FAC damper rebuild information

Moto Guzzi V7 Sport, 750 S, 750 S3, 850 T, 850 T3, 850 T3 California, V1000 I-Convert, V1000 G5, 1000 SP, Le Mans, Le Mans II, Le Mans CX 100, Le Mans III, Le Mans 1000, 1000 SP III, 1000 S, California II, California III, California 1100, California Jackal, California EV, California EV Touring, California Aluminium, California Titanium, California Special, California Special Sport, California Stone-Metal, California Stone-Touring, California Classic, California Touring, and California Vintage models

Created: 2011 January 25

Updated: 2020 January 09

Thanks to Allen Mamet for sending me this information via email:

FAC damper manufacturer: CDB s.r.l.

Allen asked the manufacturer about what oil and amount should be used. Here is what he learend from CDB s.r.l.

You can use Mobil ATF 220. You must fill with the extended stem and when you compress it must be able to reach the end of the stroke without hitting the cap but only touching.

Allen interpreted this response as:

Mobil ATF 220 isn't available here. Was told to use Mobil ATF D/M from Mobil tech support. As far as filling, also I guess the exact amount isn't all that important except not to overfill but to get it just below the cap level when its screwed back on. At least thats how I understand it. Extend the damper rod, fill and compress making sure there's no air in the movement range and fill to just below cap level.

Thanks to Mike Jones for sending me this information via email:

I recently had to rebuild the FAC fork dampers on my Convert. They had 50,000 miles on them. One had leaked all of its oil and the other had leaked half of it. They were doing very little damping by that time, of course! I had a hard time finding rebuild kits, though I did find one European supplier, but eventually I opted to just buy new seals and O-rings, basically assembling my own rebuild kit. The hard part was finding the seals. On your web site you list a Canadian company that has the seals in stock, but I opted to buy SEA seals from McMaster-Carr instead (cheaper and faster than ordering from the Canadian company). I bought part number 9505K14, which is a ⁵⁄₁₆ inch × ⁹⁄₁₆ inch × ¹⁄₈ inch O-ring supported cup seal. I removed the O-rings (they pop out easily) so that they are just cup seals like the originals. They seem to fit well and seal well. There's some stiction when I work the damper by hand, but I don't notice it now that they're installed on the bike. I have no way of knowing how long they will last, but at USD $2.94 each, they certainly are affordable.

Thanks to SA Guzzi, Greg Field, Kiwi_Roy, geodoc, and Goose for posting this information on the Wild Guzzi and GuzziTech forums. In their own words:

SA Guzzi

Checked my front shocks on my 83 LM3 this evening and found one of the dampers not working at all.

So started a strip down. Once i was able to get the bottom fitting undone, she came apart quite easily. There was no oil in the damper at all, must have leaked out from the lower seal. Been searching the web for a seal kit but no go so far.

Have also found the reason the seals leaked. Inside the lower part of the damper, there are two aluminium parts separated by an O-ring. Inside the threaded half, are the two shaft seals. These are the ones i have been trying to get. The upper half is a round aluminium bush with a small hole in. This is the part that is worn oval causing excessive sideways movement of the shaft. When this happens, the oil inside the damper runs out through the two seals.

Off to the engineering shop in the morning to have a new bush made up.

Here are some pics so far.

Greg Field

George Dockray has the seal number. If he doesn't pipe in here, I'll get it fir you.

Kiwi_Roy

I was told by a Guzzi owner who also owns a machine shop that all seals are standard dimensions, fork seals also.

He said just take the seals into a good bearing or seal supplier and they can match it up and sell you seals at a fraction of the dealer cost. I don't know if this is true but it makes perfect sense, I'm sure Guzzi aren't in the business of manufacturing seals.

SA Guzzi

Thanks for the info guys.

The seals i am looking for are the two small ones inside the lower damper fitting, there are two back to back with a washer between them.

A friend of mine with a machine shop made me two new aluminium bushes yesterday, they fit perfectly, no more sideways play. He incidentally also has Guzzi's, a 750S3, a LM III and two LM IV's. He also made me a proper tool to remove the lower fitting on the damper. Will post pics soon.

Anybody know what weight oil i should refill the damper with. I can get Castrol 10W fork oil. Motul has a range 5W, 10W and 20W, they call it light, medium and heavy fork oil. I measured about 65 ml in the damper that was still working.

Thanks again guys,

Raoul

Greg Field

ATF is what comes in them.

FACs have almost zero compression damping. You can improve that by filling in one or more of the damper holes with epoxy.

geodoc

Link with seal #'s is here:

http://www.guzzitech.com/forums/threads/fac-damper-seals.3998/

Extract from GuzziTech forum:

I see that this has been a topic before, but with no answer. Maybe now somebody has the low-down:

Have some FAC's installed on an 850 Le Mans that are being refreshed. Like to install new seals, but before emailing the usual suspects, has anyone gotten them from a particular source? The cap are easy, but the 2 per side cup seals are a little unusual. I'll be trying Fluid Seal in Vancouver tomorrow for a match-up, but they look a bit special so I doubt a generic match-up.

George

Paydirt!

I stopped in at the seal place and here are the part numbers for the shaft seals:

Cup seal: 840400312/4180

Spacer: 8-203/N1444

The installation takes 2 seals per side and 1 spacer in between. The spacer is needed because the cup seals are slightly shorter than the originals so they take u that clearance.

The numbers are supposed to be generic so any large fluid seal dealer can match them.

GD

SA Guzzi

Thanks for the info Greg and George,

Will Motul fork oil work in the damper and give better damping than the ATF?

Cheers,

Raoul

Greg Field

I have used fork oil everytime I've gone inside FACs. The Motul should work fine.

Goose

What weight and what volume?

SA Guzzi

Goose,

Motul or Castrol 10W, i used Motul and about 70 ml in each damper.

Raoul