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Author Topic: Cb550k shifting up but not down  (Read 351 times)

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Offline bert1

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Cb550k shifting up but not down
« on: September 20, 2023, 04:12:17 PM »
75 550k, and I notice that the it's very very difficult to downshift, especially from 2nd into 1st. but shifting up is smooth.

The clutch slips as well, as I didn't change the friction plates and springs when I went through the engine.

P/o put 20k on it many years ago, sat for a while. Even when rocking the bike back and forth, the bike stays in 2nd or 3rd especially after riding in that gear for a little, it's very difficult to shift down at all, it helps a little if the bike isn't running. Once i get it to click down, shifter does not stick.

So i'm confused as to why it shifts up nicely but sometimes won't even go from 4th into 3rd without pulling over and rocking the bike for 2 minutes. Is this all caused by the clutch/ springs being worn?
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Offline newday777

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Re: Cb550k shifting up but not down
« Reply #1 on: September 20, 2023, 05:43:23 PM »
What oil are you using?
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Stu
Honda Parts manager in the mid 1970s Nashua Honda
My current rides
1975 K5 Planet Blue my summer ride, it was a friend's bike I worked with at the Honda shop in 76, lots of fun to be on it again
1976 K6 Anteres Red rebuilding project, was originally my brother's that I set up from the crate, it'll breath again soon!
Project 750s, 2 K4, 2 K6, 1 K8
2008 GL1800 my daily ride and cross country runner

Prior bikes....
1972 Suzuki GT380 I had charge of it for a year in 1973 while my friend was deployed and learned to love street riding....
New CB450 K7 after my friend returned...
New CB750 K5 Planet Blue, demise by ex cousin in law at 9,000 miles...
New CB750 K6 Anteres Red, to replace the totaled K5, I sold this K6 at 45k in 1983, I had heavily modified it, many great memories on it and have missed it greatly.....
1983 GL1100A, 1999 GL1500 SE, 1999 GL1500A

Offline calj737

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Re: Cb550k shifting up but not down
« Reply #2 on: September 20, 2023, 05:48:55 PM »
Quote from: newday777 on September 20, 2023, 05:43:23 PM
What oil are you using?
The incorrect oil won’t cause the symptoms he describes.

If the clutch is not fully disengaging, shifting down will be utterly impossible. You need to open the basket, probably change the friction discs and springs, and pay close attention to the sequence of assembly. Also, it might be prudent to inspect your clutch cable. If pulling in the lever doesn’t fully disengage the clutch, no shifting.

Having to rock the bike back and forth to downshift is a serious indication something is mechanically wrong.
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"Of all tyrannies, a tyranny sincerely exercised for the good of it's victim may be the most oppressive. It may be better to live under robber barons than under omnipotent moral busybodies. The robber baron's cruelty may sometimes sleep, his cupidity may at some point be satiated, but those who torment us for our own good will torment us without end for they do so with the approval of their own conscience." - C.S. Lewis

Offline brianc

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Re: Cb550k shifting up but not down
« Reply #3 on: September 20, 2023, 09:26:12 PM »
Carefully look at the clutch centre for wear. The steels wear dents into the alloy and it won't release properly. My F2 750 did that, gear changing and selecting improved significantly after I did a bit of rework on it. I have a new centre to fit when I get a chance.
« Last Edit: September 21, 2023, 02:26:11 AM by brianc »
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Offline bert1

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Re: Cb550k shifting up but not down
« Reply #4 on: September 21, 2023, 08:21:57 PM »
Worse than i thought, fibers were 2.55mm thick on avg so they wore into the metal fingers. Caught it early so i'm happy. As for the poor downshifts, the spring on the shift shaft had an odd gap on it, so it wouldn't engage with the downshifting mechanism.
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Online bryanj

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Re: Cb550k shifting up but not down
« Reply #5 on: September 22, 2023, 12:15:40 AM »
That spring needs replacing
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Semi Geriatric ex-Honda mechanic and MOT tester (UK version of annual inspection). Garage full of "projects" mostly 500/4 from pre 73 (no road tax in UK).

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Offline bert1

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Re: Cb550k shifting up but not down
« Reply #6 on: September 22, 2023, 09:37:34 AM »
Quote from: bryanj on September 22, 2023, 12:15:40 AM
That spring needs replacing

It was crossed in an "x" put it back parallel tension is fine. One of the dumber things ive done.
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