Mystery brake part

[michaelb]

I just rebuilt my forks. I'm putting the calipers back on and realize I'm missing a part. Only I don't see it on any oem diagram. The caliper is held on by two cap screws. The lower one is smaller. It passes through a hole in the fork, and in this hole is a nylon (?) Tube and a steel mushroom tube spacer. Is there a name and or part number for this?

[mlkmn89]

I just rebuilt my forks. I'm putting the calipers back on and realize I'm missing a part. Only I don't see it on any oem diagram. The caliper is held on by two cap screws. The lower one is smaller. It passes through a hole in the fork, and in this hole is a nylon (?) Tube and a steel mushroom tube spacer. Is there a name and or part number for this?

I am not sure about what part you mean, but could part 35 & 43 be what you are looking for? Here is a link to what I am talking about. https://www.partzilla.com/catalog/honda ... front-fork

[Rambozo]

Sounds like maybe someone cobbled a replacement bushing. Maybe some photos would help.

[michaelb]

This is on the lower bolt. The uppers look good. The bushing and part look too much like OEM and fit too well to be cobbled, especially given the state of the rest of the bike (previous owners were clearly none too bright or capable).

Lower caliper bolt-to-fork

Bolt removed, caliper aside

actual part

[WingAdmin]

That is the anti-dive piston that the caliper screws into.

Anti-Dive mechanism

In the piston is a hole, and a nylon bushing goes into that hole. It is round on the outside (to fit into the hole in the piston) and oblong on the inside (to allow the pivot collar some free play):

Bushing inserted

The part number for the nylon bushing is 51545-MJ0-003

A metal pivot collar goes into the nylon bushing:

Collar inserted

The part number for that pivot collar is 51423-MJ0-003

[michaelb]

Spot-on, thanks!! I have the bushing, just not the pivot. You could spend a month's salary on little parts like this, they add up fast. Fortunately I think I have a guy that can make one.

On a related note, could you explain how the anti-dive mechanism works?

[WingAdmin]

Spot-on, thanks!! I have the bushing, just not the pivot. You could spend a month's salary on little parts like this, they add up fast. Fortunately I think I have a guy that can make one.

On a related note, could you explain how the anti-dive mechanism works?

When you get on the brakes, the top caliper pin acts as a pivot, and the rotation of the brake rotor pulls the bottom caliper pin inwards towards the fork. This presses inwards on that piston. Inside the fork, when that piston is pressed inward, it restricts the valving on the fork, to create more resistance against compression. That keeps the front end of the bike from "diving" when you brake, yet leaves the forks soft and compliant when you are not braking.

[michaelb]

When you get on the brakes, the top caliper pin acts as a pivot, and the rotation of the brake rotor pulls the bottom caliper pin inwards towards the fork. This presses inwards on that piston. Inside the fork, when that piston is pressed inward, it restricts the valving on the fork, to create more resistance against compression. That keeps the front end of the bike from "diving" when you brake, yet leaves the forks soft and compliant when you are not braking.

TODAY I LEARNED!

[4given]

Spot-on, thanks!! I have the bushing, just not the pivot. You could spend a month's salary on little parts like this, they add up fast. Fortunately I think I have a guy that can make one.

On a related note, could you explain how the anti-dive mechanism works?

When you get on the brakes, the top caliper pin acts as a pivot, and the rotation of the brake rotor pulls the bottom caliper pin inwards towards the fork. This presses inwards on that piston. Inside the fork, when that piston is pressed inward, it restricts the valving on the fork, to create more resistance against compression. That keeps the front end of the bike from "diving" when you brake, yet leaves the forks soft and compliant when you are not braking.

Great explanation Scott. Nobody explains better. Even I can comprehend.