Rear Master Rebuild - Seal direction and hose

[XJSRider]

Today was a good day. Got the clutch master and slave off, all cleaned up, waiting on rebuild kits to come. PO had been in both of these. They looked nasty, like half the parts weren't replaced.

Stripped, cleaned, rebuilt and remounted front brake master (the first piece to actually go back ON the bike).

Out back got to the promised land, rear master off the bike and rebuilt. More on that in a bit...

Also got the final stainless brake line on, the little one under the tank by the swing arm pivot. With the collector off to get to the rear master, there was a heat shield type thing with a transformer on it. I was able to do that last brake line by removing this piece of tin and didn't need to remove swing arm or gas tank.

So the rear master:

1. It seems that seal are supposed to have the "open" end point towards the high pressure, so that when fluid pushes back against them they expand and seal better. This is how I installed the seal on the piston... I found it facing what I thought was backwards. There is evidence that someone has been in here before...

2. The hose that goes from rear brake fluid reservoir to rear master... I wanted to replace it. Went down to autoparts store the guy insisted that fuel line would work... nice rubber with meaty wall thickness... but something in my head said maybe not... any opinions?

Thanks guys.

[XJSRider]

I'll answer my own question for #2... Fail. Fuel line is no good. Would have checked google at parts store but phone is dead. Tygon online seems good... but I want to remount this thing tomorrow. Can someone recommend something I can find locally? The auto store did not have any other types of hose.

[Elmobile]

Correct. It must be compatible with brake fluid DOT4. Fuel line won't cut it!
Personally I would go to OEM part
I would also suggest replacing the O ring between the connector for this hose and the body of the master cylinder.

At the end of the push rod, there is a "washer" with a little dome on it. Make sure it facing toward the outside. Putting it the other way will reduce the stroke for the piston to get back to its resting position...

[Elmobile]

As to the orientation of the main seal, you're correct. The small end of the spring get inside the seal. The flat face of the seal rest against the flat end of the piston...

[XJSRider]

Hey Elmobile... question was for the other seal... the once close to where the pushrod hits the piston.

Tried to post parts fiche link with the number for reference but I am not seeing it here:

https://www.partzilla.com/catalog/honda ... r-cylinder

Part 16 is the piston assembly. From left to right on the screen, it shows the spring, the seal you talked about, the piston, then the pushrod... but there was another seal on the pushrod side of the piston and my rebuild kit came with one. It was similar to the other masters on the bike... a ring seal with an opening all the way around.

The opening faced away from the piston when I found it, but I reversed it thinking the fluid pressure should push into the seal opening to expand it.

The oring came with the rebuild kit so that's all set (part 34).

[XJSRider]

I'll post my own answer again re: seal direction.
Here is fiche for clutch master:
https://www.partzilla.com/catalog/honda ... r-cylinder

Item 4 is piston assembly they show my mystery seal here. Looks to be flared towards the fluid and I was able to confirm that's how it was in my clutch MC.

I do need to check on the dome though... I tried it both ways can't remember which one I picked.

[XJSRider]

Can you clarify on the dome please?

Mine is installed so the "bump", part that sticks out, faces back of bike, away from pushrod.

looking at it again I can see on the back of the bump some wear marks and the way I have it installed now looks like nothing would contact the washer in that place.

So please confirm, the "bump out" should face towards the pushrod (pushrod side of the washer has the bumpout that sits proud of the face of washer). Pretty sure that is correct. Thanks.

[Elmobile]

Correct, the bump must face toward the "outside" of the master cylinder, ie: toward the pushrod.
Otherwise it will restrict the piston returning to its home position and not clearing the pressure relief hole.

Not sure about the mystery seal for the clutch master cylinder. It is on my winter list to rebuilt along with the slave cylinder. Did not have one for the rear brake master cylinder...

[XJSRider]

Thank you. Got it sorted out. You may have saved me a huge headache.

Ended up ordering a piece of Tygon 2375 for the reservoir hose.

Happy to be putting parts back on the bike.