Shifting the good ole' 915

[OsoMoore]

Many of us have this "classic" transmission, in various states of repair. And, for the most part, we know the basic rule.

Take it slow going from 1st into 2nd.

Obviously there are a lot of things we can do to improve the shifting - transmission oils, shift kits, etc. But what are some practical tips in the way we drive that can make shifting more enjoyable?

Something I read somewhere on this forum (I don't recall, I think I was thread dredging) is that the 915 likes to be shifted at higher revs. On my way to work this morning, I gave it a try. I always ran 1st up to 3.5K before shifting into 2nd. And it shifted better! Less resistance, and a quicker engagement.

Any other driving style tips for the transmission from another era?

[mhall131313]

I have found the same with my 915 transmission. Take it easy from first to second and the rest seemed to slide in seamlessly. I will usually take the rpm's up a little higher, into the 4k realm before shifting from 1st to 2nd, and for that matter the rest as well.

[manbridge 74]

A little known fact I picked up from, I believe, Zimmerman's tutorial: Don't use 5th too soon as it will not get adequate lubrication at low road speeds.

Also, at a stop ease it into 2nd before engaging 1st. If 1st is still difficult try partially letting clutch out while in 2nd. Just enough to feel engagement.

[SilberUrS6]

I found the same thing - rev it up to 3.5k in first, ease it into second. Pause before engaging any gear. Even a slight pause is good.

The second thing I was switch from SWEPCO to Kendall. Switching gears with SWEPCO in was notchy and fiddly until the trans has COMPLETELY warmed up, and then it was merely acceptable. Switched to Kendall, and the shifts became very smooth, even with the trans cold. And when warm, the trans shifts just like any other manual transmission. I was very pleasantly surprised about the magnitude of the change.

[Geary]

For visualization purpose:

As the 2nd gear synchro band wears and loses it's rough friction surface ..



... the more it spins on the entry ramp of the shift sleeve's engagement teeth, eventually forming a small spur on each tooth:



As this spur grows, the width of the slot between the sleeve's engagement teeth effectively shrinks, and it becomes more difficult to engage 2nd gear .. because of the narrowed slot AND because of the sharp little spur (on each of 30 teeth).

It's sometimes worth the time to knock these spurs off with a dremel, but it's usually more cost effective to replace the shift sleeve (and other associated bits).

[mnez]

At high revs it'll drop nicely into 2nd from fifth - happened once, but I managed not to release the clutch. Now I have a WEVO.

[Elombard]

Wow thanks Geary that is great to know!