Topic: 1975 cb750f rear master cylinder

[sixthwisconsin]

Can't seem to find a rebuild kit for the rear master cylinder. Honda OEM is listed as unavailable and aftermarket does not seem to exist. Anybody have any suggestions?

Your help is appreciated.

[Powderman]

You're not looking hard enough or at all. I found this on Ebay:
http://www.ebay.com/itm/Honda-750-NOS-Rear-Brake-Master-Cylinder-Kit-1975-1976-CB750F-43510-392-305-/221215399354

[sixthwisconsin]

Powderman,
While I appreciate your post, I am not looking for someone charging twice MSRP for an NOS kit on ebay. Nice to know its there though. $80, really? I hope it doesn't come to that and I really doubt it will.

Was really looking for info on aftermarket kits or insight as to when NOS became unavailable. I searched  ALL saved links of reputable dealers for NOS or aftermarket and that is an extensive list. Let me know if you found anybody willing to sell at a reasonable price.

[sixthwisconsin]

Cross checking the GL1000, I found 43510-371-305 available for $39. Same rebuild kit?

[Powderman]

If you read your post you said you couldn't find one. I found one so didn't go any further on advising you to just Google the part # and you will find all the options for locating that part# no matter what bike it is for. Next time be more specific that you couldn't find a reasonable price one, not that you couldn't find one at all. Sometime owning a vintage bike gives you no choice but to get reamed for NOS parts.

[BeSeeingYou]

Cross checking the GL1000, I found 43510-371-305 available for $39. Same rebuild kit?

I strongly suspect it is.  The MC and caliper are nearly identical though the GL caliper mounts on the left side.  The only difference in the MC is the F takes a banjo and the GL takes a flair fitting on the outlet port.  When my F1 MC was locked up I researched this as best I could and planned on using a GL 1000 MC as a replacement but at the last minute I was able to salvage mine and get a F0/1 rebuild kit so I never got the definitive answer.  A few other F0/1 owners have also thought this was a possible fit but I don't know if anyone has actually had to try it. Until recently the rear MC kit was available.  So my advice would be give it a shot...it's only $40 and if it works you can report back to us.  You will earn the gratitude and respect of other F owners and get your bike fixed at the same time...how cool is that.

[seanbarney41]

Sixth, it seems rear masters for all 750f's are pretty scarce.   I was recently needing a new master cylinder for my f3 project bike, as the internals of the one I had turned to one solid blob of rust.  I could not find a working one for less than $120, rebuildable cores were around $80.  I ended up buying a working gl1000 rear master for $80.  It bolted right up and functions properly.  It appears to be identical to what was on the f0/f1 bikes.  The f2/f3 have a remote reservoir, but the f0/f1/gl1000 masters still bolt right up.

oops, Srust has got it, I did have to get an adapter for the brake line.

[sixthwisconsin]

srust, sean,
That is great input!!
I am going to order up the gl1000 OEM kit and will report back here and on my build thread.
Thanks a million!

[Jerry Rxman Griffin aka MuthaF'er]

Cross checking the GL1000, I found 43510-371-305 available for $39. Same rebuild kit?

I strongly suspect it is.  The MC and caliper are nearly identical though the GL caliper mounts on the left side.  The only difference in the MC is the F takes a banjo and the GL takes a flair fitting on the outlet port.  When my F1 MC was locked up I researched this as best I could and planned on using a GL 1000 MC as a replacement but at the last minute I was able to salvage mine and get a F0/1 rebuild kit so I never got the definitive answer.  A few other F0/1 owners have also thought this was a possible fit but I don't know if anyone has actually had to try it. Until recently the rear MC kit was available.  So my advice would be give it a shot...it's only $40 and if it works you can report back to us.  You will earn the gratitude and respect of other F owners and get your bike fixed at the same time...how cool is that.

Steve, et al,

I'm looking at and comparing 2 nos masters. One is a GL and the other is a late 75 750F/76 750F.

3 differences:

The 750F has the hose/banjo exit at an almost 90 degree angle and incorporates a "stop" cast into it to prevent the hose from rotating loose. The GL has the hose exit straight outward.

The GL uses a flair as you say due the fact it has what appears to be a flow restrictor inside the threads presumably to reduce the flow of fluid to prevent rear brake lockup which the F will do in a heartbeat. Not a bad idea! That could probably be removed since it had to be added.

Third, and most important for the sake of THIS discussion is the fact that the threaded rod on the GL kit is about 5 to 6mm longer than the F. Nothing a saw wouldn't overcome or just a simple adjustment of the rod by loosening the lock bolt and screwing that and the end fitting higher onto the threaded rod then retightening both.

In conclusion - buy the -371 GL part and screw the always opportunistic JT Marks and his vulturistic ways. OR buy one from JT while they are available at twice the cost. He knows what he has and prices them accordingly. I bought probably the last NOS -341 speedo in existence from him for $425 but I wanted it BADLY for my less than 1 mile restoration to match the mostly NOS bike and the very nice NOS tach I got from DSS for $80. I justified that purchase by averaging out the cost of the 2. Just depends on the depth of your pockets and the desire to buy a non-existent NOS restoration part.

[BeSeeingYou]

Cross checking the GL1000, I found 43510-371-305 available for $39. Same rebuild kit?

I strongly suspect it is.  The MC and caliper are nearly identical though the GL caliper mounts on the left side.  The only difference in the MC is the F takes a banjo and the GL takes a flair fitting on the outlet port.  When my F1 MC was locked up I researched this as best I could and planned on using a GL 1000 MC as a replacement but at the last minute I was able to salvage mine and get a F0/1 rebuild kit so I never got the definitive answer.  A few other F0/1 owners have also thought this was a possible fit but I don't know if anyone has actually had to try it. Until recently the rear MC kit was available.  So my advice would be give it a shot...it's only $40 and if it works you can report back to us.  You will earn the gratitude and respect of other F owners and get your bike fixed at the same time...how cool is that.

Steve, et al,

I'm looking at and comparing 2 nos masters. One is a GL and the other is a late 75 750F/76 750F.

3 differences:

The 750F has the hose/banjo exit at an almost 90 degree angle and incorporates a "stop" cast into it to prevent the hose from rotating loose. The GL has the hose exit straight outward.

The GL uses a flair as you say due the fact it has what appears to be a flow restrictor inside the threads presumably to reduce the flow of fluid to prevent rear brake lockup which the F will do in a heartbeat. Not a bad idea! That could probably be removed since it had to be added.

Third, and most important for the sake of THIS discussion is the fact that the threaded rod on the GL kit is about 5 to 6mm longer than the F. Nothing a saw wouldn't overcome or just a simple adjustment of the rod by loosening the lock bolt and screwing that and the end fitting higher onto the threaded rod then retightening both.

In conclusion - buy the -371 GL part and screw the always opportunistic JT Marks and his vulturistic ways. OR buy one from JT while they are available at twice the cost. He knows what he has and prices them accordingly. I bought probably the last NOS -341 speedo in existence from him for $425 but I wanted it BADLY for my less than 1 mile restoration to match the mostly NOS bike and the very nice NOS tach I got from DSS for $80. I justified that purchase by averaging out the cost of the 2. Just depends on the depth of your pockets and the desire to buy a non-existent NOS restoration part.

I think the brass/copper? "cone" you are seeing inside the out port is just the other half of the flair fitting.  I don't have one to look at but looking at another caliper from one of my XS650's that have a similar fitting inside the out port the hole in the "cone" is about the same diameter as the ID of the brake line.  Jerry, take a look at the ones you have and see what the hole diameter looks like.  If it looks much smaller than maybe it has some other purpose than just the other half of a seal. My gut feeling on the GL MC is that the out port surface may not be machined as smooth as one designed for a banjo and could have some leak potential.  And like you said it does not have the stop tab to hold the banjo in position.  If using the GL MC I would just get a new brake line with the flair on one end and banjo on the other or maybe a short 90 degree flare fitting if needed for the bend.

[sixthwisconsin]

Great insight, thank you!
I ordered up the 371 kit from SouthSound Honda for $39 and should hopefully have it by the end of the week. I'll post up a comparo of what I took out of the 750f rear master and the new kit.

[sixthwisconsin]

See update on the 371 kit on my build thread.

http://forums.sohc4.net/index.php?topic=101126.new#new

[754]

I may have a couple of cores, one with the metal reservoir, the other is plastic.