Doing the 750 Seca's Forks.. (Rebuild.. now a HOW TO!)

Yay! Now, does that come with my next order will it be a separate shipment?

 

Ah crap. Doing these seals again because my tubes were too pitted and ruined my new seals. Also to replace the springs. I've almost gotten one done, but I can't get the dampening rod bolt to tighten. It's just spinning, and these are the 750 seca forks that don't have the fluting for the dampening rod hold down tool. Any ideas on how I can tighten this down or did I miss something? Can I final tighten the bolt when everything is reassembled on the bike, forks loaded down?

 

Nope, gotta tighten the correct way: remove the anti-dive assembly, and take a look in the bottom hole. You need to ensure that the middle hole of the three holes on the bottom of the valve (inside the fork) is lined up with the bottom hole for the AD. Use a round punch or equivalent to hold the valve in place while tightening the bolt. IIRC, it only needs maybe 10 ft-lbs.

 

well my problem seems to be that I can hold the lower part of the oil control valve assembly with an allen wrench as you describe, but I can see the actual damper rod turning. And I have the parts assembled in the same order you do skillz.

 

Ok, put the spring etc in and install the cap. the spring will hold the damper rod. Then you can just pull the cap and finish up anything else you need to do.
You could also just wait until it's on the bike, but you have to tighten the bolt before putting the oil in or it'll leak right out the bottom.

 

haha..that's great...I'll have to do the hardest part of a 750 seca fork rebuild (getting the circlip out of the top) 3 times for the right fork (1 for the fork to repair, 1 for the donor tube, and now one to refill)...and I still have to do the left! Thought this would be easier the second time around :roll:

 

wrap the tube in a rag and clamp it in your vice. Use a wooden dowel to push down on the cap (under my chin is how I did it). Then you have both hands free, use a mechanics pick to pluck the circlip out. 15 seconds tops.

 

haha awesome...never thought to use my chin! Actually, it was a lot easier when I had a vice, but I moved recently to a rented place, so now I really need the third hand or fourth, hand. But at least someone is around for the next couple of days to help me out

 

Alright, so I got this done. I'm not sure why the allen bolt going into the damper rod wouldn't tighten without help on one of my forks, but could with the other, but my procedure was as follows (two man job, but I'm sure a talented mechanic can do it while making a sandwich for lunch and posting on this forum):
1. try to tighten bolt as instructed in this thread
2. it doesn't work, so keep trying the same thing and cursing for hours
3. put the spring in and the cap.
4. turn fork assembly upside down and put a socket extension in the axle hole.
5. put all your weight on the fork as a buddy tightens the bolt to the appropriate torque.
6. take the cap and spring out, and continue as described in this thread.

Again, I don't know why my damper rod wouldn't hold itself in place in only one fork. And it will probably take you a couple of days less time without all the cursing/trying the same thing :roll: . And me and buddy got really good at taking off that cap.

 

Doesn't the hole in the oil lock valve unit go "all the way through", so that the allen wrench actually goes through the oil hole in the damper rod......in other words, when the center (?) hole in the oil lock valve is aligned with the hole in the damper rod, then the allen wrench actually holds the damper rod........and that's what allows you to tighten the damper rod screw.........

 

I could see the damper rod spinning through the middle oil lock valve hole, but didn't see the damper rod hole line up.

 

The oil lock valve was too far "down" (or up) to allow the holes to line up.......

 

Great breakdown and photos. Thanks!

 

need to do mine but im a 600 and clear up in 1998. this write up seems rocking but anyone know any major changes i should prepare for?

 

The 750 seca forks are unique, even compared to other '80s xj forks due to the anti dive. I'd look for other guides specific to seca II or at least the more standard xj forks.

A manual will help. The most important differences are the top caps and the oil control valves at the bottom and a manual can give you those specifics.

 

ive bounced through the manual and everything looks pretty straightforward. its just been my experience with the other bike that for each job the manual excludes some key piece of information. im a little dense and just looking to go in as well armed as possible.

 

But that's what I'm trying to tell you. This write up IS awesome (I used it myself for my 750 seca forks, Chorca did a very good job). However, the "key" pieces of information that are covered within are not of use to someone who doesn't have the 750 seca fork (and other bikes don't because the design isn't actually very good).

I assume this thread came about because there are so many differences between the 750 seca forks and other XJ forks, and the other excellent How-To's on this site didn't cover those differences. But the evolution of the motorcycle fork hits a dead end with the 750 seca fork and it's anit-dive, so it's not going to be applicable to your Seca II fork.

 

thanks, ive been running through old threads looking for a good write up for my forks. havent found one and was just wondering how similar things are. i'll keep searching.

 

This is a great writeup. Thanks Chorca!

 

Great instructions and photos unfortunately I completed everything on my 81 seca 750 front end rebuild before I saw your old post.
Did you have any difficulty bleeding the brakes ? I haven't been able to get the air out of the lines no matter what I do. The spring in
the master cylinder does not want to return the piston so there is no way to pump the fluid from the reservoir to the calipers. I tried
pumping fluid from the anti dive bleeder towards the top. I couldn't get the fluid to go through the master cylinder to the reservoir,but I
was able to trace the fluid to the top of the metal tube where it screws into the master cylinder. Some where the fluid is being blocked
inside the master cylinder, Let me know if you had an easier time. I have rebuilt the MC twice and have polished the bore so it's mirror smooth
and used parts i got from chacal. I also rebuilt the whole anti dive unit on bothe ssides with Len's parts it's a real head scratcher.

 

For everybody's sake, I made this a sticky, so it's always right up top.

Dave Fox

 

Hi,

I am trying this job, but have run in to a problem with this step:

The next step is to get the dampening rod's bolt off. This is at the bottom end of the fork.

I am using a hex-key on a long wrench, but the little bolt of joy is not moving. So I have 2 questions:

1. is the hex key for this 6mm? (That is what I am using, but there is some wiggle-room that terrifies me, and the last thing I want to do is round out that hole)
2. Who has hints for how to loosen this thing?

Right now, the well is full of WD40 and every so often, I go out there, and tap the nut with a hammer. And then every few hours I try to remove it without rounding out the nut hole...

the fear..

 

Is the bolt turning but not loosening? or just not turning at all?

A hex bit on a socket is usually best, so you can get a lot of torque on it. Also, install the springs and spacers which should hold the damper rod in place. An impact gun will also help.

 

From your avatar, it looks like you have a 750 SECA, is this correct? Are the forks out of the triple tree? Are the anti-dive actuators still attached? Have you already removed the cap at the top? The 750 Seca's forks
are different than most other XJ's. More information can help us guide you.

 

Remove the anti-dive unit from the fork body. In the lower anti-dive hole you will see a chunk of aluminum with holes in it. Stick an Allen key into the hole. That will hold the oil lock in place and keep the bolt from spinning.

 

Hey!
Awesome, and thanks for the replies! Yes, a 1981 seca (Australia model). I have the forks off the bike, I have the fork cap off, the spring out, the oil drained, the anti-dive actuator off. I have a 6mm socket on a torque wrench (long, lots of leverage), and the fork in a bench-vice, and the bolts just aren't turning. If I didn't know better, I'd say they're seized. The have been marinating over night in wd40, so I'll give them another go now, and see what happens. The only thing I don't have is an impact driver. If they don't come off soon, I'll think about taking them to the mechanic.. it's like admitting defeat though :/

Holy hell. It came out (1 so far) eventually. The WD40 had soaked down overnight, I suppose all along the threads, and allowed me to get it out. Man. I am not certain they need to be that tight.

Also: should I put thread lube on it before it goes back in? My feeling is yes.

 

The damper rod bolts are held in place with thread-locking compound. Using thread lube on them is ill-advised and may result in you being badly hurt when the damper rod bolts back out.
Use a mediium strength thread locking compound on clean threads.

 

very good point. Threadlocker it is.

 

Well, I followed the instructions, but I have a conundrum. One fork is now longer than the other. The short fork bounces back quite quickly to its extent. The long one bounces back quickly, to the length (approx, I suppose) of the short one, then extends slowly. Now I am not certain whether they were different lengths when I took them off the bike. And so now... What, I ask?

The short one took almost a week for me to get the fork seal out, so the other is all nicely put together and filled with oil, but I recall that the insert was longer in the long one when I was tapping the oil seal down - I used a tube of PVC to push the seal down, and it aligned with the top of the "long" fork, but was a good 2cm clear of the short one. Anyone know anything about this?

 

that looks to be the length of one of the inner bushings. You didn't accidently put both on one side, or forget to remove the old one did you?

 

Check to make sure you don't have a damper rod spring laying around. The length is determined by the inner tube and the damper rod, provided the damper rod is properly secured.. You should be able to feel the damper rod spring if you pull on the inner tube trying to extend it to its fullest length.

 

I took apart the short fork again for photos (since it wan't yet full of oil), and I have kept it in the order of assembly (in photos).

When I was first removing the oil seal, it was stuck like a bastard and took days of work and persuasion to get it out. It also turns out it doesn't match the other side oil seal (suspicious). That aside, see the photos here. Note, it seems one of the bushings can almost slide over the other easily, and the washer above the bushing can slide over the bushing. I feel like I will have to take the other apart also to check it out. A shame since it is full of oil. Oh well, new seals all round (x2).

 

well, I think I have found the problem. It is, as suggested, about one shim-length of an issue. The washer that goes above the shim is different in the left and the right. I think I need to somehow source a new washer :/ see the attached pic! you can see one washer is cup-like and the other washer is ridge-like. The cup-like washer (original, I think) doesn't even look like it might go over the shim. The ridge-like washer goes over the shim. Ohhhh b-jessus...

anyone have an idea where I might get a new washer?

I think this is the description:
Fits: Yamaha
Product Number: 1KH2314700
CMS Product Number: YA0003.9920

 

I've got a spare set of forks for a 750 seca that I was going to offer for the cost of shipping, but then realized you're in Australia...I could see if I've got that washer in the forks (probably do) but it's be $30-40 US to ship just the washers in a small box if you can't find another option

 

This is what you need, note that the currently available version are slightly different in appearance/shape, but perform properly. The washer in the "lower" fork pictured in IMAG0633.jpg is the correct (original style "cupped" washer) one:


HCP3092 OEM lower fork tube OIL SEAL SPACER WASHER, fits either left or right tube on the following models: all 1981-83 XJ750 Seca and XJ750 Euro models. One washer does one tube. This washer goes below the oil seal, and above the metal slider bushing! NOTE: original spacer washers were "cupped" at the outer edges; these replacements are flat, but fit and perform as original. Each:
$

 

Great tutorial!
One question tough, if i shorten the spring (to make the bike lower), is it the same process with opening and reassembly?

 

1. Yes.
2. Shortening the spring alone will not make the bike ride lower without causing problems. You have to also make a spacer for the damper rod to limit travel or the fork will slam itself around internally.
Also just shortening the spring will tend to make the suspension ride like crap. It's better to slide the forks upward in the triple tree (you'll have to move the air collars up above the top clamp), or swap the front end from another model of motorcycle.

3. You will also need to pay attenion to the rear suspension, since altering the ride height at the front also alters the suspension geometry, and handling. The Seca 750 is already somewhat prone to headshake (under some conditions); lowering the front will make that more likely to occur.

4. If you already know all of that, then go ahead with the work. This commentary is also here for others who may not know.

 

Anybody ever loose one of these? I just bought 25 of them. Let me know if you need a couple.

 

That isn't the correct part.
Those aren't dust caps that are in the anti-dive, and what you have will very likely make the anti-dive inoperative.
Chacal has the correct part.

 

" swap the front end from another model of motorcycle.

3. You will also need to pay attention to the rear suspension, since altering the ride height at the front also alters the suspension geometry, and handling. The Seca 750 is already somewhat prone to head shake (under some conditions); lowering the front will make that more likely to occur."



I have no idea what the Seca 750 geometry is in stock configuration but my 82 750 Maxim is listed at 31.5* de-raking results in a greater front end load on the bike. I would think that in general more weight on the front end and less rake (caster) would help eliminate head shake? I have never liked the leading axle feature either. I am changing the front end on my Maxim.
Cheers, 50gary

 

Great work very helpful only thing I really think it's good idea to get everything clean as heck I use starting fluid soft cotton paper towels and air then cotton no lint towels . That was a lot of dirty stuff in the bottom of my tubes my brother-in-laws Exxon research and development and he told me that all or oil has microbes in it in the microbes actually do eat the oil and what they secrete in the process is that black muck same thing to be found in the bottom of a home heating oil tank and just as brake fluid turns black when it absorbs water that water also corrodes parts God smiles on the details

 

Any Post on anti dive rebuild ???

 

Nothing aside from this and the thread with all the parts laid out.
Anti-Dive Fork Explosion
The anti-dive units themselves are pretty simple. Just a piston and a few seals. Once you have it off of the forks it becomes pretty evident what to do IMO.
Chacal has all of the replacement parts for the anti-dive.

 

We need more YouTube videos LOL

 

The 900 anti-dive is similar, and this writeup may help you.
XJ900RK Anti-Dive stripdown how-to with pics...

 

My seca 750 XJ anti-dive is different I got it apart it does look very simple I ordered the parts from Lenny but under the top where the bleeder screw is looks like there's a center pin not sure if it comes out or moves to actuate the spring anti dive system tried to pull them out but they won't budge now I'm thinking you there just a casting not knowing thanks for your replies

 

Look closely at the anti-dive fork explosion thread I linked earlier. The top of the brake-side piston does look like a centering pin. I did (mostly) rebuild mine several years ago (most parts weren't available at the time).

 

Yes, the piston is what you are calling the "pin" in the upper part of the entire anti-dive unit (that is the piston that moves down in response to brake fluid pressure entering the housing)….that pin then pushes down onto the piston in the lower (main body) of the anti-dive unit, and the movement of that piston is what controls/restricts the fluid movement thru the fork damper rod assembly, and helps to moderate the compression of the fork tubes during braking (and the harder the braking, the more the upper and lower pistons move "down", and thus the more the fluid flow is restricted, and thus the stiffer the fork becomes, hence "ant-dive during hard braking"……..).