CB400A Front Brake Lever Issue

kinorot

kinorot

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Hello!

Recently I got a 1978 CB400A Hondamatic. I am new to fixing motorcycles so please forgive my lack of knowledge and terminology.

As of right now, I think the carburetors and the brakes are the only thing I need to fix to get it running. The left carburetor has a crack on it, which I’m sure can’t be fixed so I’ll need to buy a new set.

Now to the reason I’m here. I was inspecting the right front brake, and wasn’t getting any pressure to the brakes when pulling the lever. I initially thought that the line was clogged, but I found that the piece that the lever actually pushes in and springs back out was stuck pushed in. I got it released and now there’s movement and I’m seeing pressure within the brake reservoir, but the rubber that surrounds the little push piece was rotted and cracked. I’m assuming that this is supposed to be airtight. Is there a replacement for the rubber part that I’m able to buy? Or do I have to buy a whole new front brake lever assembly to replace it?

Any advice would be appreciated! Thanks!
 
Sounds like your master cylinder is doing what most do when they get older, possible have been idle for some time and as they all do, absorbed moisture into the brake fluid that helps turn it into mud. The dirty fluid and inactivity clogs small orifices and the muddy fluid causes the piston (that the lever pushes to create braking pressure) to stick in the bore of the master cylinder body. Here's an exploded view of it all

1784903651140.png

As to your carburetors, before you buy anything you should start a new thread in the SOHC Twins Carburetion section and post a picture of what you believe is damaged so others can help verify.
 
ancientdad said:
Sounds like your master cylinder is doing what most do when they get older, possible have been idle for some time and as they all do, absorbed moisture into the brake fluid that helps turn it into mud. The dirty fluid and inactivity clogs small orifices and the muddy fluid causes the piston (that the lever pushes to create braking pressure) to stick in the bore of the master cylinder body. Here's an exploded view of it all

View attachment 59718

As to your carburetors, before you buy anything you should start a new thread in the SOHC Twins Carburetion section and post a picture of what you believe is damaged so others can help verify.
Click to expand...
Yep. OP should likely just buy a rebuild kit.
 
Thanks for the responses! I will be sure to start a new forum after I get off of work with pictures of the carburetor.

Now to the master cylinder. The piston was stuck, but with some work it released and is now springing back to what it should be. The 1 to 3 left most parts on section 10 of the diagram are the pieces I have an issue with. I guess if I were to decide to keep this master cylinder instead of replacing the whole thing, it would for sure need a full cleaning. I found a new master cylinder a while back on eBay for it, but when I was talking to the seller, asking if it had all of the internals (pistons, springs, etc) or if it was just the “shell” (lever and reservoir). The seller wasn’t any help, just responded with “you get what’s in the pictures” (couldn’t see any details). I’m not sure if I’m allowed to post any eBay links in here to see if any of you guys could spot anything.

I will also take some pictures when I’m home of the master cylinder
 
kinorot said:
Thanks for the responses! I will be sure to start a new forum after I get off of work with pictures of the carburetor.

Now to the master cylinder. The piston was stuck, but with some work it released and is now springing back to what it should be. The 1 to 3 left most parts on section 10 of the diagram are the pieces I have an issue with. I guess if I were to decide to keep this master cylinder instead of replacing the whole thing, it would for sure need a full cleaning. I found a new master cylinder a while back on eBay for it, but when I was talking to the seller, asking if it had all of the internals (pistons, springs, etc) or if it was just the “shell” (lever and reservoir). The seller wasn’t any help, just responded with “you get what’s in the pictures” (couldn’t see any details). I’m not sure if I’m allowed to post any eBay links in here to see if any of you guys could spot anything.

I will also take some pictures when I’m home of the master cylinder
Click to expand...
Ebay links are totally welcome - buying parts on Ebay can be tough without knowing exactly what you're looking at. There's also a very good chance that a part on EBay would also be in the same condition yours is in. There are some decent aftermarket masters that are direct plug and play (just avoid the sub-$40 Amazon crap)

There are also master cylinder rebuild kits that would enable you to replace all the seals and repair the master - to AD's point above they can be a challenge (specifically removing the circlip inside to release the plunger) with about a 25% shot that the bore is corroded and unusable.
 
This isn’t the eBay post I was mentioning earlier, but it is one I just found a bit ago. They say that they’ve identified/taking it off of another Hondamatic. Description says that the plunger is moving, no visible damage, but it is dirty. Would you guys recommend I look into a new master cylinder that’s already been cleaned out? Or is this a viable option, but I clean it out myself without taking it apart?
 
Here’s a decent aftermarket but period correct alternative.

4into1.com

80's Style Honda Complete Brake Master Cylinder

This is a reproduction 80's style Honda brake master cylinder. You can use it on any single or dual disc brake bike you want. Perfect for 80's bikes where you want to replace the bars and need a new master cylinder that doesn't have an angled reservoir.
4into1.com 4into1.com

Advantage here is it’s just a bolt on, fill with brake fluid, bleed brakes and you’re done project.
 
EzPete said:
Ebay links are totally welcome - buying parts on Ebay can be tough without knowing exactly what you're looking at. There's also a very good chance that a part on EBay would also be in the same condition yours is in. There are some decent aftermarket masters that are direct plug and play (just avoid the sub-$40 Amazon crap)

There are also master cylinder rebuild kits that would enable you to replace all the seals and repair the master - to AD's point above they can be a challenge (specifically removing the circlip inside to release the plunger) with about a 25% shot that the bore is corroded and unusable.
Click to expand...

Yeah, that clip is a bear...

Solution depends on how 'pure' he wants to try to get. ;) It could leak after the rebuild if the bore is badly pitted. Gamble on the kit, potential leak versus a functional option but not 'correct.'
 
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