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

[twowheels]

Originally Posted by n_green

Twowheels I believe you had a fix for the mid-valve, can I ask what that was?

You could ask, and I could sell it to you. Suspension work helps pay for my GasGas habit

[n_green]

Originally Posted by twowheels

You could ask, and I could sell it to you. Suspension work helps pay for my GasGas habit

PM sent

[n_green]

Ok I got the base valve back in. All I did was re-assemble the fork without oil and then turn the fork upside down and compress it, this held the cartridge in place and allowed me to tighten the base valve using a ratchet. Only downside of this method is you can't torque the valve up as all that is stopping the whole thing spinning is your hand. Minimum setting on my bigger torque wrench is 28nm and they aren't there, so they are at the specification of 'tight'.

I've filled them back up with oil and they are the right way up again and on the bike and no leaks yet so I'm going to call that a success. Now to see the difference between the stock compression stack and the one I got from Simmo.

[n_green]

Tried the base valve shim stack Simmo originally tried today:

23.1 (2)
14.1
23.1
22.1 (3)
20.1 (2)
18.1
16.1
12.3
washer

left the rebound and mid-valve alone.

Then I went to my local rock garden riding area and rode 35k's of it. Big rocks, little rocks, rock ledges to bash into, rock ledges to drop off, logs, roots, ruts you name it it's in this place.

It definitely made a difference to the feeling of the fork. They are better in that the harshness has all but gone from them when hitting square edged objects, however I believe it comes at the cost of the fork diving through its' stroke.

I played with the comp and rebound clickers throughout the day and the best I could get it was plush over typical trail trash and then some bigger stuff, it was also very good over larger (big rocks, ledges, logs etc) stuff.

The problem was the fork seemed to dive under hard braking or big hits, this in turn caused savage rebound and pogo'd the bike front to back. It also upset the rear shock, which up to this point I've been happy with.

I upped the compression and settled on 7 clicks out, also had to wind rebound in the around 7 clicks. This firmed up the forks so they didn't dive as often and the rebound was slightly more controlled, though still savage during big hits or sandy whoops/multiple downhill ledges.

Firming it up again to 5 clicks of compression brought the harshness back into the stroke and also started deflecting a lot more.

The fork has also lost its' ability to perform better the harder and faster you push it, it felt amazing initially when I was riding through the slower technical stuff but as soon as you start hitting the same and slightly bigger stuff in 2nd or 3rd it gets scary as the whole bike pogo's front to back.

In short, this stack isn't a magic fix for me and I think I need to play a bit more with it along with making a mid-valve stack/using two wheels mid-valve kit.

[n_green]

Off topic but also on topic, just saw a photo of a Sachs base valve piston from new '13 Beta 300, looks identical to mine (6 ports) except where my piston has 2 ports going to valve stack and 4 ports going to the rebound check plate the newer Beta piston has 3 and 3 ports. So (without measuring them to confirm they are in fact same sized piston with same size ports) the new Beta seems to have improved flow through the compression stroke but less flow through the rebound stroke. (Not taking into account what is occurring at the Rebound piston and mid valve)

Random info huh.

[swazi_matt]

Originally Posted by n_green

Off topic but also on topic, just saw a photo of a Sachs base valve piston from new '13 Beta 300, looks identical to mine (6 ports) except where my piston has 2 ports going to valve stack and 4 ports going to the rebound check plate the newer Beta piston has 3 and 3 ports. So (without measuring them to confirm they are in fact same sized piston with same size ports) the new Beta seems to have improved flow through the compression stroke but less flow through the rebound stroke. (Not taking into account what is occurring at the Rebound piston and mid valve)

Random info huh.

And to add to the randomness i believe that the new Sachs forks now use a more common shim size ID

[n_green]

Originally Posted by swazi_matt

And to add to the randomness i believe that the new Sachs forks now use a more common shim size ID

Nope, the '13 Beta Sachs forks are still running 7mm ID shims. Not sure if the mid valve shims are still 9mm though.

I was told there is a company in US making new base valve and rebound taps that accepted 6 & 8mm shims, should be able to buy them, swap them over and hey presto normal shims to play with. Hopefully be getting more info on that today but I imagine it would be costly, not to mention you would have to get a new piston for each tap.

[n_green]

Haven't updated this in a while, I've done a few more tests using a few difference stacks, the first was using stock rebound stack, twowheels mid-valve kit and this base valve:
23.1 (1)
14.1
23.1 (5)
22.1
20.1
18.1
16.1
14.1
12.3

I rode about 80k's of rocky, root infested, off-camber steep up and downhill single trail. I wasn't happy with the fork at all, the initial compression on square edges was good but the fork couldn't hold itself up in the stroke during repeated impacts and I'm pretty sure on moderately paced downhills it started cavitating as it would pogo like a mutha and seemed to have no rebound damping at all. I also had little confidence in the front end on off-camber trails. It just wanted to push and not turn in.

Following this I went back to using the stock base valve, stock rebound and two wheels mid valve kit. I rode at the same place almost the same tracks.

Big difference, the fork could hold itself up in the stroke, I had a lot more confidence in its ability to stick going into corners, both flat and off-camber, it's nowhere near as harsh on square edges any more.

Negatives are it is still harsh to a degree on square edges, and the harder/faster they are hit the harsher it is. It is still no-where near as harsh as what it used to be. Also when the speed picks up it returns to its natural preference of deflecting off the object rather then soaking it up, again it doesn't deflect as badly as stock valving but it does still deflect.

My rebound stack is also too soft, to gain the confidence in the fork going into turns I had to tighten the rebound past where it started affecting the compression damping, this obviously led to the fork getting some of its harshness back and if I were to simply beef up the rebound stack I reckon these forks would be fine.

Twowheels midvalve kit is a good simple solution to fix the forks quickly and for the majority of punters, myself included, with a tweak to the rebound stack these forks would satisfy most people.

However, I have started playing with this suspension stuff now and I kind of like it, so I'm going to continue playing. As I mentioned the kit fixed the harshness on low speed square edges, it ate up the slow speed rock gardens and root infested climbs/descents. But because they eat it up it inspires confidence which builds speed and they just can't handle the same square edges at a decent speed.

The weak rebound stack definitely isn't helping things. I'm going to continue playing and try and sort these forks out, I have no idea what I'm doing but I have a bucket load of shims so I may as well have a go.

[GMP]

A few thoughts:

Rebound clicker should not affect compression to the point of feeling a difference, if its a normal mid/rebound piston setup as I suspect it is.

Light HS rebound sometimes feels like a comp spike as the fork starts to reset from a deep compression with a lot of spring force behind it. Zoke 45s and 48s need help here too.

Maybe you should consider upping the spring rate, lowering the oil level, and dropping the preload. I've found this works pretty well in increasing the scope of a fork as far as terrain, as I have to race in everything from rocks to sand.

What is stock comp stack?

[n_green]

Originally Posted by GMP

A few thoughts:

Rebound clicker should not affect compression to the point of feeling a difference, if its a normal mid/rebound piston setup as I suspect it is.

Light HS rebound sometimes feels like a comp spike as the fork starts to reset from a deep compression with a lot of spring force behind it. Zoke 45s and 48s need help here too.

Maybe you should consider upping the spring rate, lowering the oil level, and dropping the preload. I've found this works pretty well in increasing the scope of a fork as far as terrain, as I have to race in everything from rocks to sand.

What is stock comp stack?

Stock comp stack is:
23.1 (5)
22.1 (3)
20.1 (2)
18.1
16.1
14.1
12.3
washer

Rebound Shim stack is:

Piston
23 x .1 (2)
20 x .1
18 x .1
16 x .1
12 x .15
10 x .3
13 x 2.15 washer (2)

There are also 2 x 1.1mm bleed holes in the rebound side of the piston



Mid-valve shim stack is:

Piston,
25 x .2 check plates (2)
and has a 1.1mm float.

The rebound clickers definitely affect compression and have done so with every stack I have tried. By closing off the bypass enough to actually get the weak rebound stack to work it is in turn also closing up the MV bypass exposing its stiffness ala harshness. Well thats my take on it anyway, as mentioned I'm a beginner hack and still learning. I could be way off the mark, but thats the joy of learning

Interesting point about the rebound feeling like compression spike, it's definitely something I may have confused, I'm just a hack and I'm also learning how to actually 'feel' what the suspension is doing. I need to set up a video camera on a rut/rocky step and hit it repeatedly to see what the suspension is doing I guess, that may offer me more of an idea of what is going on.

I have re-sprung the front to suit my weight, I have .46 springs up front with 3mm preload and a 110mm air gap. I haven't tested the sag figures though so maybe I need to look at that. I agree I could probably take some oil out as I rarely (read never) bottom, that I can feel and after an average trail ride will still have an inch or two of travel that wasn't used.

Thanks for the info though I'll take it on board and look at it next time I have them apart.