Topic: '78 750 F - bolt-on rear master?

[Patrick]

I tore down Frankenbike this week. I'm going to get some paint on the frame and get the suspension right before I transplant in its new heart: a K2 750 motor. The rest will be F3 - side cases, tank, carbs (good idea?), except for the fork tubes, sliders and calipers that come from a 81 or later DOHC 750. The fenders and some body work will be from some other 750s within that late 70s to early 80s half decade or so, but I haven't actually pinpointed the year for each.

When I took the master cylinders off I knew I had a problem. These masters are solid. As in they will never move freely again. I didn't think that parts from a low mileage bike stored indoors could rust to deeply. Of course, as the F3 motor is frozen I should have had at least one good clue to work with.

Since actual masters and calipers from these late F bikes are pretty rare I was hoping someone could offer bolt on replacement masters from other models. I am pretty confident others have faced this before, with the relative rarity of the F bikes and all. I would refer Honda stuff, but I'm open to suggestions. The front is not an issue as any master designed to drive two dual piston calipers that mount 7/8 bars will work, how about the rear master? Also, does anyone if all Goldwings use 7/8 bars? I know early ones did, but I know nothing of later model Goldwings.   

Thanks in advance for any help.

Patrick   

[bubbafun101]

I just fitted a GL1100 rear caliper and master cylinder with remote reservoir to a 76 F. The hozzel ( axle hole) is about 10 mm narrower ( side to side) than a stock 750 caliper. so you will have to cut new spacers, but its very doable. It took me about 2 hours, and trust me I am no kind of bike expert.
Good luck

[Patrick]

So the master is a bolt on then? I looked at pictures online and the master looked very similar and the rebuild kit is the same, but I couldn't tell whether the mounting holes were proportional. Sometimes it looks like it will work, but then doesn't quite line up or sit right.

That's very helpful. At this point I'm assuming my calipers can be restored. Won't know until I have a working master.

Patrick

[jtb]

I think there's a rear brake ass'y on ebay right now.  There are always front masters.

[Wayne Meuir]

Has anyone tried to install one of the dual piston rear calipers/master cyl from a DOHC, like a CBX or CB100 circa 79-82.  They look to be close to the original dimension and you get the benefit of a dual piston caliper.

Wayne

[Geeto67]

why not rebuild it? the master cylinder itself is aluminum and you can get a kit from honda to rebuild the entire thing (I am staring at one on my desk as I type this).

I run 1982 cb750F brakes on one of my 78 cb750Fs. Bolts right on as long as you have all the mounting brackets from the later bike. I used the master from the 78 however as that was already bolted to the bike and had been rebuilt recently. Works so much better.

[Patrick]

Rebuilding is my first choice, G, but I am not optimistic about this rear master. The bottom of the master is a mass of rust. I am having difficulty even finding a ring or a clip to remove to pull the innards from the cylinder. Buying a used master is often no cheaper than rebuilding a used master, since I have often found I needed to rebuild them anyway. In this case rebuilding may not be an option.

Patrick

[Jerry Rxman Griffin aka MuthaF'er]

The dual piston calipers are nice, too nice perhaps. Mine locks the rear wheel in a heart beat! I can see the advantage for riding 2 up but the lock up issue from the 75/76 F is probably why they went to the single piston on your model. The 77/78 master cylinder does show up fairly often on EBay. Getting the correct part sure makes life easy rather than trying to adapt one. Just ask the right questions before buying, check the number of sales the seller has had, then check his feedback. 

[78 k550]

Just ask the right questions before buying,

I might have an extra.
pm me I'll check on sunday. Are you in a rush?

Paul

[Patrick]

No rush, Paul. PM sent.

Patrick