Main gear seal problem

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Main gear seal problem


Post by doc308 » Sat Jul 17, 2010 4:29 pm

I had my 1950 panhead tranny totally rebuilt. After reinstalling, it leaked as badly as ever. I returned it to the shop that did the rebuild and they replaced the main gear seal. After again reinstalling, it continued to leak just like before. So, I bring it back again and they point out that the main gear surface , where the seal sits, is bent in a number of locations--so that it looks like an octagon shape, instead of round ( I've attached a couple of pics). They say that they've never seen anything like this before. They claim that I must have done something to cause this to happen.

I should point out that I've put about 50 , slow miles on the bike since the tranny rebuild. Since the engine is being broken in, I've driven it very easy. The chains were adusted properly--maybe slightly on the loose side. Once again, this is a completely rebuilt tranny with a new gear set, bushings, etc all installed. However, the mechanic said that they used the original main gear with the new set. I know that there are 2 types of panhead main gears. Could it be that they matched up the wrong main gear with the new shaft/ gear set?

So--does anyone have any ideas about what might cause this to warp like this? It looks like it was pryed to me, but the mechanic denies that this was done. Help please!
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Re: Main gear seal problem


Post by Panacea » Sat Jul 17, 2010 6:31 pm

Looks like the MDG should have been replaced as well, I does look like somebody was prying on it...

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Re: Main gear seal problem


Post by bandit67 » Sat Jul 17, 2010 6:40 pm

Have no idea why yours looks bent, but , on a shovelhead forum I was veiwing, this guy is making and selling the a coller that goes behind the main seal that has a machined groove cut in for an o-ring . I think he has a video on you tube that tells all. This is supposed to cure those pesky leaks once and for all. I have pulled mine down twice.....and it still leaks . I am planning on purchasing one.

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Re: Main gear seal problem


Post by Bigincher » Sat Jul 17, 2010 7:09 pm

The guy goes by "saddlebagrail", and here's a link that shows the procedure in full. Some machining is required. I've purchased one of his spacers myself, it will go on the shelf until such time I need to do this to one of my 4-speeds. ... -solution/" onclick=";return false;

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Re: Main gear seal problem


Post by drinner-okc » Sun Jul 18, 2010 7:35 pm

Was there ever a "supernut" or similar product installed on that gear" if you look close, there is a peak in all the splines where the sprocket slides on. Almost looks like something conical
(a cone or taper) pressed evenly all the way around the end of the threads. the splines, being the thinnest area, collapsed under the pressure. How hard was it to get the sprocket off?
My custom pan had a supernut (or similar product), when tightened it mashed the end threads, when I removed it, it peeled all the threads from the nut. I filed & filed but was unable to clean the threads enough to start a new nut. Last piece out, first piece in.
I will use a 65 & later gear with the factory seal.

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Re: Main gear seal problem


Post by Bosheff » Mon Jul 19, 2010 12:42 am

MDG seals were not used buy the factory until 1965. 64 and earlier were not machined to accept this seal. A -65 MDG can be used in any 4 speed mixer. Why would anybody replace all the other gears in the tranny and not replace the MDG? If the other gears were worn to the point of not falling within service specs, I would expect the MDG would be equally worn. I've seen a pre 65 MDG that someone tried to hammer a seal in, and they pretty well thrashed the end of the gear to the point that I had to replaced the gear. A MDG with an excessively worn MDG bushing can leak to the point that the MDG seal won't stop the leak, as the seal will fail prematurely. Also, if the mainshaft is worn beyond service limits, a leak is probable. A tranny rebuild should include renewing the MDG bushing, and sizing to fit the mainshaft to the factory specs. The MDG and mainshaft are two of the most commonly worn parts in a rebuild of a tranny with many miles on it, or a tranny that have been continually run low on oil. A properly renewed transmission that has been rebuilt with quality parts will give many years of service if taken care of, and oil changes are a regular part of the maintenance routine. The main reason people don't replace main drive gears and mainshafts is cost. These are 2 of the most costly internal parts of the tranny....bosheff
Last edited by Bosheff on Mon Jul 19, 2010 5:36 pm, edited 1 time in total.

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Re: Main gear seal problem


Post by doc308 » Mon Jul 19, 2010 5:22 pm

Yes--a super nut was installed and , when i picked up the tranny, I saw the mecanic installing it with an air gun. So-you're saying that an overtightened supernut could have caused this distortion ?

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