Removing HSC without turning everything to mush

I've had a few attempts at revalving the Ohlins TTX shock on my gasser with some advice from some reputable people, and a little bit of thought of my own. Through the tests I've determined that the main issue is the HSC. The shock is unable to react fast enough to square edges or impacts that create high shaft speeds. Think rock, root, pothole, or log across the trail. Obviously the larger the object the more deflection I am getting, and if moving fast enough its in turn kicking the whole back end up high. Lofting the front and driving the full impact into the shock helps to keep it settled, but itsn't always practical or ideal. I have lightened the whole stack by removing 3 x face shims, which showed some improvement, but the trade seemed to be that the bike would wallow a bit and use more stroke than I was comfortable with.

 

Next step was adding the 2 face shims back in and going up a spring rate to get some preload off the spring and get slightly better sag figures. Same as before. Very nice and stable, but now deflecting again on hsc. How can I achieve the best of both?

 

Also note the TTX has the bidirectional bleed/csc adjuster.

Have you tried or considered using a smaller diam clamp shim on your comp stack? And ensure it's thick enough to act as the clamp. Or you could try a softer spring in your HSC adjuster, assuming/guessing TTX shocks work that way.

 

Have you considered removing a face shim off the rebound stack, or using a slightly thicker x-over in the reb stack? To speed up the LSR and let the rear ride a little higher in those wallowing type situations.  Rear packing is I think evil if you also think your HSC is on the firm side.

I haven't tried going to a smaller clamp, but its always an option. Rebound wise the back end feels ok. By using the CSC (chasis stabiity control) and the external adjuster there is a huge range of adjustment on the rebound circuit. I can slow it down until it basically doesn't rebound at all, or make it so busy you feel like you're riding a pogo. I guess I used the term wallow, but it wasn't that it would wallow down low and ride low in the stroke often, it would just use too much stroke on smallish landings before recovering.

 

The compression I can also dial with the external adjuster and CSC both they seem to have more effect on the low speed circuits. I have no external HSC adjuster so everythings done by the stacks.

 

The stock compression stack looked like this:

38x.2(11)
26x.15
38x.2
36x.2
34x.2
32x.2
30x.2
28x.2
26x.2
24x.2
22x.2
20x.2

 

So I could add say an 18x.2/.25 as a clamp, but would need to source one. I do have a 23x.2 and a 25x.2, what effect would you imagine to see by changing the lower 22 and 24 with these? would the larger shims on the same sized pivot flex some more and offer the change I'm looking for?

I would go to a smaller clamp and keep as much of the LS stack as you are comfortable with.  Gotta keep it in the right place in the travel.

 

Are you sure it's not reacting fast enough or just blowing through the stroke?  Is the bottom-out bumper contacting and causing problems?

reducing the clamp will soften the whole stack.it won,t reduce the high speed only.reducing the whole stack may make the shock too soft.

So I could add say an 18x.2/.25 as a clamp, but would need to source one. I do have a 23x.2 and a 25x.2, what effect would you imagine to see by changing the lower 22 and 24 with these? would the larger shims on the same sized pivot flex some more and offer the change I'm looking for?

Jakobi, if you want the softer HSC and don't want the mushy low speed, then yes, try a smaller 18mm clamp, and you could consider a larger and slightly thinner 28.12 crossover shim. So your stack has a less progressive (less "staged") damping curve. Done deal, would be my prediction.

 

The 2mm smaller clamp will have a big effect. 

 

I think you should just buy a pack of them. To soften the high speed, you could replace the 24 and 26 with your 23 and 25 but that wont be nearly as noticeable, and you have to support the outer edges of those face shims to keep some good low speed damping.

 

Interesting the TTX shock and no external HSC adjustment. That would annoy me.

Thanks for the feedback and suggestions. I'm taking it all on board.

 

I had the shock serviced by Ohlins once originally and they threw in a free shim swap. All they did was exchange the 22x.2 for a 23x.2 and while it wasn't hugely noticable, it was a definite step in the right direction. With the TTX I can also use the CSC bleed to add in more Low speed stability (and rebound) quite easily. A click here and there makes a hugely noticable difference in LS.

 

GHILL28, I was questioning this myself for quite some time, but after making some changes and also doing some video taping (but more so trying different valve stacks) I'm quite certain its too much HSC. The last videos I showed you was my attempt at softening the whole stack by removing 3 x face shims. It resulted in a much better action when hitting up the square edges and fallen trees, but as you saw, the whole bike was then way down in the stroke. Since then I've gone up a spring rate to take some preload off, and then added 2 x face shims back in, and swapped a couple of the .2 shims deep in the stack for .25's. Without a doubt its too firm and not banging the bump stop through the linkage. Thats whats lead to this question. I want to retain the LS firmness I have now, but just have the shock eat up the hard hits instead of deflecting. Very close indeed.

Heres some video from earlier in the year. You can see the way the chasis jolts around when hitting fallen logs at speed. Just looking to settle that some more.

 

http://www.youtube.com/watch?v=mYAWM1oTEio

Add low speed shims and back the adjuster a lot further out.

Add low speed shims and back the adjuster a lot further out.

 

 

Which adjuster? The CSC or the Comp adjuster? The CSC will effect the rebound more than the comp and running it further out will make everything way too lively, The external comp adj works primarily on low speed circuits/bleed too doesn't it? Adding LSC will also add HSC, so even with more bleed on the LS circuits, I don't think it'll address the stiffness in the HS, and may even make it harder.

Comp adjuster.

 

Not an end-all fix, but a good indicator.

I haven't tried going to a smaller clamp, but its always an option. Rebound wise the back end feels ok. By using the CSC (chasis stabiity control) and the external adjuster there is a huge range of adjustment on the rebound circuit. I can slow it down until it basically doesn't rebound at all, or make it so busy you feel like you're riding a pogo. I guess I used the term wallow, but it wasn't that it would wallow down low and ride low in the stroke often, it would just use too much stroke on smallish landings before recovering.

 

The compression I can also dial with the external adjuster and CSC both they seem to have more effect on the low speed circuits. I have no external HSC adjuster so everythings done by the stacks.

 

The stock compression stack looked like this:

38x.2(11)

26x.15

38x.2

36x.2

34x.2

32x.2

30x.2

28x.2

26x.2

24x.2

22x.2

20x.2

 

So I could add say an 18x.2/.25 as a clamp, but would need to source one. I do have a 23x.2 and a 25x.2, what effect would you imagine to see by changing the lower 22 and 24 with these? would the larger shims on the same sized pivot flex some more and offer the change I'm looking for?

 

 

I  would try a more traditional Showa or KYB arrangement -

 

38x.2(6)

30x.1

38x.2

36x.2

34x.2

32x.2

30x.2

28x.25

26x.25

24x.25

22x.25

20x.25

 

The larger crossover provides support to the face shims to keep the bike up in the stroke while overall the stack is softer - using the correct spring will help with bottoming resistance.

Thanks for the feedback everyone. I have a few options to try now. I'll update once I get a feel for it all. I think there will be

 

Nasty1, that was kind of the direction I was travelling - removing face shims to soften the stack, adding some hsc deeper in the stroke with thicker shims, however had not considered the larger crossover. I do however have all the shims you have suggested so your stack could very well be implemented somewhere through the process.

 

I do know that removing the 3 x face shims was a huge improvement in the high speed damping, and I do think taking more out would have only got better. The low speed suffered with this setup though. I think its really going to take some more trial and error before I grasp how much each change will effect things. Being my first time revalving its all new.

 

Edited by Jakobi

Further to last, I'm all for a methodic approach rather than simply having a stab at various peoples suggestions and hoping one will be right. Seems to net the best results, and also provide the most opportunity for learning as you can directly evaluate each change within the stack.

I would dial in the compression clicker a few clicks, and for the shimstack I would change the crossover with a larger diameter (30) and for the clamp I would change the 20 by a 18 and if that is not soft enough for the high speed I would add a 16mm clamp.

Thanks for the feedback everyone. I have a few options to try now. I'll update once I get a feel for it all. I think there will be

 

Nasty1, that was kind of the direction I was travelling - removing face shims to soften the stack, adding some hsc deeper in the stroke with thicker shims, however had not considered the larger crossover. I do however have all the shims you have suggested so your stack could very well be implemented somewhere through the process.

 

I do know that removing the 3 x face shims was a huge improvement in the high speed damping, and I do think taking more out would have only got better. The low speed suffered with this setup though. I think its really going to take some more trial and error before I grasp how much each change will effect things. Being my first time revalving its all new.

 

 

If you have all the shims then you've got no reason not to try it - once you get good at it a revalve won't take long at all. What's important is planning out what you want to do first instead of trying to decide when it's all torn down.

 

Also make sure you use the proper spring  to help with bottoming resistance and use only that spring during the revalve process.

Well I've made some changes and got it all back together but stll haven't had a chance to get out and ride since doing it well over a week ago. Time short! Hopefully next week!

hey fellas this is a 09 crf450 ttx comp stack that I had awhile back not sure if it had been changed at all prior me pulling it apart. just something you might be able to use as a quide from mx to endure setup!

 

38 x .25 - 8

26 x .15

38 x .20

36 x .25

34 x .25

32 x .25

30 x .25

28 x .25

26 x .25

24 x .25

22 x .25

20 x .25

 

I recall it being quite harsh at highspeed square edge

From what I have read/been told there is a lot more to the TTX than a typical shock, due to the twin chamber and how the oil circulates in a push/pull fashion. Changing the shim stack on the main piston does make a difference, however it also redirects more flow through the adjuster stack. The needle and jet also has to work in conjunction with the 2 x pistons, so unless if we're going to confirm that they are using the same piston, needle, jet, and adj stacks the difference between 2 models could vary greatly. In any case, it seems they both share the same trait of having too much HSC.

 

When I had mine set at stock and clickers in a comfortable position to handle being pushed hard and exhibiting general chasis behaviour that felt right, it would thud into almost every square edge. Mate behind said it looked like I would use about 1/3rd of the travel and then it would kick up. Trying to soften the whole lot via clickers just resulted in it getting too busy and wallowing around on the general changes in terrain. My biggest issue is the hardness/harshness/deflection when hitting either a single head sized rock, a similar 20-30cm tree across the track, or a pothole. Everywhere else things feel great but hitting almost any one of these is like slamming into a wall and the back end will either kick up or delfect to the side. Lifting the front end over and putting more force into the rear feels better, where if allowing the front to soak the impact first and then expecting the rear to do the same highlights the issue further.   

Sounds similar to my pds. The front compresses which also weights the rear and squats. This then gets the rear into the harsh part of travel and causes a kick. In theory it sounds like you need stiffer lsc to keep it up more.

But I know jack chit so just throwing ideas out there.

Edited by StuartO

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