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Old 10-26-2013, 05:08 PM   #39
Brevis illi vita est
Joined: Jun 2010
Oddometer: 4,615
Originally Posted by 685 View Post
Now that the OP has reached a satisfactory conclusion, I'll continue the thread and introduce my trannie problem.

Mine is a 76 R90/6, according to the engine number it was manufactured November 1975. I'm assuming, hoping in fact, that it's all the later 5 speed trannie components.

Here's the picture. Won't stay in first gear under load, tho on the centerstand it works just fine. Jumps out of 1st under load at anything more than idle speed. All the other gears are smooth and stay in the selected gear.

From what I've read, it's the 1st gear shift dogs. I haven't been inside the box yet, but found a 1976 complete lay shaft assembly (is that right?) the complete output shaft assembly. For about $100. Shaft, gears, bushings, etc. all still on the shaft as it was taken out of the trans and clean and unmolested.

Side note, the p-o built out the engine from a 900 to about 1050 cc, it has Mikuni VM38's, and electronic ignition & 2 spark plug heads. He did a lot of work, before he abandoned the project. I basically got it for nothing--a bike for my brother to ride when he comes to Tucson and he's paying for the parts while I provide the labor. The transmission is the main thing wrong with the bike--as long as I don't try to start out on a hill, starting in second seems to be okay.

I was hoping it was a matter of cracking the case open, pulling the old layshaft out (I have sources of heat, btw,) and putting the new one in, and buttoning it all up. From what I read on this forum, it sounds like rocket science--I've never done an airhead trans. but have done 4 & 5 speed automotive trannies. I can read a bunch and there seems to be a lot of specific info on the internet. I'm a newbie to airheads. Not a newbie to mechanicals, tho. I have a stable, well lit work space, a drill press and welder to fab. tools if needed, and stuff for taking accurate measurement. Air, airtools, and many, many mechanicking tools as well.

Is it really that unforgiving and complicated?
You need some special pulling tools to get it open. See the home made tools thread. Also various support and alignment plates.

You need a depth mic. to set up the bearing preloads---that's the critical part.

Sometimes the shift dogs can be salvaged. They were on my 4 speed with the same symptoms.

If you want a tranny you can count on for a long, long time, have a seasoned pro work on it rather than taking it to a beginner just learning, and making their first mistakes, on your transmission. Let 'em learn on somebody elses. There are judgement calls to be made after looking inside. The pro can make them well. The newbie, unless very well supervised, cannot---indeed, won't even know what to look at or what they're seeing when they do.
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