Anti dive system evaluation and diagnosis

What are the correct ways to evealuate and diagnose anti-dive system promblems?

Currenty bringing an 82 Seca back to life and have found loads of helpful information, tips, how to's, etc.. on xj bikes.

Seems as though I was quite lucky and have aquired a bike that went unmolested and undamaged for 3+decades. Of course the maintenance was neglected for about the last ten years and catching up on that has been the majority of my adventures thus far.

During this search I have located quite a few post about removing or blanking it, a few more threads about what it does and how it operates, But..

does the brake side piston/valve assembly operate in a similar fashion as a master cylinder?

would a bench evaluation involve removal, cleaning, reassembly, and then ...BLANK....?

What are the signs to look for that would help me determine if certain parts are junk and in need of replacing?

Thank you in advance for your sharing your comments, advice, and experience.

 

I can only offer this:

Back in the day, when the 750 Seca came out, ALL of the major Motorcycle magazines (Cycle, Cycle World, Motorcyclist, Rider magazine) said the same things about the anti dive:

that it didn't seem to do much, if anything; and that changing the settings on it made no difference in the apparent lack of functionality.

Again, back then, blocking it off was a common mod. I'm NOT speaking from experience; other than the experience of reading the magazine road tests.

 

Whatever you do, you need to fully clean out anything that touches brake fluid. So if you keep the anti-dive unit, fully disassemble it, flush it with brake cleaner, and replace the necessary o-rings. You don't want it to contaminate fresh brake fluid or introduce a leak. However, other than a full cleaning, there's not much to evaluate.

It functions just like the caliper (not master cylinder).

Also, if you keep the anti-dive, fully clean and replace o-rings in the fork side, for the same reasons as above.

I haven't removed my anti-dive and don't plan to (since I did rebuild it) so I can't speak to the pros/cons of that. But if you do keep it, you don't want 30 gunk in there to contaminate the fluids.

 

That sounds like, as a result of the anti dive being the juntion of the braking and fork assemblies, that any service or maintenance work on the anti dive unit must also include a brake fluid and a fork oil service as well.

 

when i took mine apart the springs were kind of rusty and the whole thing was generally gunked up but it cleaned up well and probably would have worked.
replaced all the o-rings and put it all back and thought "what if it doesn't?" what if i hit a hole and the brakes come on or use the brake and the forks lock up or one works and one don't, then i thought about buying two more brake lines and that was it, i blocked them off.

 

Well that is a SCARY thought!

But isn't it a one way valve?

Meaning that (unless defective and stuck open) it may only be activate by the brakes to effect a pressure on the fork oil? And also when it is at rest the valve is actually seated against a lip of sorts within the metal housing? Kind of like the float needle and seat assemblies?

 

I just went thru this very same issue with my Seca. In the spirit of keeping the bike original (except SS brake lines and Progressive shocks) I ended up disassembling, cleaning, and reassembling my anti-dive units and reinstalling them. I did not replace any parts, not even the o-rings. Not leaking yet...

There is a nice diagram of the units somewhere on this site; I printed out a copy and tucked it into my shop manual. Not sure how functional they are; I intend to do some test rides with the anti-dive screws set the the min compared with them set to the max. IMO, they do add an interesting (if not annoying) touch to the bike and Yamaha's desire for it to be "modern".

 

This is a link to the discussion that had the diagram within it.... decent amount of detail.


http://www.xjbikes.com/Forums/viewtopic ... +dive.html

 

There it is; that's the thread and diagram I was referring to. There should be a special section for stuff like that... I tested the functionality of my anti-dive units in the garage tonight; here's how:
1) Remove rubber covers from anti-dive adjustment screws
2) Turn adjustment screws fully counterclockwise (lowest anti-dive effect) until they stop
3) Sitting on the bike, grab the front brake lever and compress (bounce) the front forks a few times
4) Now turn anti-dive adjustment screws fully clockwise until they stop (highest anti-dive effect)
5) Repeat step 3 and compare
With the screws turned fully clockwise the forks should be harder to compress. Mine are working as advertised; I look forward to a road test to see if I can tell the difference while riding.

 

...and I believe that brings us full circle to a typical xj problem...



Front brakes that need to be refurbed.

 

I like to check the antidive by putting the front wheel against a convenient fence post and comparing "pumping" the forks with and without front brake engaged. There is an obvious difference at all antidive settings on my bike, but I have cleaned all the 30 year old crude out too. Does it help riding...I doubt it. I occasionally grab the front brake and try to get some noticable reaction but honestly I am just a mild "point a" to "point b"
rider and if it does anything it is wasted on me. Just extra unsprung weight