I thought the Bump stop was looking a bit tatty but until I compared to a new one I realize it was long overdue! this was on a 2004 Sachs shock and probably the original rubber.

Note! The picture is only a comparison not how the shock is reassembled the rubber is fitted the other way up.

 

 

How do you remove the aluminium mount from the shaft?

I made a clamp to grip the shaft in the vice. I ended up using a bit heat on the aluminium because they have put loc-tite on the thread. Use a good spanner on the square section of the Ally mount and shock it loose then it unscrewed easily. (normal right hand thread)

Also when the mount is off the damping adjuster screw can be removed to clean and lube it.

Edited October 25, 20196 yr by richt
detail added

Your old one IS knackered but it was quite common to cut down the bump stop to give more travel before bottoming out. I used to cut about 10mm from the bottom (not the tapered end).

Also the damping adjuster was set all the way out and NEVER altered.

Not as good quality wise as the Ohlins but always seemed to work well on the GG.

Reiger shock and updated linkage on the 2012 was the first improvement in 10 years.

Edited October 25, 20196 yr by bumpy_ltd

Here's an excellent video from Cascao on rebuilding the Sach (and shows how to remove the bottom mount to replace the bumper). There are English subtitles which you can enable. There's a thread on ADV/Trials which is also very good: "Rebuild the Unrebuildable Sachs ZF Shock = GasGas and Other".

 

Edited October 25, 20196 yr by d2w

 

5 hours ago, bumpy_ltd said:

Your old one IS knackered but it was quite common to cut down the bump stop to give more travel before bottoming out. I used to cut about 10mm from the bottom (not the tapered end).

Also the damping adjuster was set all the way out and NEVER altered.

The damper screw on mine has always been wound fully out as well. I couldn't tell if my old rubber had ever been cut down but its compressed and gone rock hard. Exactly like you said "IS knackered" 

While the spring and the rubber were removed, I checked the damping was consistent through the total length off the stroke which was spot on.

Edited October 25, 20196 yr by richt

when you removed the bottom mount does the shock loose all its oil/gas?  My 2003 is in the same state, but seeing that there is a lot of work invloved in making the shock servicable I didn't want to risk it

Removing the bottom clevis shock doesn't lost gas pressure.

No gas or oil came out ?

awesome, thanks.  Any gasgas quirks i need to know about other than adding heat to remove it?  do i need to put the comp adjuster all the way in/out?

Use aluminium ou other soft material to clamp the axle. You will need a good clamp custom made for this stem diameter. 

Clamp the axle on the clevis nearest part. Where seals are less likely to go

Heat can damage rebound screw O ring. Maybe you will need replace them

It is a good opportunity to change or lub dust seal. Just pop the shock cap off.

Edited January 14, 20206 yr by cascao

You don't need to do anything with the rebound screw until after you get the bottom mount off. The screw can only be removed afterwards. I didn't need to get it very hot it's more a case heating it quickly to expand the aluminium before the steel rod and it breaks the "loctite" on the threads.

The o-ring on mine was okay but I changed it anyway.

Edited January 14, 20206 yr by richt

Thanks for the responses.  

New to this trials thing and my rear shock is in need of a new bump stop. Where are you guys sourcing the rubber stop and rebound adjuster o-ring? I am in the US? Thanks.

I got mine from a local dealer in the UK. but they are not showing it anymore on their website.

My 04 250 has a Sachs rear shocker fitted but from memory I think the 06 Gassers have Ohlins rear shocks fitted and I don't know if any of the parts are compatible between them. 

It may be worth contacting https://trialendurodirect.com/ formerly the UK GasGas importer.