Teledraulic Forks 1950

[DWS]

Ok, I have just stripped one fork leg on my 1950 G3L, not as difficult as I was expecting. However, one thing has surprised/puzzled me, when I removed the fork seal, removed the bolt at the bottom of the fork leg (the one that sits in a recess under where the axle is) I pulled the stanchion out of the slider (a little force was needed here) the whole 'innards' came out with out too much trouble, leaving the slider empty.

I then noticed that the tapered steel piece, the one that the bottom bolt in the recess screws into, was left loose inside the slider, it fell out when I turned the slider upside down.

I have looked at the exploded diagram in the manual and compared all the parts in the picture to what I actually have and they are both the same with nothing missing, as far as I can see.

Now my question is: If the bottom bolt (the one in the recess etc.) goes through the hole in the bottom of the slider, then screws into the steel tapered piece inside the slider, and this steel tapered piece (which seems to be a guide only?) is not fixed in any way I can see to the stanchion/damper etc. What stops the slider assembly falling off the end of the forks, other than the very tight fit of the upper steel (a second look at this part seems to indicate that it is not steel but some sort of plastic?) bush just below the fork seal in the upper part of the slider?



Edited by - DWS on 04 Nov 2010 4:48:23 PM

[Don Madden]

There are two kinds of the damped hydralic fork, one uses a cartrdge with internal piston & valve, the other is a shuttle valve damper.
On compression the shuttle valve opens allowing oil to flow from the slider into the inside of the stantion tube with little restriction until the tapered piece enters the bottom, progressively restricting flow. At full compression, there is very little flow, easing the travel to a stop. On rebound the valve closes forcing the oil through a small hole in the tube as the forks extend. At near top-out, the short internal buffer spring between the top & bottom bushes cushions the sliders' travel to prevent it banging on the stop & preventing more travel.

The cartridge type is similar except the rebound damping valve, rod & piston are contained inside another smaller tube inside the stantion. The factory experamented with the shuttle type for only a couple of years or so & returned to the cartridge type. The shuttle type became popular on other makes in the 60s & many use it today.

Cheers, Don.

[DWS]

Thanks for that Don.

I am now feeling very foolish

I've just realised that it's the Chrome Extension screwed into the top of the slider above the fork seal that holds everything in place, I had taken these off and never gave them a second thought as to what they were doing! That'll teach me to put virtual pen to paper without thinking first

Edited by - DWS on 04 Nov 2010 4:48:00 PM

[Malleon]

Huh. Typical of a Snowdrop!!

[DWS]

[Peter Lecompte]

Hi , I am in the process of building the same set of forks for my 1949 AJS 18. A couple of things/questions. What is the size socket (tube spanner) needed for the bottom damper cone bolt head? I have recently bought a new set of fork inner tubes 1 1/8th (JSL part no. 016322) and they arrived yesterday. When I compared them to my old set (Part No. 013348) there are several differences. 1. The oil holes layout is different at the bottom of the tube. 2. There is no sleeve (ring) on the bottom of the tube which locates the aluminium damper. 3. There is no slot milled out on the very end of the tube where the circlip fits. This slot would fit in with the slot on the top of the damper cone. Can I use these new tubes or are they for another set of forks? My old tubes have pitting/gouging around the seal and top plastic bushing area - hence the need for a new set of tubes. thanks Peter

[Don Madden]

Without seeing pics of the two side-by-side it is difficult to be sure but it looks like they sent the wrong tubes for your year. 1941 G3L-1947 all models used an internal cartridge type damper. 1948-50 used the shuttle damper as your original & in 1951 went back to the cartridge type. Your tubes should be p/n: 013348. The location & size of the holes in the stantion tube are important to work as a set with the other parts & the circlip retains the shuttle valve in the correct position. You can upgrade to the later type by replacing all internal parts to match the tubes you got.

The bolt is a 5/16in BSC & you will have to have a thin wall socket to fit in. A standard one can be ground down by fitting it on an extention & holding it against a grinding wheel while tuning it to grind it evenly.

Cheers, Don.

[Lance]

Hi Peter,

Exactly as Don says. I encountered what you are seeing. My '48 tubes were both pitted and bent when I went to rebuild them. I was informed that no repro 48-50 types were available so I upgraded everything to the '51 style and all is well.

Just grab the '51 Spares List and you'll see the differences. I used good second hand dampers acquired from AMC Classic Spares and the rest of the bits were new.

Regards,
Lance

[DWS]

It appears that Andrews Engineering supply the correct '48-'50 Shuttle Valve Stanchions - part number 013348. Worth checking out.

[Lance]

Thanks Dave. Ahhh, always the way. It was a few years ago so not sure if they had them then (at least that's what I'll tell myself).

Either way, I'm happy with moving to the later style as there must have been a valid reason for AMC to switch back. I remember reading somewhere about reduced hydraulic pressure and less leaking...and something about rattling.

I'll definitely keep Andrews Engineering in mind for my '49 G80S project then if those fork tubes are useless.

Regards,
Lance