Really odd blown fork seal issue

[Patmac6075]

Looking for some input on a really odd blown fork seal problem I’m having.

First some background, about 2 years ago (15,000 mi) I’d done a complete fork and brake rebuild...I replaced or rebuilt just about everything I could. Fast forward to this spring, I bought a used set of anti-dive block off plates from a previous member (apparently his ‘84 VR finally died). The plates looked to be legit, as in, they seemed to be professionally made...made of stainless, cut to size with milled edges, and the cutouts for the o-rings were milled.

Anyway, on to my problem....my anti-dives had been leaking so replacing them with block off plates was a natural fit and they worked perfectly! That is until last weekend I’d noticed one of my dust seals had popped off. I popped it back in and went for about an hour long ride. When I stopped for gas I noticed oil running down the other fork leg! That seal had completely blown out!

I had ridden for two years without any seal issues, I’d gone most of the summer without an issue....and now, both side popped within hours of one another?

What could have caused this?

I’ve tapped both seal back in, made sure the retaining spring is properly seated and tapped the dust seals back in. I’m set to go out riding for a couple hours...I’ll report my results.

[Patmac6075]

I should have noted, I don’t ride aggressively, I ride one up, and I have replaced the front springs with Progressives and I don’t pressurize the front forks.

[Bob K.]

What about a marginally high fork oil level? Might the springs and shocks be compressing more than usual with the anti-dive units off, which could cause unwanted hydraulic pressure. Just a WAG.

[Prairiehammer]

Looking for some input on a really odd blown fork seal problem I’m having.

First some background, about 2 years ago (15,000 mi) I’d done a complete fork and brake rebuild...I replaced or rebuilt just about everything I could. Fast forward to this spring, I bought a used set of anti-dive block off plates from a previous member (apparently his ‘84 VR finally died). The plates looked to be legit, as in, they seemed to be professionally made...made of stainless, cut to size with milled edges, and the cutouts for the o-rings were milled.

Anyway, on to my problem....my anti-dives had been leaking so replacing them with block off plates was a natural fit and they worked perfectly! That is until last weekend I’d noticed one of my dust seals had popped off. I popped it back in and went for about an hour long ride. When I stopped for gas I noticed oil running down the other fork leg! That seal had completely blown out!

I had ridden for two years without any seal issues, I’d gone most of the summer without an issue....and now, both side popped within hours of one another?

What could have caused this?

I’ve tapped both seal back in, made sure the retaining spring is properly seated and tapped the dust seals back in. I’m set to go out riding for a couple hours...I’ll report my results.

 

The block off plates for the anti-dive should have a passage between the ports. A block off plate that is just flat internally will blow seals. It is as if the anti dive is on all the time.

 

[Patmac6075]

As usual Kevin, outstanding information!

My plate are fairly thick stainless, but do not have a passage....time for plan B

[Patmac6075]

Although I thought I’d read somewhere that for the hydraulic anti-dives once they were blocked, they were always off. The electric anti-dives once blocked were always on?

I must have got it wrong.

[Patch]

If yours are flat not ported then on for every speed bump, pothole and ramp angle;)

 

If your shocks were more worn then, we likely would be having this conversation.

 

Following Keven's drawing the piston is opened by lower coil spring then pressed close by hydraulics to reduce dive.