Topic: 1972 CB750 Four K2 -- Rebuilt to NEW OLD STOCK -- PIX ON PAGE 50

[edwardmorris]

All three points check out, still won't go on

[jerry h]

If I'm looking at the pics correctly,  maybe you need to rotate the front rubbers, so the carbs angle down a little more in the rear?.... so the airbox rubbers sit fully on the carbs at both the top and bottom...  if this makes any sense. 

[evanphi]

If I'm looking at the pics correctly,  maybe you need to rotate the front rubbers, so the carbs angle down a little more in the rear?.... so the airbox rubbers sit fully on the carbs at both the top and bottom...  if this makes any sense. 

This is what I suggested in my previous post.

Hmmm... I always have the clamps on my rubbers when installing, then I lightly tighten them and use the band to scoot the rubber the last bit of the way on.

[edwardmorris]

Thanks guys, I did have to rotate them when installing to line up the carbs. I'll be pulling them off tonight and trying again, will turn them some more towards the center like Evan suggested and see if it helps. There are two things I forgot anyway in my hurry, doing the idle screw adjustment and installing the Franken Finserts

[edwardmorris]

Had very little time last night so I installed the levers. Torqued up the brake line banjos to 15ft-lbs and started the bleeding process but at a very puzzling dead end. Lines, bolts and crush washers are all new as posted earlier, but for some reason the fluid isn't making it to the second hose. The middle junction is clean. A whole bunch of bubbles came out as expected but that stopped too quickly so I got suspicious. Pulled out the end at the caliper and its dry as a bone, so for somehow the fluid isn't making it down all the way. I tapped the upper line a bit and just a few more bubbles came out then stopped again. Now every time I pump the brake, I can see the fluid move but no bubbles, and most definitely no braking   What am I messing up here?

[calj737]

is the bleeder screw open at the caliper?

[edwardmorris]

is the bleeder screw open at the caliper?

It is. I had the lower line disconnected at the caliper to see if there's any fluid coming through and there was none, the lower line is bone dry.

[calj737]

and if you tie back the handle, caliper line disconnected and draining safely into a bucket, what happens after a few minutes? The level in the reservoir should drop and fluid should begin to creep out of the lower line.

[edwardmorris]

and if you tie back the handle, caliper line disconnected and draining safely into a bucket, what happens after a few minutes? The level in the reservoir should drop and fluid should begin to creep out of the lower line.

That was basically what I tried, leaving it sit, or pumping it through there's no diff, could it be that big of an air lock? Or worse a blocked line?

[oldhatt45]

Rafi,
When I bled my front brake down after the rebuild of master, caliper and New Brake lines, I had to pump the brake lever probably 30 - 40 times before I started getting brake fluid out.  Once I started getting fluid out I gave it a few more pumps for good measure before locking up the caliper bleeder.  LOL
While doing the pumping, I added fluid once to refill the master cylinder.
After getting fluid at the bleeder, I tied the brake lever back half way, and came back the next day, and the brake worked fine.  Total engagement at between 1/3 and 1/2 of travel.
The pumping was done very slowly so I got no back splash with the cap on to start and then after getting fluid, with the cap off. 
The bubbles I got were really, really tiny.
I also turned the bars all the way to the left to make sure the master was the absolute highest point of the system.

One other little thing.  When you rebuilt the master, the rubber seal that mounts on the piston, did you put it on in the right direction???  and slid it over the metal lip???  I had to look at that assembly a couple of times to make sure it was on there correctly.

Hope this at least gives you some ideas,

Charlie

[jerry h]

Quote from: jerry h on May 26, 2015, 11:49:45 PM

    If I'm looking at the pics correctly,  maybe you need to rotate the front rubbers, so the carbs angle down a little more in the rear?.... so the airbox rubbers sit fully on the carbs at both the top and bottom...  if this makes any sense. 


This is what I suggested in my previous post.

Sorry Evanphi - your correct.  I was doing a quick before bed SOHC forum scan and missed your advice in the previous post.

[edwardmorris]

Air box and Carbs: No amount of adjusting the boot orientation is aiding with the air box boots slipping on all the way, but came pretty damn close. 1 and 4 are on fully, 2 and 3 are on fully but still show a tiny lip on the carb side. Once clamps are tightened down, it looks air tight.

The front brake: Big thanks to Dave Z for walking me through a few things and some pointers. No matter what there was no fluid moving. I tried Dave's idea of using a vacuum bleeding pump and that damn thing was just holding the vacuum steady So I figured fluid isn't leaving the master cyl at all. Took off the top banjo and sure enough, dry as a bone. It seems to me that the rubber piece that goes on the broad end of the spring was somehow bent all funny. I think its a check valve of sorts. I wiggled it a little with a fine blunt drift and heard a "plop" as if something just fell into place and the fluid started gushing out. Tied it all back together, used the vacuum pump and it was so ridiculously strong, it drained the master through the lines , nothing but air. Started over with a full cyl and only gently pumping till I saw it reach the other end.

So now, I have fluid through the lines but still no braking. The pad hasn't moved through all this. Tried bleeding it the old fashioned way and still spongy as hell Quit before I did something regrettable out of frustration.

[danyo]

Few days ago I found on the forum nice trick. Fill caliper with brake fluid, install piston and push it slowly into caliper (watch for fluid level in MC). This will push the air up through the lines leaving you with clear fluid. After that I had my brakes back without bleeding. I understand that your caliper is already assembled so its different story but if you don't want to pump lever gazillion times you can try this.

[Davez134]

So, glad you got fluid through the lines! After getting fluid through with vacuum pump, that just means lines are filled with fluid, but without pumping brake lever afterwards the piston will not move. I'm assuming you squeezed lever in between pulling fluid through, but it must be done a couple times. Also, if you did not replace crush washer with a new one after removing the banjo bolt from master cylinder, it is probably sucking air in

[edwardmorris]

Thanks guys, ordered some new crush washers and a spare rebuild kit. For peace of mind, I'm going to redo the master as now my mind it clouded with doubt that I didn't do it right. While I wait, I think I'll get the wiring started, hopefully tonight if I'm not drafted for night shifts. Any pointers for installing the main harness, especially any gotchas?

[evanphi]

Thanks guys, ordered some new crush washers and a spare rebuild kit. For peace of mind, I'm going to redo the master as now my mind it clouded with doubt that I didn't do it right. While I wait, I think I'll get the wiring started, hopefully tonight if I'm not drafted for night shifts. Any pointers for installing the main harness, especially any gotchas?

Harness ground attaches to the horizontal bolt for the seat latch. PO messed with mine so it goes right to the battery (-)! Make sure it is bare metal, and same goes for the big grounding wire from the battery.

[Restoration Fan]

You're going to find that a good portion (maybe 70% or so) of the wiring goes REALLY fast.  That's because you'll have a connector and you look at it and there are 6 slots but only five are taken up...with the missing one in the bottom center.  Then you look at the wires coming from the battery box and there's only one that matches up to that.  Snap, click.  That one's done.

Even in the headlight where all the rat's nest goes, you'll find the same kind of deal.  It's the loose wires that you have to take the time with.

Here's what worked for us:  take the time to print out 2 copies of your wiring diagram...as big as you can get them.  On one of them, every time you connect something, take a highlighter and highlight those wires on one of the diagrams.  That way you will know what's left to be done when you get deep into the process.

Also, if you'll look at the diagram, you will notice "OK...there are 4 wires coming in here...looks like they come from...ok, they come from the ignition switch and they should be color a, b, c, and d."  So you go find that bundle coming from the ignition switch and trace the bundle into the headlight...then you locate those 4 wires you're looking for.  Then you find the other four that they should match up to coming out of the bundle...connect them...mark them with the highlighter on the diagram and voila...four more wires taken care of.  It really is as simple as matching color to color when you break it down like that.

One last thing.  We didn't do it but I think it would have been easier had we done so.  We went ahead and poked all the wiring bundles (from the rear brake, from the clutch, from the ignition, etc) into the hole to get them all into the wiring harness before we started to connect them.  I think it might have been easier had we left them outside the headlight and just originally pushed the wiring harness bundle through.  Then, do one "system" or bundle at a time.  In other words, poke the bundle through from the front brake.  Find those on your diagram...match up those wires and mark them off your sheet.  Once you're finished with one set of wires, poke the next one through and continue the process for that group.  Otherwise, you end up with a whole bunch of loose wires and makes it a bit more difficult to trace the origins.

[edwardmorris]

Thanks for the pointers Ron, I have a flash file for the wiring with show/hide buttons for individual systems, so I was planing on having my laptop with me (sorta similar to marking off done connections).

Harness ground attaches to the horizontal bolt for the seat latch. PO messed with mine so it goes right to the battery (-)! Make sure it is bare metal, and same goes for the big grounding wire from the battery.

I knew about the grounding contact at the seat latch, but didn't think about the negative cable one. I thought that was only grounding the engine Looked it up in the Phaedrus log, I'll be removing that long bolt and scraping the powder off.

http://forums.sohc4.net/index.php/topic,36459.msg1105352.html#msg1105352

Which brings up the next question, is dielectric grease good to use to keep things from rusting at these points without hurting connectivity?

[evanphi]

Which brings up the next question, is dielectric grease good to use to keep things from rusting at these points without hurting connectivity?

From what I understand, that is exactly what DGrease is for... keeps the elements away without changing conductivity.

[edwardmorris]

 
http://forums.sohc4.net/index.php/topic,148265.0.html

[edwardmorris]

Well, the brake is finally working at least when parked. Cleaned up the master, sooooooo glad I had it powder coated (Thanks Marc!) because this this was soaked in brake fluid when I rebuilt it a second time. Not a spot affected  But the caliper didn't fare as well, will need a touch up job around the bleeder.

Installed this pesky little rebound damper rubber.

Zinced up retainer for it, I'd have had it chromed along with the pivot bolt, but I didn't get the correct master until much later in my build (Thanks Nick!).

[edwardmorris]

New washers for the rear axle and swingarm pivot bolt, they were both missing on the bike.

Finished up with the drain hoses, gotta straighten the out some more. Redid the greasing on the swingarm following the steps described by Mark/Hondaman.

Cleaned and sealed up the valve train cover with White Diamond while I could still get to it easily.

[edwardmorris]

New hardware for the ignition bracket along with rezinced collar. This piece is how I met Billy B, he responded to my wanted ad when I was new

Added extra sheathing to the neutral switch wire as it takes so much crap from the chain.

Adjusted the throttle cables, then installed the Gordon Frame Kit  This is such a convenience, basically a requirement for these bikes, so if you're still debating, just get it!

[Restoration Fan]

I so love mornings when I get up and you have posted additions to this thread.  Watching this bike come back together is truly like watching time in reverse.  This bike is going to be a show piece, it's going to be so beautiful.

[Bill/BentON Racing]