'85 Tonti forks fluid fill sanity check

[brider]

I THINK I replaced the fork seals on my '85 Cal 2 years ago when I swapped in new dampers and springs, but now the left one is weeping a little. Before I decide whether or not to pull the forks off and replace the seals, is fluid added merely by un-screwing the top caps (with a jack under the front timing cover) and slowly lowering the front until the springs/dampers protrude enough to dribble oil down the tube? I have a fuzzy memory of doing it this way.

Also, I suppose the only way to know if the forks have the correct amount of fluid is to drain them then re-fill, but would adding a little extra stiffen up the compression in the last couple of inches, or would I be at risk of hydraulic lock and blowing off the top caps? How much extra might be OK?

[matt franklin]

Isn't the oil in a cartridge fork, only there to lubricate it?  I don't think adding additional oil will affect the damping.  Too much will blow the seals out, I think.

[brider]

Yes, I'm talking about the lubrication oil.

I think my original phraseology was misleading; by "stiffen up the compression" I mean provide a higher spring rate in the last couple of inches, since the fork is essentially sealed and the resultant volume of air gets compressed as the fork compresses. I think that's the idea behind the air caps, but AFAIK adding static air pressure isn't recommended.

Probably over-thinking this.

[acguzzi]

thats how I've done it, you may already know but you need to loosen the top clamp to make the caps easier to remove, otherwise they are jammed by the compression force.

[Cdn850T5NT]

I have Schrader valves for ea. drain plug. I haven't done it yet but I have a cut off tire stem chunk that, effectively is a through-bore nipple that threads-in and I can rig-up with a 50cc syringe, to, in separate goes, inject the requisite amount of ATF (Dexron?) for my T5. Other than venting the high-point, guarding against pressuring-up the forks, you as should be able to do all from below.

[John Croucher]

Before going to far, pull the rubber boots up, wipe of the excess fluid. You probably blew out the excess fluid. Leave the boots up and pump the shocks.  Wipe some more. The seal is not a high pressure seal. Just a wiper.

[brider]

You probably blew out the excess fluid. Leave the boots up and pump the shocks.  Wipe some more. The seal is not a high pressure seal. Just a wiper.

This is a great reminder. If I DID in fact replace the seals lo those many years ago (10? maybe only 35k miles, sad to say...) they may well be just fine, which is why I was hesitant to pull the forks apart, but just wanted to drain and re-fill back to spec.

[FarmallA]

I've had pretty good luck with this on more than one occasion:

https://www.amazon.com/Squatch-Racing-Seal-Mate-Cleaning/dp/B07QF7HS5R/ref=asc_df_B07QF7HS5R/?tag=hyprod-20&linkCode=df0&hvadid=632124669053&hvpos=&hvnetw=g&hvrand=9004227633797427166&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9001718&hvtargid=pla-829910257600&psc=1

FarmallA
Steve

[bigbikerrick]

I did the same as you with the forks on my 84 Cal II auto. with the 35mm Guzzi made forks. I added oil through the top, slowly, between the cap and tube. measuring, and draining is the only way to know if its the right amount. FWIW, on mine I experimented with adding a few ounces more and also less , but could not tell a big difference. It rode like a big old cadillac, or Buick. Fairly plush ride, but I never got to try FAC dampers in it. It had stock springs, and dampers during the time I owned it.
Rick D.

[brider]

I did the same as you with the forks on my 84 Cal II auto. with the 35mm Guzzi made forks. I added oil through the top, slowly, between the cap and tube. measuring, and draining is the only way to know if its the right amount. FWIW, on mine I experimented with adding a few ounces more and also less , but could not tell a big difference. It rode like a big old cadillac, or Buick. Fairly plush ride, but I never got to try FAC dampers in it. It had stock springs, and dampers during the time I owned it.
Rick D.

FAC...THOSE are the dampers I installed, and also upgraded springs, thanks for that memory-jog. And thanks for confirming the oil-ad process, my memory WAS correct. Based on your testimony, I think I'll add a bit more than spec and see if I can sense a diff.