Leaky anti dive units

Patient is an 83 Seca 900. I have narrowed down my "weeping" fork oil leak to coming from where the antidive piston housing joins the antidive actuator housing. Now according to parts fische, there's no gasket sealing these 2 parts together.

Anyone had a similar problem? I've got all parts on order to renew fork seals and all associated o-rings and gaskets, but I'm wondering what I'm going to find once I tear this thing apart. what internal component (piston seal?) could be leaking and can i fix it with a hardware store oring?

A search in the archives returned a post about rebuilding the antidive units, but wasn't very clear in a couple descriptions. Yamaha says to replace the whole thing, but they're NLA.

TIA for any help.

-Matt, CO

 

You know ... those Anti-Dives are totally overhaul-able. First, check the tiny "setting screw" at the bottom to see that it still moves. Be careful ... use a perfectly fitting screwdriver ... EVEN if you have to sacrifice one out of your toolbox to fabricate the head by doing some grinding.

The "Dives" are a two-part assembly. The UPPER is the activator ... connected to the front brake hydraulics. The LOWER is the fork oil regulator. That LOWER Unit strips-down. Its a little tricky if it's never been done before.

Remove rubber dust cover. Remove circlip. Use clean brake fluid to lube housing. "Try" extracting the rod and aluminum bushing ... if it won't go ... DO NOT HEAT ... NO HEAT!!! There's a nylon bush in there that will be destroyed if you heat it. Try prying it out from the upper fluid hole. Use a socket of larger diameter and try tapping the inside mechanism out into the big socket.

The guts are pretty basic. Spring, nylon bushing and the rod. The rod needs to be able to move within the nylon bushing without binding or sticking.

Clean the nylon bushing with a strong detergent and warm water. Refinish the rod if it is pitted or rusted. Working on it -- with strips of # 600 finishing paper using brake fluid as the wetting agent. Put a new shine on it after you do the 600 by bumping up to 800 and then 1200.

Make a little roll of 1200 and do the INSIDE diameter of the nylon bushing. When the rod will travel within the bushing without binding and sticking. Clean-out the whole deal with spray Disc Brake Kleen.

IF the tiny screw at the bottom will turn ... exercise it in and out using brake fluid as lube. When (if) you get the screw to adjust in and out -- COAT the threads of that adjustment screw with ANTI SEIZE Compound.

It goes back together real simple. You just want to make sure that the O-ring on the top ... surrounding the aluminum bush that the rod extends through is -- clean; along with the locating channel.

Smear some fork oil in the inside diameter of the top end when you re-insert the aluminum bush to help that O-ring along.

Lock it up with the circlip ... get it back on the forks taking care not to pinch the pair of O-ring seals.

Bingo!!! WORKING Dives ... with 3 Positions!

Good luck with those little adjustment screws. If they don't move -- PM me and I'll walk you through a little procedure you can try to free them.

 

Yep ... hardware store O-ring will do the trick ... and, its a neat trick. The hardware store O-ring that "works" is a good match on circumference. But, the working outside diameter if the o-ring is a couple thousandths larger than the one surrounding the aluminum bush. This makes pressing it in an adventure. Once you get it all stuffed in there without it rolling out of the locating channel ... it's going to be an angry press fit. It DOES go.
There's good news ... and, there's bad news. The good news is that if you get the slightly-fatter o-ring in ... you really want to make sure that you did a spectacular job overhauling the lower dive ... there's NO way it'll leak! The bad news ... That fatter o-ring is going to make any future extraction a job for ... how do the Japanese say??? ... God-zere-ah !!!

"Crick, ... Lun-array. Eitz -- GOD-ZERE-AH"

 

no clear where? would have helped.

oil leaks from where they bolt on , brake fluid leaks from "little piston" so there is 2 large o rings that seal em up when bolted on , just remove the whole thing off the fork leg and you will see em...

little piston more than likely stuck after all these years and one would have to get a brake fluid compatable one for them ....

 

Damn the no edit what edit thought up that.... and the actuator on the fork side also has a smallish o ring , pull it all apart you cayn't hurt it....

 

Thanks for all the words, guys:

Rick, thanks for the repost- that was the write-up I turned up with a search. More clarification about the piston and it's oring is what i was looking for, and that's a huge help - Thanks!

Hoo, i believe it's FORK fluid that's leaking, and i believe it's coming around a (possibly) jammed piston inside the actuator and making itself known at the joint between the 2 housings. Though I won't know untill i tear it down. The orings sealing the antidive unit to the lower fork tube are good - no leaks there.

I don't believe it's brake fluid as Front brakes are perfect and the fluid weep doesn't get worse with repeated front brake application. It gets worse after a bumpy ride... but i may be misdiagnosing the problem.

I've got access to a couple carb oring assortment's from K&L, if i find one in there that works and can provide a p/n i'll let you all know.

-Matt, CO
83 Seca 900R

 

Oh, and the adjusters do move freely in both directions...

-M

 

My 900 leaked as well. I had the anti-dive off several times, replaced the o-rings and thought I had it licked, but it kept coming back. Good luck.

 

Guys ... Just because Yamaha didn't put a gasket between the hydraulic activator and the dive unit ... doesn't mean you can't put one in there that you make-up yourself. A nice thin piece of gasket paper ... coated with some Permatex High-Tack Spray-A-Gasket ought to put an end to any seepage coming from where the two mechanism's mate.

 

ricko , the reason for no gaskit is there is a tiny hole in the top part i think , its there to let one know if there is a brake fluid leak i gather? i think i'm just being factual , as if put gaskit there it still come ot of tiny hole!

 

The3 facts are he facts ... if there's a bleed hole bleeding ... that's a leak. But, I think that lower unit probably needs an )-ring or two to be de-leaked. I hope so!

 

Will keep you posted - brought home tools from work tonight so that I can pull the forks and tear them down. Parts should be in middle of next week

I'm hoping for a couple bum orings too!

-Matt, CO

 

Well, parts are off the bike.

The actuators move freely when gently moved with pliers. No evidence of a brake fluid leak from there...

...And the pistons move up and down as well (with a finger). Not quite as free as I'd think they should be - but it appears no ones ever put fork seals on this thing, so I'm guessing the fluid is original and filthy (15,400+ miles). They may move a bit easier with clean oil.

I don't like the fact that I can't determine an exact cause of the seepage i was seeing. The only thing that looks worn-out is the rubber seal that goes on top of the circlip (which holds in the piston on the valve side.) One has some crud built up on the lower mating surface and is beginning to separate from the rubber "boot" part which partially covers the hydraulic actuator. I would like to renew these, but i don't know if they're really the cause of the seepage either - i doubt it. There's no evidence of fork oil getting by the pistons. I'll take them apart at work tomorrow, along with the forks.

Sorry if some of these descriptions are confusing... let me know if you have any thoughts!

-Matt, CO
83 900R

 

pictures would be better...

 

True, but as almost everything's disassembled and cleaned up, they would be useless. It's what Rick calls "dust seals" in his write-up.

I took apart and cleaned out the actuator (hydraulic) side of the anti-dive.
Found that one of the oring seals was leaking; tested with some gentle compressed air, and it wouldn't hold all of it. Removed the "cap" (*rant* what kind of special tool do they use to assemble THAT during production? Long allen socket with a hole in the middle to clear the plunger? WTF? "end rant*) and cleaned out all the guts. plunger was fine, oring looked ok too, probably just some debris caught between the oring and the side of the housing causing a slight leak.

Been too busy to get to the fork oil regulator side of things... hopefully tomorrow.

-Matt

 

May be a bit late but, here's a picture of an anti-dive unit from an XJ750.
Finally got a chance to get into it, had a heck of a time getting the plunger out of the top section of the housing.

 

Well done , a nice picture. i thought there was a o ring on that damper shaft assy , i did not do mine as it was not leaking when i had mine nearly all apart...good stuff.....

Did you not read the post about using a pin punch or equive through the bleeder hole to knock out the plunger? , no matter as yours is out...

 

Musta missed that one somehow.... tried looking thru the bleeder hole, couldn't see the other end of the plunger.... ohhh well

 

Sweet pic, Nick... thanks for posting that.

Mine are all back together and not leaking. Also cleaned out the m.cyl as the brake fluid in there (and the lines) was pathetic. could have been contributing to the problem. I did wind up using a yamaha o-ring on the plunger as a replacement, worked beautifully and didn't break my finger getting it back together again, and it still comes back apart. It's not specifically made for this task, but did work. Can get a p/n if anyone is interested.

Thanks for the words, everyone. lot's of good knowledge here!

-Matt, CO
83 XJ 900R

 

Outstanding Pic Nick (no pun intended)! That is one I'm printing out to pop into my maintenance manual! We otta get you to perform similar shots of starters and such. Do you charge by the hour or by the job???