Middle Drive - What should it feel like?

[mayor_mccheese]

Ok so I've been chasing a sluggish feeling at the rear wheel throughout my rebuild process. The bike felt VERY stiff when being pushed in both neutral and in gear with the clutch engaged. Things I've checked so far:

• I've taken most of the engine apart for a rebuild, and the clutch assembly, while definitely needing new plates, spun freely so no issues there.
• Rear wheel bearings spin freely
• Final drive spins fine with no abnormal resistance
• Engine rotating assembly spins fine when disengaged from clutch, but clutch spins fine so still no worries

Which leads me to the last piece... The middle drive. I pulled it today and it feels, well, kind of sticky or gummy. It certainly doesn't spin freely like most of the other rotating items I've checked. When wiping oil away from the inner surfaces, I also noticed a black soot of sorts on most of the surfaces between the middle gear assembly and the case. I'm guessing that's bearing wear and I'll need to pop them out and check them.

My question for you all is does the middle drive spin freely or does it carry some resistance to it? I think I know the answer but we all know what happens when we assume...

[bikerphil]

I believe the MD has some drag to it, the final drive also. When you said the bike was hard to push around, you never mentioned checking if the brakes were dragging, probably the most common cause. You can wash the MD out with kerosene if it is gummed up from dirty oil.

[mayor_mccheese]

Oh yea I did forget to mention that. The rear pot is toast. The pads weren't installed straight and the pot is totally warped. I've got parts for that, but I was still getting a fair amount of drag with it off and the bike on the center stand. I was getting a lot of resistance turning the wheel by hand.

I'll wash out the MD with some kerosene and see what happens. Thanks for the reply!

[bikerphil]

Yup, just keep in mind, the whole drive train drag on these bikes is more than a chain driven bike would be, resulting in a significant loss of HP at the rear wheel.

[mayor_mccheese]

Haha yea "maintenance free" until you ride one long enough so that it isn't. I've had a few shift drives over the years and even my big M109 you could still get a nice spin on the back wheel by hand.

The oil seemed way too thick and heavy to be 80W so hopefully just a goober PO or it's the original oil from 40 years ago and a good rinsing will solve it.

[bikerphil]

I"m sure things will loosen up some after some riding. Haha maintenance free all right.

[red bandit]

With the rear brake caliper off and the middle drive off how does the rear wheel turn/spin?

[2WheelFun]

Mine rolls around easily, and bikerphil is probably right on the money with post #2. Pop the front wheel in the air and check for drag.

[mayor_mccheese]

Hey Red, it spins just fine without the brake or the middle drive. I've hand spun all the various pieces and so far the middle drive seems to be the culprit as it has quite a bit of drag in it. I can turn it by hand, but it won't actually continue to spin if thay makes sense.

Thanks 2Wheel, it's almost entirely torn apart right now. She's my Corona project lol. Cleaning things and prepping parts for reassembly and powder coating as we speak.

[DiverRay]

Replace the "U"-joint! That is something overlooked on these, and time is not kind to them. I don't have the part number handy, but it's the same one used in the Datsun B210, IIRC.

[mayor_mccheese]

Thanks Ray! That's good info, I had no idea there was a part out there for it. I'm doing all this other work I might as well throw a new U in there.