Bad Speedo Key or Driveshaft Bearing? - Snowmobile Forum: Your #1 Snowmobile Forum

meburdick · 01-02-2013, 07:20 AM

Last year, I noticed that my speedo had stopped working. I bought a new speedo key and installed it as a "test" to see if it was a fluke with the key or if the bearing is actually bad.

Since then, I've put 75 miles or so on the sled at speeds up to 80MPH and the speedo is still working fine. What's the consensus at this point? Did the speedo key just break or is there a pending failure here?

indytriumph600 · 01-02-2013, 09:32 AM

Replace the bearing when bearing are bad they do funny things. If it blows it won't be good

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meburdick · 01-02-2013, 09:36 AM

Quote:

Originally Posted by indytriumph600

Replace the bearing when bearing are bad they do funny things. If it blows it won't be good

Yes, I'm well aware. When I first noticed the issue last year, I loosened the track and looked for any free rotational play in the driveshaft and found none.

My question is not "should I replace the bearing if it's bad", it's "is there a high or low likelihood that my bearing is bad given these conditions."

**RJ Gleason** · 01-02-2013, 02:21 PM

If there was any sign of rust on the seal, replace it.
As long as it is running fine, leave it alone.
If that bearing fails, it will take out the speedo key and then you will know it.

meburdick · 01-02-2013, 02:26 PM

I pulled the cover off of the end when I replaced the key (obviously). Everything appeared to be rust-free inside of there. The grease looked a bit "old" (as it was likely from the end of the previous season), but not dirty or moisture-ridden.

I put in the new key, greased everything well, and have been riding it.

I guess my ultimate question is: If the bearing is headed toward failure, within how many miles of replacing that key should I expect to see it fail again?

**RJ Gleason** · 01-02-2013, 02:28 PM

Depends on the bearing.

meburdick · 01-02-2013, 02:33 PM

I would imagine that, in a sort of worst-case scenario, the key would break off again with a matter of a few miles. That would indicate that the bearing is excessively worn and should already be considered "failed".

On the other end of the spectrum... If I get a couple hundred miles out of it and it hasn't failed again, could I consider it to generally be ok at that point?

I have a bearing kit to do the job. But, considering it's riding season and it would be a big PITA for me to get the work done, I'd rather hold off and do the job in the spring if I could (unless it's actually failing, then I have to do what's required).

**RJ Gleason** · 01-02-2013, 02:36 PM

Exactly!!

meburdick · 01-02-2013, 02:45 PM

Ugh. Clear as mud.

Phaze · 01-02-2013, 06:02 PM

The worst case scenario is, you break a key again, the bearings completely go since you broke one key already and now you take out your chaincase too. Yep, had it happen.....

JheLrey · 01-02-2013, 07:04 PM

Had a key sheer once... All because I sank the sled in a creek and it froze up. Replaced the key, checked bearing, greased, and I was set. Just saying it is possible.

meburdick · 01-02-2013, 07:40 PM

My understanding is that, when the bearing is "pre-fail", the key breaks because there is play in the bearing. If that play is very small, it should take some length of time before a key would break again (minimal play over time, or increasing play over time). If the bearing is already reasonably worn, I would expect the key to break again "quickly."

Now, if my reasoning and understanding are correct, what I'm trying to figure out what would be "quick" and what would be "a while" in terms of the number of miles.

smokingcrater · 01-02-2013, 09:03 PM

Its really a simple test... Lift the back of the sled up, and then get under and push/pull on the left side of the drive shaft. If the bearing is bad enough to break the key, you will notice it.

meburdick · 01-02-2013, 09:12 PM

Quote:

Originally Posted by smokingcrater

Its really a simple test... Lift the back of the sled up, and then get under and push/pull on the left side of the drive shaft. If the bearing is bad enough to break the key, you will notice it.

See post #3. I believe that is what you are referring to?

I felt no discernible movement of the driveshaft other than some slight play side-to-side.

**RJ Gleason** · 01-03-2013, 07:53 AM

There should be no side to side at all when the bearings are locked to the drive shaft.

meburdick · 01-03-2013, 07:55 AM

I'll have to check it again, then. I remember there being a slight bit of side-to-side movement, but I suppose it's worth checking again to be absolutely certain of its condition.