I have had a significant leak at the speedometer drive gear housing on my 240. I pulled the housing and gear as it was loose and am now trying to source the o-ring that holds the housing for the gear in place. I do know I can get it online, but with shipping it is quite expensive. I have no dealership in my area as well.

Does anyone know what size the o-ring is? I have measured the old one and think I have a close match. Given that it is not only the seal but also the only thing that holds the unit in place; I want it to be exact.

Also, since the gear housing on mine was partially out of the tailshaft bore, what is the proper depth to push it back in to. I have looked at my manuals and green books, but they only say to reference the cut at the top shoulder of the housing. Does the housing need to go flush with the surface of the tailshaft bore? or does it go in so the cut part is flush?

 

You are asking pretty esoteric questions and I doubt anyone here can answer them. If the Green Book doesn't help, you are in a pretty specialized inquiry...

How expensive can the shipping of an O ring can possibly be?

 

$12.93 shipping, $4.58 for the o-ring. (iPD)


Hoping someone on here has replaced this part or the speedo gear itself. There is just no locating point for this part in the bore. I *think* mine was not seated fully when I got to it. Don't want to put undue pressure on the nylon speedometer gear against the worm gear on the shaft.

 

The external measurement of the gear housing is 24.5mm, The slot for the o-ring is 20mm x 3.5mm. I placed a 20mm. i.d. X 3mm (26mm o.d.) o- ring and reinstalled the housing and gear. I believe the size should be 20mm i.d. x 3.5mm (27mm o.d.), but I did not have that size and will look around for one locally.

Looking at the gear housing, it is apparent from the wear marks that the housing is pressed into the tailhousing bore flush with the to the cut on the shoulder. The cut should be aligned with the unused threaded hole just rearward of the speedo gear housing. As added insurance, I cut a 2 inch strip of 1/2 inch spring steel and drilled a hole at about 3/4 in. and screwed the strip into the unused threaded hole bending the longer section to act as a "finger" to hold down on the cut part of the housing. I used a #6x16 flange screw with a lock washer to fasten the spring.

When I first addressed the housing, it seems like it could have fallen out entirely if I had not noticed the leak. (I'm sure the speedo becoming inoperable would have also alerted me to the problem, although I may have thought it was odometer related). Looking around, it seems like a lot of other transmissions use a set screw arrangement to locate and secure the housing. Seems a risky arrangement to just rely on the o-ring.

Anyway, that's what I did.

Edit: Looks like there is a retaining tab which must have been removed by a P.O., this is basically what I fabricated.