Dual discs

Ok, this has probably been covered a million times, but I have an 81 XJ with a single disc up front. If I want to put dual discs on, what model has the forks for that and will they "drop in" to my bike?

Thanks!
Dean

 

you need 750 forks. I believe they drop in though there are some differences. PM member gitbox I know he's done it.

 

Thanks for the tip! One other question: the 750 forks have some sort of air adjustment feature. Can I just cap that off or something?

 

It isn't that easy. The internals are built to work with the air pressure required in the system. You would need to re-engineer the internals to eliminate the system. Just service the system as recommended (it's only air after all and only a few psi at that) and enjoy being able to tweak the system to your satisfaction. Another positive point is that the air system on the 750 Max has only one port, no two like the Seca (a royal PITA to keep balanced).

 

Robert,

Thanks for the info. I really don't know anything about the 750's. Is there just a valve, like adding air to a tire? I was thinking there was some sort of built-0in air compressor on the 750.

Thanks again,
Dean

 

The air service port is a standard Schrader valve, just like bicycle tires. I've not seen anyone plumb up a compressor for this purpose but it could be done rather easily.
The air is introduced to the internal part of the fork through a set of collars with internal o-ring seals that seal against the fork slider. There is a hole in the fork that passes the air pressure through to the internals. In order to eliminate the air adjustment, you would need to figure out how to seal that hole (hint: RTV isn't going to cut it due to the pressures involved in fork compression). You could weld the hole shut but that is a very permanent process and I wouldn't do it on the bike with the forks assembled. The fork tube is hardened steel with heavy chrome plating so I would ask around as to what issues you might encounter should you want to have some one weld them up for you.
I hope you find what you are looking for, good luck!

 

I eliminated the air on mine, all i did was drill the hole out to a tape size for some small allen head screws. I used loctite to make sure they won't come out, just make sure they are cut short so the internal spring doesn't catch on them and install the screw after the forks are installed, can't tell you how it reacts because I have dealing with engine issues since the dual disc conversion. Hope this helps

 

Or... you can do what I did and use the inner fork tubes from the 650 in the 750 fork legs.

 

Ok, I really need the expertise of the forum. After reading Spanish Cafe Racer I decided I had to have wire rims. So following his advice, I got a set of rims from a Virago 750. The rear went on fine. (see here). However, when I bought a pair of discs for a Seca 750, I ran into a problem. As you can see from the pictures, the disc is too small to fit the rim. Also, if I get discs to fit the rim, are they going to fit the calipers for a Seca 750?? Please, somebody point me in the right direction!!!!





Many thanks!

Dean

 

1981 XJ 750 seca brake discs are one inch larger in diameter than my 650 seca discs. I just went thru the process trying to replace my 650 discs and found that I would have to change my forks to the 750 model. Too much hassle so I will find new 650 discs in the future. Hope this helps. Jack

 

you may be able to use a virago disc and make a bracket to relocate your calipers if need be.

 

also upon looking at the spanish cafe racer, those do not look like stock caliper or anything on there

 

You can weld the holes shut on the Seca forks then grind them down smooth and touch it up with emery cloth so they are smooth as new. I changed my fork seals a couple years ago and added heavier oil to allow for a stiffer rebound to elliminate the need for air in the forks.

 

Does anyone know if a Virago front end will fit on the XJ without much trouble? If it's not too difficult, then you'd have the spoke wheel and dual discs and only have to worry about fitting the stem to the neck.

 

I have some discs that may work. They are from a 1988 FZ600 The picture shows the FZ disc on top of the Seca disc. I have the forks from the FZ as well that are 1mm bigger in diameter byt will fit in the clamps with a little help. Both the 2 discs and forks are for sale. BTY the forks will need to be straigtend as they are tweeked a bit.

 

Thrasher,

Could you give me some measurements for those discs? Both total diameter and the diameter where the bolt holes are?

Thanks,

Dean

 

OD 10.5" ID 5.5" bolt to bolt 3" aprox.
$40 each & shipping.