thanks,

Peter
P G Gilvarry

Peter,
Yes, 7/8" is correct
Regards
Declan
Declan Burns

NAPA here has them, I use them on my hydraulic equipment which exceeds 3000 pounds of pressure. PJ
PJ Jennings

Paul:

I looked at the NAPA website (Dowty, Bonded, metal/rubber). I saw just a few listed under metal/rubber, but not sure any of those would work. Is there a better way to query NAPA on specific sizes since the size needed here seems to be 7/8" BSP. I think that converts to ~1.189 inches US.
Jim Rice

I believe the Dowty PN is 400-829-4490-41

400 = Industrial

829 = is 7/8" BSP 30.81MM ID, 38.10mm OD, 2.47mm thick

4490 = Medium Nitrile (suitable for engine lube oils)

41 = Mild Steel Zinc Plated

Found in the UK, still looking for US source

Peter
P G Gilvarry

I've not yet found a source here in the U.S. that carries a specific 7/8" BSP Dowty seal with the measurements provided by Declan and Peter. I did find a seal that measures pretty darn close. A company called British Metrics (Maryland) carries a variety of such bonded seals. The one I think may work measures 30.7 MM ID, 39MM OD, and 2MM thick. Dowty cross-reference # 400-331-4490-41. Their part number is: BONDED 331. They run $0.70 each, and indicating in stock. I think I may order one to see how it fits. Assuming it does...would that then negate the need for the crush washer?

Jim
Jim Rice

Thanks Jim. That looks to be so close to make it worthwhile trying.

This link will get you access to a catalog using the Dowty numbering system. It is a UK company but their sizing is sued for a lot of the Bonded Seals available.

https://supaseal.co.uk/product/catalogue/

Look for the download on the page.

It has become apparent that 7/8" BSP is the poor cousin, I have seen lots of sets that have all sizes up to 1" BSP in 1/8" increments, but omit the 7/8".

Peter
P G Gilvarry

Hi Pete:

The bonded seals I ordered arrived and I installed one in the drain location last night. That said, there was a small drop of fluid on the outside of the drain plug earlier today. My 1st impression is that the seal didn't work. On closer inspection, there appears to also be fluid coming from a bolt on the underside of the gearbox, aft of the drain plug by about 4-5 inches. It's rather small comparatively, and sits higher and centerline with the drain plug, so any leak there would run down the underside center of the gearbox, and collect around the drain plug. At least that's what I surmise may be happening. It's possible the drain plug may still leak despite the new bonded seal, and the other leak may be compounding it. I was thinking about backing off the small bolt and using some thread sealer or something similar to try and stop that apparent leak, but the bolt is identified as the "cluster shaft lock bolt". Sounds like a key item that should not be disturbed. Unless someone can advise otherwise, I think I should just leave things as they are, and just plan on checking/refilling fluid levels a couple times a year.

Jim
Jim Rice

This thread was discussed between 18/05/2022 and 29/05/2022

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