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Discussion Starter #1
Transmission rebuild question #2...

Can anyone give me a proper replacement size of the 3 o-ring seals for the shift forks, located within the front of the gearbox case. The originals were dried up and leaking badly. All I can find is household plumbing-sized rings that will fit & might work, but seem a bit too loose. The usual Alfa parts suppliers drew a blank on this one.

Thanks,
 

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I measured these up once when I ran my workshop. I used to buy them and replace them when I rebuilt trannies, to no avail. They would always start leaking again after a year or so.

After a good look and measure, I worked out that the grooves that the seals sit in are not machined concentrically with the shaft bores. And there is not a tight enought fit on the seals to overcome this. Take a good look at the wear on the O-ring and you will see this... It is not even.

A good machinist could fix this, or you could use a post 74 transmission that is different in that the shafts do not protrude into the bellhousing. This was obviously Alfa's fix after yonks building them with a weep.
 

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I have never found O'rings other than the ones sold by Alfa dealers that are not dimensionally "off", and even the Alfa ones I bought seeped eventually.

Now I shorten the rails and block off the bell housing. Problem solved!

I do have a set of the correct Alfa Orings I'll sell for less than what I paid. (Over $20 as I remember). $15??
 

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Discussion Starter #5
Thanks for the replies to my question on this.
I thought of welding up some sort of a cap inside the bellhousing, now I see it's been done before. Didn't realize the rods could be shortened... that might make capping the opening easier.

George, since my gearbox is all apart at the moment, can you give me any idea roughly how much gets removed from the shift rods? E-mail sent to you on the O-rings.
 

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The reverse shift rod protruding through the bellhousing is what activates the backup light switch. If you seal off the bellhousing and shorten the rods, you'll need to drill and tap a hole for the screw-in type backup light switch. Same deal if you use a '74 or later transmission with the short rods. Here's what I did with a piece of aluminum bar stock, cut for an interference fit and JB welded from the back.
 

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I am dealing with similar problem with leakage through the O-rings and I wondered if someone here has shortened the shifter rods and by how much?

cheers Robin

PS Also interested if someone knows the size of the O-rings.
 

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Old thread I know...but I'm doing a rebuild of my tranny and needed to know this info as well. I measure the rods at 14 mm in diameter....the o rings are 2,5mm section width. In guessing that the I.D. of the o ring should be slightly less than that to allow proper sealing on the rods.....maybe 13,7mm x 2,5mm (i see this size available on e-bay). I might also try empirical measure seal at 1/2" (12.5mm) x .100" (2,5mm)....see if it fits better.
 

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o-rings viton

I used Viton 14 mm by 2.5mm with success. no more leakage form the selector fork shafts
 
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