Telesco Fork Damping

[Duccout]

I have two Mototrans Ducatis, fitted with Telesco forks, and I am baffled as to how they can produce any rebound damping. When the forks compress, the oil is forced up into the inside of the stanchion, but as they rebound I cannot see how there is any way that the oil is restricted to slow the extension of the forks.

To try to produce some semblance of damping I have progressively upped the viscosity of the oil, until I have reached treacle (SAE 40) which results in very slow movement in winter, perfect damping in mild weather and still no damping at all in the recent hot weather; the forks flapping up and down like a pogo stick. AFAIK the oil is in the forks just for lubrication.

If anyone knows otherwise please post!

Cheers,

Colin

[themoudie]

Aye Colin,

Enter "Telesco" into the 'Search' window, top right of the forum window and you will display a whole list of 165 matches to your query!

Eldert's post of 6th December 2023, is probably going to be what you are looking for, but I shall leave that in your capable hands.

N.B. the 'Search' displays the posts in date order, so, your post appears at the top of the list and Eldert's post is 6th from the top of the list.

Good health, BillR

[Duccout]

Hi Bill,

Thanks, but none of those posts shows how the forks can produce any semblance of damping, apart from the innards moving up and down in oil! If one looks at a Marzocchi or Ceriani fork internals it is obvious how the damping works, but the Telesco forks have no obvious means of producing rebound damping.


Cheers,

Colin

[themoudie]

Morning Colin, apologies for the vexatious reply that didn't help!

This may not be of any help, but .....!

This link refers to Ossa Tr80 Telesco forks and the cryptic comment by the responder says it all: Trials_Central_Forum There are other postings on this forum about Telesco forks, all with a paucity of technical replies.

This link appears to be the "Telesco" website, which is in Spanish and now they appear to be manufacturing hydraulic door closers!
Telesco_manufacturers_website

Finally, this company may be able to assist: Classic_and_Vintage_Suspension_UK and another contact might be Norman Blakemore, of NJB shocks, who whilst not selling Telesco stuff is knowledgeable about the Classic trials bike world and the equipment used: NJB_Shocks.

Good health, BillR

[blethermaskite]

Colin,
I has a set of telesco forks on an old ( Italian) narrow case 250 many years ago I didn't know they were telesco's back then.....I just knew they were not Ducati. So same problem as you now describe "pogo stick!" like you I just put heavy oil in but they were never any good.....bike long gone with them on it and never had another set on anything, so sorry no answer, maybe they just don't have rebound damping???
Cheers, George.

[Jon Pegler]

I think the only rebound damping in the Telesco forks is controlled by the holes at the top of the damper units, and the speed that the oil can return on rebound.
Those forks do take a large volume of oil in each leg, 280cc, half a pint.
Whilst the Spanish handbook states a 20w oil, I once used 20/50 engine oil with more success before I found any information on these bikes.

[Duccout]

Thanks all! It looks like rebound damping was not of great interest to Telesco......

Cheers,

Colin

[A.I.M]

I share your frustrations with Telescos, Colin.
In addition to the damping issues, I have trouble with a persistent leak at the sliding seal on one of my forks. The stanchions and seals are new, and I have replaced the new / leaking seal with no improvement.
I've started wondering if it might be possible to find a compatible set from a different manufacturer, or somehow get an upgrade to solve both problems. So I'd be grateful if anyone has suggestions.
Cheers,
Al

[Duccout]

Hi Al,

I think that I have found the answer to the seals leaking. The standard seals are 35 45 8, but if you go on to a bearing company website (I use Simply Bearings) you will see that the seals are available in 35 45 4, so I fit two in each seal holder. I also carefully run around the top of the stanchion with an oil stone to ensure that there are no sharp edges to cut the seal when the holder is pushed over it. I also smear some silicone over the surface where the seals fit inside the holder, as often the holders are distorted and there is a possibility of oil being pumped around the back of the seals.

Another area which definitely leaks (although you would think that the tightness of the thread would avoid this) is the thread where the seal holders screw into the sliders. Possibly the threads are too stiff to fully squash the o ring, or maybe the sealing surface is damaged. To stop this I wind PTFE plumbers tape around the threads before screwing the seal holders in. I wish that somebody would commission a batch of new seal holders, as the originals are almost always bashed about.

I'm crossing my fingers, but since using these methods I have had no more oil leaks.

Cheers,

Colin

[Jon Pegler]

I think part of the problem with leaking seals is caused by the heavy weight of oil used in the Telesco forks.
Some of the later Telescos with the seal holder screwing into a thread internally on the slider used a proper hydraulic seal, not an ordinary oil seal.
The hydraulic seals have no spring in them and are used in heavy machinery, e.g. hydraulic rams etc..
It may be worth trying a pair of those seals if you have trouble with ordinary oil seals.
At least the later seal holders on post-1975 Telescos had seal holders that stay put. Earlier seal holders with the external thread on the slider often come loose. They can sometimes be fixed but not always.