Topic: 1978 CB750A No Drive in First, Drive in Second

[LiveeviL81]

Hey Guys,
This is a bit of a cross post from my build log, hoping to get some more eyes on this problem before I rip the engine back out of the frame.

After my first start, I was shifting through the gears on the center stand and notice no drop in RPM or increase in rear wheel speed when engaging first gear. Even reving up the engine or trying to Brake-Torque does not seem to load the torque converter or clutch packs of first in first gear.

Shifting into second seems to work correctly and seems to be actually second gear. I brake-torqued a bit but wasn't able to ride due to an oil leak.

The oil leak seems to be on the torque converter cover cap, near the check valve, which in the troubleshooting web on 8-1 in  manual describes it could be poor acceleration in L or D. Ordered new gaskets, but I don't think this leak is causing the issue in only L.

I have thought about doing the transmission oil pressure test, but I don't think that is the issue since D seems to work.

Is there a good place I can blow compressed air and test to see if the L or D Clutch are engaging?

Can anyone highlight what the "Damaged L Clutch Piston O-ring or sticking piston" "Worn L Clutch Disk" and "Sealing or Sealing Guide" in the Torque Converter Troubleshooting would be in the manual?

I have attached the a photo of my shifting mechanism, which lets me correctly shift through all the gears, and the kickstand return works as well, but maybe I missed something obvious.

Thanks!
Kaleb

[LiveeviL81]

Ended up pulling off the shifting mechanism cover, and got to the orifice holes for the feed, L and D gear. Used some low pressure compressed air to see if L and D gear sounded the same or I could try to actuate the clutches using compressed air. Blowing through D, I could hear the air "leaking" out somewhere inside the engine, I am assuming this is correct since my D gear was engaging and spinning the rear wheel. Blowing air through L was completely sealed and holding pressure. I assume this means either my passaged are blocked, or my o-ring is caught somewhere? I upped the air pressure to 30psi, but was afraid of doing damage or anything if I went higher. So it looks like the engine is coming out of the frame tomorrow so I can split the cases and check the oil passages for a clog. Very Sad

Kaleb

[Don R]

 I never had one apart but it sounds like you are on the right track. The leak/no leak sound is opposite of what I would expect. Maybe an expert will stop to read.

[LiveeviL81]

Figured out the issue!
Ended up needing to split the cases and it was pretty apparent that my Low Gear oil feel/Bearing Race was not seated on the alignment pin and rotated. Should be an easy fix, but it did end up causing another issue I believe where the main oil gallery seems to have cracked, I wonder if its related to excess tension in the case halves since it was pressed together with the pin not in the hole.

[LiveeviL81]

Working on re-assembly of the case halves and it seems that the low clutch alignment pin is pressed further into the case half than the other alignment pins. I wasnt able to get a grip on it, or even get it to pop out with heat. I worry it wont be enough to engage alignment hole on the clutch pack. Sticks out about 10 thou.