Diving into the Sachs 48mm forks - wish me luck?

[n_green]

Cheers mate. I've actually enjoyed it for the most part, still have no idea how such a thin bit of metal affects the suspension so greatly

I'm using this thread (and the mirrored one on DBW) to record the stacks I've tried and what I thought of them. So mods please don't delete this

Hopefully this will give tinkerers like me a place to start from if they ever dive into their own Sachs.

Should Gas Gas ever use them again I don't think this thread will be relevant. The newer Sachs as found in new Betas has a smaller cartridge ID (23mm opposed to 30mm in mine) and uses the same size cart rod (13mm).
The rebound and base valve still uses 7mm ID shims but the mid valve now uses 8mm ID shims

 

[n_green]

Re-valved the front again:

This is the stack I used:

BV (unchanged from the last ride):
23.1
14.1
23.1 (3)
20.1
18.1
16.1
14.1
12.3

MV:
24.1
12.1
24.1 (2)
22.1
20.1
18.1
16.1
11.2

Float = 0.5mm

Rebound:
23 x .1 (3)
16.1
23.1
22.1
20 .1
18 .1
16 .1
12 .15
10 .3

2 x 1.2mm bleed holes in piston - closed using JB weld.


I removed a face shim from the MV stack and added a shim in the HS stack to keep the float at .5mm.
Also beefed up the rebound a fair bit.

My first ride was through techy single with some evil root infested hills and a mean mutha of a rocky hill section. All of it was the slipperiest terrain I've ever ridden.

Following a few mid track adjustments to rebound and compression I think I'm pretty happy with this suspension at the moment. It was perhaps slightly too firm in the initial part of the stroke but it was very very hard to judge in the conditions. It was so slippery I had to all but close the rebound clickers to stop the front from washing out, I even had to add 4-5 clicks of rebound to the rear which I've always been very very happy with.
Overall it seemed to eat up the angled trees across the track and square edged hits and that was in the wet. Prior to declaring this stack a success I need to test it in the dry, but so far so good.

Follow up to the above, went out today and rode the same track in the dry, well most of it was dry, the lower section of the track is almost rainforest like and constantly wet. Track is good for testing purposes as it has everything in it, tight tecky single, faster flowing single and twin trail with lots of rocky step ups / drop offs.

I was going a fair bit faster today then the other day due to the drier grippier conditions. Overall I'm pretty bloody happy with these settings although I will be changing it slightly.

The rebound is still too fast and whilst I got it to a good setting with clickers I'm at 3-4 out so have bugger all adjustment left should I require more rebound due to conditions. The high speed rebound is still too fast as well, going off the drop offs which would be using most of the travel caused a harsh pogo back up.

Compression is awesome once the initial travel starts, is sits up very nicely in its stroke and doesn't dive or fall through at all no matter what its being put through. My only complaint is that it is still the slightest bit harsh at speed on the usual square edged trail trash and after a while does lead to arm fatigue. Pick a larger object though, square edged or not and it just eats it up, we done a pretty gnarly hill climb today with lots and lots of rocks and rock ledges where a lot of momentum was required to get up cleanly and the bike just tracked exactly where I wanted it to.

Plan is to beef up low speed and high speed rebound and try and address the initial harshness in the compression.

 

[n_green]

Success!

Okay I'm officially calling this a success. Using this stack:

BV (unchanged from the last ride):
23.1
14.1
23.1 (3)
20.1
18.1
16.1
14.1
12.3

MV (unchanged from last ride):
24.1
12.1
24.1 (2)
22.1
20.1
18.1
16.1
11.2

Float = 0.5mm

Rebound:
23.1 (4)
16.1
23.1 (2)
22.1
20 .1
18 .1
16 .1
12 .15
10 .3

2 x 1.2mm bleed holes in piston - closed using JB weld then a 1.5mm bleed hole drilled in.


I beefed up the LS rebound and HS rebound by adding a face shim to each.

Left the compression stacks alone and just opened up one of the previously closed bleed holes in the MV piston. Reason I did this is the valving seemed really good but it was lacking in small trail trash compliance (fist sized rocks, potholes etc at a decent (3rd/4th gear) pace which after reading through my notes in this thread only started appearing when I closed the bleed holes up. I didn't want to open them both up as I'm already battling with the LS rebound, although I may open the bleed up to 2mm (2 x 1mm holes) as it made a dramatic difference for the better.

Rebound is still slightly fast, I did a lot of fire trail at a good speed on marble sized gravel and could feel the front trying to push out on me unless I was right over the front wheel. Through singles its a similar story with the front pushing ever so slightly and climbing ruts. I must admit I didn't play with the clickers too much as I was enjoying riding and its probably something I could dial in with the rebound clickers but I was already at 5 out so winding them in further would mean if I really had to slow it down in pouring down rain/slippery moss covered rocks I wouldn't be able to so I will probably beef up the LS rebound again in the future.
High speed rebound is good, flew down some downhills with decent drop offs and the rebound was nice and controlled on the return with no pogoing.

Compression is unreal. I dunno why people whine about Sachs they are bloody brilliant after 2000000 revolves

This thing is a single track weapon now it just eats up rocks and roots, hit it at will, even if its wet they'll soak it up and roll over it and keep going. No deflecting, no jarring, no spikes. No diving or riding low in the stroke. They are great on the more open stuff too, cracking along fire trail in 4th or 5th and they just roll over the potholes. Hit drainage humps/whoops and they are nice and compliant and smooth. I was using most of the travel on a nice fast downhill twin trail with decent sized drainage humps but wasn't quite bottoming. Bottomed them once by dropping about 1.2m onto a flat at walking pace in first, even then they were nice and smooth.

The only thing I will nitpick about is that they are still the smallest bit harsh/jarry on the quicker trail trash and I will experiment with the bleed holes in an effort to get rid of this completely.

They are also not quite as stable at the high high speed stuff as they used to be, i.e. WOT 5th and 6th gear fire trail hitting pot holes/erosion ruts they eat it up but then the front head shakes a small amount before settling. I'm not too sure what is the cause of this, I will blame the shock at the moment, as the forks are now so good it showed the shock up as being a bit harsher (read firmer) in the compression and quicker in the rebound then the forks which unbalanced the bike the slightest amount. I can probably tune this out with the clickers but I couldn't be bothered during the ride so clearly it wasnt that much of an issue.

In summary I love these forks now and I'm calling this stack a success.

I will play with the bleed holes (I have a spare set of MV pistons here with the stock 2 x 1.2mm bleed holes) to see if that improves with trail trash compliance without sacrificing its ability to ride high in the stroke and will also beef up the LS rebound slightly but they are that good at the moment there is no rush at all to get this done.

Can you tell I'm happy with these forks now

 

[jorgenlidholm]

Excellent thread!

I started riding less then a year ago on a -98 Yammaha WR250Z and just bought my second bike a GG EC 300 -10 only rode it once.
I've serviced the old KYB fork a couple of times and of course consider my self a newbie.

Are there any manuals on the Sachs 48mm fork? I would like to better understand what you refer to when you write BV/MV/... since I'm interested in possibly revalving my fork.

/J?rgen

 

[Jakobi]

Mid Valve and Base Valve.

The Base Valve being quite easy to access (with some decent tooling and careful hands), The Mid Valve requires you to open up the cartridge itself. In terms of what you'll find inside the 48mm Sachs, well.. its very much the same as any other open cartridge fork out there. The shims however, run some qwerky sizes which you may/may not have trouble sourcing.

 

[jorgenlidholm]

Ok, thanks!
Probably I'll have a better understanding once I pop the cork.

 

[Anders]

Jorgen,
If you want to learn more about how suspension components work, I would recommend reading the "Racetech's motorcycle suspension bible" as a start. That book is a combination of suspension theory and workshop practice. Although all the practical examples are shown on Kyb or Showa components, it's still quite relevant.

Another option is the Wilbers book Motorcycle suspension technology in detail
This book is smaller and gives less prectical workshop hints, but is still a nice addition to your MC related library.
I have them both

 

[jorgenlidholm]

Thanks for the tip Anders, I'll look into those!

 

[n_green]

Another good source of information though very technical in some parts is the shim restackor website. http://www.shimrestackor.com/

 

[n_green]

I had to fiddle

I rode with these forks at Zig Zag (a very very rocky place - rocks from fist size to basketball size, tree roots, fallen trees, off-camber loose dirt single) this place has it all and its all pretty quick. I was happy with them overall but the LS rebound was still annoying me, it was always trying to push and the clickers were fully closed. Trying to compensate by adding HSC to the shock and keep the rear end higher worked to a degree but I still wasn't happy with it.

So I came home and played with the LS Rebound. Compression stacks remained the same.

BV (unchanged from the last ride):
23.1
14.1
23.1 (3)
20.1
18.1
16.1
14.1
12.3

MV (unchanged from last ride):
24.1
12.1
24.1 (2)
22.1
20.1
18.1
16.1
11.2

Float = 0.5mm

Rebound:
23.1 (5)
16.1
23.1 (1)
22.1
20 .1
18 .1
16 .1
12 .15
10 .3

2 x 1.2mm bleed holes in piston - closed using JB weld then a 1.5mm bleed hole drilled in.

I moved a face shim from the HSR stack and put it above the crossover in the LSR stack. It seems that is has made a difference to the LSR, I wound the clickers out to 8 (they had been at 2) and LSR was ok. Unfortunately what I seem to have done is once again soften up the HSR and back came the pogo effect on steep downhills with lots of drop-offs.

Where I really went wrong though was I pushed the forks up through the triples by 6mm to get the rear sitting higher so it would turn in and not push. I've learnt my lesson not to try and tune suspension with chassis changes, doing this turned everything awful. The shock which had been pretty good just three days previous was now a harsh kicking PITA, which led to even more front end washouts then usual, and the front starting blowing through its stroke on rocks and square edges for the first time. I'll be dropping the forks back flush and re-evaluating this stack prior to making any changes but my gut feeling is that the rebound will still need more work.

I'm thinking of closing the rebound bleed holes again (which were re-opened to soften the initial LSC - but obviously had the effect of allowing LSR to do the same) and using a bleed shim on the MV. Anyone have an opinion on this?

 

[Jakobi]

Do you have anymore shims? or a source for some of those 7mm shims? or are you limited to shuffling what you have in the stack Nath?
You could try removing the 10x.3 clamp on the rebound stack which should make the whole lot firmer.

Saw you wash the front in your video too. How far through the clamps did you push the forks?

 

[n_green]

Do you have anymore shims? or a source for some of those 7mm shims? or are you limited to shuffling what you have in the stack Nath?
You could try removing the 10x.3 clamp on the rebound stack which should make the whole lot firmer.

Saw you wash the front in your video too. How far through the clamps did you push the forks?

Unfortunately the stock shims (what came in the rebound and BV stacks) is all I have. Since I have simmo's old carts I have twice as many. I don't want to firm up the HSR too much, with the old stack I could get it to pack using the clickers, just - the clickers were wound right in, and even then it still pushed a bit - which leads me to the conclusion its the bleed hole. I can't really source any more shims, the place I was going to didn't have that big a range and last time I enquired was sold out.

That front washout in the video wasn't suspension related it was me being a gumby. I've had right knee dramas for years and on this ride I noticed I was favouring it by not bending it properly, so I was going round the corner with a straight leg and leaning into the corner with the bike. Had several of those moments throughout the ride, always round left hand bends. It's prompted me to book into a specialist when I'm back from leave and get the knee looked at.

 

[n_green]

And the forks were pushed through the triples by 6mm. I'm going to return them to flush for now until I really dial in the suspension and then I'll play with all that stuff.

 

[Jakobi]

Give it a go man! Let me know how it works

The bleed should be primarily LS right? Stiffening the whole stack as it is now by removing the 10x.3 clamp should add more across the board, which will bring your HS back under control (you said its too fast since removing the 23x.1, HS face shim). Then if you have too much LS you can always pull another face shim out to speed it back up.

Disclaimer. I have NFI what I'm talking about

 

[n_green]

Haha me neither so it doesn't matter.

 

[Jakobi]

Can of worms.. Shes been cracked now! I wouldn't mind having a play with that Shim restackor program to get a visual idea of what is actually happening as opposed to trying to do it all in the minds eye.

 

[n_green]

Can of worms.. Shes been cracked now! I wouldn't mind having a play with that Shim restackor program to get a visual idea of what is actually happening as opposed to trying to do it all in the minds eye.

I bought the restackor program, I didn't get much value out of it but then I didn't really spend much time learning how to use it properly. It did show on the screen the differences between various stacks but I'm a practical guy and seeing it on paper means nothing to me until I've experienced it.

 

[n_green]

I rode at Nowra on the weekend, was a good track half of the motor cross track, then 20k's of single, sandy, loose gravel, head sized rocks and bigger rocks with lots of step ups and drop offs.
Had to wind the rebound in to 3 clicks out to control the pogoing from deep in the stroke off drop offs. Even then it was still rebounding a bit too quick for my liking. Any further in on the clickers and they started packing.
I softened the compression up, I'm roughly 10 clicks out and it's not too bad, good over the mx jumps, sandy whoops, rock faces etc but it is still harsh on initial compression. It seems the faster I go the harsher it gets as well. It wasn't harsh until I closed the rebound bleed holes (2 x 1.3mm holes) and even now that I've opened one up (1.5mm) it's still a bit harsh.
The saga continues...

 

[n_green]

Started playing with them again. Based on my thoughts re compression I am going to add a bleed shim to the face of the MV, I'll leave the float alone. This should allow the forks to get moving immediately but they shouldn't dive too much as the float is reasonably small.

With the rebound I think with the last shuffle I got the LSR pretty close. I could get them to pack using the clickers and the front wasn't wanting to push, even in the sandy corners. The only reason I had to touch the clickers last ride was to try and control the HSR from deep in the stroke, which the clickers aren't very good at doing.

So I now have the following stacks:

BV (unchanged from the last ride):
23.1
14.1
23.1 (3)
20.1
18.1
16.1
14.1
12.3

MV:
12.1
24.1 (3)
22.1
20.1
18.1
16.1
11.2

Float = 0.5mm

Rebound:
23.1 (5)
16.1
23.1 (1)
22.1
20 .1
18 .1 (2)
16 .1 (2)
12 .15 (2)
10 .3

2 x 1.2mm bleed holes in piston - closed using JB weld then a 1.5mm bleed hole drilled in.


The MV is the same, I've just moved the 12mm crossover shim up to the face to act as a bleed shim. Fingers crossed this allows things to get moving quickly to get rid of the harshness, but doesn't allow the forks to start diving under braking etc.

Rebound is the same, I've just beefed up the HSR at the bottom of the stack to try and control the pogoing from deep in the stroke.

Going riding tomorrow, lets see how this goes

 

[n_green]

Interestingly I serviced a mates set of Sachs 48mm forks the other day. They have been re-valved by a professional tuner. While I won't say what stacks were inside (they are very very different to mine) I will reveal that there was no work done at all to the mid valve. All of the work done was to the BV (it was quite soft and actually used bleed holes in the comp side of the piston).

I've ridden his bike and while I don't love the forks they are a LOT better then stock. They have a dead feeling to me, it sounds strange but I feel very removed from the trail when riding the bike, whereas with mine and other bikes I've ridden you can feel the trail, if that makes any sense. They are still quite firm, and when approaching square edges I found myself bracing for the harshness, but they aren't harsh at all and just soak it up and keep going.

Goes to show there is more then one way to skin a cat, and you don't appear to need any 9mm shim to do so.