Another 900 Seca Anitdive question

A long time ago I seriously looked at a 1983 Seca 900. I didn't pull the trigger and have regretted it since. Now 38 years later I'm waiting for my E-Bay purchase to arrive. I do have a question concerning the antidive system While I have never riden a 900 Seca I did have a 750 Seca for a while. I liked the antidive system OK except for one issue. It seemed that under hard braking, if you hit a hard bump in the road the system would send a pressure pulse into the breaking system and briefly lock up the front brake. In my 52 years of riding I have only locked up the front brake twice and both times it was on the 750 Seca. Was this just an issue with my technique or this particular bike or was this a common issue with the Yamaha system. Is this why so many people seem to want to disconnect the system? I would like to keep the system but would need to find a cure for this issue? Any comments or suggestions?

Bob C.

 

I've never had the front brake lock up under any condition. I've been riding my 750 Seca for 9 years, and rebuilt the anti-dive before she was put into regular service with me.
It's possible that your machine had an undiagnosed issue with the anti-dive unit. So far as I can tell there is no way that the system can cause increased pressure in the brake lines if it is all working properly.

Most people disable the system because they either don't like it, don't understand it, don't want to service it when they service the forks, or want to convert to cartridge emulators.

 

the anti-dive feature is essentially a flutter valve. think of a baloon in a pipe, and you lightly push one side of the baloon it pushes out on the other side.
It counter acts back and forth absorbing brake pressuer in one instance, and shock compression in the other instance "Flutter" between applied brake pressure and suspension compression.

when you pull the brake laever (medium to hard) the front fork compresses under forward momentum forces, the anti-dive valve "flutters" internally these pressures to normalize and even them, thus preventing a sudden front end dive.

Anti dive unit attached to the fork has internal dampining and springs at set compression ratios to prevent its effect during normal braking, so if yours was actuating when hitting bumps in road, the internal valving/spring was malfunctioning and likely needed rebuilt and/or replaced/ or removed all together.

its a system that derived from the start of ABS. ABS uses an electric pump to pulse the brake pressure to prevent it from just locking up. your system is no different in this aspect, it is just geared towards the suspension.