Topic: CB400F transmission slipping

[minimo]

My X-Ray senses tell me that I have worn dogs on my 1st gear.

Taking off from idle (about 3/8th throttle, 2,500rpm) is egregious and stutters as though it’s slipping in/out of gear, almost sounding as though it’s trying to engage but cannot. I have to quickly engage clutch and shift into 2nd. I even have avoided 1st gear entirely and take off from 2nd gear, which I loathe.

I’m about to crack open my lower crankcase as I’ve done already now numerous times, yet the last time discovering and replacing my shift fork due to some noticeable wear:

I addressed the obvious issue by replacing the shift fork but didn’t think about nor look into why it occurred which brings me back to opening up the crankcase to examine the gears a little more carefully, zeroing in on 1st gear especially.

I know it’s probably been covered here before but I can find no definitive answer on what to look for when inspecting these potentially worn dogs. Rounded edges? Non-rounded corners? Undercuts?

I’m about to find out and I expect it to be obvious, but if any of y’all have some good references, I’d appreciate it.



Sent from my iPhone using Tapatalk

[Bodi]

Look for wear in the shift drum grooves. That fork wear looks pretty bad, if the grooves are worn the forks will not be positioned correctly. The dogs should be close to fully engaged when in gear. Also, is the detent working correctly, is the drum in the correct position to have the forks fully moved into place?

[minimo]

I will check. Thanks, Bodi.

[scottly]

My X-Ray senses tell me that I have worn dogs on my 1st gear.

Taking off from idle (about 3/8th throttle, 2,500rpm) is egregious and stutters as though it’s slipping in/out of gear, almost sounding as though it’s trying to engage but cannot. I have to quickly engage clutch and shift into 2nd. I even have avoided 1st gear entirely and take off from 2nd gear, which I loathe.

Sounds like very worn sprockets??

[minimo]

Sounds like very worn sprockets??

Wuuuuut? Ya think?
I think it’s more gear related because it’s consistent at a specific rpm and gear selection 1st gear


Sent from my iPhone using Tapatalk

[jgger]

Probably easier to break down the trans than it is to check the chain and sprockets........NOT. Just sayin'.

[minimo]

Yeah, I wish it were the sprockets.


Sent from my iPhone using Tapatalk

[scottly]

Worn dogs usually cause the trans to jump out of gear into a false neutral, and usually when under heavy load. Your problem sounds different; maybe there are teeth broken off 1st gear?

[minimo]

Well, the stutter is kinda like a jump. All the teeth were intact. This time I’ll be sure to inspect the dogs. Engine dismount will be tonight. Tomorrow night I’ll have the lower case open for inspection.


Sent from my iPhone using Tapatalk

[minimo]

When it begins to jump I never want to leave it to see if it falls into gear or into a “false neutral”. The sound and sensation are too egregious to even be curious about what would happen so that’s why I quickly pull the clutch I. And shift to 2nd. I’ve even made it a practice to start out of 2nd gear to avoid 1st entirely


Sent from my iPhone using Tapatalk

[scottly]

If it helps, I have a 400 trans loose to compare with...

[minimo]

Yes, please! As many references I can get my eyes/ears on would help!
I pulled this from YouTube:

It’d be cool to see the splay of all the gears, washers, retaining rings...


Sent from my iPhone using Tapatalk

[scottly]

I'll try to dig it out tomorrow before it gets too hot...

[minimo]

I'll try to dig it out tomorrow before it gets too hot...

Sent from my iPhone using Tapatalk

[bryanj]

400 tranny is normaly bullet proof but as Mcginty sez, one of everything will go bad sometime.

[scottly]

The 400 trans I have is missing the large gear on the left side of the counter shaft, which I *think* is 1st gear. When in 1st, the dogs on the gear to the right of it would engage holes in the big gear, locking it to the shaft.

[minimo]

Thanks, scottly. Those pics are helpful.

I popped the case tonight. Here are my findings. These may be all telling, certainly can’t be normal:
Here’s before I popped the case. Sorry, got a smudge of oil on the lens
https://drive.google.com/file/d/1Y5CPZoz7dAAW0aKKCdNNIdCHv5L9Dmpf/view?usp=drivesdk
Here’s 1st gear engaged per that YouTube vid above:
https://drive.google.com/file/d/1eFDHieCCAc7-Ji9UMXYGBST5Eo-aGaZ2/view?usp=drivesdk
If this is normal...
https://drive.google.com/file/d/1V3pKv60Jr5mtyEBh4MrnYUlLsnuZv4AE/view?usp=drivesdk
Here are the dogs on the countershaft gear that gear that pushes up against the low gear comp. Pretty rounded.

Even found some wear on the inside of the casing...

Full disclosure, on a previous occasion I had this engine apart I found that washer that gets sandwiched between the low gear comp and the 20mm needle bearing was omitted so that would have undoubtedly left some marring if not even worn out the bushing on that gear :-/

There aren’t any teeth missing and other than the rounded edges on the countershaft gear dogs, all the gear teeth look intact.

None of the other gears exhibit the kind of slop as what you see above.

Replacement time?


Sent from my iPhone using Tapatalk

[Bodi]

It could indeed be the transmission and you seem pretty convinced your sprockets and chain are not suspect.
However, this is usually chain jump on the sprocket. Wheel torque and chain tension is highest in first gear, sprocket and chain speed lowest. I have seen this many times, with the owner certain the gears are jumping out but... it is really from the chain, with the skip/jump usually only happening in first gear.
A worn engine sprocket - even with correct chain tension - will do it. Just reversing a worn sprocket can stop the skipping and prove a new sprocket and chain set is required soon.

[scottly]

Looks like the dogs were only slightly engaged into the mating holes, maybe only 1mm? The missing washer would account for maybe 1mm, but the dogs should be engaged much deeper.

[minimo]

No sharp points or wild wear on front/rear sprockets:


Aside from the rusty chain and bad photo, I’m not convinced that it was the sprocket causing the 1st gear weirdness. Especially after seeing this:
https://drive.google.com/file/d/1eFDHieCCAc7-Ji9UMXYGBST5Eo-aGaZ2/view?usp=drivesdk
I mean, if this isn’t a problem...


Sent from my iPhone using Tapatalk

[scottly]

I had to use a different computer to see your videos. I think the flat side of the big gear  is supposed to be facing the dogs. Turn her over.

[minimo]

I had to use a different computer to see your videos. I think the flat side of the big gear  is supposed to be facing the dogs. Turn her over.

What a really old timer-ish thing to suggest
Had me looking hard at the parts fiche to check. Either way, still an unacceptable amount of slop for a gear - bushing is toast.

[scottly]

Show me a spec for how much side-to-side slop is unacceptable. Your problem is due to  an improper installation of the gear, which positions the holes the dogs engage too far away.

[minimo]

Show me a spec for how much side-to-side slop is unacceptable. Your problem is due to  an improper installation of the gear, which positions the holes the dogs engage too far away.

Well, I’m looking for that spec myself. Seems obvious enough though that it’s waaay off. I’m waiting on a replacement part to compare. Also, the gear shift drum assembly dictates how far in the dogs need to go, so any difference in the position of this sloppy low gear will exhibit some kind of issue, would it not?


Sent from my iPhone using Tapatalk

[scottly]

The gear was installed backwards. Turn it over, re-assemble the trans/motor and report back after a road test.