Topic: '78 750F Inline Hydraulic Pressure Brake Line Switch

[wildxcard]

Hello.

I am a new 1978 CB750F owner and a novice wrencher. One of the first issues I want to tackle is the front brake. When I first bought the bike the front brake didn't work, but it didn't take long to figure out why:
https://i.imgur.com/AIP6WT6.jpg (also seen in attachment 1)

I used Partzilla to look up the OEM part number for the front brake master cylinder (BMC)
https://www.partzilla.com/catalog/honda/motorcycle/1978/cb750f-a-750-super-sport/front-master-cylinder

From the image, I could see that what was on the bike when I bought it was not original so I was kind of excited to replace it with something more stock looking. A quick search of the OEM part number (45500-410-671) directed me to a few different sites including this listing:
https://www.ebay.com/itm/HONDA-CB750-CB550-Front-Brake-Master-Cylinder-CB-550-500-450-400-5-8-16mm-NEW/230816517066

I guess I liked the seller's enthusiasm and in his description, he wrote "CB's have an inline hydraulic pressure switch hooked up to their brake line." (Foolishly?) Assuming that the brake switch wiring for the BMC that was on my bike was added due to maybe a lack of availability of parts that could take advantage of the "inline hydraulic pressure switch", I bought one.

It has since arrived, but the more I research and think about it, the less this "inline hydraulic pressure switch" thing makes sense. Can anyone explain what is going on here?

I have since looked at a couple of other replacements that have, what looks like, some kind of wiring post on the bottom:
https://www.ebay.com/itm/322709704602?ul_noapp=true
https://www.vintagecb750.com/parts/480/08-0253.jpg

I would like to find a replacement that is as close to OEM as possible, would I be able to integrate the stock wiring into the bolts on the bottom of these BMCs?

Additionally, I'm not even sure that the brake line from the BMC to the joint assembly is right:
https://i.imgur.com/iYZRlXa.jpg (also seen in attachment 2)
https://i.imgur.com/ygHsQVJ.jpg (also seen in attachment 3)

The fitting is bent maybe 15°, and the whole hose is 90° off from fitting nicely. I can make it work but the hose doesn't seem like it is built to be twisted that way.

Any advice in on any of my issues, big or small would be so very much appreciated

[enwri]

No. 2 in this diagram is where my inline pressure switch is. My k7 tee piece is slightly different, only having one disc. Bolted to the lower fork yoke. Another hose from there to the caliper.

https://www.partzilla.com/catalog/honda/motorcycle/1978/cb750f-a-750-super-sport/front-master-cylinder

[bryanj]

I am not 100%sure but i think the F2 has a small switch under the master to work the brake light and not the pressure switch in the line. Here in UK you can get a banjo bolt that incorporates a pressure switch as you have already laid out for a master.
When trawling for parts remember the F2/3(78/79) are very different from earlier modles so you need to be certain of your bikes heritage

[wildxcard]

No. 2 in this diagram is where my inline pressure switch is. My k7 tee piece is slightly different, only having one disc. Bolted to the lower fork yoke. Another hose from there to the caliper.

https://www.partzilla.com/catalog/honda/motorcycle/1978/cb750f-a-750-super-sport/front-master-cylinder

Hey enwri, thanks for the feedback. I think No. 2 on my bike is right, or at least its all hooked up and seems right for now.

My concern is about my No. 3, Hose A, the line from the Three Way Joint Assembly (No. 2) up to the Brake Master Cylinder. It seems twisted in a way that it wouldn't like a hook up to a more traditional BMC.

[wildxcard]

I am not 100%sure but i think the F2 has a small switch under the master to work the brake light and not the pressure switch in the line. Here in UK you can get a banjo bolt that incorporates a pressure switch as you have already laid out for a master.
When trawling for parts remember the F2/3(78/79) are very different from earlier modles so you need to be certain of your bikes heritage

Hi bryanj, I really appreciate your thoughts. The brake master cylinder that was on the bike when I bought it does have the small switch you are talking about.
https://i.imgur.com/0CjPsdW.jpg (Attachment 1)

Is it possible that this BMC, with the rectangular reservoir, was OEM?
https://i.imgur.com/yJwjf6E.jpg (Attachment 2)

When shopping for new BMCs I have seen banjo bolts offered that incorporate a pressure switch, I am just very confused buy how switching out the banjo bolt that attaches the brake line (No. 3) to the BMC would activate a brake light system. And if it is that easy, why was the wiring and the switch used in the first place?

Scratch the second part, as this is a crash course, I am learning things by the minute. I pulled up one of the aftermarket banjo bolts
https://www.ebay.com/itm/Hydraulic-Banjo-Bolt-Brake-Switch-HONDA-Yamaha-Kawasaki-10mm-x-M1-25/230795918444
and i think I understand how it works now. For any other clueless armatures that stumble upon this post, this bolt (linked above) replaces the stock bolt and then the brake electrical lines plug into it.

This doesn't answer my question about the BMC with the rectangular reservoir being OEM though, any thoughts on that?
And if not are are you aware of any BMCs out there with round reservoirs that could accept the switch shown in attachment 2?

Thanks again for your feedback and for any future help.

[Scott S]

No. 2 in this diagram is where my inline pressure switch is. My k7 tee piece is slightly different, only having one disc. Bolted to the lower fork yoke. Another hose from there to the caliper.

https://www.partzilla.com/catalog/honda/motorcycle/1978/cb750f-a-750-super-sport/front-master-cylinder

 #1 in that diagram is the brake switch.

 I'm not aware of any round style BMC that has the switch, though I really haven't looked.
 Just use the banjo bolt brake switch you bought with the round master cylinder.

 And consider replacing those old rubber hoses!
 Find a hydraulic supply shop near you. Take in the old houses and they can make new ones, either in rubber or braided stainless.

[bryanj]

The F2 should have a round master with seperate switch underneath, middle number 410.
The rectangular one is probably from a 750/900 DOHC

[wildxcard]

No. 2 in this diagram is where my inline pressure switch is. My k7 tee piece is slightly different, only having one disc. Bolted to the lower fork yoke. Another hose from there to the caliper.

https://www.partzilla.com/catalog/honda/motorcycle/1978/cb750f-a-750-super-sport/front-master-cylinder

 #1 in that diagram is the brake switch.

 I'm not aware of any round style BMC that has the switch, though I really haven't looked.
 Just use the banjo bolt brake switch you bought with the round master cylinder.

 And consider replacing those old rubber hoses!
 Find a hydraulic supply shop near you. Take in the old houses and they can make new ones, either in rubber or braided stainless.

Thanks for the advice, Scott. I'll look for a shop to freshen up the hoses

[1976cb750f836]

I have a 78F, front end on my 76F bike. My switch is under the master. I would Highly recommend a different than stock master(they feel like pulling on wood). I use a square cap master similar to the 1 in top pic, it has a smaller bore, and gives Way Better feel , and more stopping power. It's off a stock Suzuki 1981 gs750, bought off eBay for around 30$  . It's a great improvement over the stock front brakes. I've done this mod to several Honda 750s, and 1 goldwing. And it comes with the switch mounted under the master.

[Bankerdanny]

The in-line pressure switch is correct for the 550 and the F0 and F1 with single disk front brakes, the twin disk switched to a different splitter and moved the brake light switch to a mechanical type attached to the underside of the lever with a screw.

If you don't mind spending some extra money (and non-original look), I would upgrade to a modern radial style. I installed a Nissin brand 5/8" piston (the size recommended by multiple sources for the Goldwings and CB750F models with twin front disk brakes). They run about $130. It was money well spent in my opinion. You then need to adapt the wiring slightly by adding narrow female spade terminals to the wires that run to the switch so they can be plugged into the switch on the replacement lever.

If you are OK with the MC you bought you can also buy a banjo bolt with the pressure switch built in that you can use either at the master or down at the splitter.

[1976cb750f836]

The in-line pressure switch is correct for the 550 and the F0 and F1 with single disk front brakes, the twin disk switched to a different splitter and moved the brake light switch to a mechanical type attached to the underside of the lever with a screw.

If you don't mind spending some extra money (and non-original look), I would upgrade to a modern radial style. I installed a Nissin brand 5/8" piston (the size recommended by multiple sources for the Goldwings and CB750F models with twin front disk brakes). They run about $130. It was money well spent in my opinion. You then need to adapt the wiring slightly by adding narrow female spade terminals to the wires that run to the switch so they can be plugged into the switch on the replacement lever.

If you are OK with the MC you bought you can also buy a banjo bolt with the pressure switch built in that you can use either at the master or down at the splitter.

That's similar to the gs master, 15mm I think, and only 30$  I had to mod wire ends also.
Do u agree, way better brakes?

[Bankerdanny]

The in-line pressure switch is correct for the 550 and the F0 and F1 with single disk front brakes, the twin disk switched to a different splitter and moved the brake light switch to a mechanical type attached to the underside of the lever with a screw.

If you don't mind spending some extra money (and non-original look), I would upgrade to a modern radial style. I installed a Nissin brand 5/8" piston (the size recommended by multiple sources for the Goldwings and CB750F models with twin front disk brakes). They run about $130. It was money well spent in my opinion. You then need to adapt the wiring slightly by adding narrow female spade terminals to the wires that run to the switch so they can be plugged into the switch on the replacement lever.

If you are OK with the MC you bought you can also buy a banjo bolt with the pressure switch built in that you can use either at the master or down at the splitter.

That's similar to the gs master, 15mm I think, and only 30$  I had to mod wire ends also.
Do u agree, way better brakes?

it's hard for me to comment on the master alone since in my case I was coming from a stock single disk setup and I also had the rotors modified and added braided lines. I do think the overall package is a substantial improvement, but I don't know how much was from the master alone. I do appreciate the adjustable lever very much.