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Discussion Starter #1
The rear shock on my 750s Brutale is binding up in rebound, feels like the valve is blocked probably with sludge (never been rebuilt). Yes I should hang my head in shame. Any one have rebuild manual for these. spring seems a bit soft too,needs a lot of preload adjustment to get sag right.Measures ok 5mm over length in fact ,much choice for new springs ?
Cheers cus
 

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I think most people chuck them away and get an Ohlins or Nitron. You can have the one from my 750 for cost of postage if you want it but I suspect it's rather well worn.
 

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Thanks Rich,
A very kind and generous offer. I ended up getting a Nitron, just put it on a couple of days ago. I cant bring myself to throw the Sachs away though when it might be repairable, I`m a compulsive fiddler I guess.
 

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Sachs rebuild?

Sachs makes F1 shocks.....Ohlins doesn't

search Dan Kyles post on Ohlins QC issues (and he IS the World's largest Ohlins dealer)

cus;
you want Ohlins series 1091 springs they are 160mm, long same as stock
the rates in my rather old chart goes from 5.4 to 11.0 N/mm my set goes from 7.5 to 10.5 no 10.0

everybody makes them, they are all 57mm ID
 

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Discussion Starter #5
Sachs makes F1 shocks.....Ohlins doesn't

search Dan Kyles post on Ohlins QC issues (and he IS the World's largest Ohlins dealer)

cus;
you want Ohlins series 1091 springs they are 160mm, long same as stock
the rates in my rather old chart goes from 5.4 to 11.0 N/mm my set goes from 7.5 to 10.5 no 10.0

everybody makes them, they are all 57mm ID
Thanks for the info Noel, I`ll keep my eyes peeled for a spring. I cant seem to find any info on rebuilding the shock itself, I`d like to give it a try myself.
 

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I have a couple of 160 mm springs here from a rebuild I did a couple years ago. I'll check the markings for rate.
 

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I am contemplating rebuilding my 910 sachs or looking for a cheap penske to rebuild. Anyone have experience with rebuild sachs with valve upgrades? Ive heard good results when replacing the internals from Cogent Dynamics
 

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I used to rebuild dampers for a living. The actual rebuild of almost all dampers or forks is pretty straight forward. Varies from make to make but in principle they are similar. There are a few that can't be rebuild because they are swaged together for example or, like the Öhlins TTX stuff you need a rig to bleed them. The problem is checking your damper afterwards. Without a Dyno you cannot test if it works correctly. There is every chance if feels ok by hand but has all sorts of issues. They are fiddly things and I have literally done hundreds if not thousands of re-builds and re-specs. You need to dyno run
before you strip it and after you put it back together. You also need to understand the data the dyno spits out. I would put my chances of getting a damper right first time at 60 percent at best.
 

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I used to rebuild dampers for a living. The actual rebuild of almost all dampers or forks is pretty straight forward. Varies from make to make but in principle they are similar. There are a few that can't be rebuild because they are swaged together for example or, like the Öhlins TTX stuff you need a rig to bleed them. The problem is checking your damper afterwards. Without a Dyno you cannot test if it works correctly. There is every chance if feels ok by hand but has all sorts of issues. They are fiddly things and I have literally done hundreds if not thousands of re-builds and re-specs. You need to dyno run
before you strip it and after you put it back together. You also need to understand the data the dyno spits out. I would put my chances of getting a damper right first time at 60 percent at best.
Do you mind if we pick your brain.

Do you do a dyno before and after the rebuild I assume and do you dyno forks as well or is it mainly for the shock?

I am due for a shock rebuild so the more I learn the better.

Do you perhaps have some old Dyno charts you can post up for us to see the data it gives back?
 

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You Dyno before and after. Before so you know if there is something wrong in the first place. If you have data from the same damper from a previous check than it gives you a good idea of the condition before you even start. That is the ideal situation. Forks are also dynoed which isn't as straight forward because of their size and the physical size of the Dyno required. It's also not as critical as almost all of them are self bleeding because of their twin tube design. if they are a pressurised design I would again insist on Dyno runs. You also Dyno at different settings. Usually full soft, half way and full stiff. This should be done at a known temperature so you can later make comparisons. I usually Dyno at 30 C. If there is a problem most good damper guys can tell you by then already what wear or damage they might find inside. You Dyno again after a rebuild to check your work. Small things wrong in a damper can have a massive effect on performance. A shim not sealing properly on a piston renders it useless but you wouldn't feel it when you just push it in by hand. A small internal O-ring nicked accidentally will have similar effects only visible on Dyno data. You want a Dyno that goes up to 300mm per second shaft speed. Lesser speeds again might hide problems. As a quick check you look at a force v Peak Velocity graph. That will tell you if it's working correctly and is also good for comparisons. I would also look at a full force v velocity graph, sometimes known as potato graph and again force v velocity on yet another way to display it which will show the amount of hysteresis and with some knowledge of a particular type of damper show the amount of friction as well. I haven't got any MV Dyno data at all. I only recently bought mine and professionally I used to work with racing cars using mainly bespoke penske dampers but also Sachs and koni. What I would say is that in my opinion it's myth that one brand of damper is considerably better than another brand. The rear Sachs on my F4 is a quality piece of kit every bit as good as a Öhlins. Now a Öhlins developed damper for that bike might perform better because of its valving but I can guarantee that a good damper technician can make the Sachs do exactly the same that the Öhlins does. Maybe there is a little bit less adjustment or some other small differences but they are both highly tunable. Some of the often felt advantages of a Öhlins fork are probably down to a more progressive spring they use rather than any of the damping it provides. For most people it's a subjective thing too. If I spend a few grand on new shiny suspension I want it to be that much better and it probably is because you believe it is and it gives confidence. Years ago I changed some stock Showa Ducati dampers to mimick a track set up Öhlins and the rider who was supremely experienced couldn't tell the difference. That was because there was near enough no difference. What I would say is that stock suspension on most sports road bikes is set up for exactly that... Road use. Of course a set of suspension specifically made for use on track or race conditions is going to be better on a track but for the cost of a rebuild and a few shims and maybe a set of springs you can have your stock suspension be every bit as good but maybe not as good looking ;)
 

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You Dyno before and after. Before so you know if there is something wrong in the first place. If you have data from the same damper from a previous check than it gives you a good idea of the condition before you even start. That is the ideal situation. Forks are also dynoed which isn't as straight forward because of their size and the physical size of the Dyno required. It's also not as critical as almost all of them are self bleeding because of their twin tube design. if they are a pressurised design I would again insist on Dyno runs. You also Dyno at different settings. Usually full soft, half way and full stiff. This should be done at a known temperature so you can later make comparisons. I usually Dyno at 30 C. If there is a problem most good damper guys can tell you by then already what wear or damage they might find inside. You Dyno again after a rebuild to check your work. Small things wrong in a damper can have a massive effect on performance. A shim not sealing properly on a piston renders it useless but you wouldn't feel it when you just push it in by hand. A small internal O-ring nicked accidentally will have similar effects only visible on Dyno data. You want a Dyno that goes up to 300mm per second shaft speed. Lesser speeds again might hide problems. As a quick check you look at a force v Peak Velocity graph. That will tell you if it's working correctly and is also good for comparisons. I would also look at a full force v velocity graph, sometimes known as potato graph and again force v velocity on yet another way to display it which will show the amount of hysteresis and with some knowledge of a particular type of damper show the amount of friction as well. I haven't got any MV Dyno data at all. I only recently bought mine and professionally I used to work with racing cars using mainly bespoke penske dampers but also Sachs and koni. What I would say is that in my opinion it's myth that one brand of damper is considerably better than another brand. The rear Sachs on my F4 is a quality piece of kit every bit as good as a Öhlins. Now a Öhlins developed damper for that bike might perform better because of its valving but I can guarantee that a good damper technician can make the Sachs do exactly the same that the Öhlins does. Maybe there is a little bit less adjustment or some other small differences but they are both highly tunable. Some of the often felt advantages of a Öhlins fork are probably down to a more progressive spring they use rather than any of the damping it provides. For most people it's a subjective thing too. If I spend a few grand on new shiny suspension I want it to be that much better and it probably is because you believe it is and it gives confidence. Years ago I changed some stock Showa Ducati dampers to mimick a track set up Öhlins and the rider who was supremely experienced couldn't tell the difference. That was because there was near enough no difference. What I would say is that stock suspension on most sports road bikes is set up for exactly that... Road use. Of course a set of suspension specifically made for use on track or race conditions is going to be better on a track but for the cost of a rebuild and a few shims and maybe a set of springs you can have your stock suspension be every bit as good but maybe not as good looking ;)
I think my brain just melted trying to absorb all that....

Interesting though, thank you.

One of the things I learnt from my 250 racing days (grass roots club level on RGV's) is getting a bike to handle and while I understand the basics of the 3 parameters and what to adjust and when, in later years the first thing I do when spending a couple of grand on the bike is a trip to K--Tech and internals changed both end for my weight and use. It makes a massive difference to handling, confidence and subsequently lap times. I rarely have tunes performed on engines, to go faster I just throw money at suspension and brakes.
 

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I think, and again it is my opinion, you need to have suspension that gives confidence to go fast . That may well be very different from a theoretical ideal. In terms of damping I always try and point out what we want it to do. We do not have shock absorbers. They don't absorb shocks. They are dampers. Damping is there to control the spring. That's it. If you had a situation where you have a known input into a known spring then you can work out the perfect damping force to control that spring. Well some people with more brains than me can. With the ever changing input on a motorbike or car, acceleration, deceleration, lateral forces etc it's always going to be a compromise. What would constitute the ideal level of damping over small ripples under acceleration is unlikely to be what you need when braking with weight transfering to the other end of the machine. Also the ideal damping for the fastest possible time theoretically tends to put the machines handling on a knife edge and therefore tends to be slower. I would also point out that large amount of damping comes from the tyre side walls. So often getting the tyre pressure right has a significant positive effect on lap time. About 20 years ago 7 post rigs were a the rage in Formula 1. You collected real track data with a myriad of sensors like accelerometers, strain gauges, linear potentiometers, lasers, gps etc to capture as much of the movement of the car on track. You then used that data to replay a lap of the track on the rig on which the identical car would sit stationary. 4 hydraulic rams sit, one each, under the wheels. Three more were attached to the body, one on the nose and two side by side roughly under the engine. The wheel rams would provide the road input, curbs, bumps etc. The other rams are there to provide roll, heave and aerodynamic input as well as weight shift under braking and acceleration etc. The idea was you simulate a fast lap on track and measure through the rig sensors and a highly complex computer program the contact time and load for each tyre. More tyre contact with the road equalling more grip. You could then change springs, damping, anti roll bars, anti squat, anti dive, all manner of things on the rig car, run it through the lap and see if you can improve the tyre contact. We would run a over night test program each Friday night during race weekends and make recommendations to the race team on how to improve their set up for the Saturday practice and qualifying. The disappointing thing is that it didn't work. It was tried time and time again and the drivers either didn't like how the car felt because it became more difficult to drive or it would simply be slower or be negative on tyre wear. Years later the team I was with even decided to not have any adjustment on the dampers at all because once you had a handle on the damping of that particular car the ever needed compromise was good enough that a small change in damping would not translate into improved track times and a big change in damping would mess with tyre wear. So the weight saving on the dampers by not having any adjustability was preferred. We would have 2 or 3 fixed specs depending the type of track. Even in the rain we wouldn't back off damping because the wet tyres provided that change through a softer construction. I don't know about you but I as your average Joe blogs with no particular talent for riding motor bikes very fast find a setting that feels best to me and then never touch it. As much as I like the look of some Öhlins TTX forks or similar I would personally never have them for any other reason than that, they look the bollocks. Ask yourself if you think that someone like Valentino Rossi would be slower on a stock F4 than you would be on a fully Öhlins equipped machine. Unless the answer of that is Yes, do you really need to improve your bike or is it cheaper and maybe more satisfying to improve yourself and your ability. To sum up a incredibly long post. If you love to make changes to your bike, individualise it's looks with expensive suspension bits, go for it. We all like bling.
 

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You hit the nail on the head - it's a confidence thing. I think therefore I am.

I often say to people it's not what you ride but how you ride - I could give most a run for their money on a 250 stroker round Mallory when I was on form. When people ask me about what bike to buy for track use, and should they get the latest modern missile that has all the gadgets, I say a 2K nail with sticky tyres and don't give a sh1t attitude is by far the fastest thing on a trackday.

Obviously in top level racing it's different when you're chasing 10th's of a second, but shaving 5 seconds off a lap time can be all in the head.
 
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