Author Topic: New (to me!) '77 CB400F - US model  (Read 38188 times)

Offline mattsz

  • SOHC Pro
  • Posts: 606
    • View Profile
Re: New (to me!) '77 CB400F - US model
« Reply #30 on: October 25, 2018, 10:26:18 PM »
Another little aside: I looked at the drive chain tension - on the center stand, I checked the vertical movement of the lower run of chain, midway between the two sprockets.  The book says 3/4 of an inch.  I wonder if the PO misread it, as the chain currently has 3 inches of movement.  "3/4" and "3" look almost the same, right?

Offline taysidedragon

  • SOHC Master
  • Posts: 1318
    • View Profile
Re: New (to me!) '77 CB400F - US model
« Reply #31 on: October 26, 2018, 12:27:53 AM »
Another little aside: I looked at the drive chain tension - on the center stand, I checked the vertical movement of the lower run of chain, midway between the two sprockets.  The book says 3/4 of an inch.  I wonder if the PO misread it, as the chain currently has 3 inches of movement.  "3/4" and "3" look almost the same, right?
New chain and sprockets? The list of new parts required starts to grow! 😈
Gareth

1977 CB400F
1965 T100SS

Offline mattsz

  • SOHC Pro
  • Posts: 606
    • View Profile
Re: New (to me!) '77 CB400F - US model
« Reply #32 on: October 26, 2018, 01:28:10 AM »
New chain and sprockets? The list of new parts required starts to grow! 😈

Yup!

I read that the tachometer cable set screw is the same as the speedo one - they were right, both screws are equally "chowdered" on my bike...  >:(

I really am going to put it away for the winter, though.  I've got the tank off; I'll pull the carbs and front brake parts, but otherwise it'll have a further rest...

Offline mattsz

  • SOHC Pro
  • Posts: 606
    • View Profile
Re: New (to me!) '77 CB400F - US model
« Reply #33 on: October 26, 2018, 12:18:28 PM »
A few other odds and ends...

Not too sure about your driver's footrest position, and it's definitely got the wrong gear lever, it should have two rose joints and a Johnson Rod for adjustment. ... might be worth checking on the rear brake pedal as well, it should have a guard fitted to it to stop your foot rubbing on the clutch cover.

I think the US models are different - here's a couple pics from the OEM owners manual:

[ Guests cannot view attachments ]

[ Guests cannot view attachments ]


Float bowl drain screw, yes?

[ Guests cannot view attachments ]

I tried to open #'s 1 and 4, stuck tight.  I gave up before breaking anything, are there any tricks?

Offline mattsz

  • SOHC Pro
  • Posts: 606
    • View Profile
Re: New (to me!) '77 CB400F - US model
« Reply #34 on: October 26, 2018, 12:22:09 PM »
A few years ago, the silencer crack seemed minor, now it's broken all the way 'round, and appears to show sooty signs of leaking on the bottom:

[ Guests cannot view attachments ]

[ Guests cannot view attachments ]

Might this be repairable - welded, perhaps?  I know it would be ugly, but function is what counts at this point...

Offline petermigreen

  • SOHC Pro
  • Posts: 563
    • View Profile
Re: New (to me!) '77 CB400F - US model
« Reply #35 on: October 26, 2018, 12:41:05 PM »
As regards foot brake and gear lever if the US variant is different then only in later modes as mine is American and has the standard items





The carb drain screw shouldn’t be too tight that you can’t release it but caution is required as it is brass and soft as doodoo. I’d get a good fitting screwdriver with a shank that will take a spanner and get extra leverage that way or if really stuck maybe get a pair of grips on them and be prepared to replace with new.

The silencer can be brazed but not welded as far too thin but looking at yours I think replacement is probably the best option.

Keep plugging away they require endurance
Peter


Sent from my iPhone using Tapatalk

Offline mattsz

  • SOHC Pro
  • Posts: 606
    • View Profile
Re: New (to me!) '77 CB400F - US model
« Reply #36 on: October 26, 2018, 01:46:18 PM »
As regards foot brake and gear lever if the US variant is different then only in later modes as mine is American and has the standard items

Your statement checks out, based on these paragraphs I found on page 42 in the April 2012 issue of your Classic Bike magazine...

Quote
There is some confusion over model designation. Only the CB400F and the CB400F2 came to the UK. The F1 is a USA- and Canada-only model introduced in 1977. The F model is the original 1975 model year machine with Pillion footrests mounted on the swingarm and an unlined fuel tank in either Light Ruby Red or Varnish Blue. For 1976, the pillion footrests were mounted on a loop coming off the rear subframe and the fuel filler gained a lock, but the model was still called the CB400F in the UK and Europe.

Many US F models were modified with higher 'bars, but the 1977 F1 has a single (rear) stay on the front mudguard, slightly higher handlebars, a locking cover to the fuel cap and foot rests re-positioned a little further forward than on the UK and European models. Rare in the UK.

Mine matches the latter description...


The carb drain screw shouldn’t be too tight that you can’t release it but caution is required as it is brass and soft as doodoo. I’d get a good fitting screwdriver with a shank that will take a spanner and get extra leverage that way or if really stuck maybe get a pair of grips on them and be prepared to replace with new.

I think I'll wait until I remove the carbs to proceed.  I found a thread here where, IIRC, someone sheared the head off, then broke an easy-out in the remainder, then finally cracked the float bowl while trying to remove that drain screw.  So I wondered if it was a common problem, and whether a pre-application of heat and/or penetrating oil might be in order...
« Last Edit: October 26, 2018, 01:52:53 PM by mattsz »

Offline K2-K6

  • Grogu
  • *
  • Posts: 5234
    • View Profile
Re: New (to me!) '77 CB400F - US model
« Reply #37 on: October 26, 2018, 03:22:38 PM »
On the carb float bowl screws,  the problem appears to be of corrosion between the two metal parts forming a particularly strong bond which ends up similar to the structural integrity.

As you've posted,  it can easily go wrong or be all but impossible.  Really it's in the realms of experimentation,  maybe if you leave them to soak in something like turpentine/paraffin (think that's kerosene over there)  for a week or so then get them in an ultrasonic cleaner before attempting to undo them?

They may of course be easy but you never know when they were last removed.

Offline mattsz

  • SOHC Pro
  • Posts: 606
    • View Profile
Re: New (to me!) '77 CB400F - US model
« Reply #38 on: October 26, 2018, 03:39:05 PM »
On the carb float bowl screws,  the problem appears to be of corrosion between the two metal parts forming a particularly strong bond which ends up similar to the structural integrity.

As you've posted,  it can easily go wrong or be all but impossible.  Really it's in the realms of experimentation,  maybe if you leave them to soak in something like turpentine/paraffin (think that's kerosene over there)  for a week or so then get them in an ultrasonic cleaner before attempting to undo them?

They may of course be easy but you never know when they were last removed.

This sounds about right.

I'll basically be readying the bike for winter storage; I was told it last ran really well, but that was two years ago.  So, I'll focus this winter on making sure the fueling components are in good order, and also the front brake components, since I know they're knackered, so I can try to evaluate the rest - safely - on the road in the spring...

Offline Bryanj

  • Grogu
  • *
  • Posts: 10693
    • View Profile
Re: New (to me!) '77 CB400F - US model
« Reply #39 on: October 26, 2018, 04:00:28 PM »
I will try a basic "how it works"

The piston seal is a square cross section O ring whilst the groove it fits into has a slightly angled base, this means that when the seal is fitted it turns into a "diamond" shape so that only one corner is rubbing on the piston surface.
When the brake is applied the seal "twists" slightly and it is this twist which retracts the piston from the pad. Thus any crap in the groove or on the seal, or tighteness on the piston stops the piston retracting and the brake sticks.

Secondly look at the bracket bolted to the fork with two small bolts at the muguard stay and one big one lower down. The big one has a steel pinthat goes through the swinging part and locates in the top bracket held by the two small bolts, this pivot also gets corroded and the pin pluss hole in the swinging bracket need thourough cleaning and copperslipingso they move very freely. The two bolts you ringed are the ones that split the caliper(no fluid will be lost) the 750 started with bolts you have to undo through the wheel spokes but 550/500/400 do not.

Hope that helps, if in doubt of assembly look at parts book

Offline mattsz

  • SOHC Pro
  • Posts: 606
    • View Profile
Re: New (to me!) '77 CB400F - US model
« Reply #40 on: October 26, 2018, 04:26:28 PM »
I will try a basic "how it works"

The piston seal is a square cross section O ring whilst the groove it fits into has a slightly angled base, this means that when the seal is fitted it turns into a "diamond" shape so that only one corner is rubbing on the piston surface.
When the brake is applied the seal "twists" slightly and it is this twist which retracts the piston from the pad. Thus any crap in the groove or on the seal, or tighteness on the piston stops the piston retracting and the brake sticks.

Secondly look at the bracket bolted to the fork with two small bolts at the muguard stay and one big one lower down. The big one has a steel pinthat goes through the swinging part and locates in the top bracket held by the two small bolts, this pivot also gets corroded and the pin pluss hole in the swinging bracket need thourough cleaning and copperslipingso they move very freely. The two bolts you ringed are the ones that split the caliper(no fluid will be lost) the 750 started with bolts you have to undo through the wheel spokes but 550/500/400 do not.

Hope that helps, if in doubt of assembly look at parts book

Thanks for the detailed explaination, Bryanj!  I do understand how the piston interacts with the seals, and why the condition you describe could cause trouble.  I'll study the brackets alongside your explanation, as I'm still not sure why the floating caliper should require manual adjustment.  I'll get there, though...

Offline mattsz

  • SOHC Pro
  • Posts: 606
    • View Profile
Re: New (to me!) '77 CB400F - US model
« Reply #41 on: October 26, 2018, 04:28:27 PM »
One of the first things you should buy if you haven't already got some are these.

http://ruggedroads.co.uk/JIS-Screwdriver-Set-Vessel-Megadora-P1-P2-and-P3

A good set of JIS screwdrivers will pay for itself very quickly by not chewing up all those screws on the bike so that you have to buy new ones.

When splitting the caliper be prepared for some real gross looking fluid coming out, I suspect the fluid hasn't been changed since it left Japan.

As for the speedo drive screw, it's clear someone has already attempted to remove it by using a punch, they may have succeeded and just reused the screw, try lightly tapping the screw with a punch and hammer counter clockwise using the existing punch mark and see if it starts to spin out, if your lucky it will.

Thanks, I'll look for some.  Does anyone know if the two "cross-head" screw driver shanks in the OEM tool kit are JIS-friendly?

Offline K2-K6

  • Grogu
  • *
  • Posts: 5234
    • View Profile
Re: New (to me!) '77 CB400F - US model
« Reply #42 on: October 26, 2018, 05:14:07 PM »
These calipers are a bit of a hybrid between manual and hydraulic.

The hydraulic,  obvious as indicated.  The back side hasn't a hydraulic retraction, just done by the little spring until the caliper swing hits the stop screw.  So you set stop screw to give clearance required,  but as the back pad wears you have to "chase " it with adjustment else the pad ends up with too much clearance,  and so increases brake lever travel just to bring pads into contact with disc.

That back part is in essence the same as any cable operated brake.

Offline mattsz

  • SOHC Pro
  • Posts: 606
    • View Profile
Re: New (to me!) '77 CB400F - US model
« Reply #43 on: October 26, 2018, 05:45:50 PM »
These calipers are a bit of a hybrid between manual and hydraulic.

The hydraulic,  obvious as indicated.  The back side hasn't a hydraulic retraction, just done by the little spring until the caliper swing hits the stop screw.  So you set stop screw to give clearance required,  but as the back pad wears you have to "chase " it with adjustment else the pad ends up with too much clearance,  and so increases brake lever travel just to bring pads into contact with disc.

That back part is in essence the same as any cable operated brake.

So... if everything is working correctly, the adjustment doesn't change how the pads wear relative to each other, just brake lever travel?  I suppose so, but doesn't the piston's movement relative to the seal affect this, too?  Why not just have no spring and no adjustment - let the caliper slide freely and the piston, on one side only, will take up any adjustment needed, like my "modern" bike's caliper?

Offline K2-K6

  • Grogu
  • *
  • Posts: 5234
    • View Profile
Re: New (to me!) '77 CB400F - US model
« Reply #44 on: October 26, 2018, 06:29:55 PM »
Yes,  as you think,  it doesn't affect the wear as that is only the hydraulic force clamping it. And also same forces as the modern ""sliding " single piston type.

It is a bit cock-eyed though (in purist engineering principles) as they've started with a swing geometry so the pads will ultimately wear in a taper, then felt the need to give some sort of assistance plus limit to the assembly. Compared to the straight up design within the engine it does appear to be an odd compromise.


 

SimplePortal 2.3.5 © 2008-2012, SimplePortal