Size of O-rings for 105/115 trans shift forks

**paulsle** · #1 (**permalink**) 05-04-2008, 09:14 AM

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,

**jarrington** · #2 (**permalink**) 05-05-2008, 10:51 AM

Bump... I'd like to know the answer to this as well.

Clayton105 · #3 (**permalink**) 05-05-2008, 11:01 PM

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.

**George Willet** · #4 (**permalink**) 05-06-2008, 09:27 AM

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??

**paulsle** · #5 (**permalink**) 05-06-2008, 11:02 AM

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.

**Bill S** · #6 (**permalink**) 05-06-2008, 02:04 PM

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.