Reworking Sachs shock ...

Ok, need some help.  There should be a schrader valve on the end of the reservoir, but there isn't.  

So it looks like this:

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It should look like this:

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Here is a guy with a Honda shock ... reservoir has an end cap, he drills a hole and pries the cap off ...    

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And underneath is the valve.

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Is it time to get bold and drill into that cap??  

What could possibly go wrong?
I recommend starting with a 6 pack.

For info about shim stacks, here is an old video with good info.  More dirt moto oriented, but good explanation of concepts.

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Drill a small hole. Screw a sheet metal screw part way in. Hook your slide hammer to the screw head and pop er out.

sideshowbob wrote:

Drill a small hole. Screw a sheet metal screw part way in. Hook your slide hammer to the screw head and pop er out.

Yup.  It is crazy ... taking a drill to a shock that supposedly has ~ 150lbs of nitrogen behind it.    Scary moments.  When it released it was just a small psssstt.  Nothing to worry about at all!

I have no idea how Sachs fills these to start with.  

All apart now.  

For refilling, options are:

1. Drill hole in center to proper size, tap threads, install a schrader valve (with bolt loctited on the inside)
2. Get an end cap from a dirt bike Sachs shock
3. Get an end cap from some place like RaceTech

#3 looks like this:
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Keep going, very interesting.

I wouldn´t drill a hole. It´s archaic und brutal to do so.

I would ask a shock service shop how they do it and would follow their advice.

Just my 2 cents.

usedtobefast wrote:

For info about shim stacks, here is an old video with good info.  More dirt moto oriented, but good explanation of concepts.

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That is a damned good video - I actually learned something today. Thanks heaps.

Georgios wrote:

I wouldn´t drill a hole. It´s archaic und brutal to do so.

I would ask a shock service shop how they do it and would follow their advice.

Just my 2 cents.

I talked with 3 suspensions shops ... all 3 said drill a hole. There really is no other method.

usedtobefast wrote:

I talked with 3 suspensions shops ... all 3 said drill a hole.  There really is no other method.  

In this case, you´re on the safe side. Still can´t unterstand why Sachs did it this way. There are better ones.

Georgios wrote:

usedtobefast wrote:

I talked with 3 suspensions shops ... all 3 said drill a hole.  There really is no other method.  

In this case, you´re on the safe side. Still can´t unterstand why Sachs did it this way. There are better ones.

This is what mine looks like after Traxxion got through with it.

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Underneath the "shock condom" they went with a re-valve and a 750lb spring for my fat arse.  A little more travel would be nice but otherwise I think this is as good as I'd ever need it to get.

$400 total.

I might have to call them up about that reservoir end cap.  Does not look like a stock one that just had a schrader valve added.

So a little update ... I'm a bit stuck on a few things.

1. Reservoir end cap ...
   A) I kind of messed mine up when I drilled the "vent out the nitrogen" hole ... so the "drill hole, tap threads, install schrader valve" plan might not work so well.
   B) My stock cap measures 45.77mm in diameter.  RaceTech sells one that is 46mm.  So, 0.23mm too large.  Seems like this is an area to be precise.    But maybe that would work.
   C) I called a few suspension places ... theory was a Sachs dirt bike shock might have the same size end cap.  No one had one, and no one seemed to know how to order one.  

2. Rear spring.  Read a lot.  Searched a lot.  Got a bit confused.  Found some new ones.  Matched new part numbers up with other bikes.  Seems a particular year GSXR shock uses the same spring.  So, off to eBay, and they had the exact shock, $25 and free shipping.  I'm hoping for a Christmas miracle!  Here's my dream ... the spring works ... the reservoir end cap is the same size ... the shims in the shock are the same as what I need to revalve mine!    But hopefully at least the spring will work.

Off for a 1.5 week trip and then my shock will be here and I'll see what kind of miracle might occur.  

Hello Usedtobefast.

I did the reworking to the stock shock of my Breva a few years ago.
Drilled a hole, put a special high pressure Schrader valve on it, Ohlins spring, new shimming kit to match the stiffer spring...
Doesn't really worth the fuss. Not to mention the risk if something goes wrong with drilling etc.

Got myself a Mupo and never been happier.
There are also other cheaper alternatives, but I wanted an extended length shock.

voulga77 wrote:

Hello Usedtobefast.

I did the reworking to the stock shock of my Breva a few years ago.
Drilled a hole, put a special high pressure Schrader valve on it, Ohlins spring, new shimming kit to match the stiffer spring...
Doesn't really worth the fuss. Not to mention the risk if something goes wrong with drilling etc.

Got myself a Mupo and never been happier.
There are also other cheaper alternatives, but I wanted an extended length shock.

On the stock shock, did you change the valving? Different piston? If so, do you have that info still?

On the Mupo, does yours have the same shock travel, just the length (height) adjuster? Seems some guys get the Stelvio based shock so it has more travel.

I changed the piston and the valving. Bought a kit from Italy (Oram srl).

You shouldn't worry about travel but eye to eye length. Stelvio shock is same travel as the Breva's (and GRiSO I suppose) shock with just a longer terminal piece.
Mupo can be ordered longer +8mm
Matris +9mm
Wilbers and Nitron (very nice by the way) are cheaper but do not offer that option.

Longer shock has two main benefits.
1. Raising the rear ride height, which reduces rake & trail which in turn helps the bike tip in quicker and turn tighter.
2. In relation to the rocker ratio, it alters the starting point of the arcs with regard to rocker arm/dog bones/shock mount etc. So the initial suspension movement starts closer to a ratio of 3:1, the feeling is more progressive and compliant.

The down side to #2 is, it is easier for the bike to squat more in the rear as you feed it into a fast sweeper, hence increasing rake and trail and the tendency to run wide on exit.
However, most people who are seeking better ride quality will compensate with heavier spring/pre-load and higher (lo-speed) compression damping.

It is all a compromise;
Remember, when you make just one alteration, you actually change 5 aspects of the bike.

Ok ... picking this back up ...

First item ... what spring to go with?

So I'm fairly light, 155 lbs (70 kg), so it seemed to me that the stock spring should be fine. But every thing I read and the two suspension shops I spoke with all said "get a stiffer spring". Even though my preload numbers all made sense with the stock spring.

So seems the stock spring is 82 N/mm ... got that from searching and reading ... but some debates on that.

Read all sorts of stuff ... seemed like a 90 N/mm or 92 or 95 would be good for me.

Ohlins springs are available, but geezz, they are short!

Stock length is ~187mm. An Ohlins spring is 150mm. That seems like a huge difference to me, and I don't really want to make a spacer.

So I start looking at springs to buy ... about $110 + maybe tax + maybe shipping. Then for the aftermarket spring I found a compatibility list ... other bikes the spring fits.

Hummm ... so I look at each one of those other bikes to see what their stock springs were ... some too light, some too stiff, and then the Goldilocks spring appears! A 2006 Suzuki GSXR 750 has a 95 N/mm spring stock.

Over to eBay, and what?!?, an entire 06 GSXR 750 shock for $25 and free shipping! Buy Now baby!

So it shows up ... I pull off the spring ... same inner and outer diameter as our stock GRiSO ... length is 192mm vs. stock 187mm, no worries there. And it should be a 95 N/mm spring. Whoo hoo!

The reservoir cap is too small, so no miracle there. But I pulled off the schrader valve so I can use that on my stock cap ... saved about $6 there.

So I pulled the GSXR shock all apart ... shims are mostly .2 and .3 thick, so that will not help me, as I would like some .1 and .15 thick shims.

So I'm still super happy with $25 for a good spring and schrader valve.

Next step ... drill and tap my reservoir cap and get the gsxr schrader valve in place.

Then sort out valving.

Then get this puppy back together!

And a discovery ... all these warnings about the high pressure in the shock ...

When I let the nitrogen out of the GSXR shock ... eye protection ... rag over valve ... valve point away and a big open space ... press the valve with a small screw driver ... and ... a small pissssft. Like a mouse sneeze.

Humm. So I get my mountain bike shock pump out, pump up the GSXR shock to 180 psi ... then repeat the careful air letting ... and a longer, but still wimpy Pissssssssft. So seems like the shock via eBay might have had 50 psi in it or less. And a properly charged shock is still a wimpy little thing.

I strongly approve of this project!

Pete

Great find on the $25 shock

A bit more on springs ...

Looks like the right spring is a Race Tech SRSP 5818 series ... so a SRSP 5818098 is a 9.8 kg/mm rate (last 3 digits is the rate).

And more fun ...

9.8 kg/mm = 96 N/mm  =  549 lb/in  

Big Race Tech chart here:   [You must be registered and logged in to see this link.]

This spring series fits the following bikes:
2008 Buell 1125R
2008 Kawasaki ZX1000 Ninja ZX-10R
2007 Kawasaki ZX1000 Ninja ZX-10R
2006 Kawasaki ZX1000 Ninja ZX-10R
2003 Kawasaki ZX1200 Ninja ZX-12R
2002 Kawasaki ZX1200 Ninja ZX-12R
2001 Kawasaki ZX1200 Ninja ZX-12R
2006 Kawasaki ZX1400 Ninja ZX-14
2008 Kawasaki ZX600 Ninja ZX-6R
2007 Kawasaki ZX600 Ninja ZX-6R
2006 Kawasaki ZX600 Ninja ZX6-RR
2005 Kawasaki ZX600 Ninja ZX6-RR
2006 Kawasaki ZX636 Ninja ZX-6R
2005 Kawasaki ZX636 Ninja ZX-6R
2008 Kawasaki ZZR 600
2007 Kawasaki ZZR 600
2006 Kawasaki ZZR 600
2005 Kawasaki ZZR 600
2006 Suzuki GSX-R600
2006 Suzuki GSX-R750
2003 Suzuki SV1000/S
2009 Triumph Daytona 675
2008 Triumph Daytona 675
2007 Triumph Daytona 675
2006 Triumph Daytona 675
2009 Triumph Speed Triple
2005 Yamaha FZS1000 FZ1
2004 Yamaha FZS1000 FZ1
2003 Yamaha FZS1000 FZ1
2002 Yamaha FZS1000 FZ1
2001 Yamaha FZS1000 FZ1
2006 Yamaha YZF-R1
2005 Yamaha YZF-R1
2004 Yamaha YZF-R1
2003 Yamaha YZF-R1
2002 Yamaha YZF-R1
2001 Yamaha YZF-R1
2000 Yamaha YZF-R1
1999 Yamaha YZF-R1
1998 Yamaha YZF-R1
2005 Yamaha YZF-R6
2004 Yamaha YZF-R6
2003 Yamaha YZF-R6
2002 Yamaha YZF-R6
2001 Yamaha YZF-R6
2000 Yamaha YZF-R6
1999 Yamaha YZF-R6


For you big guys, looks up uzidzit posts, at some point the spring gets too big to fit the GRiSO ... my notes say 84mm od is too big, 83mm od fits ... I'm not sure at what rate the spring gets too big

usedtobefast wrote:

Cleaned things up a bit.

Now at this point I would want to use the schrader valve to release the nitrogen from the shock.  But, don't have one.  Just that little allen screw.  Hum, a screw with nitrogen pressure and oil behind it.  What could possibly go wrong with that!    

Off to google I go.  No great info.  Saw some crazy youtube videos of guys drilling into a shock body!  So if they can drill into it, I guess I can remove that screw.

I get 2-3 shop rags, working in an oil drain tub, fit the allen wrench between the rags, slowly loosen the screw, a bit worried/scared ... it was a tiny pissssss and a tablespoon of oil.  Whew.  I pumped the shock and very nice looking blue oil comes out.  Nothing bad in the oil, looked really good actually.  Shock had ~5000 miles on it.

Usedtobefast, Great write up ,     If you can't find the correct size reservoir cap, a local machine shop would be able to skim one down to size pretty quick. Or make a new one from Aluminium stock perhaps ?
Question : What kind of pressure do you intend to apply to the reservoir when done ?  The pressure is there primarily to prevent the oil from foaming , yes ?

waterbottle wrote:

Usedtobefast, Great write up ,     If you can't find the correct size reservoir cap, a local machine shop would be able to skim one down to size pretty quick. Or make a new one from Aluminium stock perhaps ?
Question : What kind of pressure do you intend to apply to the reservoir when done ?  The pressure is there primarily to prevent the oil from foaming , yes ?

For the pressure, seems most shocks are 150psi - 180psi.  From internet searches, seems 180 psi came up a couple of times for our shocks.

The stock Sachs shock has a piston in the reservoir (some shocks have a bladder) ... on one side of the piston is the oil, the other side is 180 psi nitrogen gas ... so there really should not be any foaming of the oil due to the nitrogen & piston.  So that part of the shock should be considered a nitrogen gas camber, and oil bleeds into when you hit a bump.  

The other side (camber) has the oil (and another piston that flows thru the oil).  Cavitation can occur in the oil from that piston (with all the holes in it) moving through the oil.  

Seems a really low reservoir pressure might increase cavitation (over in the chamber with the oil) ...  

Here is a video showing this (crazy this stuff is on youtube!).  They start with low pressure, you see the cavitation (foaming), they increase pressure, cavitation goes away.



Here is a longer one showing more cavitation




So ...  low pressure in the shock reservoir can cause (or increase) cavitation, it would make the compression lighter (easier for the oil to move the reservoir piston on a bump), and you'd have weaker rebound action.

Well that's easy to see , great videos New question, What oil weight are you going to use ?

waterbottle wrote:

Well that's easy to see , great videos  New question, What oil weight are you going to use ?

My local shop recommended Motul Factory Line Shock Oil VI 400 Ester Technosynthese.  Whew, it's gotta be good with that many words on the label!    

It has a viscosity index of 400, and weight is 2.5.

If you want your head to hurt, read this!   [You must be registered and logged in to see this link.]

I mean, I guess I'm glad there are people in the world that can deal with this ... viscosity index formula:

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