Topic: CB750 F Word 3

[seanbarney41]

I don't know about this thing.  I have been dicking around with it, off and on, for almost a year now.  Hopefully I am starting to win.  But it has not been cooperative.


Picked it up on a tip from a buddy for $425, very complete, relatively un-molested(at least 'til I got ahold of it), title, engine turned out to be stuck from setting.  I used the ATF/Acetone trick and had it unstuck within' a few days.  I grabbed up this seat from member 736cc early on...I dig the vintage Superbike style of it.

Another early mod, were these Renthal bars...rejects from a dirt bike racing friend of a friend.  Love how they feel sitting in the shop going vroom vroom...about 18,000mi showing on the clock.

[seanbarney41]

The bike came with the stock header on it, but in place of the stock muffler was a rusty, mashed up Supertrapp that was just kinda smashed onto the end.


 I pulled that off and put this old MAC on instead.  I don't know if it will stay.  Depends on if anything better comes along for cheap.  If it does stay, it will get repainted.


Note the above condition of the back tire...the po actually told me that he had been using this bike for "doing burnouts at my parties"...and I still bought it.

[Stev-o]

Subscribed, great deal at 425.  Will it be your race bike?  Already has a slick.

[seanbarney41]

Lol Steve-0...interesting enough that back tire works better than the visibly intact but un-round front, after "extensive" road testing.     ....Back to the story...So I cleaned the tank.  Tip for other f bike guys; don't put a bunch of nuts and bolts in these tanks to shake around to help in the cleaning process, because that recessed filler is going to prevent you from getting them all out again.  Maybe this bike will be named "the Rattler" .  I spent a lot of time cleaning and rebuilding the PD42's...and that is what fueled the first start up.  But I still can't get the thing to idle or run worth a #$%* with 'em.  So. I slapped an old spare set of unidentified round tops on there and she purrs like the proverbial kitten.

As you can see, fuel line routing and petcock clearance is a problem and something must be done.

[seanbarney41]

Next, I got to work on the brakes.  The front master cylinder was non-existent, so I am attempting to use this spare, of probably Chinese manufacture.  I have several early k masters that I could use but am assuming there must be some internal difference to go with the dual disks and floating calipers.

The rear master cylinder's internals had turned to a solid mass of rust colored mud...seriously.  I discovered that f2/3 rear masters are seemingly rare, and very expensive if found.  I ended up buying a gl1000 master on ebay in working condition for $80.  It bolts right up, only needing a brake line adapter to function.  I did spring for all new brake lines from Pampadori and he had the adapter as well.

 I overhauled the front calipers, called 'em good, but ended up having to replace the piston seals and one leaky bleeder screw.  These brakes seem impossible to bleed in any normal way I have found.  The only method that has got any results, is to strap the handle to the bars and let it sit that way for about a week.

Lots of broken brake work images...

[seanbarney41]

Currently working on the headlight dimmer switch, in an effort for road worthiness by spring...yes it will get new tires, chain and sprockets.  I'm not buying the expensive stuff until I know this thing can go.  If it makes it through the summer, maybe I will make it pretty, or at least clean it!

[70CB750]

Subscribed.

[dlhoulton]

Subscribed. Currently working on restoring/rebuilding same bike. Will be following to see how your work go's.

[calj737]

Sean - if you're using a brake line between the front calipers to balance the pressure, then the best method for bleeding is to start on the left side. Bleed it entirely, them move to the right. If you were switching back and forth, you'll be there for a VERY long time.

The fluid runs to the primary caliper first (duh, hence the name primary) then is routed to the secondary. This provides "some" measure of redundancy should one caliper fail; you'd still have braking.

Forgive me if you already knew this and followed this method. But I've seen lots of people not correctly bleed dual brakes and spend a week trying to get them pressurized properly.

[SOHC Digger]

The master on the F has a different piston diameter than the K's.

Also, the hex head bolt on top of the junction block will let you bleed the block. I fought my front brakes for a long time. Then I bleed that block and everything went smoother.

[slikwilli420]

Now that we both have projects going, we really need to get together and talk shop. I live in Portage right off Westnedge.

[KayOne]

I would kill for a F3.

[martin99]

I'm on my third F3 (well, F2 over here). First one was a banana yellow hardtail chop, back in the eighties. Second was the one in my avatar, which received quite a few cosmetic changes. Total wreck when I bought it. Was never sure if I liked the F tank, so fitted a K7 one and built a seat unit to suit. Ran with S&B pods and Marshall 4 into 1. I always felt this gave me the best of both worlds - the extra grunt of the F motor with the K stylie look which I preferred. Of all the bikes I've owned over the years I've never regretted selling one as much as that one. Last year I bought F2 #3. It's gonna be a keeper whatever happens, and cosmetically will get similar treatment to my old one. I'll be tucking away all the original parts though, prices are beginning to climb for a good one.

I was never able to bleed the fronts from the calipers, always did it at the lever. Half a dozen pulls on the lever, hold tight to the grip on pull #6. Wait ten seconds, and repeat. Eventually got a good brake after about ten minutes.

[seanbarney41]

Sean - if you're using a brake line between the front calipers to balance the pressure, then the best method for bleeding is to start on the left side. Bleed it entirely, them move to the right. If you were switching back and forth, you'll be there for a VERY long time.[/qote]I am using the stock brake line set-up, please explain what line between the calipers you are talking about

The fluid runs to the primary caliper first (duh, hence the name primary) then is routed to the secondary. This provides "some" measure of redundancy should one caliper fail; you'd still have braking.[/quote]  Which caliper is primary?  I don't see any reason why the fluid would choose one caliper over the other after the splitter.
[/quote]
Forgive me if you already knew this and followed this method. But I've seen lots of people not correctly bleed dual brakes and spend a week trying to get them pressurized properly.
[/quote]please explain in more detail...I have already spent a week bleeding!



Calj, I hope you can sort out this post.  I got the quotes all screwed up.

[seanbarney41]

The master on the F has a different piston diameter than the K's.

Also, the hex head bolt on top of the junction block will let you bleed the block. I fought my front brakes for a long time. Then I bleed that block and everything went smoother.

That's what I figured on the master, but what diameter piston should I be using?  I did find that bleeder on top of the junction and it did help move fluid down to the calipers

[seanbarney41]

Now that we both have projects going, we really need to get together and talk shop. I live in Portage right off Westnedge.

That's pretty funny Willi.  I bought this bike in Portage, right off Westnedge!  Yeah, I wanna come drool on the sweet parts you are using(weber, webers, webers...)  I got projects on the go non-stop, but have not been doing project threads because of a crappy 'puter that would only run in safe mode.  Thats all fixed now.  ...semi recent pick of my shop that I share with some other heads...

[seanbarney41]

I would kill for a F3.

please don't do that...you could simply make me an offer for this one, I do kinda like it, but it really has not been cooperating

[seanbarney41]

I was never able to bleed the fronts from the calipers, always did it at the lever. Half a dozen pulls on the lever, hold tight to the grip on pull #6. Wait ten seconds, and repeat. Eventually got a good brake after about ten minutes.

that's a new technique I have never heard of.  I will have to try it.  I like the f tank shape and paint scheme just fine.  77/78k?  el blecho!!! vomit-o-rama!

[calj737]

Sean - left side is Primary.

You asked "Why choose one over the other...?" A explained to me, the routing is from MC to the left side caliper, then to the balance line, then to the right side caliper.

If the left caliper is pressurized, the "air" is then trapped between the right caliper and the left caliper, in the balance line. By bleeding from the right you draw the air to the right, through the right side caliper and out of the system.

Hope that helps-

[seanbarney41]

Sean - left side is Primary.

You asked "Why choose one over the other...?" A explained to me, the routing is from MC to the left side caliper, then to the balance line, then to the right side caliper.

If the left caliper is pressurized, the "air" is then trapped between the right caliper and the left caliper, in the balance line. By bleeding from the right you draw the air to the right, through the right side caliper and out of the system.

Hope that helps-

where is this "balance line" you speak of?  My lines go from mc to splitter, splitter has two equal length lines to each caliper...are you calling left facing the front of the bike?, or from the riders seat?

[Jerilee]

Subscribed! The F3 was my first bike, and first CB750, I did a lot of the same things that first summer!  It was the same color and condition too, I got a little heartsick there when I saw the first pics, nostalgia! 

I'm building an F2 now, but from the frame up. Good luck with your refresh!

[calj737]

Left side as described is from the seated position looking forward.

I am describing the splitter as the balance line. Is your splitter mounted to the frame, behind the head stock? Another method for bleeding dual brakes is to open the bleeder valves, depress the brake lever and keep it "tied" to handle bar. Keep filling MC. Fluid pressure should force the air out as gravity and pressure behind the fluid works it's magic.

I don't personally care for that method, but I've seen others use it. I do it caliper by caliper for assured results.

[MoMo]

subscription entered.    Left is sitting on the bike,  start at the MC, then bleed left and  lastly the right

[seanbarney41]

MoMo, that's what I did.....for the second half of the week.  It really seems like those calipers have some kinda air trapping pocket and the only thing that is gonna get it out is lengthy time.  I have gotten it so that one or two squeezes gets me some brake.

[Stev-o]

Hey Sean - have you considered a power bleeder?  I'm having an issue bleeding the frt brake on my RD, so I recently bought one like this.  Have not tried it yet.


http://www.ebay.com/itm/One-Man-Brake-Bleeder-4-Bleeder-Cap-Screw-Covers-and-Flush-Kit-/271382646838?pt=Motors_Automotive_Tools&hash=item3f2faa9036